Understanding image quality and compression settings
'Quality 80' means something different in every tool and every format. Here is what the number actually controls, and how to use it with confidence.
Published Updated 8 min read
"Quality" sliders in image tools all look similar — a number from 0 to 100 — but they don't mean the same thing across formats, and the relationship between the number and the visible result is not a straight line. Understanding what's actually happening under the slider makes it much easier to pick a sensible value on the first try.
Lossy vs lossless, briefly
Lossless compression (PNG, and the lossless mode of WEBP) rearranges data more efficiently without discarding any of it — decompress it and you get back exactly the original pixels. Lossy compression (JPG, and normal WEBP) deliberately throws away information the human eye is least likely to notice, and that loss is permanent. Only lossy formats have a meaningful quality slider, because only they have something to trade against.
What the JPG/WEBP quality number actually controls
Both formats break the image into small blocks and represent each one as a mix of frequency components — smooth gradual changes plus increasingly fine detail. The quality setting controls how aggressively the fine, high-frequency detail gets rounded off. At high quality almost nothing is rounded away; at low quality only the coarse shape of each block survives, which is what produces visible blocky artefacts and colour smearing.
| Quality range | What you'll see | Good for |
|---|---|---|
| 90–100 | No visible loss, largest file | Print, archival, close-up product detail |
| 75–89 | No visible loss at normal viewing distance | Most web and email images |
| 50–74 | Slight softening in fine texture, fine for busy photos | Thumbnails, background imagery, long feeds |
| Below 50 | Visible blocking and smeared colour in flat areas | Rarely worth it outside extreme size constraints |
Quality numbers don't compare across formats
WEBP quality 80 is not the same amount of visual loss as JPG quality 80 — WEBP's encoder is generally more efficient, so it typically looks better at the same number, or equal quality at a smaller file size. Never assume a number carries across formats; judge by the actual output image and its byte count, not the setting alone.
The same setting behaves differently on different images
Compression exploits redundancy — similarity between neighbouring pixels. A plain sky or a smooth studio background compresses extremely well even at high quality; dense foliage, fabric texture or film grain resists compression and needs a higher quality setting to avoid visible artefacts at the same perceptual result. There's no universal 'right' number — there's a right number for a given image, found by looking at the actual result.
How to pick a setting without guessing repeatedly
- Start at quality 80 for JPG or WEBP — it's a reasonable default for the vast majority of photographic content.
- View the result at 100% zoom, not in a shrunk preview, where artefacts are invisible.
- If it looks fine, try dropping 10 points and check again — you may have headroom.
- If you see blocking or smearing, go back up in steps of 5 rather than jumping straight to 95.
- Always check the reported file size alongside the visual check — the goal is the smallest file that still looks right, not the smallest file possible.
Tools for this
- Image CompressorUse it to see quality and byte count change together in real time.
- JPG CompressorUse it for fine control over the most common lossy format.
- WEBP CompressorUse it for the format that squeezes the most out of a given quality level.
- PNG CompressorUse it to understand what lossless compression can and can't do.
Keep reading
- How to reduce image file size without wrecking the pictureMost oversized images are oversized for one boring reason: the dimensions are far larger than anywhere they're displayed. Fix that first, then compress.
- Image dimensions vs file size: why a bigger picture isn't always a bigger filePixels, quality and format each move file size independently. Understanding how they interact stops you fixing the wrong one.
- How to compress an image to 100KB (without it looking terrible)100 KB is the most common upload limit on the web. Here is what actually gets you there, in what order, and where the quality really goes.