September 20, 2026 · fileo Compress

What JPEG quality 80 actually means

The quality slider on this site defaults to 80 because that number is a truce, not a scientific constant. Photoshop, cameras, and browsers do not share one table. “80” in Chrome’s encoder is not “80” in libjpeg-turbo’s -quality. Treat the slider as a named preset: higher is gentler, lower is cheaper.

Quantization, not a percentage

The encoder splits the image into 8×8 blocks, runs a DCT, and divides the coefficients by a table. A higher quality setting uses smaller divisors, so more of those coefficients survive. You are not keeping 80% of pixels. You are keeping more of the frequency data that makes edges look expensive.

How I actually pick a number

Hero image on a marketing page: 80–85, then look at the sky. Product tile in a grid of twenty: 70–75, because no one pinches-zooms a tile. Thumbnail: 60 is often enough. Screenshots: I refuse JPEG entirely.

If you type 200 into the target box, you are saying the form matters more than the preset. The tool will hunt quality, then shrink dimensions. Dimension shrink is a different artifact (softness) than quantization (blocks). Watch which one you are seeing.

Compare with your own file

Internet examples use stock sunsets. Your file might be a dim indoor JPEG that was already saved four times. Re-compressing a dirty JPEG at 80 will not restore the first generation; it will add another generation. If the source is already blotchy, go back to the original camera file. This compressor is an export step, not a restoration lab.

Chroma subsampling, briefly

Most JPEG encoders store color at half the resolution of brightness, because the eye is picky about edges and lazy about hue. That is why a red letter on blue can look smeared while a grey ladder stays clean. If your image is mostly text, you are fighting the codec. If it is a face, you are in the codec’s comfort zone. Quality 80 on a face is a different visual event than quality 80 on a spreadsheet screenshot.

Further reading: JPEG tool · page speed