Reduce PNG colour data while keeping a PNG image and transparent areas

The Compress PNG page is a dedicated browser-based tool for reducing the size of PNG images. It keeps PNG as the output format and applies a colour-palette reduction process rather than converting the file to JPEG. This matters when the image contains transparent pixels, interface graphics, product cut-outs, icons, diagrams or artwork that should remain in a PNG file.

PNG is a lossless file format, but that does not mean every way of making a PNG smaller is lossless. This tool uses palette quantization: it groups similar colours and maps pixels to a smaller set of representative colours. The result is still a PNG, but the visible colours can change. On a simple logo or illustration the difference may be hard to notice; on a photograph, gradient or soft shadow, reduced colours may create visible banding or less subtle transitions.

The current Compress PNG page provides three levels:

These are palette levels, not JPEG quality percentages. The processing code draws the PNG to a canvas, applies the selected palette reduction and exports a PNG result. It does not provide a target-KB input, custom pixel dimensions or a resize slider on this particular page. When your task requires a specific maximum such as 50 KB or 100 KB, use the separate Compress PNG to Size page, which has target-size controls and optional downscaling.

The tool applies the same palette level to the selected batch. It does not analyse each image and automatically choose a different colour limit for each one, so a level that looks good on a simple icon may be too aggressive for a photograph. Check more than one file when you process a mixed folder.

A PNG can contain millions of possible RGB colour combinations. Palette reduction maps the image to fewer representative colours. In this tool the selected level corresponds to around 32, 128 or 256 colours, depending on the chosen compression setting. If the input already contains fewer distinct colours than the selected limit, the palette routine may not need to change the colour map substantially.

The quantizer treats highly transparent pixels separately and retains an alpha channel in the output. Fully transparent areas remain transparent, and semi-transparent alpha values are normalized into cleaner steps. That makes the result suitable for many transparent graphics, but it is not a guarantee that every anti-aliased edge will look pixel-identical to the source. Inspect logos, cut-out products and fine line art against both light and dark backgrounds.

PNG is often chosen for graphics where edges, transparency or repeated flat colours matter. Palette reduction is most useful when the source contains broad areas of similar colours rather than complex photographic texture. Examples include:

It is less predictable for full-colour photographs, skin tones, smooth skies, gradients, glows and subtle semi-transparent shadows. Those images can show banding or visible colour steps when forced into a small palette. For photographic content where PNG is not required, consider whether JPG or WebP is acceptable. A different format may reduce the file more effectively than strong PNG quantization.

This page offers compression levels rather than a specific KB ceiling. Choosing Extreme does not promise that the result will be under 10 KB, 20 KB, 50 KB or any other limit. The amount of reduction depends on source dimensions, the number of colours, texture, transparency and how efficiently the original PNG was already encoded. The page does not resize the pixel dimensions in this quality-mode workflow.

When a form or website specifies a maximum file size, check the actual downloaded PNG. If the result is still too large, the target-size PNG tool offers more controls: it can test several palette sizes and, when enabled, reduce the pixel dimensions proportionally. That may change visual detail and pixel dimensions, so it should be used only when the receiving requirement allows those changes.

The compression workflow runs in the browser using Canvas and a local palette-quantization helper. The page allows multiple PNG files to be processed and bundles multiple results into a ZIP. It is intended for PNG inputs; use an image converter first if the original file is a JPG or WebP image.

Before replacing an image on a website, compare the output at its actual display size. Check small text, curved edges, gradients, shadows and transparent margins. Keep the original file if you may need to revise the artwork later. The best compression setting is the strongest level that still preserves the appearance required for the image's real use.