How Much Can You Compress an Image Before It Looks Bad?

Search this question and you will get the same answer everywhere: use quality 80. It is a reasonable default and it is where most people should start.

It is also not an answer, because the number that is safe depends entirely on what is in the image, and because the "80" on your software's slider may not be the same 80 the article meant. More usefully, you can learn to see the damage yourself in about ten minutes, and then you never need a rule of thumb again.

The quality slider is not a percentage of anything

First, a practical trap.

JPEG quality is a setting fed to an encoder, not a measurement. Different software uses different scales and different internal mappings. Photoshop's Save for Web offers 0 to 100, but its older Save As dialog uses 0 to 12. GIMP, Lightroom, ImageMagick and the browser's own encoder all have their own curves.

So "quality 10" in one tool can mean something entirely different in another, and quality 80 in two different programs will not produce identical files. When someone tells you a number, it only means something alongside the software they used.

The one thing that is consistent: the same setting produces very different file sizes for different pictures, because the setting controls how aggressively detail is discarded, not how many bytes come out. That is why hitting an exact file size needs a different approach entirely.

Where the damage shows up first

This is the part that surprises people, and it is the single most useful thing to know.

You would expect a busy, detailed photograph to fall apart first and a simple one to survive. It is the other way round.

Smooth areas break first. A clear sky, a gradient, skin, a plain wall. These are where you see banding — the smooth transition breaks into visible steps of flat colour — and it appears at quality settings where the rest of the image still looks fine. Photographers testing this consistently find the sky posterising while an intricately detailed brick wall in the same frame still looks perfect.

Busy areas hide damage. Foliage, gravel, fabric weave, crowds. There is so much visual noise that the compression artefacts blend in and your eye does not separate them out.

Hard edges are the worst case. Text, interface elements, line art, logos. JPEG works in 8x8 pixel blocks and approximates what is inside each one. A sharp black-on-white edge is nothing but fine detail, so you get faint ripples spreading out from it — ringing — plus colour smearing, because JPEG stores colour at lower resolution than brightness.

The practical consequence: a landscape full of trees can go far lower than you expect. A portrait against a plain backdrop, or anything containing text, cannot.

The four things to look for

Learn these names and you will spot the problem immediately.

Blocking. Visible 8x8 squares, usually in dark areas or around high-contrast edges. The classic sign of pushing too far.

Banding or posterisation. Smooth gradients breaking into bands. Look at skies, out-of-focus backgrounds and shadows.

Ringing. Faint halos or ripples around sharp edges and text.

Colour bleed. Coloured edges losing definition, most visible on saturated colours against contrasting backgrounds — red text on white is the giveaway.

How to test properly

Most people evaluate a compressed image wrong, by looking at the whole thing on screen, where it is already scaled down and everything looks fine.

Do this instead:

1. View at 100 percent zoom. One image pixel to one screen pixel. Anything less is hiding the damage from you.
2. Look at the smooth areas first, not the detailed ones. Sky, skin, shadows, backgrounds.
3. Then look at any edges and text.
4. Check on a phone as well as a monitor. Small bright screens reveal banding that a large display can mask.
5. Compare against the original, then look at the compressed one alone. If you can only see the difference when flicking between the two, it does not matter. Nobody will ever have your original to compare against.

That last point matters more than any number. A/B comparison makes you far more critical than any real viewer will be.

A working approach

Rather than picking a number, walk down until you see something.

Start at 85. Export, view at 100 percent, check the smooth areas. Drop to 75 and look again. Then 65. Somewhere along that path you will notice banding appear in a gradient or ripples around an edge — go back one step. That is this image's limit.

Do it for a handful of representative pictures and you will develop an instinct for your own material within an afternoon.

Our compressor lets you see the resulting file size as you change the setting, so you can judge what each step is actually buying you. Very often you will find the drop from 85 to 75 saves a lot and costs nothing visible, while 75 to 65 saves much less and costs more.

Resize before you compress

If you are pushing quality low to reach a file size, you are probably solving the wrong problem.

A photo displayed at 800 pixels does not need 4000 pixels of data. Reduce the dimensions with the resizer first and the file collapses on its own, letting you keep a high quality setting. Downscaling also hides existing artefacts, because averaging pixels together smooths them out.

Aggressive compression at full resolution and gentle compression at sensible dimensions can produce the same file size. The second one looks dramatically better.

Some cases where the usual advice does not apply

Screenshots and graphics. Do not use JPEG at all. Keep them as PNG, which is lossless and compresses flat colour efficiently. A screenshot at JPEG quality 80 often looks worse and weighs more than the PNG.

Anything you will edit later. Compress once, at the end. Every save discards more, and the losses accumulate across generations. Keep a high-quality master.

Print. Screen artefacts and print artefacts are not the same. Stay at 90 or above, and let the printer tell you what they want.

Images with your logo or fine branding. Small text and thin lines degrade long before the photograph around them does. Judge by the logo, not the photo.

The short version

Quality 80 is a decent starting point, not a rule, and the number is not comparable between programs. Damage appears first in smooth gradients and around text, not in busy detail, so that is where to look. View at 100 percent, walk the setting down until you see banding or ringing, then step back once. And if you are having to push the quality low, resize the image first instead — you will get the same file size and a much better picture.