If I compress the same image several times, does it lose quality every time?
Yes. Every new JPEG or WebP encode throws away a little more detail, and after the first pass the file barely gets smaller. Always keep the original, and when you need a different size later, compress again from that original, not from a copy that was already compressed.
Why the loss piles up
When you compress an image, the encoder does not just store the original less precisely; it produces a new image that differs slightly from it. Compress that new image again and the encoder starts from it, artifacts and all, and adds a fresh round of approximation on top. The damage is never corrected; it accumulates. With JPEG at a fixed quality it builds slowly, but it does not stop.
Five passes, in numbers
A 1600×1200 product photo of 689.5 KB, compressed in Chrome as JPEG at quality 80, then the result compressed again and again at the same setting:
Pass 1: 250.9 KB, mean pixel difference from the original 4.304.
Pass 2: 248.3 KB, difference 4.523.
Pass 5: 247.7 KB, difference 4.728.
From pass 1 to pass 5 the file shrank only 1.3%, while the difference from the original grew on every pass.
The same photo as WebP at quality 75:
Pass 1: 203.8 KB, difference 4.077.
Pass 2: 176.6 KB, difference 4.857.
Pass 3: 169.5 KB, difference 5.183.
With WebP the size kept falling, but the price was clear: the difference from the original jumped more in the second pass than in five passes of JPEG. The mean difference is the average gap per color channel on a 0 to 255 scale.
Where this happens in everyday work
- You download a product photo from your store to tweak it, then compress it and upload it again.
- A supplier sends you a photo over WhatsApp, you compress it, then send it on to a customer over WhatsApp.
- You compress a photo for your store, then use that same compressed copy to make a smaller version for ads.
- You edit a photo in a phone app that saves a JPEG after every change.
The rule that protects you
- Keep a folder of originals that no compressor ever touches.
- Make every version you need, for the store, for ads, for WhatsApp, directly from the original in the Image compressor.
- If the original is gone, compress the copy you have once only, and read the Change column. If the saving is small, do not compress.
- The -compressed suffix the tool adds helps you tell compressed copies apart, so do not remove it and later mistake one for an original.
Common questions
Does compressing at a higher quality the second time bring detail back?
No. Lost detail does not come back; a higher quality only stores the artifacts more faithfully, and the file may grow.
Does resizing count as another compression?
Yes, if the image is saved as JPEG or WebP afterwards. Save intermediate steps as PNG to avoid that.
Does uploading to a platform compress the image too?
Many platforms process images on upload. That is why you should upload a clean copy made from the original.