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nimPNG
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nimPNG/png.nim

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initial commit
2015-08-28 15:56:55 +00:00
import unsigned, streams, endians, tables, hashes, math, nimz
const
NIM_PNG_VERSION = "0.1.0"
type
PNGChunkType = distinct int32
PNGcolorType* = enum
LCT_GREY = 0, # greyscale: 1,2,4,8,16 bit
LCT_RGB = 2, # RGB: 8,16 bit
LCT_PALETTE = 3, # palette: 1,2,4,8 bit
LCT_GREY_ALPHA = 4, # greyscale with alpha: 8,16 bit
LCT_RGBA = 6 # RGB with alpha: 8,16 bit
PNGFilter0 = enum
FLT_NONE,
FLT_SUB,
FLT_UP,
FLT_AVERAGE,
FLT_PAETH
PNGSettings = ref object of RootObj
PNGDecoderSettings = ref object of PNGSettings
colorConvert*: bool
#if false but rememberUnknownChunks is true, they're stored in the unknown chunks
#(off by default, useful for a png editor)
readTextChunks*: bool
rememberUnknownChunks*: bool
ignoreCRC*: bool
PNGInterlace = enum
IM_NONE = 0, IM_INTERLACED = 1
PNGChunk = ref object of RootObj
length: range[1..0x7FFFFFFF]
chunkType: PNGChunkType
crc: uint32
data: string
pos: int
PNGHeader = ref object of PNGChunk
width, height: range[1..0x7FFFFFFF]
bitDepth: int
colorType: PNGcolorType
compressionMethod: int
filterMethod: int
interlaceMethod: PNGInterlace
RGBA8 = object
r, g, b, a: char
RGBA16 = object
r, g, b, a: uint16
ColorTree8 = Table[RGBA8, int]
PNGPalette = ref object of PNGChunk
palette: seq[RGBA8]
PNGData = ref object of PNGChunk
idat: string
PNGTime = ref object of PNGChunk
year: range[0..65535]
month: range[1..12]
day: range[1..31]
hour: range[0..23]
minute: range[0..59]
second: range[0..60] #to allow for leap seconds
PNGPhys = ref object of PNGChunk
physX, physY: int
unit: int
PNGTrans = ref object of PNGChunk
keyR, keyG, keyB: int
PNGBackground = ref object of PNGChunk
bkgdR, bkgdG, bkgdB: int
PNGText = ref object of PNGChunk
keyword: string
text: string
PNGZtxt = ref object of PNGChunk
keyword: string
text: string
PNGItxt = ref object of PNGChunk
keyword: string
text: string
languageTag: string
translatedKeyword: string
PNGGamma = ref object of PNGChunk
gamma: int
PNGChroma = ref object of PNGChunk
whitePointX, whitePointY: int
redX, redY: int
greenX, greenY: int
blueX, blueY: int
PNGStandarRGB = ref object of PNGChunk
renderingIntent: int
PNGICCProfile = ref object of PNGChunk
profileName: string
profile: string
PNGSPEntry = object
red, green, blue, alpha, frequency: int
PNGSPalette = ref object of PNGChunk
paletteName: string
sampleDepth: int
palette: seq[PNGSPEntry]
PNGHist = ref object of PNGChunk
histogram: seq[int]
PNGSbit = ref object of PNGChunk
PNGPass = object
w, h: array[0..6, int]
filterStart, paddedStart, start: array[0..7, int]
PNGColorMode = ref object
colorType: PNGcolorType
bitDepth: int
paletteSize: int
palette: seq[RGBA8]
keyDefined: bool
keyR, keyG, keyB: int
PNG = ref object
settings: PNGSettings
chunks: seq[PNGChunk]
pixels: string
PNGResult* = ref object
width*: int
height*: int
data*: string
proc makeDefaultPNGDecoderSettings*(): PNGDecoderSettings =
var s: PNGDecoderSettings
new(s)
s.colorConvert = true
s.readTextChunks = false
s.rememberUnknownChunks = false
s.ignoreCRC = false
result = s
proc signatureMaker(): string {. compiletime .} =
const signatureBytes = [137, 80, 78, 71, 13, 10, 26, 10]
result = ""
for c in signatureBytes: result.add chr(c)
proc makeChunkType(val: string): PNGChunkType {. compiletime .} =
assert (val.len == 4)
result = PNGChunkType((ord(val[0]) shl 24) or (ord(val[1]) shl 16) or (ord(val[2]) shl 8) or ord(val[3]))
proc `$`*(tag: PNGChunkType): string =
result = newString(4)
let t = int(tag)
result[0] = chr(toU32(t shr 24) and 0xFF)
result[1] = chr(toU32(t shr 16) and 0xFF)
result[2] = chr(toU32(t shr 8) and 0xFF)
result[3] = chr(toU32(t) and 0xFF)
proc `==`(a, b: PNGChunkType): bool = int(a) == int(b)
proc isAncillary(a: PNGChunkType): bool = (int(a) and (32 shl 24)) != 0
proc isPrivate(a: PNGChunkType): bool = (int(a) and (32 shl 16)) != 0
proc isSafeToCopy(a: PNGChunkType): bool = (int(a) and 32) != 0
proc crc32(crc: uint32, buf: string): uint32 =
const kcrc32 = [ 0'u32, 0x1db71064, 0x3b6e20c8, 0x26d930ac, 0x76dc4190,
0x6b6b51f4, 0x4db26158, 0x5005713c, 0xedb88320'u32, 0xf00f9344'u32, 0xd6d6a3e8'u32,
0xcb61b38c'u32, 0x9b64c2b0'u32, 0x86d3d2d4'u32, 0xa00ae278'u32, 0xbdbdf21c'u32]
var crcu32 = not crc
for b in buf:
crcu32 = (crcu32 shr 4) xor kcrc32[(crcu32 and 0xF) xor (ord(b) and 0xF)]
crcu32 = (crcu32 shr 4) xor kcrc32[(crcu32 and 0xF) xor (ord(b) shr 4)]
result = not crcu32
const
PNGSignature = signatureMaker()
IHDR = makeChunkType("IHDR")
IEND = makeChunkType("IEND")
PLTE = makeChunkType("PLTE")
IDAT = makeChunkType("IDAT")
tRNS = makeChunkType("tRNS")
bKGD = makeChunkType("bKGD")
pHYs = makeChunkType("pHYs")
tIME = makeChunkType("tIME")
iTXt = makeChunkType("iTXt")
zTXt = makeChunkType("zTXt")
tEXt = makeChunkType("tEXt")
gAMA = makeChunkType("gAMA")
cHRM = makeChunkType("cHRM")
sRGB = makeChunkType("sRGB")
iCCP = makeChunkType("iCCP")
sBIT = makeChunkType("sBIT")
sPLT = makeChunkType("sPLT")
hIST = makeChunkType("hIST")
# shared values used by multiple Adam7 related functions
ADAM7_IX = [ 0, 4, 0, 2, 0, 1, 0 ] # x start values
ADAM7_IY = [ 0, 0, 4, 0, 2, 0, 1 ] # y start values
ADAM7_DX = [ 8, 8, 4, 4, 2, 2, 1 ] # x delta values
ADAM7_DY = [ 8, 8, 8, 4, 4, 2, 2 ] # y delta values
proc PNGError(msg: string): ref Exception =
new(result)
result.msg = msg
proc newColorMode(colorType=LCT_RGBA, bitDepth=8): PNGColorMode =
new(result)
result.keyDefined = false
result.keyR = 0
result.keyG = 0
result.keyB = 0
result.colorType = colorType
result.bitDepth = bitDepth
result.paletteSize = 0
proc copyTo(src, dest: PNGColorMode) =
dest.keyDefined = src.keyDefined
dest.keyR = src.keyR
dest.keyG = src.keyG
dest.keyB = src.keyB
dest.colorType = src.colorType
dest.bitDepth = src.bitDepth
dest.paletteSize = src.paletteSize
if src.palette != nil:
newSeq(dest.palette, src.paletteSize)
for i in 0..src.palette.len-1: dest.palette[i] = src.palette[i]
proc `==`(a, b: PNGColorMode): bool =
if a.colorType != b.colorType: return false
if a.bitDepth != b.bitDepth: return false
if a.keyDefined != b.keyDefined: return false
if a.keyDefined:
if a.keyR != b.keyR: return false
if a.keyG != b.keyG: return false
if a.keyB != b.keyB: return false
if a.paletteSize != b.paletteSize: return false
for i in 0..a.palette.len-1:
if a.palette[i] != b.palette[i]: return false
result = true
proc `!=`(a, b: PNGColorMode): bool = not (a == b)
proc readInt32(s: PNGChunk): int =
if s.pos + 4 > s.data.len: raise PNGError("index out of bound 4")
result = ord(s.data[s.pos]) shl 8
result = (result + ord(s.data[s.pos + 1])) shl 8
result = (result + ord(s.data[s.pos + 2])) shl 8
result = result + ord(s.data[s.pos + 3])
inc(s.pos, 4)
proc readInt16(s: PNGChunk): int =
if s.pos + 2 > s.data.len: raise PNGError("index out of bound 2")
result = ord(s.data[s.pos]) shl 8
result = result + ord(s.data[s.pos + 1])
inc(s.pos, 2)
proc readInt32BE(s: Stream): int =
var val = s.readInt32()
bigEndian32(addr(result), addr(val))
proc readByte(s: PNGChunk): int =
if s.pos + 1 > s.data.len: raise PNGError("index out of bound 1")
result = ord(s.data[s.pos])
inc s.pos
proc setPosition(s: PNGChunk, pos: int) =
if pos < 0 or pos > s.data.len: raise PNGError("set position error")
s.pos = pos
proc hasChunk(png: PNG, chunkType: PNGChunkType): bool =
for c in png.chunks:
if c.chunkType == chunkType: return true
result = false
proc getChunk(png: PNG, chunkType: PNGChunkType): PNGChunk =
for c in png.chunks:
if c.chunkType == chunkType: return c
proc bitDepthAllowed(colorType: PNGcolorType, bitDepth: int): bool =
case colorType
of LCT_GREY : result = bitDepth in {1, 2, 4, 8, 16}
of LCT_PALETTE: result = bitDepth in {1, 2, 4, 8}
else: result = bitDepth in {8, 16}
method validateChunk(chunk: PNGChunk, png: PNG): bool = true
method parseChunk(chunk: PNGChunk, png: PNG): bool = true
method validateChunk(header: PNGHeader, png: PNG): bool =
if header.width < 1 or header.width > 0x7FFFFFFF:
raise PNGError("image width not allowed: " & $header.width)
if header.height < 1 or header.height > 0x7FFFFFFF:
raise PNGError("image width not allowed: " & $header.height)
if header.colorType notin {LCT_GREY, LCT_RGB, LCT_PALETTE, LCT_GREY_ALPHA, LCT_RGBA}:
raise PNGError("color type not allowed: " & $int(header.colorType))
if not bitDepthAllowed(header.colorType, header.bitDepth):
raise PNGError("bit depth not allowed: " & $header.bitDepth)
if header.compressionMethod != 0:
raise PNGError("unsupported compression method")
if header.filterMethod != 0:
raise PNGError("unsupported filter method")
if header.interlaceMethod notin {IM_NONE, IM_INTERLACED}:
raise PNGError("unsupported interlace method")
result = true
method parseChunk(chunk: PNGHeader, png: PNG): bool =
if chunk.length != 13: return false
chunk.width = chunk.readInt32()
chunk.height = chunk.readInt32()
chunk.bitDepth = chunk.readByte()
chunk.colorType = PNGcolorType(chunk.readByte())
chunk.compressionMethod = chunk.readByte()
chunk.filterMethod = chunk.readByte()
chunk.interlaceMethod = PNGInterlace(chunk.readByte())
result = true
method parseChunk(chunk: PNGPalette, png: PNG): bool =
let paletteSize = chunk.length div 3
if paletteSize > 256: raise PNGError("palette size to big")
newSeq(chunk.palette, paletteSize)
for px in mitems(chunk.palette):
px.r = chr(chunk.readByte())
px.g = chr(chunk.readByte())
px.b = chr(chunk.readByte())
px.a = chr(255)
result = true
proc numChannels(colorType: PNGcolorType): int =
case colorType
of LCT_GREY: result = 1
of LCT_RGB : result = 3
of LCT_PALETTE: result = 1
of LCT_GREY_ALPHA: result = 2
of LCT_RGBA: result = 4
proc LCTBPP(colorType: PNGcolorType, bitDepth: int): int =
# bits per pixel is amount of channels * bits per channel
result = numChannels(colorType) * bitDepth
proc getBPP(header: PNGHeader): int =
# calculate bits per pixel out of colorType and bitDepth
result = LCTBPP(header.colorType, header.bitDepth)
proc getBPP(color: PNGColorMode): int =
# calculate bits per pixel out of colorType and bitDepth
result = LCTBPP(color.colorType, color.bitDepth)
proc idatRawSize(w, h: int, header: PNGHeader): int =
result = h * ((w * getBPP(header) + 7) div 8)
proc getRawSize(w, h: int, color: PNGColorMode): int =
result = (w * h * getBPP(color) + 7) div 8
proc getRawSizeLct(w, h: int, colorType: PNGcolorType, bitDepth: int): int =
result = (w * h * LCTBPP(colorType, bitDepth) + 7) div 8
method validateChunk(chunk: PNGData, png: PNG): bool =
var header = PNGHeader(png.getChunk(IHDR))
var predict = 0
if header.interlaceMethod == IM_NONE:
# The extra header.height is added because this are the filter bytes every scanLine starts with
predict = idatRawSize(header.width, header.height, header) + header.height
else:
# Adam-7 interlaced: predicted size is the sum of the 7 sub-images sizes
let w = header.width
let h = header.height
predict += idatRawSize((w + 7) div 8, (h + 7) div 8, header) + (h + 7) div 8
if w > 4: predict += idatRawSize((w + 3) div 8, (h + 7) div 8, header) + (h + 7) div 8
predict += idatRawSize((w + 3) div 4, (h + 3) div 8, header) + (h + 3) div 8
if w > 2: predict += idatRawSize((w + 1) div 4, (h + 3) div 4, header) + (h + 3) div 4
predict += idatRawSize((w + 1) div 2, (h + 1) div 4, header) + (h + 1) div 4
if w > 1: predict += idatRawSize((w + 0) div 2, (h + 1) div 2, header) + (h + 1) div 2
predict += idatRawSize((w + 0) div 1, (h + 0) div 2, header) + (h + 0) div 2
if chunk.idat.len != predict: raise PNGError("Decompress size doesn't match predict")
result = true
method parseChunk(chunk: PNGData, png: PNG): bool =
var nz = nzInflateInit(chunk.data)
chunk.idat = zlib_decompress(nz)
result = true
method parseChunk(chunk: PNGTrans, png: PNG): bool =
var header = PNGHeader(png.getChunk(IHDR))
if header.colorType == LCT_PALETTE:
var plte = PNGPalette(png.getChunk(PLTE))
# error: more alpha values given than there are palette entries
if chunk.length > plte.palette.len:
raise PNGError("more alpha value than palette entries")
#can contain fewer values than palette entries
for i in 0..chunk.length-1: plte.palette[i].a = chr(chunk.readByte())
elif header.colorType == LCT_GREY:
# error: this chunk must be 2 bytes for greyscale image
if chunk.length != 2: raise PNGError("tRNS must be 2 bytes")
chunk.keyR = chunk.readInt16()
chunk.keyG = chunk.keyR
chunk.keyB = chunk.keyR
elif header.colorType == LCT_RGB:
# error: this chunk must be 6 bytes for RGB image
if chunk.length != 6: raise PNGError("tRNS must be 6 bytes")
chunk.keyR = chunk.readInt16()
chunk.keyG = chunk.readInt16()
chunk.keyB = chunk.readInt16()
else:
raise PNGError("tRNS chunk not allowed for other color models")
result = true
method parseChunk(chunk: PNGBackground, png: PNG): bool =
var header = PNGHeader(png.getChunk(IHDR))
if header.colorType == LCT_PALETTE:
# error: this chunk must be 1 byte for indexed color image
if chunk.length != 1: raise PNGError("bkgd must be 1 byte")
chunk.bkgdR = chunk.readByte()
chunk.bkgdG = chunk.bkgdR
chunk.bkgdB = chunk.bkgdR
elif header.colorType in {LCT_GREY, LCT_GREY_ALPHA}:
# error: this chunk must be 2 bytes for greyscale image
if chunk.length != 2: raise PNGError("bkgd must be 2 byte")
chunk.bkgdR = chunk.readInt16()
chunk.bkgdG = chunk.bkgdR
chunk.bkgdB = chunk.bkgdR
elif header.colorType in {LCT_RGB, LCT_RGBA}:
# error: this chunk must be 6 bytes for greyscale image
if chunk.length != 6: raise PNGError("bkgd must be 6 byte")
chunk.bkgdR = chunk.readInt16()
chunk.bkgdG = chunk.readInt16()
chunk.bkgdB = chunk.readInt16()
result = true
proc initChunk(chunk: PNGChunk, chunkType: PNGChunkType, data: string, crc: uint32) =
chunk.length = data.len
chunk.crc = crc
chunk.chunkType = chunkType
chunk.data = data
chunk.pos = 0
method validateChunk(chunk: PNGTime, png: PNG): bool =
if chunk.year < 0 or chunk.year > 65535: raise PNGError("invalid year range[0..65535]")
if chunk.month < 1 or chunk.month > 12: raise PNGError("invalid month range[1..12]")
if chunk.day < 1 or chunk.day > 31: raise PNGError("invalid day range[1..32]")
if chunk.hour < 0 or chunk.hour > 23: raise PNGError("invalid hour range[0..23]")
if chunk.minute < 0 or chunk.minute > 59: raise PNGError("invalid minute range[0..59]")
#to allow for leap seconds
if chunk.second < 0 or chunk.second > 60: raise PNGError("invalid second range[0..60]")
result = true
method parseChunk(chunk: PNGTime, png: PNG): bool =
if chunk.length != 7: raise PNGError("tIME must be 7 bytes")
chunk.year = chunk.readInt16()
chunk.month = chunk.readByte()
chunk.day = chunk.readByte()
chunk.hour = chunk.readByte()
chunk.minute = chunk.readByte()
chunk.second = chunk.readByte()
result = true
method parseChunk(chunk: PNGPhys, png: PNG): bool =
if chunk.length != 9: raise PNGError("pHYs must be 9 bytes")
chunk.physX = chunk.readInt32()
chunk.physY = chunk.readInt32()
chunk.unit = chunk.readByte()
result = true
method validateChunk(chunk: PNGText, png: PNG): bool =
if(chunk.keyword.len < 1) or (chunk.keyword.len > 79):
raise PNGError("keyword too short or too long")
result = true
method parseChunk(chunk: PNGText, png: PNG): bool =
var len = 0
while(len < chunk.length) and (chunk.data[len] != chr(0)): inc len
if(len < 1) or (len > 79): raise PNGError("keyword too short or too long")
chunk.keyword = chunk.data.substr(0, len)
var textBegin = len + 1 # skip keyword null terminator
chunk.text = chunk.data.substr(textBegin)
result = true
method validateChunk(chunk: PNGZtxt, png: PNG): bool =
if(chunk.keyword.len < 1) or (chunk.keyword.len > 79):
raise PNGError("keyword too short or too long")
result = true
method parseChunk(chunk: PNGZtxt, png: PNG): bool =
var len = 0
while(len < chunk.length) and (chunk.data[len] != chr(0)): inc len
if(len < 1) or (len > 79): raise PNGError("keyword too short or too long")
chunk.keyword = chunk.data.substr(0, len)
var compMethod = ord(chunk.data[len + 1]) # skip keyword null terminator
if compMethod != 0: raise PNGError("unsupported comp method")
var nz = nzInflateInit(chunk.data.substr(len + 2))
chunk.text = zlib_decompress(nz)
result = true
method validateChunk(chunk: PNGItxt, png: PNG): bool =
if(chunk.keyword.len < 1) or (chunk.keyword.len > 79):
raise PNGError("keyword too short or too long")
result = true
method parseChunk(chunk: PNGItxt, png: PNG): bool =
if chunk.length < 5: raise PNGError("iTXt len too short")
var len = 0
while(len < chunk.length) and (chunk.data[len] != chr(0)): inc len
if(len + 3) >= chunk.length: raise PNGError("no null termination char, corrupt?")
if(len < 1) or (len > 79): raise PNGError("keyword too short or too long")
chunk.keyword = chunk.data.substr(0, len)
var compressed = ord(chunk.data[len + 1]) == 1 # skip keyword null terminator
var compMethod = ord(chunk.data[len + 2])
if compMethod != 0: raise PNGError("unsupported comp method")
len = 0
var i = len + 3
while(i < chunk.length) and (chunk.data[i] != chr(0)):
inc len
inc i
chunk.languageTag = chunk.data.substr(i, i + len)
len = 0
i += len + 1
while(i < chunk.length) and (chunk.data[i] != chr(0)):
inc len
inc i
chunk.translatedKeyword = chunk.data.substr(i, i + len)
let textBegin = i + len + 1
if compressed:
var nz = nzInflateInit(chunk.data.substr(textBegin))
chunk.text = zlib_decompress(nz)
else:
chunk.text = chunk.data.substr(textBegin)
result = true
method parseChunk(chunk: PNGGamma, png: PNG): bool =
if chunk.length != 4: raise PNGError("invalid gAMA length")
chunk.gamma = chunk.readInt32()
result = true
method parseChunk(chunk: PNGChroma, png: PNG): bool =
if chunk.length != 32: raise PNGError("invalid Chroma length")
chunk.whitePointX = chunk.readInt32()
chunk.whitePointY = chunk.readInt32()
chunk.redX = chunk.readInt32()
chunk.redY = chunk.readInt32()
chunk.greenX = chunk.readInt32()
chunk.greenY = chunk.readInt32()
chunk.blueX = chunk.readInt32()
chunk.blueY = chunk.readInt32()
result = true
method parseChunk(chunk: PNGStandarRGB, png: PNG): bool =
if chunk.length != 1: raise PNGError("invalid sRGB length")
chunk.renderingIntent = chunk.readByte()
result = true
method validateChunk(chunk: PNGICCProfile, png: PNG): bool =
if(chunk.profileName.len < 1) or (chunk.profileName.len > 79):
raise PNGError("keyword too short or too long")
result = true
method parseChunk(chunk: PNGICCProfile, png: PNG): bool =
var len = 0
while(len < chunk.length) and (chunk.data[len] != chr(0)): inc len
if(len < 1) or (len > 79): raise PNGError("keyword too short or too long")
chunk.profileName = chunk.data.substr(0, len)
var compMethod = ord(chunk.data[len + 1]) # skip keyword null terminator
if compMethod != 0: raise PNGError("unsupported comp method")
var nz = nzInflateInit(chunk.data.substr(len + 2))
chunk.profile = zlib_decompress(nz)
result = true
method parseChunk(chunk: PNGSPalette, png: PNG): bool =
var len = 0
while(len < chunk.length) and (chunk.data[len] != chr(0)): inc len
if(len < 1) or (len > 79): raise PNGError("keyword too short or too long")
chunk.paletteName = chunk.data.substr(0, len)
chunk.setPosition(len + 1)
chunk.sampleDepth = chunk.readByte()
if chunk.sampleDepth notin {8, 16}: raise PNGError("palette sample depth error")
let remainingLength = (chunk.length - (len + 2))
if chunk.sampleDepth == 8:
if (remainingLength mod 6) != 0: raise PNGError("palette length not divisible by 6")
let numSamples = remainingLength div 6
newSeq(chunk.palette, numSamples)
for p in mitems(chunk.palette):
p.red = chunk.readByte()
p.green = chunk.readByte()
p.blue = chunk.readByte()
p.alpha = chunk.readByte()
p.frequency = chunk.readInt16()
else: # chunk.sampleDepth == 16:
if (remainingLength mod 10) != 0: raise PNGError("palette length not divisible by 10")
let numSamples = remainingLength div 10
newSeq(chunk.palette, numSamples)
for p in mitems(chunk.palette):
p.red = chunk.readInt16()
p.green = chunk.readInt16()
p.blue = chunk.readInt16()
p.alpha = chunk.readInt16()
p.frequency = chunk.readInt16()
result = true
method parseChunk(chunk: PNGHist, png: PNG): bool =
if not png.hasChunk(PLTE): raise PNGError("Histogram need PLTE")
var plte = PNGPalette(png.getChunk(PLTE))
if plte.palette.len != (chunk.length div 2): raise PNGError("invalid histogram length")
newSeq(chunk.histogram, plte.palette.len)
for i in 0..chunk.histogram.high:
chunk.histogram[i] = chunk.readInt16()
result = true
method parseChunk(chunk: PNGSbit, png: PNG): bool =
let header = PNGHEader(png.getChunk(IHDR))
var expectedLen = 0
case header.colorType
of LCT_GREY: expectedLen = 1
of LCT_RGB: expectedLen = 3
of LCT_PALETTE: expectedLen = 3
of LCT_GREY_ALPHA: expectedLen = 2
of LCT_RGBA: expectedLen = 4
if chunk.length != expectedLen: raise PNGError("invalid sBIT length")
var expectedDepth = 8 #LCT_PALETTE
if header.colorType != LCT_PALETTE: expectedDepth = header.bitDepth
for c in chunk.data:
if (ord(c) == 0) or (ord(c) > expectedDepth): raise PNGError("invalid sBIT value")
result = true
proc make[T](): T = new(result)
proc createChunk(png: PNG, chunkType: PNGChunkType, data: string, crc: uint32): PNGChunk =
var settings = PNGDecoderSettings(png.settings)
if chunkType == IHDR: result = make[PNGHeader]()
elif chunkType == PLTE: result = make[PNGPalette]()
elif chunkType == IDAT:
if not png.hasChunk(IDAT): result = make[PNGData]()
else:
var idat = PNGData(png.getChunk(IDAT))
idat.data.add data
return idat
elif chunkType == tRNS: result = make[PNGTrans]()
elif chunkType == bKGD: result = make[PNGBackground]()
elif chunkType == tIME: result = make[PNGTime]()
elif chunkType == pHYs: result = make[PNGPhys]()
elif chunkType == tEXt:
if settings.readTextChunks: result = make[PNGTExt]()
else:
if settings.rememberUnknownChunks: new(result)
elif chunkType == zTXt:
if settings.readTextChunks: result = make[PNGZtxt]()
else:
if settings.rememberUnknownChunks: new(result)
elif chunkType == iTXt:
if settings.readTextChunks: result = make[PNGItxt]()
else:
if settings.rememberUnknownChunks: new(result)
elif chunkType == gAMA: result = make[PNGGamma]()
elif chunkType == cHRM: result = make[PNGChroma]()
elif chunkType == iCCP: result = make[PNGICCProfile]()
elif chunkType == sRGB: result = make[PNGStandarRGB]()
elif chunkType == sPLT: result = make[PNGSPalette]()
elif chunkType == hIST: result = make[PNGHist]()
elif chunkType == sBIT: result = make[PNGSbit]()
else:
if settings.rememberUnknownChunks: new(result)
if result != nil:
result.initChunk(chunkType, data, crc)
proc parsePNG(s: Stream, settings: PNGDecoderSettings): PNG =
var png: PNG
new(png)
png.chunks = @[]
if settings == nil: png.settings = makeDefaultPNGDecoderSettings()
else: png.settings = settings
let signature = s.readStr(8)
if signature != PNGSignature: raise PNGError("signature mismatch")
while not s.atEnd():
let length = s.readInt32BE()
let chunkType = PNGChunkType(s.readInt32BE())
if chunkType == IEND: break
let data = s.readStr(length)
let crc = cast[uint32](s.readInt32BE())
let calculatedCRC = crc32(crc32(0, $chunkType), data)
if calculatedCRC != crc and not PNGDecoderSettings(png.settings).ignoreCRC:
raise PNGError("wrong crc for: " & $chunkType)
var chunk = png.createChunk(chunkType, data, crc)
if chunkType != IDAT and chunk != nil:
if not chunk.parseChunk(png): raise PNGError("error parse chunk: " & $chunkType)
if not chunk.validateChunk(png): raise PNGError("invalid chunk: " & $chunkType)
if chunk != nil: png.chunks.add chunk
if not png.hasChunk(IHDR): raise PNGError("no IHDR found")
if not png.hasChunk(IDAT): raise PNGError("no IDAT found")
var header = PNGHeader(png.getChunk(IHDR))
if header.colorType == LCT_PALETTE and not png.hasChunk(PLTE):
raise PNGError("expected PLTE not found")
# IDAT get special treatment because it can appear in multiple chunk
var idat = PNGData(png.getChunk(IDAT))
if not idat.parseChunk(png): raise PNGError("IDAT parse error")
if not idat.validateChunk(png): raise PNGError("bad IDAT")
result = png
# Paeth predicter, used by PNG filter type 4
proc paethPredictor(a, b, c: int): int =
let pa = abs(b - c)
let pb = abs(a - c)
let pc = abs(a + b - c - c)
if(pc < pa) and (pc < pb): return c
elif pb < pa: return b
result = a
proc readBitFromReversedStream(bitptr: var int, bitstream: cstring): int =
result = ((ord(bitstream[bitptr shr 3]) shr (7 - (bitptr and 0x7))) and 1)
inc bitptr
proc readBitsFromReversedStream(bitptr: var int, bitstream: cstring, nbits: int): int =
result = 0
var i = nbits - 1
while i > -1:
result += readBitFromReversedStream(bitptr, bitstream) shl i
dec i
proc `&=`(a: var char, b: char) =
a = chr(ord(a) and ord(b))
proc `|=`(a: var char, b: char) =
a = chr(ord(a) or ord(b))
proc setBitOfReversedStream0(bitptr: var int, bitstream: var cstring, bit: int) =
# the current bit in bitstream must be 0 for this to work
if bit != 0:
# earlier bit of huffman code is in a lesser significant bit of an earlier byte
bitstream[bitptr shr 3] |= cast[char](bit shl (7 - (bitptr and 0x7)))
inc bitptr
proc setBitOfReversedStream(bitptr: var int, bitstream: var cstring, bit: int) =
#the current bit in bitstream may be 0 or 1 for this to work
if bit == 0: bitstream[bitptr shr 3] &= cast[char](not (1 shl (7 - (bitptr and 0x7))))
else: bitstream[bitptr shr 3] |= cast[char](1 shl (7 - (bitptr and 0x7)))
inc bitptr
# index: bitgroup index, bits: bitgroup size(1, 2 or 4), in: bitgroup value, out: octet array to add bits to
proc addColorBits(output: var cstring, index, bits, input: int) =
var m = 1
if bits == 1: m = 7
elif bits == 2: m = 3
# p = the partial index in the byte, e.g. with 4 palettebits it is 0 for first half or 1 for second half
let p = index and m
var val = input and ((1 shl bits) - 1) #filter out any other bits of the input value
val = val shl (bits * (m - p))
let idx = index * bits div 8
if p == 0: output[idx] = chr(val)
else: output[idx] = chr(ord(output[idx]) or val)
proc unfilterScanLine(recon: var cstring, scanLine, precon: cstring, byteWidth, len: int, filterType: PNGFilter0) =
# For PNG filter method 0
# unfilter a PNG image scanLine by scanLine. when the pixels are smaller than 1 byte,
# the filter works byte per byte (byteWidth = 1)
# precon is the previous unfiltered scanLine, recon the result, scanLine the current one
# the incoming scanLines do NOT include the filtertype byte, that one is given in the parameter filterType instead
# recon and scanLine MAY be the same memory address! precon must be disjoint.
case filterType
of FLT_NONE:
for i in 0..len-1: recon[i] = scanLine[i]
of FLT_SUB:
for i in 0..byteWidth-1: recon[i] = scanLine[i]
for i in byteWidth..len-1: recon[i] = chr((ord(scanLine[i]) + ord(recon[i - byteWidth])) mod 256)
of FLT_UP:
if precon != nil:
for i in 0..len-1: recon[i] = chr((ord(scanLine[i]) + ord(precon[i])) mod 256)
else:
for i in 0..len-1: recon[i] = scanLine[i]
of FLT_AVERAGE:
if precon != nil:
for i in 0..byteWidth-1:
recon[i] = chr((ord(scanLine[i]) + ord(precon[i]) div 2) mod 256)
for i in byteWidth..len-1:
recon[i] = chr((ord(scanLine[i]) + ((ord(recon[i - byteWidth]) + ord(precon[i])) div 2)) mod 256)
else:
for i in 0..byteWidth-1: recon[i] = scanLine[i]
for i in byteWidth..len-1:
recon[i] = chr((ord(scanLine[i]) + ord(recon[i - byteWidth]) div 2) mod 256)
of FLT_PAETH:
if precon != nil:
for i in 0..byteWidth-1:
recon[i] = chr((ord(scanLine[i]) + ord(precon[i])) mod 256) #paethPredictor(0, precon[i], 0) is always precon[i]
for i in byteWidth..len-1:
recon[i] = chr((ord(scanLine[i]) + paethPredictor(ord(recon[i - byteWidth]), ord(precon[i]), ord(precon[i - byteWidth]))) mod 256)
else:
for i in 0..byteWidth-1: recon[i] = scanLine[i]
for i in byteWidth..len-1:
# paethPredictor(recon[i - byteWidth], 0, 0) is always recon[i - byteWidth]
recon[i] = chr((ord(scanLine[i]) + ord(recon[i - byteWidth])) mod 256)
proc unfilter(output: var cstring, input: cstring, w, h, bpp: int) =
# For PNG filter method 0
# this function unfilters a single image (e.g. without interlacing this is called once, with Adam7 seven times)
# output must have enough bytes allocated already, input must have the scanLines + 1 filtertype byte per scanLine
# w and h are image dimensions or dimensions of reduced image, bpp is bits per pixel
# input and output are allowed to be the same memory address (but aren't the same size since in has the extra filter bytes)
var prevLine = cstring(nil)
var inp = input
# byteWidth is used for filtering, is 1 when bpp < 8, number of bytes per pixel otherwise
let byteWidth = (bpp + 7) div 8
let lineBytes = (w * bpp + 7) div 8
for y in 0..h-1:
let outIndex = lineBytes * y
let inIndex = (1 + lineBytes) * y # the extra filterbyte added to each row
let filterType = PNGFilter0(input[inindex])
let scanLine: cstring = addr(inp[inIndex + 1])
var outp: cstring = addr(output[outIndex])
unfilterScanLine(outp, scanLine, prevLine, byteWidth, lineBytes, filterType)
prevLine = addr(output[outIndex])
proc removePaddingBits(output: var cstring, input: cstring, olinebits, ilinebits, h: int) =
# After filtering there are still padding bits if scanLines have non multiple of 8 bit amounts. They need
# to be removed (except at last scanLine of (Adam7-reduced) image) before working with pure image buffers
# for the Adam7 code, the color convert code and the output to the user.
# in and out are allowed to be the same buffer, in may also be higher but still overlapping; in must
# have >= ilinebits*h bits, out must have >= olinebits*h bits, olinebits must be <= ilinebits
# also used to move bits after earlier such operations happened, e.g. in a sequence of reduced images from Adam7
# only useful if (ilinebits - olinebits) is a value in the range 1..7
let diff = ilinebits - olinebits
var
ibp = 0
obp = 0 # input and output bit pointers
for y in 0..h-1:
for x in 0..olinebits-1:
var bit = readBitFromReversedStream(ibp, input)
setBitOfReversedStream(obp, output, bit)
inc(ibp, diff)
# Outputs various dimensions and positions in the image related to the Adam7 reduced images.
# passw: output containing the width of the 7 passes
# passh: output containing the height of the 7 passes
# filter_passstart: output containing the index of the start and end of each
# reduced image with filter bytes
# padded_passstart output containing the index of the start and end of each
# reduced image when without filter bytes but with padded scanLines
# passstart: output containing the index of the start and end of each reduced
# image without padding between scanLines, but still padding between the images
# w, h: width and height of non-interlaced image
# bpp: bits per pixel
# "padded" is only relevant if bpp is less than 8 and a scanLine or image does not
# end at a full byte
proc Adam7PassValues(pass: var PNGPass, w, h, bpp: int) =
#the passstart values have 8 values:
# the 8th one indicates the byte after the end of the 7th (= last) pass
# calculate width and height in pixels of each pass
for i in 0..6:
pass.w[i] = (w + ADAM7_DX[i] - ADAM7_IX[i] - 1) div ADAM7_DX[i]
pass.h[i] = (h + ADAM7_DY[i] - ADAM7_IY[i] - 1) div ADAM7_DY[i]
if pass.w[i] == 0: pass.h[i] = 0
if pass.h[i] == 0: pass.w[i] = 0
pass.filterStart[0] = 0
pass.paddedStart[0] = 0
pass.start[0] = 0
for i in 0..6:
# if passw[i] is 0, it's 0 bytes, not 1 (no filtertype-byte)
pass.filterStart[i + 1] = pass.filterStart[i]
if (pass.w[i] != 0) and (pass.h[i] != 0):
pass.filterStart[i + 1] += pass.h[i] * (1 + (pass.w[i] * bpp + 7) div 8)
# bits padded if needed to fill full byte at end of each scanLine
pass.paddedStart[i + 1] = pass.paddedStart[i] + pass.h[i] * ((pass.w[i] * bpp + 7) div 8)
# only padded at end of reduced image
pass.start[i + 1] = pass.start[i] + (pass.h[i] * pass.w[i] * bpp + 7) div 8
# input: Adam7 interlaced image, with no padding bits between scanLines, but between
# reduced images so that each reduced image starts at a byte.
# output: the same pixels, but re-ordered so that they're now a non-interlaced image with size w*h
# bpp: bits per pixel
# output has the following size in bits: w * h * bpp.
# input is possibly bigger due to padding bits between reduced images.
# output must be big enough AND must be 0 everywhere if bpp < 8 in the current implementation
# (because that's likely a little bit faster)
# NOTE: comments about padding bits are only relevant if bpp < 8
proc Adam7Deinterlace(output: var cstring, input: cstring, w, h, bpp: int) =
var pass: PNGPass
Adam7PassValues(pass, w, h, bpp)
if bpp >= 8:
for i in 0..6:
var byteWidth = bpp div 8
for y in 0..pass.h[i]-1:
for x in 0..pass.w[i]-1:
var inStart = pass.start[i] + (y * pass.w[i] + x) * byteWidth
var outStart = ((ADAM7_IY[i] + y * ADAM7_DY[i]) * w + ADAM7_IX[i] + x * ADAM7_DX[i]) * byteWidth
for b in 0..byteWidth-1:
output[outStart + b] = input[inStart + b]
else: # bpp < 8: Adam7 with pixels < 8 bit is a bit trickier: with bit pointers
for i in 0..6:
var ilinebits = bpp * pass.w[i]
var olinebits = bpp * w
for y in 0..pass.h[i]-1:
for x in 0..pass.w[i]-1:
var ibp = (8 * pass.start[i]) + (y * ilinebits + x * bpp)
var obp = (ADAM7_IY[i] + y * ADAM7_DY[i]) * olinebits + (ADAM7_IX[i] + x * ADAM7_DX[i]) * bpp
for b in 0..bpp-1:
var bit = readBitFromReversedStream(ibp, input)
# note that this function assumes the out buffer is completely 0, use setBitOfReversedStream otherwise
setBitOfReversedStream0(obp, output, bit)
proc postProcessscanLines(png: PNG) =
# This function converts the filtered-padded-interlaced data
# into pure 2D image buffer with the PNG's colorType.
# Steps:
# *) if no Adam7: 1) unfilter 2) remove padding bits (= posible extra bits per scanLine if bpp < 8)
# *) if adam7: 1) 7x unfilter 2) 7x remove padding bits 3) Adam7_deinterlace
# NOTE: the input buffer will be overwritten with intermediate data!
var header = PNGHeader(png.getChunk(IHDR))
let bpp = header.getBPP()
let w = header.width
let h = header.height
let bitsPerLine = w * bpp
let bitsPerPaddedLine = ((w * bpp + 7) div 8) * 8
var idat = PNGData(png.getChunk(IDAT))
png.pixels = newString(idatRawSize(header.width, header.height, header))
var input = cstring(idat.idat)
var output = cstring(png.pixels)
zeroMem(output, png.pixels.len)
if header.interlaceMethod == IM_NONE:
if(bpp < 8) and (bitsPerLine != bitsPerPaddedLine):
unfilter(input, input, w, h, bpp)
removePaddingBits(output, input, bitsPerLine, bitsPerPaddedLine, h)
# we can immediatly filter into the out buffer, no other steps needed
else: unfilter(output, input, w, h, bpp)
else: # interlace_method is 1 (Adam7)
var pass: PNGPass
Adam7PassValues(pass, w, h, bpp)
for i in 0..6:
var outp: cstring = addr(input[pass.paddedStart[i]])
var inp: cstring = addr(input[pass.filterStart[i]])
unfilter(outp, inp, pass.w[i], pass.h[i], bpp)
# TODO: possible efficiency improvement:
# if in this reduced image the bits fit nicely in 1 scanLine,
# move bytes instead of bits or move not at all
if bpp < 8:
# remove padding bits in scanLines; after this there still may be padding
# bits between the different reduced images: each reduced image still starts nicely at a byte
outp = addr(input[pass.start[i]])
inp = addr(input[pass.paddedStart[i]])
removePaddingBits(outp, inp, pass.w[i] * bpp, ((pass.w[i] * bpp + 7) div 8) * 8, pass.h[i])
Adam7Deinterlace(output, input, w, h, bpp)
proc getColorMode(png: PNG): PNGColorMode =
var header = PNGHeader(png.getChunk(IHDR))
var cm = newColorMode(header.colorType, header.bitDepth)
var plte = PNGPalette(png.getChunk(PLTE))
if plte != nil:
cm.paletteSize = plte.palette.len
newSeq(cm.palette, cm.paletteSize)
for i in 0..cm.paletteSize-1: cm.palette[i] = plte.palette[i]
var trans = PNGTrans(png.getChunk(tRNS))
if trans != nil:
if cm.colorType in {LCT_GREY, LCT_RGB}:
cm.keyDefined = true
cm.keyR = trans.keyR
cm.keyG = trans.keyG
cm.keyB = trans.keyB
result = cm
proc RGBFromGrey8(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 3
output[x] = input[i]
output[x+1] = input[i]
output[x+2] = input[i]
proc RGBFromGrey16(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 3
let y = i * 2
output[x] = input[y]
output[x+1] = input[y]
output[x+2] = input[y]
proc RGBFromGrey124(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
var highest = ((1 shl mode.bitDepth) - 1) #highest possible value for this bit depth
var obp = 0
for i in 0..numPixels-1:
let val = chr((readBitsFromReversedStream(obp, input, mode.bitDepth) * 255) div highest)
let x = i * 3
output[x] = val
output[x+1] = val
output[x+2] = val
proc RGBFromRGB8(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 3
output[x] = input[x]
output[x+1] = input[x+1]
output[x+2] = input[x+2]
proc RGBFromRGB16(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 3
let y = i * 6
output[x] = input[y]
output[x+1] = input[y+2]
output[x+2] = input[y+4]
proc RGBFromPalette8(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 3
let index = ord(input[i])
if index >= mode.paletteSize:
# This is an error according to the PNG spec, but most PNG decoders make it black instead.
# Done here too, slightly faster due to no error handling needed.
output[x] = chr(0)
output[x+1] = chr(0)
output[x+2] = chr(0)
else:
output[x] = mode.palette[index].r
output[x+1] = mode.palette[index].g
output[x+2] = mode.palette[index].b
proc RGBFromPalette124(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
var obp = 0
for i in 0..numPixels-1:
let x = i * 3
let index = readBitsFromReversedStream(obp, input, mode.bitDepth)
if index >= mode.paletteSize:
# This is an error according to the PNG spec, but most PNG decoders make it black instead.
# Done here too, slightly faster due to no error handling needed.
output[x] = chr(0)
output[x+1] = chr(0)
output[x+2] = chr(0)
else:
output[x] = mode.palette[index].r
output[x+1] = mode.palette[index].g
output[x+2] = mode.palette[index].b
proc RGBFromGreyAlpha8(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 3
let val = input[i * 2]
output[x] = val
output[x+1] = val
output[x+2] = val
proc RGBFromGreyAlpha16(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 3
let val = input[i * 4]
output[x] = val
output[x+1] = val
output[x+2] = val
proc RGBFromRGBA8(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 3
let y = i * 4
output[x] = input[y]
output[x+1] = input[y+1]
output[x+2] = input[y+2]
proc RGBFromRGBA16(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 3
let y = i * 8
output[x] = input[y]
output[x+1] = input[y+2]
output[x+2] = input[y+4]
proc RGBAFromGrey8(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 4
output[x] = input[i]
output[x+1] = input[i]
output[x+2] = input[i]
if mode.keyDefined and (ord(input[i]) == mode.keyR): output[x+3] = chr(0)
else: output[x+3] = chr(255)
proc RGBAFromGrey16(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 4
let y = i * 2
output[x] = input[y]
output[x+1] = input[y]
output[x+2] = input[y]
let keyR = 256 * ord(input[y + 0]) + ord(input[y + 1])
if mode.keyDefined and (keyR == mode.keyR): output[x+3] = chr(0)
else: output[x+3] = chr(255)
proc RGBAFromGrey124(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
var highest = ((1 shl mode.bitDepth) - 1) #highest possible value for this bit depth
var obp = 0
for i in 0..numPixels-1:
let val = chr((readBitsFromReversedStream(obp, input, mode.bitDepth) * 255) div highest)
let x = i * 4
output[x] = val
output[x+1] = val
output[x+2] = val
if mode.keyDefined and (ord(val) == mode.keyR): output[x+3] = chr(0)
else: output[x+3] = chr(255)
proc RGBAFromRGB8(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 4
output[x] = input[x]
output[x+1] = input[x+1]
output[x+2] = input[x+2]
if mode.keyDefined and (mode.keyR == ord(input[x])) and
(mode.keyG == ord(input[x+1])) and (mode.keyB == ord(input[x+2])): output[x+3] = chr(0)
else: output[x+3] = chr(255)
proc RGBAFromRGB16(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 4
let y = i * 6
output[x] = input[y]
output[x+1] = input[y+2]
output[x+2] = input[y+4]
let keyR = 256 * ord(input[y]) + ord(input[y+1])
let keyG = 256 * ord(input[y+2]) + ord(input[y+3])
let keyB = 256 * ord(input[y+4]) + ord(input[y+5])
if mode.keyDefined and (mode.keyR == keyR) and
(mode.keyG == keyG) and (mode.keyB == keyB): output[x+3] = chr(0)
else: output[x+3] = chr(255)
proc RGBAFromPalette8(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 4
let index = ord(input[i])
if index >= mode.paletteSize:
# This is an error according to the PNG spec, but most PNG decoders make it black instead.
# Done here too, slightly faster due to no error handling needed.
output[x] = chr(0)
output[x+1] = chr(0)
output[x+2] = chr(0)
output[x+3] = chr(0)
else:
output[x] = mode.palette[index].r
output[x+1] = mode.palette[index].g
output[x+2] = mode.palette[index].b
output[x+3] = mode.palette[index].a
proc RGBAFromPalette124(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
var obp = 0
for i in 0..numPixels-1:
let x = i * 4
let index = readBitsFromReversedStream(obp, input, mode.bitDepth)
if index >= mode.paletteSize:
# This is an error according to the PNG spec, but most PNG decoders make it black instead.
# Done here too, slightly faster due to no error handling needed.
output[x] = chr(0)
output[x+1] = chr(0)
output[x+2] = chr(0)
output[x+3] = chr(0)
else:
output[x] = mode.palette[index].r
output[x+1] = mode.palette[index].g
output[x+2] = mode.palette[index].b
output[x+3] = mode.palette[index].a
proc RGBAFromGreyAlpha8(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 4
let val = input[i * 2]
output[x] = val
output[x+1] = val
output[x+2] = val
output[x+3] = input[i * 2 + 1]
proc RGBAFromGreyAlpha16(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 4
let val = input[i * 4]
output[x] = val
output[x+1] = val
output[x+2] = val
output[x+3] = input[i * 4 + 2]
proc RGBAFromRGBA8(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 4
let y = i * 4
output[x] = input[y]
output[x+1] = input[y+1]
output[x+2] = input[y+2]
output[x+3] = input[y+3]
proc RGBAFromRGBA16(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode) =
for i in 0..numPixels-1:
let x = i * 4
let y = i * 8
output[x] = input[y]
output[x+1] = input[y+2]
output[x+2] = input[y+4]
output[x+3] = input[y+6]
type
convertRGBA = proc(output: var cstring, input: cstring, numPixels: int, mode: PNGColorMode)
convertRGBA8 = proc(p: var RGBA8, input: cstring, px: int, mode: PNGColorMode)
convertRGBA16 = proc(p: var RGBA16, input: cstring, px: int, mode: PNGColorMode)
pixelRGBA8 = proc(p: RGBA8, output: var cstring, px: int, mode: PNGColorMode, ct: ColorTree8)
pixelRGBA16 = proc(p: RGBA16, output: var cstring, px: int, mode: PNGColorMode)
proc hash*(c: RGBA8): THash =
var h: THash = 0
h = h !& ord(c.r)
h = h !& ord(c.g)
h = h !& ord(c.b)
h = h !& ord(c.a)
proc RGBA8FromGrey8(p: var RGBA8, input: cstring, px: int, mode: PNGColorMode) =
p.r = input[px]
p.g = input[px]
p.b = input[px]
if mode.keyDefined and (ord(p.r) == mode.keyR): p.a = chr(0)
else: p.a = chr(255)
proc RGBA8FromGrey16(p: var RGBA8, input: cstring, px: int, mode: PNGColorMode) =
let i = px * 2
let keyR = 256 * ord(input[i]) + ord(input[i + 1])
p.r = input[i]
p.g = input[i]
p.b = input[i]
if mode.keyDefined and (keyR == mode.keyR): p.a = chr(0)
else: p.a = chr(255)
proc RGBA8FromGrey124(p: var RGBA8, input: cstring, px: int, mode: PNGColorMode) =
let highest = ((1 shl mode.bitDepth) - 1) #highest possible value for this bit depth
var obp = px * mode.bitDepth
let val = chr((readBitsFromReversedStream(obp, input, mode.bitDepth) * 255) div highest)
p.r = val
p.g = val
p.b = val
if mode.keyDefined and (ord(val) == mode.keyR): p.a = chr(0)
else: p.a = chr(255)
proc RGBA8FromRGB8(p: var RGBA8, input: cstring, px: int, mode: PNGColorMode) =
let y = px * 3
p.r = input[y]
p.g = input[y+1]
p.b = input[y+2]
if mode.keyDefined and (mode.keyR == ord(input[y])) and
(mode.keyG == ord(input[y+1])) and (mode.keyB == ord(input[y+2])): p.a = chr(0)
else: p.a = chr(255)
proc RGBA8FromRGB16(p: var RGBA8, input: cstring, px: int, mode: PNGColorMode) =
let y = px * 6
p.r = input[y]
p.g = input[y+2]
p.b = input[y+4]
let keyR = 256 * ord(input[y]) + ord(input[y+1])
let keyG = 256 * ord(input[y+2]) + ord(input[y+3])
let keyB = 256 * ord(input[y+4]) + ord(input[y+5])
if mode.keyDefined and (mode.keyR == keyR) and
(mode.keyG == keyG) and (mode.keyB == keyB): p.a = chr(0)
else: p.a = chr(255)
proc RGBA8FromPalette8(p: var RGBA8, input: cstring, px: int, mode: PNGColorMode) =
let index = ord(input[px])
if index >= mode.paletteSize:
# This is an error according to the PNG spec,
# but common PNG decoders make it black instead.
# Done here too, slightly faster due to no error handling needed.
p.r = chr(0)
p.g = chr(0)
p.b = chr(0)
p.a = chr(255)
else:
p.r = mode.palette[index].r
p.g = mode.palette[index].g
p.b = mode.palette[index].b
p.a = mode.palette[index].a
proc RGBA8FromPalette124(p: var RGBA8, input: cstring, px: int, mode: PNGColorMode) =
var obp = px * mode.bitDepth
let index = readBitsFromReversedStream(obp, input, mode.bitDepth)
if index >= mode.paletteSize:
# This is an error according to the PNG spec,
# but common PNG decoders make it black instead.
# Done here too, slightly faster due to no error handling needed.
p.r = chr(0)
p.g = chr(0)
p.b = chr(0)
p.a = chr(255)
else:
p.r = mode.palette[index].r
p.g = mode.palette[index].g
p.b = mode.palette[index].b
p.a = mode.palette[index].a
proc RGBA8FromGreyAlpha8(p: var RGBA8, input: cstring, px: int, mode: PNGColorMode) =
let i = px * 2
let val = input[i]
p.r = val
p.g = val
p.b = val
p.a = input[i+1]
proc RGBA8FromGreyAlpha16(p: var RGBA8, input: cstring, px: int, mode: PNGColorMode) =
let i = px * 4
let val = input[i]
p.r = val
p.g = val
p.b = val
p.a = input[i+2]
proc RGBA8FromRGBA8(p: var RGBA8, input: cstring, px: int, mode: PNGColorMode) =
let i = px * 4
p.r = input[i]
p.g = input[i+1]
p.b = input[i+2]
p.a = input[i+3]
proc RGBA8FromRGBA16(p: var RGBA8, input: cstring, px: int, mode: PNGColorMode) =
let i = px * 8
p.r = input[i]
p.g = input[i+2]
p.b = input[i+4]
p.a = input[i+6]
proc RGBA16FromGrey(p: var RGBA16, input: cstring, px: int, mode: PNGColorMode) =
let i = px * 2
let val = 256 * ord(input[i]) + ord(input[i + 1])
p.r = val
p.g = val
p.b = val
if mode.keyDefined and (val == mode.keyR): p.a = 0
else: p.a = 65535
proc RGBA16FromRGB(p: var RGBA16, input: cstring, px: int, mode: PNGColorMode) =
let i = px * 6
p.r = 256 * ord(input[i]) + ord(input[i+1])
p.g = 256 * ord(input[i+2]) + ord(input[i+3])
p.b = 256 * ord(input[i+4]) + ord(input[i+5])
if mode.keyDefined and (int(p.r) == mode.keyR) and
(int(p.g) == mode.keyG) and (int(p.b) == mode.keyB): p.a = 0
else: p.a = 65535
proc RGBA16FromGreyAlpha(p: var RGBA16, input: cstring, px: int, mode: PNGColorMode) =
let i = px * 4
let val = 256 * ord(input[i]) + ord(input[i + 1])
p.r = val
p.g = val
p.b = val
p.a = 256 * ord(input[px + 2]) + ord(input[px + 3])
proc RGBA16FromRGBA(p: var RGBA16, input: cstring, px: int, mode: PNGColorMode) =
let i = px * 8
p.r = 256 * ord(input[i]) + ord(input[i+1])
p.g = 256 * ord(input[i+2]) + ord(input[i+3])
p.b = 256 * ord(input[i+4]) + ord(input[i+5])
p.a = 256 * ord(input[i+6]) + ord(input[i+7])
proc RGBA8ToGrey8(p: RGBA8, output: var cstring, px: int, mode: PNGColorMode, ct: ColorTree8) =
output[px] = p.r
proc RGBA8ToGrey16(p: RGBA8, output: var cstring, px: int, mode: PNGColorMode, ct: ColorTree8) =
let i = px * 2
output[i] = p.r
output[i+1] = p.r
proc RGBA8ToGrey124(p: RGBA8, output: var cstring, px: int, mode: PNGColorMode, ct: ColorTree8) =
# take the most significant bits of grey
let grey = (ord(p.r) shr (8 - mode.bitDepth)) and ((1 shl mode.bitDepth) - 1)
addColorBits(output, px, mode.bitDepth, grey)
proc RGBA8ToRGB8(p: RGBA8, output: var cstring, px: int, mode: PNGColorMode, ct: ColorTree8) =
let i = px * 3
output[i] = p.r
output[i+1] = p.g
output[i+2] = p.b
proc RGBA8ToRGB16(p: RGBA8, output: var cstring, px: int, mode: PNGColorMode, ct: ColorTree8) =
let i = px * 6
output[i] = p.r
output[i+2] = p.g
output[i+4] = p.b
output[i+1] = p.r
output[i+3] = p.g
output[i+5] = p.b
proc RGBA8ToPalette8(p: RGBA8, output: var cstring, px: int, mode: PNGColorMode, ct: ColorTree8) =
output[px] = chr(ct[p])
proc RGBA8ToPalette124(p: RGBA8, output: var cstring, px: int, mode: PNGColorMode, ct: ColorTree8) =
addColorBits(output, px, mode.bitDepth, ct[p])
proc RGBA8ToGreyAlpha8(p: RGBA8, output: var cstring, px: int, mode: PNGColorMode, ct: ColorTree8) =
let i = px * 2
output[i] = p.r
output[i+1] = p.a
proc RGBA8ToGreyAlpha16(p: RGBA8, output: var cstring, px: int, mode: PNGColorMode, ct: ColorTree8) =
let i = px * 4
output[i] = p.r
output[i+1] = p.r
output[i+2] = p.a
output[i+3] = p.a
proc RGBA8ToRGBA8(p: RGBA8, output: var cstring, px: int, mode: PNGColorMode, ct: ColorTree8) =
let i = px * 4
output[i] = p.r
output[i+1] = p.g
output[i+2] = p.b
output[i+3] = p.a
proc RGBA8ToRGBA16(p: RGBA8, output: var cstring, px: int, mode: PNGColorMode, ct: ColorTree8) =
let i = px * 8
output[i] = p.r
output[i+2] = p.g
output[i+4] = p.b
output[i+6] = p.a
output[i+1] = p.r
output[i+3] = p.g
output[i+5] = p.b
output[i+7] = p.a
proc RGBA16ToGrey(p: RGBA16, output: var cstring, px: int, mode: PNGColorMode) =
let i = px * 2
output[i] = chr((ord(p.r) shr 8) and 255)
output[i+1] = chr(ord(p.r) and 255)
proc RGBA16ToRGB(p: RGBA16, output: var cstring, px: int, mode: PNGColorMode) =
let i = px * 6
output[i] = chr((ord(p.r) shr 8) and 255)
output[i+1] = chr(ord(p.r) and 255)
output[i+2] = chr((ord(p.g) shr 8) and 255)
output[i+3] = chr(ord(p.g) and 255)
output[i+4] = chr((ord(p.b) shr 8) and 255)
output[i+5] = chr(ord(p.b) and 255)
proc RGBA16ToGreyAlpha(p: RGBA16, output: var cstring, px: int, mode: PNGColorMode) =
let i = px * 4
output[i] = chr((ord(p.r) shr 8) and 255)
output[i+1] = chr(ord(p.r) and 255)
output[i+2] = chr((ord(p.a) shr 8) and 255)
output[i+3] = chr(ord(p.a) and 255)
proc RGBA16ToRGBA(p: RGBA16, output: var cstring, px: int, mode: PNGColorMode) =
let i = px * 8
output[i] = chr((ord(p.r) shr 8) and 255)
output[i+1] = chr(ord(p.r) and 255)
output[i+2] = chr((ord(p.g) shr 8) and 255)
output[i+3] = chr(ord(p.g) and 255)
output[i+4] = chr((ord(p.b) shr 8) and 255)
output[i+5] = chr(ord(p.b) and 255)
output[i+6] = chr((ord(p.a) shr 8) and 255)
output[i+7] = chr(ord(p.a) and 255)
proc getColorRGBA16(mode: PNGColorMode): convertRGBA16 =
if mode.colorType == LCT_GREY: return RGBA16FromGrey
elif mode.colorType == LCT_RGB: return RGBA16FromRGB
elif mode.colorType == LCT_GREY_ALPHA: return RGBA16FromGreyAlpha
elif mode.colorType == LCT_RGBA: return RGBA16FromRGBA
else: raise PNGError("unsupported converter16")
proc getPixelRGBA16(mode: PNGColorMode): pixelRGBA16 =
if mode.colorType == LCT_GREY: return RGBA16ToGrey
elif mode.colorType == LCT_RGB: return RGBA16ToRGB
elif mode.colorType == LCT_GREY_ALPHA: return RGBA16ToGreyAlpha
elif mode.colorType == LCT_RGBA: return RGBA16ToRGBA
else: raise PNGError("unsupported pixel16 converter")
proc getColorRGBA8(mode: PNGColorMode): convertRGBA8 =
if mode.colorType == LCT_GREY:
if mode.bitDepth == 8: return RGBA8FromGrey8
elif mode.bitDepth == 16: return RGBA8FromGrey16
else: return RGBA8FromGrey124
elif mode.colorType == LCT_RGB:
if mode.bitDepth == 8: return RGBA8FromRGB8
else: return RGBA8FromRGB16
elif mode.colorType == LCT_PALETTE:
if mode.bitDepth == 8: return RGBA8FromPalette8
else: return RGBA8FromPalette124
elif mode.colorType == LCT_GREY_ALPHA:
if mode.bitDepth == 8: return RGBA8FromGreyAlpha8
else: return RGBA8FromGreyAlpha16
elif mode.colorType == LCT_RGBA:
if mode.bitDepth == 8: return RGBA8FromRGBA8
else: return RGBA8FromRGBA16
else: raise PNGError("unsupported converter8")
proc getPixelRGBA8(mode: PNGColorMode): pixelRGBA8 =
if mode.colorType == LCT_GREY:
if mode.bitDepth == 8: return RGBA8ToGrey8
elif mode.bitDepth == 16: return RGBA8ToGrey16
else: return RGBA8ToGrey124
elif mode.colorType == LCT_RGB:
if mode.bitDepth == 8: return RGBA8ToRGB8
else: return RGBA8ToRGB16
elif mode.colorType == LCT_PALETTE:
if mode.bitDepth == 8: return RGBA8ToPalette8
else: return RGBA8ToPalette124
elif mode.colorType == LCT_GREY_ALPHA:
if mode.bitDepth == 8: return RGBA8ToGreyAlpha8
else: return RGBA8ToGreyAlpha16
elif mode.colorType == LCT_RGBA:
if mode.bitDepth == 8: return RGBA8ToRGBA8
else: return RGBA8ToRGBA16
else: raise PNGError("unsupported pixel8 converter")
proc getConverterRGB(mode: PNGColorMode): convertRGBA =
if mode.colorType == LCT_GREY:
if mode.bitDepth == 8: return RGBFromGrey8
elif mode.bitDepth == 16: return RGBFromGrey16
else: return RGBFromGrey124
elif mode.colorType == LCT_RGB:
if mode.bitDepth == 8: return RGBFromRGB8
else: return RGBFromRGB16
elif mode.colorType == LCT_PALETTE:
if mode.bitDepth == 8: return RGBFromPalette8
else: return RGBFromPalette124
elif mode.colorType == LCT_GREY_ALPHA:
if mode.bitDepth == 8: return RGBFromGreyAlpha8
else: return RGBFromGreyAlpha16
elif mode.colorType == LCT_RGBA:
if mode.bitDepth == 8: return RGBFromRGBA8
else: return RGBFromRGBA16
else: raise PNGError("unsupported RGB converter")
proc getConverterRGBA(mode: PNGColorMode): convertRGBA =
if mode.colorType == LCT_GREY:
if mode.bitDepth == 8: return RGBAFromGrey8
elif mode.bitDepth == 16: return RGBAFromGrey16
else: return RGBAFromGrey124
elif mode.colorType == LCT_RGB:
if mode.bitDepth == 8: return RGBAFromRGB8
else: return RGBAFromRGB16
elif mode.colorType == LCT_PALETTE:
if mode.bitDepth == 8: return RGBAFromPalette8
else: return RGBAFromPalette124
elif mode.colorType == LCT_GREY_ALPHA:
if mode.bitDepth == 8: return RGBAFromGreyAlpha8
else: return RGBAFromGreyAlpha16
elif mode.colorType == LCT_RGBA:
if mode.bitDepth == 8: return RGBAFromRGBA8
else: return RGBAFromRGBA16
else: raise PNGError("unsupported RGBA converter")
proc convert(output: var cstring, input: cstring, modeOut, modeIn: PNGColorMode, numPixels: int) =
var tree: ColorTree8
if modeOut.colorType == LCT_PALETTE:
let palSize = min(1 shl modeOut.bitDepth, modeOut.paletteSize)
tree = initTable[RGBA8, int]()
for i in 0..palSize-1:
tree[modeOut.palette[i]] = i
if(modeIn.bitDepth == 16) and (modeOut.bitDepth == 16):
let cvt = getColorRGBA16(modeIn)
let pxl = getPixelRGBA16(modeOut)
for px in 0..numPixels-1:
var p = RGBA16(r:0, g:0, b:0, a:0)
cvt(p, input, px, modeIn)
pxl(p, output, px, modeOut)
elif(modeOut.bitDepth == 8) and (modeOut.colorType == LCT_RGBA):
let cvt = getConverterRGBA(modeIn)
cvt(output, input, numPixels, modeIn)
elif(modeOut.bitDepth == 8) and (modeOut.colorType == LCT_RGB):
let cvt = getConverterRGB(modeIn)
cvt(output, input, numPixels, modeIn)
else:
let cvt = getColorRGBA8(modeIn)
let pxl = getPixelRGBA8(modeOut)
for px in 0..numPixels-1:
var p = RGBA8(r:chr(0), g:chr(0), b:chr(0), a:chr(0))
cvt(p, input, px, modeIn)
pxl(p, output, px, modeOut, tree)
proc convert(png: PNG, colorType: PNGcolorType, bitDepth: int): PNGResult =
#TODO: check if this works according to the statement in the documentation: "The converter can convert
# from greyscale input color type, to 8-bit greyscale or greyscale with alpha"
if(colorType notin {LCT_RGB, LCT_RGBA}) and (bitDepth != 8):
raise PNGError("unsupported color mode conversion")
let header = PNGHeader(png.getChunk(IHDR))
let modeIn = png.getColorMode()
let modeOut = newColorMode(colorType, bitDepth)
let size = getRawSize(header.width, header.height, modeOut)
let numPixels = header.width * header.height
let input = cstring(png.pixels)
new(result)
result.width = header.width
result.height = header.height
result.data = newString(size)
var output = cstring(result.data)
if modeOut == modeIn:
copyMem(output, input, size)
return result
convert(output, input, modeOut, modeIn, numPixels)
proc PNGDecode*(s: Stream, colorType: PNGcolorType, bitDepth: int, settings: PNGDecoderSettings): PNGResult =
if not bitDepthAllowed(colorType, bitDepth):
raise PNGError("colorType and bitDepth combination not allowed")
var png = s.parsePNG(settings)
png.postProcessscanLines()
if PNGDecoderSettings(png.settings).colorConvert:
result = png.convert(colorType, bitDepth)
else:
let header = PNGHeader(png.getChunk(IHDR))
new(result)
result.width = header.width
result.height = header.height
result.data = png.pixels
proc loadPNG*(fileName: string, colorType: PNGcolorType, bitDepth: int, settings: PNGDecoderSettings): PNGResult =
try:
var s = newFileStream(fileName, fmRead)
if s == nil: return nil
result = s.PNGDecode(colorType, bitDepth, settings)
except:
echo getCurrentExceptionMsg()
result = nil
proc loadPNG32*(fileName: string, settings = PNGDecoderSettings(nil)): PNGResult =
result = loadPNG(fileName, LCT_RGBA, 8, settings)
proc loadPNG24*(fileName: string, settings = PNGDecoderSettings(nil)): PNGResult =
result = loadPNG(fileName, LCT_RGB, 8, settings)
proc pngDecode32*(input: string, settings = PNGDecoderSettings(nil)): PNGResult =
try:
var s = newStringStream(input)
if s == nil: return nil
result = s.PNGDecode(LCT_RGBA, 8, settings)
except:
echo getCurrentExceptionMsg()
result = nil
proc pngDecode24*(input: string, settings = PNGDecoderSettings(nil)): PNGResult =
try:
var s = newStringStream(input)
if s == nil: return nil
result = s.PNGDecode(LCT_RGB, 8, settings)
except:
echo getCurrentExceptionMsg()
result = nil
#Encoder/Decoder demarcation line-----------------------------
type
PNGFilterStrategy = enum
#every filter at zero
LFS_ZERO,
#Use filter that gives minimum sum, as described in the official PNG filter heuristic.
LFS_MINSUM,
#Use the filter type that gives smallest Shannon entropy for this scanLine. Depending
#on the image, this is better or worse than minsum.
LFS_ENTROPY,
#Brute-force-search PNG filters by compressing each filter for each scanLine.
#Experimental, very slow, and only rarely gives better compression than MINSUM.
LFS_BRUTE_FORCE,
#use predefined_filters buffer: you specify the filter type for each scanLine
LFS_PREDEFINED
PNGKeyText = object
keyword, text: string
PNGIText = object
keyword: string
text: string
languageTag: string
translatedKeyword: string
PNGEncoderSettings = ref object of PNGSettings
#automatically choose output PNG color type. Default: true
autoConvert*: bool
#If true, follows the official PNG heuristic: if the PNG uses a palette or lower than
#8 bit depth, set all filters to zero. Otherwise use the filter_strategy. Note that to
#completely follow the official PNG heuristic, filter_palette_zero must be true and
#filter_strategy must be LFS_MINSUM
filterPaletteZero*: bool
#Which filter strategy to use when not using zeroes due to filter_palette_zero.
#Set filter_palette_zero to 0 to ensure always using your chosen strategy. Default: LFS_MINSUM
filterStrategy*: PNGFilterStrategy
#used if filter_strategy is LFS_PREDEFINED. In that case, this must point to a buffer with
#the same length as the amount of scanLines in the image, and each value must <= 5.
#Don't forget that filter_palette_zero must be set to false to ensure this is also used on palette or low bitdepth images.
predefinedFilters*: string
#force creating a PLTE chunk if colorType is 2 or 6 (= a suggested palette).
#If colorType is 3, PLTE is _always_ created.
forcePalette*: bool
#add nimPNG identifier and version as a text chunk, for debugging
addID*: bool
#encode text chunks as zTXt chunks instead of tEXt chunks, and use compression in iTXt chunks
textCompression*: bool
textList*: seq[PNGKeyText]
itextList*: seq[PNGIText]
interlaceMethod*: PNGInterlace
backgroundDefined*: bool
backgroundR*, backgroundG*, backgroundB*: int
physDefined*: bool
physX*, physY*, physUnit*: int
timeDefined*: bool
year*: range[0..65535]
month*: range[1..12]
day*: range[1..31]
hour*: range[0..23]
minute*: range[0..59]
second*: range[0..60] #to allow for leap seconds
PNGColorProfile = ref object
colored: bool #not greyscale
key: bool #if true, image is not opaque. Only if true and alpha is false, color key is possible.
keyR, keyG, keyB: int #these values are always in 16-bit bitdepth in the profile
alpha: bool #alpha channel or alpha palette required
numColors: int #amount of colors, up to 257. Not valid if bits == 16.
palette: seq[RGBA8] #Remembers up to the first 256 RGBA colors, in no particular order
bits: int #bits per channel (not for palette). 1,2 or 4 for greyscale only. 16 if 16-bit per channel required.
PNGEnd = ref object of PNGChunk
proc makeDefaultPNGEncoderSettings*(): PNGEncoderSettings =
var s: PNGEncoderSettings
new(s)
s.filterPaletteZero = true
s.filterStrategy = LFS_MINSUM
s.autoConvert = true
s.forcePalette = false
s.predefinedFilters = nil
s.addID = false
s.textCompression = true
s.interlaceMethod = IM_NONE
s.backgroundDefined = false
s.backgroundR = 0
s.backgroundG = 0
s.backgroundB = 0
s.physDefined = false
s.physX = 0
s.physY = 0
s.physUnit = 0
s.timeDefined = false
s.textList = @[]
result = s
proc makeColorProfile(): PNGColorProfile =
new(result)
result.colored = false
result.key = false
result.alpha = false
result.keyR = 0
result.keyG = 0
result.keyB = 0
result.numcolors = 0
result.bits = 1
result.palette = @[]
proc writeByte(s: PNGChunk, val: int) = s.data.add chr(val)
proc writeString(s: PNGChunk, val: string) = s.data.add val
proc writeInt32(s: PNGChunk, val: int) =
s.writeByte((val shr 24) and 0xff)
s.writeByte((val shr 16) and 0xff)
s.writeByte((val shr 8) and 0xff)
s.writeByte(val and 0xff)
proc writeInt16(s: PNGChunk, val: int) =
s.writeByte((val shr 8) and 0xff)
s.writeByte(val and 0xff)
proc writeInt32BE(s: Stream, value: int) =
var val = cast[int32](value)
var tmp: int32
bigEndian32(addr(tmp), addr(val))
s.write(tmp)
proc make[T](chunkType: PNGChunkType, estimateSize: int): T =
new(result)
result.chunkType = chunkType
if estimateSize > 0: result.data = newStringOfCap(estimateSize)
else: result.data = ""
method writeChunk(chunk: PNGChunk, png: PNG): bool = true
method writeChunk(chunk: PNGHeader, png: PNG): bool =
#estimate 13 bytes
chunk.writeInt32(chunk.width)
chunk.writeInt32(chunk.height)
chunk.writeByte(chunk.bitDepth)
chunk.writeByte(int(chunk.colorType))
chunk.writeByte(chunk.compressionMethod)
chunk.writeByte(chunk.filterMethod)
chunk.writeByte(int(chunk.interlaceMethod))
result = true
method writeChunk(chunk: PNGPalette, png: PNG): bool =
#estimate 3 * palette.len
for px in chunk.palette:
chunk.writeByte(int(px.r))
chunk.writeByte(int(px.g))
chunk.writeByte(int(px.b))
result = true
method writeChunk(chunk: PNGData, png: PNG): bool =
var nz = nzDeflateInit(chunk.idat)
chunk.data = zlib_compress(nz)
result = true
method writeChunk(chunk: PNGTrans, png: PNG): bool =
var header = PNGHeader(png.getChunk(IHDR))
if header.colorType == LCT_PALETTE:
#estimate plte.palette.len
var plte = PNGPalette(png.getChunk(PLTE))
#the tail of palette values that all have 255 as alpha, does not have to be encoded
var amount = plte.palette.len
for i in countdown(amount-1, 0):
if plte.palette[i].a == chr(255): dec amount
else: break
for i in 0..amount-1: chunk.writeByte(int(plte.palette[i].a))
elif header.colorType == LCT_GREY:
#estimate 2 bytes
if chunk.keyR != -1: chunk.writeInt16(chunk.keyR)
elif header.colorType == LCT_RGB:
#estimate 6 bytes
if chunk.keyR != -1:
chunk.writeInt16(chunk.keyR)
chunk.writeInt16(chunk.keyG)
chunk.writeInt16(chunk.keyB)
else:
raise PNGError("tRNS chunk not allowed for other color models")
result = true
method writeChunk(chunk: PNGBackground, png: PNG): bool =
var header = PNGHeader(png.getChunk(IHDR))
if header.colorType == LCT_PALETTE:
#estimate 1 bytes
chunk.writeByte(chunk.bkgdR)
if header.colorType in {LCT_GREY, LCT_GREY_ALPHA}:
#estimate 2 bytes
chunk.writeInt16(chunk.bkgdR)
elif header.colorType in {LCT_RGB, LCT_RGBA}:
#estimate 6 bytes
chunk.writeInt16(chunk.bkgdR)
chunk.writeInt16(chunk.bkgdG)
chunk.writeInt16(chunk.bkgdB)
result = true
method writeChunk(chunk: PNGTime, png: PNG): bool =
#estimate 7 bytes
chunk.writeInt16(chunk.year)
chunk.writeByte(chunk.month)
chunk.writeByte(chunk.day)
chunk.writeByte(chunk.hour)
chunk.writeByte(chunk.minute)
chunk.writeByte(chunk.second)
result = true
method writeChunk(chunk: PNGPhys, png: PNG): bool =
#estimate 9 bytes
chunk.writeInt32(chunk.physX)
chunk.writeInt32(chunk.physY)
chunk.writeByte(chunk.unit)
result = true
method writeChunk(chunk: PNGText, png: PNG): bool =
#estimate chunk.keyword.len + chunk.text.len + 1
chunk.writeString chunk.keyword
chunk.writeByte 0 #null separator
chunk.writeString chunk.text
result = true
method writeChunk(chunk: PNGZtxt, png: PNG): bool =
#estimate chunk.keyword.len + 2
chunk.writeString chunk.keyword
chunk.writeByte 0 #null separator
chunk.writeByte 0 #compression method(0: deflate)
var nz = nzDeflateInit(chunk.text)
chunk.writeString zlib_compress(nz)
result = true
method writeChunk(chunk: PNGItxt, png: PNG): bool =
#estimate chunk.keyword.len + 2
# + chunk.languageTag.len + chunk.translatedKeyword.len
chunk.writeString chunk.keyword
chunk.writeByte 0 #null separator
chunk.writeByte 1 #compression flag(0: uncompressed, 1: compressed)
chunk.writeByte 0 #compression method(0: deflate)
chunk.writeString chunk.languageTag
chunk.writeByte 0 #null separator
chunk.writeString chunk.translatedKeyword
chunk.writeByte 0 #null separator
var nz = nzDeflateInit(chunk.text)
chunk.writeString zlib_compress(nz)
result = true
method writeChunk(chunk: PNGGamma, png: PNG): bool =
#estimate 4 bytes
chunk.writeInt32(chunk.gamma)
result = true
method writeChunk(chunk: PNGChroma, png: PNG): bool =
#estimate 8 * 4 bytes
chunk.writeInt32(chunk.whitePointX)
chunk.writeInt32(chunk.whitePointY)
chunk.writeInt32(chunk.redX)
chunk.writeInt32(chunk.redY)
chunk.writeInt32(chunk.greenX)
chunk.writeInt32(chunk.greenY)
chunk.writeInt32(chunk.blueX)
chunk.writeInt32(chunk.blueY)
result = true
method writeChunk(chunk: PNGStandarRGB, png: PNG): bool =
#estimate 1 byte
chunk.writeByte(chunk.renderingIntent)
result = true
method writeChunk(chunk: PNGICCProfile, png: PNG): bool =
#estimate chunk.profileName.len + 2
chunk.writeString chunk.profileName
chunk.writeByte 0 #null separator
chunk.writeByte 0 #compression method(0: deflate)
var nz = nzDeflateInit(chunk.profile)
chunk.writeString zlib_compress(nz)
result = true
method writeChunk(chunk: PNGSPalette, png: PNG): bool =
#estimate chunk.paletteName.len + 2
#if sampleDepth == 8: estimate += chunk.palette.len * 6
#else: estimate += chunk.palette.len * 10
chunk.writeString chunk.paletteName
chunk.writeByte 0 #null separator
if chunk.sampleDepth notin {8, 16}: raise PNGError("palette sample depth error")
chunk.writeByte chunk.sampleDepth
if chunk.sampleDepth == 8:
for p in chunk.palette:
chunk.writeByte(p.red)
chunk.writeByte(p.green)
chunk.writeByte(p.blue)
chunk.writeByte(p.alpha)
chunk.writeInt16(p.frequency)
else: # chunk.sampleDepth == 16:
for p in chunk.palette:
chunk.writeInt16(p.red)
chunk.writeInt16(p.green)
chunk.writeInt16(p.blue)
chunk.writeInt16(p.alpha)
chunk.writeInt16(p.frequency)
result = true
method writeChunk(chunk: PNGHist, png: PNG): bool =
#estimate chunk.histogram.len * 2
for c in chunk.histogram:
chunk.writeInt16 c
result = true
proc isGreyscaleType(mode: PNGColorMode): bool =
result = mode.colorType in {LCT_GREY, LCT_GREY_ALPHA}
proc isAlphaType(mode: PNGColorMode): bool =
result = mode.colorType in {LCT_RGBA, LCT_GREY_ALPHA}
proc isPaletteType(mode: PNGColorMode): bool =
result = mode.colorType == LCT_PALETTE
proc hasPaletteAlpha(mode: PNGColorMode): bool =
for p in mode.palette:
if ord(p.a) < 255: return true
result = false
proc canHaveAlpha(mode: PNGColorMode): bool =
result = mode.keyDefined or isAlphaType(mode) or hasPaletteAlpha(mode)
#Returns how many bits needed to represent given value (max 8 bit)*/
proc getValueRequiredBits(value: int): int =
if(value == 0) or (value == 255): return 1
#The scaling of 2-bit and 4-bit values uses multiples of 85 and 17
if(value mod 17) == 0:
if (value mod 85) == 0: return 2
else: return 4
result = 8
proc differ(p: RGBA16): bool =
# first and second byte differ
if (p.r and 255) != ((p.r shr 8) and 255): return true
if (p.g and 255) != ((p.g shr 8) and 255): return true
if (p.b and 255) != ((p.b shr 8) and 255): return true
if (p.a and 255) != ((p.a shr 8) and 255): return true
result = false
proc getColorProfile(input: string, w, h: int, mode: PNGColorMode): PNGColorProfile =
var prof = makeColorProfile()
let
numPixels = w * h
bpp = getBPP(mode)
var
coloredDone = isGreyscaleType(mode)
alphaDone = not canHaveAlpha(mode)
bitsDone = bpp == 1
numColorsDone = false
sixteen = false
maxNumColors = 257
tree = initTable[RGBA8, int]()
if bpp <= 8:
case bpp
of 1: maxNumColors = 2
of 2: maxNumColors = 4
of 4: maxNumColors = 16
else: maxNumColors = 256
#Check if the 16-bit input is truly 16-bit
if mode.bitDepth == 16:
let cvt = getColorRGBA16(mode)
var p = RGBA16(r:0, g:0, b:0, a:0)
for px in 0..numPixels-1:
cvt(p, cstring(input), px, mode)
if p.differ():
sixteen = true
break
if sixteen:
let cvt = getColorRGBA16(mode)
var p = RGBA16(r:0, g:0, b:0, a:0)
prof.bits = 16
#counting colors no longer useful, palette doesn't support 16-bit
bitsDone = true
numColorsDone = true
for px in 0..numPixels-1:
cvt(p, cstring(input), px, mode)
if not coloredDone and ((p.r != p.g) or (p.r != p.b)):
prof.colored = true
coloredDone = true
if not alphaDone:
let matchKey = (int(p.r) == prof.keyR and
int(p.g) == prof.keyG and int(p.b) == prof.keyB)
if(p.a != 65535) and (p.a != 0 or (prof.key and not matchKey)):
prof.alpha = true
alphaDone = true
if prof.bits < 8: prof.bits = 8 #PNG has no alphachannel modes with less than 8-bit per channel
elif(p.a == 0) and not prof.alpha and not prof.key:
prof.key = true
prof.keyR = int(p.r)
prof.keyG = int(p.g)
prof.keyB = int(p.b)
elif(p.a == 65535) and prof.key and matchKey:
# Color key cannot be used if an opaque pixel also has that RGB color.
prof.alpha = true
alphaDone = true
if alphaDone and numColorsDone and coloredDone and bitsDone: break
else: # < 16-bit
let cvt = getColorRGBA8(mode)
var p = RGBA8(r:chr(0), g:chr(0), b:chr(0), a:chr(0))
for px in 0..numPixels-1:
cvt(p, cstring(input), px, mode)
if not bitsDone and (prof.bits < 8):
#only r is checked, < 8 bits is only relevant for greyscale
let bits = getValueRequiredBits(int(p.r))
if bits > prof.bits: prof.bits = bits
bitsDone = prof.bits >= bpp
if not coloredDone and ((p.r != p.g) or (p.r != p.b)):
prof.colored = true
coloredDone = true
if prof.bits < 8: prof.bits = 8 #PNG has no colored modes with less than 8-bit per channel
if not alphaDone:
let matchKey = (int(p.r) == prof.keyR and
int(p.g) == prof.keyG and int(p.b) == prof.keyB)
if(p.a != chr(255)) and (p.a != chr(0) or (prof.key and not matchKey)):
prof.alpha = true
alphaDone = true
if prof.bits < 8: prof.bits = 8 #PNG has no alphachannel modes with less than 8-bit per channel
elif(p.a == chr(0)) and not prof.alpha and not prof.key:
prof.key = true
prof.keyR = int(p.r)
prof.keyG = int(p.g)
prof.keyB = int(p.b)
elif(p.a == chr(255)) and prof.key and matchKey:
#Color key cannot be used if an opaque pixel also has that RGB color.
prof.alpha = true
alphaDone = true
if prof.bits < 8: prof.bits = 8 #PNG has no alphachannel modes with less than 8-bit per channel
if not numColorsDone:
if not tree.hasKey(p):
tree[p] = prof.numColors
if prof.numColors < 256: prof.palette.add p
inc prof.numColors
numColorsDone = prof.numColors >= maxNumColors
if alphaDone and numColorsDone and coloredDone and bitsDone: break
# make the profile's key always 16-bit for consistency - repeat each byte twice
prof.keyR += prof.keyR shl 8
prof.keyG += prof.keyG shl 8
prof.keyB += prof.keyB shl 8
result = prof
#Automatically chooses color type that gives smallest amount of bits in the
#output image, e.g. grey if there are only greyscale pixels, palette if there
#are less than 256 colors, ...
#Updates values of mode with a potentially smaller color model. mode_out should
#contain the user chosen color model, but will be overwritten with the new chosen one.
proc autoChooseColor(modeOut: PNGColorMode, input: string, w, h: int, modeIn: PNGColorMode) =
var prof = getColorProfile(input, w, h, modeIn)
modeOut.keyDefined = false
if prof.key and ((w * h) <= 16):
prof.alpha = true #too few pixels to justify tRNS chunk overhead
if prof.bits < 8: prof.bits = 8 #PNG has no alphachannel modes with less than 8-bit per channel
#grey without alpha, with potentially low bits
let greyOk = not prof.colored and not prof.alpha
let n = prof.numColors
var paletteBits = 0
if n <= 2: paletteBits = 1
elif n <= 4: paletteBits = 2
elif n <= 16: paletteBits = 4
else: paletteBits = 8
var paletteOk = (n <= 256) and ((n * 2) < (w * h)) and prof.bits <= 8
#don't add palette overhead if image has only a few pixels
if (w * h) < (n * 2): paletteOk = false
#grey is less overhead
if greyOk and (prof.bits <= palettebits): paletteOk = false
if paletteOk:
modeOut.paletteSize = prof.palette.len
modeOut.palette = prof.palette
modeOut.colorType = LCT_PALETTE
modeOut.bitDepth = paletteBits
if(modeIn.colorType == LCT_PALETTE) and (modeIn.palettesize >= modeOut.palettesize) and
(modeIn.bitdepth == modeOut.bitdepth):
#If input should have same palette colors, keep original to preserve its order and prevent conversion
modeIn.copyTo(modeOut)
else: #8-bit or 16-bit per channel
modeOut.bitDepth = prof.bits
if prof.alpha:
if prof.colored: modeOut.colorType = LCT_RGBA
else: modeOut.colorType = LCT_GREY_ALPHA
else:
if prof.colored: modeOut.colorType = LCT_RGB
else: modeOut.colorType = LCT_GREY
if prof.key and not prof.alpha:
#profile always uses 16-bit, mask converts it
let mask = (1 shl modeOut.bitDepth) - 1
modeOut.keyR = prof.keyR and mask
modeOut.keyG = prof.keyG and mask
modeOut.keyB = prof.keyB and mask
modeOut.keyDefined = true
proc addPaddingBits(output: var cstring, input: cstring, olinebits, ilinebits, h: int) =
#The opposite of the removePaddingBits function
#olinebits must be >= ilinebits
let diff = olinebits - ilinebits
var
obp = 0
ibp = 0 #bit pointers
for y in 0..h-1:
for x in 0..ilinebits-1:
let bit = readBitFromReversedStream(ibp, input)
setBitOfReversedStream(obp, output, bit)
for x in 0..diff-1: setBitOfReversedStream(obp, output, 0)
proc filterScanLine(output: var cstring, scanLine, prevLine: cstring, len, byteWidth: int, filterType: PNGFilter0) =
case filterType
of FLT_NONE:
for i in 0..len-1: output[i] = scanLine[i]
of FLT_SUB:
for i in 0..byteWidth-1: output[i] = scanLine[i]
for i in byteWidth..len-1:
output[i] = chr(ord(scanLine[i]) - ord(scanLine[i - byteWidth]))
of FLT_UP:
if prevLine != nil:
for i in 0..len-1:
output[i] = chr(ord(scanLine[i]) - ord(prevLine[i]))
else:
for i in 0..len-1: output[i] = scanLine[i]
of FLT_AVERAGE:
if prevLine != nil:
for i in 0..byteWidth-1:
output[i] = chr(ord(scanLine[i]) - (ord(prevLine[i]) div 2))
for i in byteWidth..len-1:
output[i] = chr(ord(scanLine[i]) - ((ord(scanLine[i - byteWidth]) + ord(prevLine[i])) div 2))
else:
for i in 0..byteWidth-1: output[i] = scanLine[i]
for i in byteWidth..len-1:
output[i] = chr(ord(scanLine[i]) - (ord(scanLine[i - byteWidth]) div 2))
of FLT_PAETH:
if prevLine != nil:
#paethPredictor(0, prevLine[i], 0) is always prevLine[i]
for i in 0..byteWidth-1:
output[i] = chr(ord(scanLine[i]) - ord(prevLine[i]))
for i in byteWidth..len-1:
output[i] = chr(ord(scanLine[i]) - paethPredictor(ord(scanLine[i - byteWidth]), ord(prevLine[i]), ord(prevLine[i - byteWidth])))
else:
for i in 0..byteWidth-1: output[i] = scanLine[i]
#paethPredictor(scanLine[i - byteWidth], 0, 0) is always scanLine[i - byteWidth]
for i in byteWidth..len-1:
output[i] = chr(ord(scanLine[i]) - ord(scanLine[i - byteWidth]))
else:
raise PNGError("unsupported fitler type")
proc filterZero(output: var cstring, input: cstring, w, h, bpp: int) =
#the width of a scanline in bytes, not including the filter type
let lineBytes = (w * bpp + 7) div 8
#byteWidth is used for filtering, is 1 when bpp < 8, number of bytes per pixel otherwise
let byteWidth = (bpp + 7) div 8
var prevLine: cstring = nil
var inp = input
for y in 0..h-1:
let outindex = (1 + lineBytes) * y #the extra filterbyte added to each row
let inindex = lineBytes * y
output[outindex] = chr(int(FLT_NONE)) #filter type byte
var outp: cstring = addr(output[outindex + 1])
let scanLine: cstring = addr(inp[inindex])
filterScanLine(outp, scanLine, prevLine, lineBytes, byteWidth, FLT_NONE)
prevLine = addr(inp[inindex])
proc filterMinsum(output: var cstring, input: cstring, w, h, bpp: int) =
let lineBytes = (w * bpp + 7) div 8
let byteWidth = (bpp + 7) div 8
#adaptive filtering
var sum = [0, 0, 0, 0, 0]
var smallest = 0
#five filtering attempts, one for each filter type
var attempt: array[0..4, string]
var bestType = 0
var inp = input
var prevLine: cstring = nil
for i in 0..attempt.high:
attempt[i] = newString(lineBytes)
for y in 0..h-1:
#try the 5 filter types
for fType in 0..4:
var outp = cstring(attempt[fType])
filterScanLine(outp, addr(inp[y * lineBytes]), prevLine, lineBytes, byteWidth, PNGFilter0(fType))
#calculate the sum of the result
sum[fType] = 0
if fType == 0:
for x in 0..lineBytes-1:
sum[fType] += ord(attempt[fType][x])
else:
for x in 0..lineBytes-1:
#For differences, each byte should be treated as signed, values above 127 are negative
#(converted to signed char). Filtertype 0 isn't a difference though, so use unsigned there.
#This means filtertype 0 is almost never chosen, but that is justified.
let s = ord(attempt[fType][x])
if s < 128: sum[fType] += s
else: sum[fType] += (255 - s)
#check if this is smallest sum (or if type == 0 it's the first case so always store the values)*/
if(fType == 0) or (sum[fType] < smallest):
bestType = fType
smallest = sum[fType]
prevLine = addr(inp[y * lineBytes])
#now fill the out values
#the first byte of a scanline will be the filter type
output[y * (lineBytes + 1)] = chr(bestType)
for x in 0..lineBytes-1:
output[y * (lineBytes + 1) + 1 + x] = attempt[bestType][x]
proc filterEntropy(output: var cstring, input: cstring, w, h, bpp: int) =
let lineBytes = (w * bpp + 7) div 8
let byteWidth = (bpp + 7) div 8
var inp = input
var prevLine: cstring = nil
var sum: array[0..4, float]
var smallest = 0.0
var bestType = 0
var attempt: array[0..4, string]
var count: array[0..255, int]
for i in 0..attempt.high:
attempt[i] = newString(lineBytes)
for y in 0..h-1:
#try the 5 filter types
for fType in 0..4:
var outp = cstring(attempt[fType])
filterScanLine(outp, addr(inp[y * lineBytes]), prevLine, lineBytes, byteWidth, PNGFilter0(fType))
for x in 0..255: count[x] = 0
for x in 0..lineBytes-1:
inc count[ord(attempt[fType][x])]
inc count[fType] #the filter type itself is part of the scanline
sum[fType] = 0
for x in 0..255:
let p = float(count[x]) / float(lineBytes + 1)
if count[x] != 0: sum[fType] += log2(1 / p) * p
#check if this is smallest sum (or if type == 0 it's the first case so always store the values)
if (fType == 0) or (sum[fType] < smallest):
bestType = fType
smallest = sum[fType]
prevLine = addr(inp[y * lineBytes])
#now fill the out values*/
#the first byte of a scanline will be the filter type
output[y * (lineBytes + 1)] = chr(bestType)
for x in 0..lineBytes-1:
output[y * (lineBytes + 1) + 1 + x] = attempt[bestType][x]
proc filterPredefined(output: var cstring, input: cstring, w, h, bpp: int, state: PNGEncoderSettings) =
let lineBytes = (w * bpp + 7) div 8
let byteWidth = (bpp + 7) div 8
var inp = input
var prevLine: cstring = nil
for y in 0..h-1:
let outindex = (1 + lineBytes) * y #the extra filterbyte added to each row
let inindex = lineBytes * y
let fType = ord(state.predefinedFilters[y])
output[outindex] = chr(fType) #filter type byte
var outp: cstring = addr(output[outindex + 1])
filterScanLine(outp, addr(inp[inindex]), prevLine, lineBytes, byteWidth, PNGFilter0(fType))
prevLine = addr(inp[inindex])
proc filterBruteForce(output: var cstring, input: cstring, w, h, bpp: int) =
let lineBytes = (w * bpp + 7) div 8
let byteWidth = (bpp + 7) div 8
var inp = input
var prevLine: cstring = nil
#brute force filter chooser.
#deflate the scanline after every filter attempt to see which one deflates best.
#This is very slow and gives only slightly smaller, sometimes even larger, result*/
var size: array[0..4, int]
var attempt: array[0..4, string] #five filtering attempts, one for each filter type
var smallest = 0
var bestType = 0
#use fixed tree on the attempts so that the tree is not adapted to the filtertype on purpose,
#to simulate the true case where the tree is the same for the whole image. Sometimes it gives
#better result with dynamic tree anyway. Using the fixed tree sometimes gives worse, but in rare
#cases better compression. It does make this a bit less slow, so it's worth doing this.
for i in 0..attempt.high:
attempt[i] = newString(lineBytes)
for y in 0..h-1:
#try the 5 filter types
for fType in 0..4:
#let testSize = attempt[fType].len
var outp = cstring(attempt[fType])
filterScanline(outp, addr(inp[y * lineBytes]), prevLine, lineBytes, byteWidth, PNGFilter0(fType))
size[fType] = 0
var nz = nzDeflateInit(attempt[fType])
let data = zlib_compress(nz)
size[fType] = data.len
#check if this is smallest size (or if type == 0 it's the first case so always store the values)
if(fType == 0) or (size[fType] < smallest):
bestType = fType
smallest = size[fType]
prevLine = addr(inp[y * lineBytes])
output[y * (lineBytes + 1)] = chr(bestType) #the first byte of a scanline will be the filter type
for x in 0..lineBytes-1:
output[y * (lineBytes + 1) + 1 + x] = attempt[bestType][x]
proc filter(output: var cstring, input: cstring, w, h: int, modeOut: PNGColorMode, state: PNGEncoderSettings) =
#For PNG filter method 0
#out must be a buffer with as size: h + (w * h * bpp + 7) / 8, because there are
#the scanlines with 1 extra byte per scanline
let bpp = getBPP(modeOut)
var strategy = state.filterStrategy
#There is a heuristic called the minimum sum of absolute differences heuristic, suggested by the PNG standard:
# * If the image type is Palette, or the bit depth is smaller than 8, then do not filter the image (i.e.
# use fixed filtering, with the filter None).
# * (The other case) If the image type is Grayscale or RGB (with or without Alpha), and the bit depth is
# not smaller than 8, then use adaptive filtering heuristic as follows: independently for each row, apply
# all five filters and select the filter that produces the smallest sum of absolute values per row.
#This heuristic is used if filter strategy is LFS_MINSUM and filter_palette_zero is true.
#If filter_palette_zero is true and filter_strategy is not LFS_MINSUM, the above heuristic is followed,
#but for "the other case", whatever strategy filter_strategy is set to instead of the minimum sum
#heuristic is used.
if state.filterPaletteZero and
(modeOut.colorType == LCT_PALETTE or modeOut.bitDepth < 8): strategy = LFS_ZERO
if bpp == 0:
raise PNGError("invalid color type")
case strategy
of LFS_ZERO: filterZero(output, input, w, h, bpp)
of LFS_MINSUM: filterMinsum(output, input, w, h, bpp)
of LFS_ENTROPY: filterEntropy(output, input, w, h, bpp)
of LFS_BRUTE_FORCE: filterBruteForce(output, input, w, h, bpp)
of LFS_PREDEFINED: filterPredefined(output, input, w, h, bpp, state)
#input: non-interlaced image with size w*h
#output: the same pixels, but re-ordered according to PNG's Adam7 interlacing, with
# no padding bits between scanlines, but between reduced images so that each
# reduced image starts at a byte.
#bpp: bits per pixel
#there are no padding bits, not between scanlines, not between reduced images
#in has the following size in bits: w * h * bpp.
#output is possibly bigger due to padding bits between reduced images
#NOTE: comments about padding bits are only relevant if bpp < 8
proc Adam7Interlace(output: var cstring, input: cstring, w, h, bpp: int) =
var pass: PNGPass
Adam7PassValues(pass, w, h, bpp)
if bpp >= 8:
for i in 0..6:
let byteWidth = bpp div 8
for y in 0..pass.h[i]-1:
for x in 0..pass.w[i]-1:
let inStart = ((ADAM7_IY[i] + y * ADAM7_DY[i]) * w + ADAM7_IX[i] + x * ADAM7_DX[i]) * byteWidth
let outStart = pass.start[i] + (y * pass.w[i] + x) * byteWidth
for b in 0..byteWidth-1:
output[outStart + b] = input[inStart + b]
else: #bpp < 8: Adam7 with pixels < 8 bit is a bit trickier: with bit pointers
for i in 0..6:
let ilinebits = bpp * pass.w[i]
let olinebits = bpp * w
var obp, ibp: int #bit pointers (for out and in buffer)
for y in 0..pass.h[i]-1:
for x in 0..pass.w[i]-1:
ibp = (ADAM7_IY[i] + y * ADAM7_DY[i]) * olinebits + (ADAM7_IX[i] + x * ADAM7_DX[i]) * bpp
obp = (8 * pass.start[i]) + (y * ilinebits + x * bpp)
for b in 0..bpp-1:
let bit = readBitFromReversedStream(ibp, input)
setBitOfReversedStream(obp, output, bit)
proc preProcessScanLines(png: PNG, input: cstring, w, h: int, modeOut: PNGColorMode, state: PNGEncoderSettings) =
#This function converts the pure 2D image with the PNG's colorType, into filtered-padded-interlaced data. Steps:
# if no Adam7: 1) add padding bits (= posible extra bits per scanLine if bpp < 8) 2) filter
# if adam7: 1) Adam7_interlace 2) 7x add padding bits 3) 7x filter
let bpp = getBPP(modeOut)
if state.interlaceMethod == IM_NONE:
#image size plus an extra byte per scanLine + possible padding bits
let scanLen = (w * bpp + 7) div 8
let outSize = h + (h * scanLen)
png.pixels = newString(outSize)
var output = cstring(png.pixels)
#non multiple of 8 bits per scanLine, padding bits needed per scanLine
if(bpp < 8) and ((w * bpp) != (scanLen * 8)):
var padded = newString(h * scanLen)
var padding = cstring(padded)
addPaddingBits(padding, input, scanLen * 8, w * bpp, h)
filter(output, padding, w, h, modeOut, state)
else:
#we can immediatly filter into the out buffer, no other steps needed
filter(output, input, w, h, modeOut, state)
else: #interlaceMethod is 1 (Adam7)
var pass: PNGPass
Adam7PassValues(pass, w, h, bpp)
let outSize = pass.filterStart[7]
png.pixels = newString(outSize)
var adam7buf = newString(pass.start[7])
var adam7 = cstring(adam7buf)
var output = cstring(png.pixels)
Adam7Interlace(adam7, input, w, h, bpp)
for i in 0..6:
if bpp < 8:
var padded = newString(pass.paddedStart[i + 1] - pass.paddedStart[i])
var padding = cstring(padded)
addPaddingBits(padding, addr(adam7[pass.start[i]]), ((pass.w[i] * bpp + 7) div 8) * 8, pass.w[i] * bpp, pass.h[i])
var outp:cstring = addr(output[pass.filterStart[i]])
filter(outp, padding, pass.w[i], pass.h[i], modeOut, state)
else:
var outp:cstring = addr(output[pass.filterStart[i]])
filter(outp, addr(adam7[pass.paddedStart[i]]), pass.w[i], pass.h[i], modeOut, state)
#palette must have 4 * palettesize bytes allocated, and given in format RGBARGBARGBARGBA...
#returns 0 if the palette is opaque,
#returns 1 if the palette has a single color with alpha 0 ==> color key
#returns 2 if the palette is semi-translucent.
proc getPaletteTranslucency(modeOut: PNGColorMode): int =
var key = 0
#the value of the color with alpha 0, so long as color keying is possible
var p: RGBA8
var i = 0
while i < modeOut.paletteSize:
let x = modeOut.palette[i]
if (key == 0) and (x.a == chr(0)):
p = x
key = 1
i = -1 #restart from beginning, to detect earlier opaque colors with key's value
elif x.a != chr(255): return 2
#when key, no opaque RGB may have key's RGB*/
elif(key != 0) and (p.r == x.r) and (p.g == x.g) and (p.b == x.g): return 2
inc i
result = key
proc addChunkIHDR(png: PNG, w,h: int, modeOut: PNGColorMode, state: PNGEncoderSettings) =
var chunk = make[PNGHeader](IHDR, 13)
chunk.width = w
chunk.height = h
chunk.bitDepth = modeOut.bitDepth
chunk.colorType = modeOut.colorType
chunk.compressionMethod = 0
chunk.filterMethod = 0
chunk.interlaceMethod = state.interlaceMethod
png.chunks.add chunk
proc addChunkPLTE(png: PNG, modeOut: PNGColorMode) =
if modeOut.paletteSize == 0: return
var chunk = make[PNGPalette](PLTE, 3 * modeOut.paletteSize)
chunk.palette = modeOut.palette
png.chunks.add chunk
proc addChunktRNS(png: PNG, modeOut: PNGColorMode) =
var chunk = make[PNGTrans](tRNS, 2)
if modeOut.colorType == LCT_PALETTE:
var plte = png.getChunk(PLTE)
doAssert plte != nil
elif modeOut.colorType == LCT_GREY:
if modeOut.keyDefined:
chunk.keyR = modeOut.keyR
else:
chunk.keyR = -1
elif modeOut.colorType == LCT_RGB:
if modeOut.keyDefined:
chunk.keyR = modeOut.keyR
chunk.keyG = modeOut.keyG
chunk.keyB = modeOut.keyB
else:
chunk.keyR = -1
png.chunks.add chunk
proc addChunkbKGD(png: PNG, modeOut: PNGColorMode, state: PNGEncoderSettings) =
var chunk = make[PNGBackground](bKGD, 6)
if modeOut.colorType == LCT_PALETTE:
#estimate 1 bytes
chunk.bkgdR = state.backgroundR
if modeOut.colorType in {LCT_GREY, LCT_GREY_ALPHA}:
#estimate 2 bytes
chunk.bkgdR = state.backgroundR
elif modeOut.colorType in {LCT_RGB, LCT_RGBA}:
#estimate 6 bytes
chunk.bkgdR = state.backgroundR
chunk.bkgdG = state.backgroundG
chunk.bkgdB = state.backgroundB
png.chunks.add chunk
proc addChunkpHYs(png: PNG, state: PNGEncoderSettings) =
var chunk = make[PNGPhys](pHYs, 9)
chunk.physX = state.physX
chunk.physY = state.physY
chunk.unit = state.physUnit
png.chunks.add chunk
proc addChunkIDAT(png: PNG, state: PNGEncoderSettings) =
var chunk = make[PNGData](IDAT, 0)
chunk.idat = png.pixels
png.chunks.add chunk
proc addChunktIME(png: PNG, state: PNGEncoderSettings) =
var chunk = make[PNGTime](tIME, 0)
chunk.year = state.year
chunk.month = state.month
chunk.day = state.day
chunk.hour = state.hour
chunk.minute = state.minute
chunk.second = state.second
png.chunks.add chunk
proc addChunktEXt(png: PNG, txt: PNGKeyText) =
var chunk = make[PNGText](tEXt, txt.keyword.len + txt.text.len + 1)
chunk.keyword = txt.keyword
chunk.text = txt.text
png.chunks.add chunk
proc addChunkzTXt(png: PNG, txt: PNGKeyText) =
var chunk = make[PNGZtxt](zTXt, txt.keyword.len + txt.text.len + 1)
chunk.keyword = txt.keyword
chunk.text = txt.text
png.chunks.add chunk
proc addChunkiTXt(png: PNG, txt: PNGIText) =
var chunk = make[PNGItxt](iTXt, txt.keyword.len + txt.text.len + 1)
chunk.keyword = txt.keyword
chunk.translatedKeyword = txt.translatedKeyword
chunk.languageTag = txt.languageTag
chunk.text = txt.text
png.chunks.add chunk
proc addChunkIEND(png: PNG) =
var chunk = make[PNGEnd](IEND, 0)
png.chunks.add chunk
proc PNGEncode*(input: string, colorType: PNGcolorType, bitDepth, w, h: int, settings: PNGEncoderSettings): PNG =
if not bitDepthAllowed(colorType, bitDepth):
raise PNGError("colorType and bitDepth combination not allowed")
var png: PNG
new(png)
png.chunks = @[]
if settings == nil: png.settings = makeDefaultPNGEncoderSettings()
else: png.settings = settings
var modeIn = newColorMode(colorType, bitDepth)
var modeOut = newColorMode(colorType, bitDepth)
let state = PNGEncoderSettings(png.settings)
if(modeOut.colorType == LCT_PALETTE or state.forcePalette) and
(modeOut.paletteSize == 0 or modeOut.paletteSize > 256):
raise PNGError("invalid palette size, it is only allowed to be 1-256")
if state.autoConvert:
autoChooseColor(modeOut, input, w, h, modeIn)
if state.interlaceMethod notin {IM_NONE, IM_INTERLACED}:
raise PNGError("unexisting interlace mode")
if not bitDepthAllowed(modeOut.colorType, modeOut.bitDepth):
raise PNGError("colorType and bitDepth combination not allowed")
if modeIn != modeOut:
let size = (w * h * getBPP(modeOut) + 7) div 8
let numPixels = w * h
var converted = newString(size)
var output = cstring(converted)
convert(output, cstring(input), modeOut, modeIn, numPixels)
preProcessScanLines(png, cstring(converted), w, h, modeOut, state)
else:
preProcessScanLines(png, cstring(input), w, h, modeOut, state)
png.addChunkIHDR(w, h, modeOut, state)
if modeOut.colorType == LCT_PALETTE: png.addChunkPLTE(modeOut)
if state.forcePalette and modeOut.colorType in {LCT_RGB, LCT_RGBA}: png.addChunkPLTE(modeOut)
if(modeOut.colorType == LCT_PALETTE) and (getPaletteTranslucency(modeOut) != 0):
png.addChunktRNS(modeOut)
if modeOut.colorType in {LCT_GREY, LCT_RGB} and modeOut.keyDefined:
png.addChunktRNS(modeOut)
#bKGD (must come between PLTE and the IDAt chunks
if state.backgroundDefined: png.addChunkbKGD(modeOut, state)
#pHYs (must come before the IDAT chunks)
if state.physDefined: png.addChunkpHYs(state)
#IDAT (multiple IDAT chunks must be consecutive)
png.addChunkIDAT(state)
if state.timeDefined: png.addChunktIME(state)
for txt in state.textList:
if state.textCompression: png.addChunkzTXt(txt)
else: png.addChunktEXt(txt)
if state.addID:
var txt = PNGKeyText(keyword: "nimPNG", text: NIM_PNG_VERSION)
png.addChunktEXt(txt)
for txt in state.itextList:
png.addChunkiTXt(txt)
png.addChunkIEND()
result = png
proc writeChunks(png: PNG, s: Stream) =
s.write PNGSignature
for chunk in png.chunks:
if not chunk.validateChunk(png): raise PNGError("combine chunk validation error")
if not chunk.writeChunk(png): raise PNGError("combine chunk write error")
chunk.length = chunk.data.len
chunk.crc = crc32(crc32(0, $chunk.chunkType), chunk.data)
s.writeInt32BE chunk.length
s.writeInt32BE int(chunk.chunkType)
s.write chunk.data
s.writeInt32BE cast[int](chunk.crc)