Every image compressor makes the same promise: smaller files, same picture. What actually happens is more interesting, and knowing the difference saves you from guessing with a slider and hoping for the best.
Lossy vs. lossless, in practice
Lossless compression (PNG, WebP in lossless mode) repacks the exact same pixel data more efficiently. Nothing is discarded, so quality never drops, but the size savings are modest — usually 20-40% for photos, more for flat-color graphics like screenshots or logos.
Lossy compression (JPEG, WebP in lossy mode) throws away detail the human eye is less likely to notice — subtle color gradients, high-frequency texture — in exchange for much larger savings, often 70-90%. The trade-off is tunable: a quality setting of 90 is nearly indistinguishable from the original, while 40 starts showing visible blocking around sharp edges.
This is why our Image Compressor gives you a quality slider instead of a single "compress" button — there's no universal correct setting, only the right trade-off for your use case.
Pick the right setting for the job
- Hero images and product photos: stay above 80% quality. These are the images people look at closely, and artifacts are easy to spot.
- Thumbnails and background images: 50-65% is usually invisible at small display sizes and cuts file size considerably.
- Screenshots with text or sharp lines: JPEG compresses these poorly, since it's tuned for photographic detail. PNG or lossless WebP will often produce a smaller, cleaner result.
When resizing beats compressing
Compression quality and pixel dimensions are two separate levers, and people often reach for the wrong one. A 4000×3000 photo displayed at 800×600 on a web page is carrying roughly 25 times more pixel data than it needs to, regardless of how aggressively you compress it. In that case, resizing first with our Image Resizer will cut the file size far more than adjusting quality alone, and it won't introduce compression artifacts at all — you're removing pixels that were never going to be seen, not degrading the ones that remain.
A practical order of operations: resize to the dimensions you'll actually display, then compress.
Does the file format itself matter?
At equivalent visual quality, WebP typically produces files 25-35% smaller than JPEG and supports both lossy and lossless modes plus transparency — PNG's main advantage — in one format. The trade-off is slightly older software support, though every modern browser handles it natively. If you're optimizing for file size on the web, converting with our WebP Converter is usually worth the five seconds it takes.
A quick checklist
- Resize to the dimensions you'll actually display — not the camera's native resolution.
- Choose PNG/lossless for screenshots and flat graphics, JPEG/WebP for photos.
- Start compression around 80% quality and lower it only until you can't tell the difference.
- Compare the before/after file size shown by the tool — if the reduction looks too good to be true for a detailed photo, check the preview closely before publishing.