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Merge pull request #2 from jangko/filter_bug 

fixed #1
This commit is contained in:
andri lim 2016-01-18 09:11:58 +07:00
parent 9b366da376 8e492e0f90
commit 42fd94a28e
1 changed files with 12 additions and 13 deletions
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17
nimPNG.nim
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@ -2376,42 +2376,41 @@ proc addPaddingBits(output: var cstring, input: cstring, olinebits, ilinebits, h
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(scanLine[i].uint8 - scanLine[i - byteWidth].uint8)
output[i] = chr(scanLine[i].uint - scanLine[i - byteWidth].uint)
of FLT_UP:
if prevLine != nil:
for i in 0..len-1:
output[i] = chr(scanLine[i].uint8 - prevLine[i].uint8)
output[i] = chr(scanLine[i].uint - prevLine[i].uint)
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(scanLine[i].uint8 - (prevLine[i].uint8 div 2))
output[i] = chr(scanLine[i].uint - (prevLine[i].uint div 2))
for i in byteWidth..len-1:
output[i] = chr(scanLine[i].uint8 - ((scanLine[i - byteWidth].uint8 + prevLine[i].uint8) div 2))
output[i] = chr(scanLine[i].uint - ((scanLine[i - byteWidth].uint + prevLine[i].uint) div 2))
else:
for i in 0..byteWidth-1: output[i] = scanLine[i]
for i in byteWidth..len-1:
output[i] = chr(scanLine[i].uint8 - (scanLine[i - byteWidth].uint8 div 2))
output[i] = chr(scanLine[i].uint - (scanLine[i - byteWidth].uint 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(scanLine[i].uint8 - prevLine[i].uint8)
output[i] = chr(scanLine[i].uint - prevLine[i].uint)
for i in byteWidth..len-1:
output[i] = chr(scanLine[i].uint8 - paethPredictor(ord(scanLine[i - byteWidth]), ord(prevLine[i]), ord(prevLine[i - byteWidth])).uint8)
output[i] = chr(scanLine[i].uint - paethPredictor(ord(scanLine[i - byteWidth]), ord(prevLine[i]), ord(prevLine[i - byteWidth])).uint)
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(scanLine[i].uint8 - scanLine[i - byteWidth].uint8)
output[i] = chr(scanLine[i].uint - scanLine[i - byteWidth].uint)
else:
raise PNGError("unsupported fitler type")