Convert PNG24 / 32 to PNG8 while maintaining transparency

The TinyPNG web service has opened , where you can quickly convert full-color PNG24 to PNG8 index ones with alpha transparency preserved. The site works on well-known open source utilities, so quantization of a palette can be done without it, but here it is just more convenient.

Habré has repeatedly published articles about quantizing the PNG palette as a way to optimize files in this format. There are a number of programs that compress PNG24 to PNG8 with alpha transparency preserved, one of them is pngnq . Unfortunately, many web designers are not ready to work with such programs and process files in batch mode with a bash script, so the appearance of such a web service will be good news for them.

TinyPNG developers themselves say that they use the pngquant , optiPNG and advpng utilities for quantization.
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All these tools can be used independently. There is even a pngquant GUI .

Since Photoshop cannot work normally with 8-bit PNGs, you can save regular PNG24s with alpha transparency (via the Save for Web menu), and then run them through TinyPNG or one of the listed programs. The resulting files are displayed correctly in all browsers, PNG transparency is preserved even in IE6.