diff options
Diffstat (limited to 'src/img/png.nim')
| -rw-r--r-- | src/img/png.nim | 32 |
1 files changed, 16 insertions, 16 deletions
diff --git a/src/img/png.nim b/src/img/png.nim index d41360a3..0b486f23 100644 --- a/src/img/png.nim +++ b/src/img/png.nim @@ -257,7 +257,7 @@ proc readtRNS(reader: var PNGReader) = for i in 0 ..< reader.palette.len: reader.palette[i].a = reader.readU8() -func paethPredictor(a, b, c: uint16): uint16 = +func paethPredictor(a, b, c: uint8): uint8 = let pa0 = int(b) - int(c) let pb0 = int(a) - int(c) let pa = abs(pa0) @@ -273,36 +273,36 @@ proc unfilter(reader: var PNGReader; irow: openArray[uint8]; bpp: int) = for i in 1 ..< irow.len: let j = i - 1 # skip filter byte let aidx = j - bpp - let x = uint16(irow[i]) - let a = if aidx >= 0: uint16(reader.uprow[aidx]) else: 0u16 - reader.uprow[j] = uint8((x + a) and 0xFF) + let x = irow[i] + let a = if aidx >= 0: reader.uprow[aidx] else: 0u8 + reader.uprow[j] = x + a of 2u8: # up for i in 1 ..< irow.len: let j = i - 1 # skip filter byte - let x = uint16(irow[i]) - let b = uint16(reader.uprow[j]) - reader.uprow[j] = uint8((x + b) and 0xFF) + let x = irow[i] + let b = reader.uprow[j] + reader.uprow[j] = x + b of 3u8: # average for i in 1 ..< irow.len: let j = i - 1 # skip filter byte let aidx = j - bpp - let x = uint16(irow[i]) - let a = if aidx >= 0: uint16(reader.uprow[aidx]) else: 0u16 - let b = uint16(reader.uprow[j]) - reader.uprow[j] = uint8((x + (a + b) div 2) and 0xFF) + let x = irow[i] + let a = if aidx >= 0: reader.uprow[aidx] else: 0u8 + let b = reader.uprow[j] + reader.uprow[j] = x + uint8((uint16(a) + uint16(b)) div 2) of 4u8: # paeth - var cmap: array[8, uint16] # max bpp is 16 bit with true color = 4 * 2 + var cmap: array[8, uint8] # max bpp is 16 bit with true color = 4 * 2 var k = 0 for i in 1 ..< irow.len: let j = i - 1 # skip filter byte let aidx = j - bpp - let x = uint16(irow[i]) - let a = if aidx >= 0: uint16(reader.uprow[aidx]) else: 0u16 - let b = uint16(reader.uprow[j]) + let x = irow[i] + let a = if aidx >= 0: reader.uprow[aidx] else: 0u8 + let b = reader.uprow[j] let kk = k mod bpp let c = cmap[kk] cmap[kk] = b - reader.uprow[j] = uint8((x + paethPredictor(a, b, c)) and 0xFF) + reader.uprow[j] = x + paethPredictor(a, b, c) inc k else: reader.err "got invalid filter" |