"Compress without losing quality" is a promise lossy formats can't fully keep — every step of compression trades some fidelity for bytes. The useful question isn't whether you lose quality but how much, for how many bytes saved. So we measured the trade directly. The method Across the 24-image Kodak reference suite — the standard set for this kind of test — we saved every photo as JPEG and WebP at qualities 20 through 95, and scored each output on SSIM (structural similarity to the original, 0 to 1) rather than eyeballing it. Every figure below is the mean over all 24 images, so it's not one lucky photo. Diminishing returns are brutal The size-vs-quality curve bends hard: the first kilobytes buy almost all of the quality, and after that it flattens into a long tail where you pay a lot for very little. The clearest example: pushing JPEG from quality 85 to 95 nearly doubles the file — from about 14% to 26% of the original — for an SSIM gain of just 0.025 (0.95 → 0.98). That is double the bytes for a difference most people can't see on most images. The habit of exporting at 95 or 100 "to be safe" is, for photographs, mostly wasted space. Format beats quality-cranking Changing the codec does more than turning the quality dial: WebP is about 30% smaller than JPEG at the same SSIM — 29.6% smaller at SSIM 0.95, 31.9% at 0.97. Same perceived fidelity, a third less weight. Staying fully lossless costs roughly 7× a quality-85 JPEG. "Keep it lossless to be safe" usually means paying seven times over for bytes no one will perceive. The practical takeaway For photographs, the sweet spot is quality 80–85, ideally in WebP. But the honest answer is that the right setting is image-dependent — a flat sky compresses beautifully, fine texture does not — so a live preview beats any single recommended number. Pick the point on the curve where the preview stops changing, not a fixed "95". Reproduce it The study is a straightforward encode-and-score sweep over the Kodak set, driven by a short script — point it at your own images and you'll get the same shape of curve. And if you just need to compress something, the image compressor and the rest of the image tools run entirely in your browser with a live preview — nothing uploaded. Originally published on LK Forge.