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How PNG compression works here
PNG is lossless, so the biggest savings come from reducing the number of colors. Below 90% quality, TinySquish converts each PNG to an indexed palette (256 colors from 65% to 89%, fewer below that) with dithering, then compresses it with the same DEFLATE algorithm PNG always uses. At 90% and above it re-encodes losslessly instead, keeping every pixel.
Transparency is preserved in both modes. If a re-encoded PNG would come out larger than your original, TinySquish keeps the original file.
What to expect
In our reproducible benchmark, quality 75% made UI screenshots 58% smaller with a mean PSNR of 58.24 dB, which is visually indistinguishable. Photos saved as PNG shrank by 63.8% at 39.56 dB. Lossless mode saved 16.8% on screenshots but nothing on the photo set, whose PNGs were already tightly compressed.
For photos, converting to WebP or JPEG usually saves far more than any PNG setting.
Frequently asked questions
Does compressing a PNG remove transparency?
No. Both the palette mode and the lossless mode keep the alpha channel. Transparency is only lost if you convert to JPEG, which has no alpha channel; transparent areas then become white.
What quality should I use for PNG?
Use 75% for screenshots, icons and illustrations: the 256-color palette is usually indistinguishable from the original. Use 90% or more when every pixel has to stay exact, for example for pixel art or images you will edit again.
Why is my PNG not getting smaller?
Some PNGs are already well optimized, and photos stored as PNG have too many colors for a palette to help much. Lower the quality, or convert photos to WebP or JPEG for much smaller files.