How to Compress a PNG and Keep Its Transparency
PNG files are big because PNG is lossless, and there is no quality slider to turn down. What you can do is reduce the pixel count, and keep the transparent areas exactly as they are.
Pick a scale from 20% to 100%, compress and download. Alpha transparency is preserved.
What "compress PNG" can and cannot mean
PNG is a lossless format: it stores every pixel exactly, so it has no quality slider like JPG does. That is why PNG files are large, and why options for shrinking one are limited. This site's Compress PNG tool is honest about it. Its one control is Scale, which makes the image smaller in pixels. Transparency is not touched by that: see-through areas stay see-through.
Shrink a PNG in four steps
- Open Compress PNG and add PNG files with Select PNG Images.
- Move the Scale slider. It goes from 20% to 100% in steps of 5, and starts at 100%.
- Press Compress Images.
- Download the result. Single files are named like
logo-compressed.png, and several come ascompressed-images.zip.
The result line shows how much space you saved, as in "Reduced total size from 3.4 MB to 0.9 MB (74% smaller)". If nothing was saved, it says only that the images were processed and gives the new total, so read the number before using the file.
How scale changes the file
Scale multiplies both width and height. At 50% a 2000 x 1000 image becomes 1000 x 500, which has a quarter of the pixels. PNG file size follows pixel count loosely, so the file often lands near a quarter of the size too, though images with big flat areas shrink less predictably, because they were already compact. A rough rule is that area, not width, drives size, so small steps in scale add up quickly:
| Scale | Pixels left (share) | Use it for |
|---|---|---|
| 90% | 81% | A light trim when the image is a little over a limit |
| 75% | about 56% | Web graphics displayed smaller than their file size |
| 50% | 25% | Large screenshots and oversized exports |
| 25% | about 6% | Thumbnails; fine detail is gone |
The percentages come from squaring the scale, which is simple arithmetic. Actual file sizes depend on content.
Keeping transparency intact
The image is redrawn on a canvas and exported as PNG, and PNG keeps the alpha channel. Soft shadows, semi-transparent glows and anti-aliased edges remain. When the image is reduced, edges are smoothed by the browser's resampling, which can make very thin lines slightly softer. Check logos and icons at 100% zoom, because tiny text can become hard to read well before the file gets small enough.
If you hoped to turn a transparent background into a solid one to save space, that is a different job. Converting to JPG fills transparent areas with a colour, as in PNG to JPG without a white background.
When scaling is the wrong tool
- You need the pixel dimensions to stay fixed. A form asking for exactly 512 x 512 will not accept a scaled-down version. Keep scale at 100%, and use another route such as changing format.
- It is a photograph. Photos are far smaller as JPG or WebP. Use PNG to JPG or PNG to WebP, which keeps transparency, as covered in this PNG to WebP guide.
- You want a pixel-exact size. Resize Image sets exact width and height rather than a percentage.
- The PNG is already tiny. A flat icon of a few kilobytes has nothing to give.
A sensible order of tries
- Decide the largest size at which the image will really be shown. If it appears at 600 pixels wide, a 2400 pixel file is carrying sixteen times the pixels it needs.
- Try a scale that gets close to that size, then check the picture at 100% zoom.
- If the file is still above the limit and has no transparency, convert to JPG or WebP.
- If transparency matters and the file is large, convert to WebP, which keeps alpha with smaller files.
Why PNG exports are so large to begin with
Screenshots on high-density screens and exports from design tools are often twice the size you need, since they are saved at double resolution for sharp display on modern phones. If the image will be placed at half its pixel width on a page, scaling to 50% costs nothing visible on ordinary screens while removing three quarters of the pixels. That is the situation where this tool does the most good. For graphics that must stay crisp at their full pixel size, think about a different format rather than a smaller scale.
Common problems
- The file did not shrink at 100%. At full scale the image is only re-encoded, and re-encoding a PNG gives little. Lower the scale.
- A file was skipped. Only PNG files are accepted. Use the JPG route in Compress JPG for photos.
- The edges look soft. Move the scale up a step or two, and view the result at 100% zoom before you decide it is too blurry.
The image never leaves your browser. For several images, the ZIP is built there as well with JSZip from a CDN.
Frequently Asked Questions
Does Compress PNG keep the transparent background?
Yes. The image is exported as PNG again, and the alpha channel is preserved.
What does the Scale slider do?
It reduces both width and height by a percentage from 20 to 100, which cuts the pixel count and the file size.
Why did my file not get smaller at 100 percent?
At full scale the image is only re-encoded, which rarely saves much for a PNG. Lower the scale.
Is there a quality setting for PNG?
No. PNG is lossless. Only the scale changes the result here.
What if I need to keep the exact dimensions?
Keep scale at 100 percent and consider converting to WebP, which keeps transparency with smaller files.
What are the output files called?
Each file ends in -compressed.png, and several files come in compressed-images.zip.