What this compressor actually does
The tool draws your image onto an HTML canvas in the browser and saves it again with the browser's own encoder. It does not use a specialised optimiser, and nothing is uploaded. The pixel dimensions stay the same, so the saving comes only from how the pixels are encoded.
That has one important consequence. The canvas encoder accepts a quality value for JPEG and WebP only. PNG ignores it. The slider (1 to 100, default 80) therefore matters when the output is JPEG or WebP, and does nothing when the output is PNG.
Lossy versus lossless
Lossless compression, which PNG uses, stores every pixel exactly and can be reversed perfectly. Lossy compression, used by JPEG and by WebP in its lossy mode, discards detail the eye is less likely to notice, in return for much smaller files. Lower quality values discard more. Once discarded, detail cannot be recovered, and each lossy re-save compounds the loss, so always compress from the original file.
| Output | Slider applies | Keeps transparency | Suits |
|---|---|---|---|
| JPEG | Yes | No. Transparency is filled with white | Photographs |
| WebP | Yes | Yes | Photos and graphics on the web |
| PNG | No (lossless, slider ignored) | Yes | Screenshots, logos, line art |
How to choose a quality value
There is no universally correct number, because the same setting produces different results on different pictures. A short procedure works better than a rule:
- 1
Decide whether you need transparency
If yes, stay with PNG or choose WebP. JPEG will flatten transparent areas onto white.
- 2
Is it a photograph or a flat graphic?
Photos shrink well as JPEG or WebP. Screenshots, logos and text-heavy graphics often stay smaller as PNG.
- 3
Start the slider at the default of 80 and look at the result
Compare the preview with the original at the size it will be shown. Move up if you see blocky edges or smudged detail, down if you cannot see a difference.
- 4
Check the size note, not just the preview
If the file is not noticeably smaller, the format or content is the limit, not the slider. Try the other lossy format.
WebP or JPEG?
WebP is often smaller than JPEG at a similar visual quality, and it also supports transparency, which JPEG cannot. The trade-off is compatibility: JPEG opens in practically every program and upload form, while some older software and a few services still reject WebP. If the file is for a website you control, WebP is a reasonable choice. If it will be emailed, printed or uploaded to an unknown system, JPEG is the safer one. For a longer comparison, see PNG vs JPG vs WebP.
How much you save depends on the picture. Detailed photographs have more to gain from lossy encoding than flat colour graphics, and an image that was already compressed has little left to give.
Other formats and batches
The compressor accepts PNG, JPG, WebP, GIF, BMP, AVIF, SVG and ICO files up to 20 MB, and up to 50 at a time. Browsers cannot write GIF, BMP, SVG, AVIF or ICO from a canvas, so with Keep Original those come out as PNG. Each finished batch lists the before and after size and the percentage change per file, then offers a ZIP. The Continue with bar can send results straight to another tool without a re-upload. To cut file size further, resize the image first, since fewer pixels is often the biggest saving; see how to compress images for the web.