How PNG compression works here
PNG has no quality slider, and a browser can only re-save a PNG losslessly, which usually reproduces the same bytes. To make a PNG meaningfully smaller, this tool reduces the image to an indexed palette of at most 256, 128 or 48 colors depending on the level you choose, dithers the result, and writes a new PNG with the same pixel dimensions. Images that already use few colors map exactly and lose nothing; images with many colors are approximated.
Measured results
These synthetic examples were measured in Playwright Chromium on 2026-10-19 by running this page's production compression code. Real savings depend on your image.
| Example | Input | Quality (256) | Smart (128) | Extreme (48) |
|---|---|---|---|---|
| Text-heavy PNG screenshot | 7.34 KB | 1.10 KB (84.97% smaller) | 1.10 KB (84.97% smaller) | 1.10 KB (84.97% smaller) |
| Photo-like PNG with sensor noise | 305.39 KB | 91.81 KB (69.94% smaller) | 74.47 KB (75.62% smaller) | 53.73 KB (82.4% smaller) |
| Transparent PNG graphic | 32.62 KB | 8.55 KB (73.77% smaller) | 7.54 KB (76.89% smaller) | 5.77 KB (82.3% smaller) |
Good PNG candidates
Interface captures, diagrams, logos, icons and flat artwork already use few colors, so they shrink with little or no visible change. Photographs and images with smooth gradients shrink the most but are the ones that can show banding at lower levels, so start with Quality or Smart.
How to evaluate the result
- Add one genuine PNG.
- Run a level; the output remains PNG at the same dimensions.
- Compare gradients, soft shadows and fine detail with the original, then keep the smallest level that still looks right.
When you need exact pixels or a smaller file still
If the PNG is a master you will edit later, keep the original: palette reduction is not reversible. For a photo-like PNG that is still too large, reduce its dimensions or change format. Read the measured format comparison before choosing WebP or JPG; those options can be smaller by accepting different trade-offs.
PNG-specific questions
How does the PNG compressor shrink a file?
Browser Canvas can only write lossless 32-bit PNG, which rarely beats an already-optimised file. FiloTool instead reduces the image to an indexed palette: 256 colors for Quality, 128 for Smart and 48 for Extreme, with dithering to soften gradients. An image that already uses few colors converts to a palette with no visible change.
Do the PNG compression levels reduce quality?
Yes, on images with many colors. Photographs and smooth gradients lose fine color detail as the palette shrinks, which can appear as banding or grain. Flat graphics and screenshots with few colors are unaffected. Compare the result with the original before replacing it.
Does PNG transparency remain?
Yes. Alpha values are kept in the palette (as a tRNS chunk), and fully transparent pixels stay transparent. Soft semi-transparent edges and shadows are the part most likely to look coarser at the Extreme level.
Why did the PNG not shrink?
A small PNG that is already indexed or very simple can be as small as it will get. If the palette version is not smaller, FiloTool returns the original rather than replacing it with a worse result.
Should I convert PNG to WebP instead?
Possibly for web delivery, but that changes format. Keep PNG when you need lossless pixels, an editable master, or broad alpha support, and compare against the measured format guide before deciding.
Does this remove metadata?
The re-encoding path writes visible pixels and ordinarily omits source metadata. Use Image Metadata when inspection and removal verification are the goal.