Compress PNG Images

How to compress a PNG

1. Drop your PNG files on the box above, click Choose images, or paste a screenshot with Ctrl+V (⌘V on a Mac). Up to 30 files, 30 MB each.
2. Leave Output format on Same as original and PNG output on Smart. Each PNG is redrawn and saved as an indexed PNG with at most 256 colors.
3. Drag the divider on the preview and zoom to 100% or 200%. Gradients and photos are where color reduction shows first; text, flat colors and sharp edges normally look identical.
4. Download one file or Download all (ZIP). If a new copy is not smaller and the original holds no EXIF or XMP block, Pixdesk keeps your original file and says so in the list.

The quality slider does nothing for PNG output, because PNG has no quality setting. The size comes from the number of colors and how well the pixels compress.

Why PNG files are big, and what Smart PNG changes

A PNG made by a screenshot tool or a design app is usually a truecolor file: every pixel stores its own red, green, blue and often alpha value, and the file is then compressed without loss. That is ideal for editing and wasteful for publishing, because a UI screenshot or a logo rarely needs millions of possible colors.

The PNG standard also has an indexed-color mode. The file carries a palette of 1 to 256 colors, and each pixel stores only a palette number. A separate transparency table gives every palette entry its own alpha value, so soft, semi-transparent edges survive. Pixdesk’s Smart mode writes exactly this kind of file:

• Already 256 colors or fewer? Pixdesk counts the colors first. If the image fits, it builds an exact palette and the result is pixel-for-pixel identical to the original, only stored more compactly.
• More colors than that? It groups similar colors with a median-cut search over the whole image, picks 256 representatives, and spreads the rounding error with light dithering so gradients do not band as hard.
• Fully transparent pixels share a single palette slot, and partly transparent ones keep their transparency, rounded to the nearest palette entry.

This is the same family of technique that TinyPNG describes on its own site: merge similar colors, store fewer bytes per pixel. The difference here is where it runs. Pixdesk encodes in a background worker in your browser tab instead of on a server, so there is no upload and no daily quota. Smart mode needs the browser’s built-in compression API (CompressionStream, in all current major browsers); where it is missing, Pixdesk saves a lossless PNG instead.

What the sample shows

We measured Pixdesk’s built-in sample graphic, a 34 KB PNG with flat shapes, text-like edges and a transparent background. The same numbers appear on our compressor and PNG to JPG pages.

Results depend on the picture. Screenshots, charts, icons and illustrations usually shrink a lot. A photograph saved as PNG is different: 256 colors are not enough for smooth skin and sky, so you may see banding at 200% zoom. For photos, PNG to JPG or PNG to WebP gives much smaller files.

Hitting a size limit with PNG

You can still type a target size in KB. With Smart PNG output Pixdesk first tries 256 colors, then 128, 64, 32 and 16, and stops at the first palette that fits. Fewer colors means a smaller file and more visible banding, so check the preview. If even 16 colors do not fit, the row tells you, and the honest options are to make the image smaller with Max width or to switch the output to WebP or JPG.

Choose Lossless under PNG output when the file will be edited again or must stay pixel-exact with more than 256 colors, for example a design master or a medical or scientific image. Lossless output is re-encoded by your browser’s own PNG encoder; it can be smaller or larger than your original depending on how that file was saved.

Which format should a PNG become?

Google reports that lossless WebP files are about 26% smaller than PNGs, which matches what we see on flat graphics. Keep a PNG when a form, an app store, a print shop or an email client asks for PNG.

What happens to your files

Everything happens inside this browser tab. Pixdesk reads your files with the browser’s own image decoder, redraws them on a canvas in a background worker and saves the new file with the browser’s encoder. There is no upload endpoint on pixdesk.cc, and the page makes no network request while it works. You can check that yourself in two minutes with your browser’s Network panel.

The new PNG contains only image data: text chunks, EXIF and other metadata blocks from the original are not copied.