pngquant

pngquant 3

pngquant is a PNG compressor that significantly reduces file sizes by converting images to a more efficient 8-bit PNG format with alpha channel (often 60-80% smaller than 24/32-bit PNG files). Compressed images are fully standards-compliant and are supported by all web browsers and operating systems.

This is the official pngquant repository. The compression engine is also available as an embeddable library.

Usage

• batch conversion of multiple files: pngquant *.png
• Unix-style stdin/stdout chaining: … | pngquant - | …

To further reduce file size, try oxipng, ImageOptim, or zopflipng.

Features

• High-quality palette generation

• advanced quantization algorithm with support for gamma correction and premultiplied alpha
• unique dithering algorithm that does not add unnecessary noise to the image

• Configurable quality level

• automatically finds required number of colors and can skip images which can't be converted with the desired quality

• Fast, modern code

• based on a portable libimagequant library
• C99 with no workarounds for legacy systems or compilers (apart from Visual Studio)
• multicore support (via OpenMP) and Intel SSE optimizations

Options

See pngquant -h for full list.

--quality min-max

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.

pngquant --quality=65-80 image.png

--ext new.png

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).

-o out.png or --output out.png

Writes converted file to the given path. When this option is used only single input file is allowed.

--skip-if-larger

Don't write converted files if the conversion isn't worth it.

--speed N

Speed/quality trade-off from 1 (slowest, highest quality, smallest files) to 11 (fastest, less consistent quality, light comperssion). The default is 4. It's recommended to keep the default, unless you need to generate images in real time (e.g. map tiles). Higher speeds are fine with 256 colors, but don't handle lower number of colors well.

--nofs

Disables Floyd-Steinberg dithering.

--floyd=0.5

Controls level of dithering (0 = none, 1 = full). Note that the = character is required.

--posterize bits

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 in ARGB444 format).

--strip

Don't copy optional PNG chunks. Metadata is always removed on Mac (when using Cocoa reader).

See man page (man pngquant) for the full list of options.

License

pngquant is dual-licensed:

• Under GPL v3 or later with an additional copyright notice that must be kept for the older parts of the code.

• Or a commercial license for use in non-GPL software (e.g. closed-source or App Store distribution). You can get the license via Super Source. Email kornel@pngquant.org if you have any questions.