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compressjpeg — Frequently Asked Questions
Everything about formats, quality, privacy and how Compress JPEG works.
General
Frequently asked questions
Is compressjpeg.onl free?
Yes — free, no watermark, no signup.
Which formats can I compress?
JPEG and PNG losslessly or lossily, plus WebP conversion. Photos compress most with JPEG or WebP.
Are uploads private?
Files are processed in an isolated workspace and deleted shortly after download.
Compress JPEG
Frequently asked questions
How much smaller will my JPEG get?
Camera photos commonly shrink 40–70%. Images that are already small or heavily compressed have less room to improve.
Does compressing a JPEG lower its quality?
JPEG is lossy, but at the quality used here the change is invisible at normal viewing sizes. You lose bytes, not visible detail.
Can I compress many JPEGs at once?
Yes — batch uploads are supported and delivered together.
Is there a watermark or signup?
No watermark and no signup — the tool is completely free.
Compress PNG
Frequently asked questions
Will optimising a PNG twice make it smaller?
Rarely. The first pass reaches the lossless minimum for that image, so a second run finds little left to remove. To shrink further, resize the image or convert it to WebP.
Does the optimiser keep transparency?
Yes. The alpha channel is preserved exactly, so transparent and semi-transparent areas look identical after optimisation.
Why did my screenshot shrink so much more than my photo?
Screenshots have large flat areas and few colours, which PNG compresses extremely well. Photos have continuous tone that PNG cannot pack tightly, so they barely shrink.
Is any image quality lost?
No. PNG optimisation is lossless. Only redundant data and bulky metadata are removed, never visible pixels.
Compress to WebP
Frequently asked questions
Can WebP keep transparency from my PNG?
Yes. WebP supports a full alpha channel, so transparent and semi-transparent areas convert across from PNG without any loss.
Does every browser support WebP now?
Every current browser displays WebP natively. Only very old, unmaintained browsers lack support, which is why some sites still keep a JPEG fallback.
Will converting a JPEG to WebP improve its quality?
No. Conversion can't restore detail already discarded by JPEG. It re-packs the existing picture into a smaller file at the same visible quality.
Should I convert photos or graphics to WebP?
Both work. Photos get a moderate size cut versus JPEG, while complex graphics with transparency often shrink dramatically compared with PNG.
Resize Image
Frequently asked questions
How is resizing different from compressing?
Resizing reduces the pixel dimensions of an image; compression reduces file size while keeping the same dimensions. Doing both produces the smallest possible file.
Will resizing distort my image?
No. The aspect ratio is preserved, so the image scales uniformly without stretching or squashing in either direction.
Why cap the longest edge at 1920 pixels?
1920 pixels still fills a full-width display on high-resolution screens, while removing the excess pixels that oversized originals waste on file size.
Should I resize before or after compressing?
Resize first. That way the compressor only encodes the pixels you'll actually show, instead of optimising data you're about to discard.