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readme.md
#nimPNG Portable Network Graphics Encoder and Decoder written in Nim store lossless image with good compression
all PNG standard color mode are supported:
- 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
both interlaced and non-interlaced mode supported
recognize all PNG standard chunks: IHDR, IEND, PLTE, IDAT, tRNS, bKGD, pHYs, tIME, iTXt, zTXt tEXt, gAMA, cHRM, sRGB, iCCP, sBIT, sPLT, hIST
unknown chunks will be handled properly
the following chunks are supported (generated/interpreted) by both encoder and decoder:
- IHDR: header information
- PLTE: color palette
- IDAT: pixel data
- IEND: the final chunk
- tRNS: transparency for palettized images
- tEXt: textual information
- zTXt: compressed textual information
- iTXt: international textual information
- bKGD: suggested background color
- pHYs: physical dimensions
- tIME: modification time
the following chunks are parsed correctly, but not used by decoder: cHRM, gAMA, iCCP, sRGB, sBIT, hIST, sPLT
Supported color conversions:
- anything to 8-bit RGB, 8-bit RGBA, 16-bit RGB, 16-bit RGBA
- any grey or grey+alpha, to grey or grey+alpha
- anything to a palette, as long as the palette has the requested colors in it
- removing alpha channel
- higher to smaller bitdepth, and vice versa
###Planned Feature(s):
- streaming for progressive loading
##Basic Usage
import nimPNG
let png = loadPNG32("image.png")
#is equivalent to:
#let png = loadPNG("image.png", LCT_RGBA, 8)
#will produce rgba pixels:
#png.width -> width of the image
#png.height -> height of the image
#png.data -> pixels data in RGBA format
if you already have the whole file in memory:
let png = decodePNG32(raw_bytes)
#will do the same as above
other variants:
- loadPNG24 -> will produce pixels in RGB format 8 bpp
- decodePNG24 -> load png from memory instead of file
to create PNG:
- savePNG32("output.png", rgba_pixels, width, height) or savePNG24
- encodePNG32(rgba_pixels, width, height) or encodePNG24
special notes:
- Use loadPNG or savePNG if you need specific input/output format by supplying supported colorType and bitDepth information.
- Use encodePNG or decodePNG to do in-memory encoding/decoding by supplying desired colorType and bitDepth information
pixels are stored as raw bytes using Nim's string as container:
Byte Order | Format |
---|---|
r1,g1,b1,a1,...,rn,gn,bn,an | RGBA 8 bit |
r1,g1,b1,r2,g2,b2,...,rn,gn,bn | RGB 8 bit |
grey1,grey2,grey3, ..., greyn | GREY 8 bit |
grey1,a1,grey2,a2,...,greyn,an | GREY ALPHA 8 bit |