mirror of https://github.com/status-im/nimPNG.git
91 lines
2.8 KiB
Markdown
91 lines
2.8 KiB
Markdown
#nimPNG
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Portable Network Graphics Encoder and Decoder written in Nim store lossless image with good compression
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all PNG standard color mode are supported:
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- LCT_GREY = 0, # greyscale: 1,2,4,8,16 bit
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- LCT_RGB = 2, # RGB: 8,16 bit
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- LCT_PALETTE = 3, # palette: 1,2,4,8 bit
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- LCT_GREY_ALPHA = 4, # greyscale with alpha: 8,16 bit
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- LCT_RGBA = 6 # RGB with alpha: 8,16 bit
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both interlaced and non-interlaced mode supported
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recognize all PNG standard chunks:
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IHDR, IEND, PLTE, IDAT, tRNS, bKGD, pHYs, tIME, iTXt, zTXt
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tEXt, gAMA, cHRM, sRGB, iCCP, sBIT, sPLT, hIST
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unknown chunks will be handled properly
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the following chunks are supported (generated/interpreted) by both encoder and decoder:
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- IHDR: header information
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- PLTE: color palette
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- IDAT: pixel data
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- IEND: the final chunk
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- tRNS: transparency for palettized images
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- tEXt: textual information
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- zTXt: compressed textual information
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- iTXt: international textual information
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- bKGD: suggested background color
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- pHYs: physical dimensions
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- tIME: modification time
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the following chunks are parsed correctly, but not used by decoder:
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cHRM, gAMA, iCCP, sRGB, sBIT, hIST, sPLT
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Supported color conversions:
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- anything to 8-bit RGB, 8-bit RGBA, 16-bit RGB, 16-bit RGBA
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- any grey or grey+alpha, to grey or grey+alpha
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- anything to a palette, as long as the palette has the requested colors in it
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- removing alpha channel
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- higher to smaller bitdepth, and vice versa
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###Planned Feature(s):
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- streaming for progressive loading
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##Basic Usage
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```nimrod
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import nimPNG
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let png = loadPNG32("image.png")
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#is equivalent to:
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#let png = loadPNG("image.png", LCT_RGBA, 8)
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#will produce rgba pixels:
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#png.width -> width of the image
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#png.height -> height of the image
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#png.data -> pixels data in RGBA format
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```
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if you already have the whole file in memory:
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```nimrod
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let png = decodePNG32(raw_bytes)
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#will do the same as above
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```
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other variants:
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* loadPNG24 -> will produce pixels in RGB format 8 bpp
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* decodePNG24 -> load png from memory instead of file
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to create PNG:
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* savePNG32("output.png", rgba_pixels, width, height) or savePNG24
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* encodePNG32(rgba_pixels, width, height) or encodePNG24
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special notes:
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* Use **loadPNG** or **savePNG** if you need specific input/output format by supplying supported **colorType** and **bitDepth** information.
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* Use **encodePNG** or **decodePNG** to do *in-memory* encoding/decoding by supplying desired colorType and bitDepth information
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pixels are stored as raw bytes using Nim's string as container:
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| Byte Order | Format |
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|:------------------------------:|:----------------:|
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| r1,g1,b1,a1,...,rn,gn,bn,an | RGBA 8 bit |
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| r1,g1,b1,r2,g2,b2,...,rn,gn,bn | RGB 8 bit |
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| grey1,grey2,grey3, ..., greyn | GREY 8 bit |
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| grey1,a1,grey2,a2,...,greyn,an | GREY ALPHA 8 bit |
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