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PNG (Portable Network Graphics) decoder and encoder written in Nim
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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

###Feature planned:

  • streaming for progressive loading