94 lines
3.3 KiB
Markdown
94 lines
3.3 KiB
Markdown
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#pngquant 2
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This is the official `pngquant` and `libimagequant`.
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[pngquant](http://pngquant.org) converts 24/32-bit RGBA PNGs to 8-bit palette with *alpha channel preserved*.
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Such images are compatible with all modern browsers, and a special compatibility setting exists which helps transparency degrade well in Internet Explorer 6.
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Quantized files are often 40-70% smaller than their 24/32-bit version.
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This utility works on Linux, Mac OS X and Windows.
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##Usage
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- batch conversion of multiple files: `pngquant *.png`
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- Unix-style stdin/stdout chaining: `… | pngquant - | …`
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To further reduce file size, try [optipng](http://optipng.sourceforge.net) or [ImageOptim](http://imageoptim.pornel.net).
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##Improvements since 1.0
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Generated files are both smaller and look much better.
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* Significantly better quality of quantisation
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- more accurate remapping of semitransparent colors
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- special dithering algorithm that does not add noise in well-quantized areas of the image
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- uses variance instead of popularity for box selection (improvement suggested in the original median cut paper)
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- feedback loop that repeats median cut for poorly quantized colors
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- additional colormap improvement using Voronoi iteration
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- supports much larger number of colors in input images without degradation of quality
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- gamma correction (output is always generated with gamma 2.2 for web compatibility)
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* More flexible commandline usage
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- number of colors defaults to 256
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- long options and standard switches like `--` and `-` are allowed
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* Refactored and modernised code
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- C99 with no workarounds for old systems
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- floating-point math used throughout
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- Intel SSE optimisations
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- multicore support via OpenMP
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- quantization moved to standalone libimagequant
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##Options
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See `pngquant -h` for full list.
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###`--quality min-max`
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`min` and `max` are numbers in range 0 (worst) to 100 (perfect), similar to JPEG. pngquant will use the least amount of colors required to meet or exceed the `max` quality. If conversion results in quality below the `min` quality the image won't be saved (if outputting to stdin, 24-bit original will be output) and pngquant will exit with status code 99.
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pngquant --quality=65-80 image.png
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###`--ext new.png`
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Set custom extension (suffix) for output filename. By default `-or8.png` or `-fs8.png` is used. If you use `--ext=.png --force` options pngquant will overwrite input files in place (use with caution).
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###`--skip-if-larger`
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Don't write converted files if the conversion isn't worth it.
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###`--speed N`
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Speed/quality trade-off from 1 (brute-force) to 11 (fastest). The default is 3. Speed 10 has 5% lower quality, but is 8 times faster than the default. Speed 11 disables dithering and lowers compression level.
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###`--nofs`
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Disables Floyd-Steinberg dithering.
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###`--floyd=0.5`
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Controls level of dithering (0 = none, 1 = full).
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###`--posterize bits`
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Reduce precision of the palette by number of bits. Use when the image will be displayed on low-depth screens (e.g. 16-bit displays or compressed textures).
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###`--version`
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Print version information to stdout.
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###`-`
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Read image from stdin and send result to stdout.
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###`--`
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Stops processing of arguments. This allows use of file names that start with `-`. If you're using pngquant in a script, it's advisable to put this before file names:
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pngquant $OPTIONS -- "$FILE"
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