JPEG Quality Settings Explained: What 60% vs 90% Actually Looks Like
What that quality percentage slider actually controls, why the difference between 90% and 100% is invisible but the difference between 40% and 60% isn't, and how to pick a number instead of guessing.
A JPEG quality slider showing "75%" doesn't mean "75% as good as the original" — the relationship between that number and what you can actually see is not a straight line, and knowing roughly where the useful range is saves a lot of guessing.
What the percentage actually controls
JPEG compression works by discarding image detail the human eye is less likely to notice, more aggressively as the quality number drops. The percentage is a setting for that algorithm, not a direct measurement of visual quality — a 75 from one encoder and a 75 from another can look slightly different, since it's an instruction, not a universal scale.
The high end (85-100%): diminishing returns
Above roughly 85-90%, further increasing quality barely changes what's visible to the eye, but keeps meaningfully increasing file size — you're paying in bytes for a difference few people could spot in a side-by-side comparison. 100% (or 'no compression') is rarely worth its file size cost for anything that will be viewed on a screen.
The low end (below ~50%): where damage becomes visible
Below roughly 50%, compression artifacts — blocky patches, color banding, blurring around sharp edges — start becoming visible, especially in areas with fine detail or text. This range is usually only acceptable for thumbnails or previews where the image will be shown very small.
A practical range instead of a guess
For most web use — photos on a page, images in an article — quality in the 70-85% range is where file size drops substantially with a visible-quality cost that's hard to spot at normal viewing size. This is roughly the range most "smart" compressors default to, because it's genuinely close to the best tradeoff for typical photos.
Quick tips
- Quality settings apply per-save — re-saving an already-compressed JPEG at a lower quality compounds the artifacts each time; keep an original if you'll need to re-export at a different quality later.
- The right quality also depends on the image itself: a busy, detailed photo hides compression artifacts better than a flat-color graphic or an image with fine text, which show them faster at the same percentage.
- If you're not sure what number to pick, File Doctor's automatic check judges this per-image instead of asking you to guess a percentage.