I compressed a photo I saved from WhatsApp and it came out larger. Why?
Because it was already squeezed hard. Chat apps and websites compress photos before passing them on, so re-encoding one at quality 80 or 90 asks the encoder to store it more faithfully than it was stored before, which costs more bytes. In that situation there is usually nothing to gain, and the best move is to keep the file you already have.
What happens inside the tool
Compression here is not trimming the existing file. It is a full rebuild: the tool decodes the photo into pixels, then encodes those pixels again at the quality you pick. The encoder has no idea the image went through compression before. It sees pixels that carry small artifacts from the first round and tries to preserve them at the requested quality. Preserving artifacts accurately costs bytes, so the new file can be heavier than the source without looking any better.
A test on an already compressed photo
A small 400×300 JPEG of 5.74 KB, previously saved at low quality, the way chat photos often are. Results in Chrome:
Quality 90: 9.82 KB, 71.2% larger.
Quality 80: 7.82 KB, 36.3% larger.
Quality 50: 6.28 KB, still 9.4% larger.
Quality 30: 5.82 KB, 1.5% larger.
Only quality 20: 5.17 KB, 9.9% smaller, at the cost of more damage stacked on the first round.
As WebP at quality 75: 8.78 KB, 53.1% larger.
Switching to WebP did not help either. The only saving came at a very low quality, and it is not worth the extra damage.
What to do when you see the warning
- When a file grows, the Image compressor shows the percentage in the Change column with a clear warning that the original is already well compressed. It does not hide the result.
- Do not download the larger file. Keep the original and use it as it is.
- If you truly need a smaller file, the lever is dimensions, not quality: reduce the width with the image resizer and then try compressing again.
- If you can get the original from the phone or the photographer, compress that instead of the chat copy. You will end up with a file that is both sharper and lighter.
When compression really pays off
The biggest savings come from photos straight out of a camera or exported from design software at maximum quality, because they carry plenty of data you can drop with no visible difference. A photo that went through a chat app or was downloaded from a website has already had that data removed by someone else. A simple rule: the lighter a file already is for its dimensions, the less there is to gain from compressing it again.
Common questions
Would converting it to PNG make it smaller?
Usually not. PNG keeps every detail, so photos saved as PNG are much heavier. That is why the compressor only outputs JPEG or WebP.
How can I tell a photo is already compressed before trying?
If its file size is very small for its dimensions, it probably is. The reliable way is to run it through the tool and read the Change column.
Does compressing again and again hurt the photo?
Yes, each new encode adds a little damage. Always compress from the best original you have.