Compress PNG Online: Reduce PNG File Size, Free and Private

Compress a PNG to an exact file size in KB

Some uploads enforce a strict cap: a forum avatar limited to 100 KB, a form field that rejects anything over 50 KB, a strict portal that wants 20 KB, or a CMS that caps hero images at 1 MB. Switch the compressor to Target size mode, choose a preset of 20 KB, 50 KB, 100 KB, 200 KB, or 1 MB, or type your own figure, and the tool compresses every PNG toward that ceiling. It does this by searching the palette from 256 colours downward and keeping the largest palette whose encoded file still fits, so the output stays as sharp as the target allows. If a target is too small to reach by colour reduction alone, usually a large photographic PNG squeezed under 20 KB, the tool returns the smallest version it can and labels it, so you know to reduce the image dimensions as well.

Colour depth and bit depth: how many colours your PNG keeps

A normal PNG is 24-bit truecolour, which can hold about 16.7 million colours. Almost no logo, icon, or interface graphic uses more than a few hundred of them, so most of that range is paid for and never used. Compression converts the image to an 8-bit indexed palette, which stores up to 256 colours and references each pixel by a palette slot instead of a full colour value. That single change is where the file size falls. In quality mode the slider sets exactly how many colours to keep, and the tool shows the live count next to it, for example about 180 colours at a higher setting or 48 at a lower one, so you can reason about the control rather than guessing. Fewer colours means a smaller file; more colours means finer gradation. An 8-bit palette with alpha still keeps full transparency.

Lossy palette reduction versus lossless optimisation

PNG compression has two paths, and this tool uses the first. Lossy palette reduction lowers the number of colours, which changes the pixels slightly but shrinks the file dramatically, the pngquant approach and the source of most of the saving. Lossless optimisation instead re-encodes the existing pixels and strips unneeded metadata chunks without altering a single colour, which is safe for pixel-exact output but saves far less, often only 5 to 20 percent. If you need the image to stay bit-for-bit identical, keep the colour detail slider at its maximum, which preserves the full palette and behaves like a lossless pass. For the large reductions in the table above, the lossy palette step is what does the work.

When PNG compression struggles: gradients and photographs

Palette reduction rewards flat colour and punishes smooth variation. A worked example: a flat logo with 12 distinct colours compresses to an 8-colour palette with no visible change, because it never needed more. A sky gradient, by contrast, contains thousands of subtly different blues, and forcing those into 256 slots produces visible steps, called banding. This is why a photograph saved as PNG only halves in size while a logo drops by 80 percent. When an image is photographic or full of gradients, two options work better: turn on dithering, which scatters palette colours to disguise the banding, or convert to JPG or WebP instead, formats built for continuous tone. The honest rule is that PNG compression is for graphics; photographs belong in a photographic format.

Provably private: compress with your connection off

Every step happens in your browser through the HTML5 Canvas API, so nothing is ever uploaded. You do not have to take that on trust. Load this page, turn off your Wi-Fi or unplug the network, and compress a PNG anyway: it still works, because the quantizing and re-encoding run on your own device. Server-based compressors cannot do this, since they must send your file away to process it. For a private contract scan, an ID, or an unreleased design asset, that difference matters, because the image never leaves the machine you are sitting at.