Image compression works on two levers at once: how much detail the encoder throws away, and how many pixels there are to begin with. This tool uses both, and it treats JPEG and PNG differently because the two formats fail in different ways.
For JPEG files it lowers the quality factor and scales the image down slightly. For PNG files it only scales — the format stays lossless, because dropping a PNG into a lossy encoder is how flat brand colours turn into mush and interface text picks up grey halos. Scaling is done with pica, a proper Lanczos resampler, rather than the browser’s default bilinear draw, so downscaled photos stay crisp instead of going soft.
Compression happens frame by frame inside your browser. Nothing is uploaded, so there is no service holding a copy of your photos after you close the tab.
| Level | JPEG quality | JPEG scale | PNG scale |
|---|---|---|---|
| Basic | 0.80 | 100% | 90% |
| Medium | 0.65 | 90% | 75% |
| Strong | 0.45 | 75% | 50% |
Basic keeps JPEG images at their full pixel dimensions and only reduces the encoding quality, which is the safest option when the picture may be printed or cropped later. Strong at 0.45 is genuinely aggressive — fine for a thumbnail or a chat attachment, visibly soft if the image is enlarged.
A PNG is normally chosen precisely because the content cannot tolerate lossy compression: a logo, a screenshot, a chart, a diagram with one-pixel rules. Re-encoding those as JPEG would defeat the purpose, so this tool never does. Instead it reduces the pixel count, which shrinks the file while keeping every remaining pixel exact. If your PNG is actually a photograph, you will save far more by converting it to JPG first with the PNG to JPG tool.
It varies enormously with content. Photographs at Medium typically drop by sixty to eighty percent. Flat graphics and screenshots save much less, because they were already efficient to store. The completion screen reports the actual figure for your batch.
At Basic, JPEG files keep their exact pixel dimensions. Every other combination scales the image down — PNG by ten to fifty percent, JPEG by up to twenty-five percent at Strong. If you need the original dimensions kept exactly, use Basic with JPEG input.
PNG output stays lossless here, so the only saving comes from scaling. That is deliberate: a screenshot or logo pushed through a lossy encoder develops visible artefacts. If the PNG is really a photograph, convert it to JPG instead for a much bigger reduction.
Use Basic. It keeps JPEG dimensions intact and a quality factor of 0.80, which holds up at normal print sizes. Medium and Strong both reduce resolution and are intended for screen use.
Yes. Select any number of images and they are processed sequentially, then delivered as a single ZIP with each file renamed with a -compressed suffix.
No. The decoder, the pica resampler and the JPEG encoder all run inside your browser, so no image data is transmitted at any point.
