Reading quality 80 as 80 percent of the original quality, when it is only a position on the encoder's quantisation scale.
Compression
Quality setting
Also called jpeg quality, quality slider or q value. Here is what it means, when it changes what you export, and what people get wrong.
CompressionRuns on your deviceUpdated 10 August 2026
The short answer
A quality setting is the number, usually 0 to 100, that tells a lossy encoder how aggressively to discard detail. It is not a percentage of quality retained: it scales the encoder's quantisation tables. Quality 80 in one tool does not match quality 80 in another, or across formats.
Updated
The short version
Quality setting at a glance
| Quick fact | Detail |
|---|---|
| Typical range | 0 to 100, encoder-specific scale |
| What it controls | Scaling of the quantisation tables |
| Quality 100 | Still lossy, not lossless |
| Comparable across tools | No, and not across formats either |
| Diminishing returns | Above roughly 90 on a JPEG scale |
Slide the table sideways to see every column.
What does the number actually change?
In a JPEG encoder, the quality value selects a scaling factor applied to the quantisation tables. Those tables hold the divisors used on each frequency coefficient in every 8x8 block. Lower quality means larger divisors, more coefficients rounding to zero, and less detail surviving. The number is an index into the encoder's own scale, not a measurement of the output.
Two consequences follow. First, there is no fixed relationship between the setting and the resulting file size, because how many coefficients round to zero depends entirely on the picture. Second, different encoders map the same number to different tables, and other formats use scales of their own. A WebP or AVIF file at 80 is not making the same trade as a JPEG at 80, and mid-range AVIF settings usually look considerably better than the same number in JPEG.
Some encoders also change other behaviour at threshold values, most commonly switching from 4:2:0 to full 4:4:4 chroma near the top of the range. That can cause a visible jump in both quality and file size from a single step on the slider.
Which values should you actually use?
Treat these as starting points on a typical JPEG scale, then check by eye at full display size.
- Around 40 to 60: thumbnails, list previews and placeholder images, where the picture is small enough that artefacts stay hidden.
- Around 70 to 80: general web photographs. Most viewers cannot distinguish this from the original at normal viewing size on a detailed photo.
- Around 82 to 90: product and listing images, anything with a plain background, and anything a customer will zoom into.
- Above 90: master exports and images that will be edited or printed. File sizes climb steeply here for very little visible gain.
- 100: still lossy, just the mildest quantisation available. If you need untouched pixels, use a lossless format instead.
Why is pushing past 90 usually a waste?
The relationship between the setting and perceived quality is a curve that flattens out. Below roughly 60, each step you gain is clearly visible. Between 75 and 90, differences get subtle. Above 90, you are mostly spending bytes preserving coefficients your eye was never going to resolve, and file size can climb sharply for a change nobody can see.
The better lever is nearly always pixel dimensions. Resizing an image to the size it is genuinely displayed at, then exporting in the mid eighties, will beat a full-resolution export at 95 on both file size and apparent sharpness. That is the order to work in, and it is why a compression tool such as Photomop's is worth pairing with a resize step rather than used alone.
What people get wrong about quality setting
Each one is a real failure mode, not a style preference.
Porting a favourite JPEG number straight across to WebP or AVIF, where the same value makes a different trade.
Exporting at 95 or 100 to be safe, which inflates file size well past marketplace limits for no visible benefit.
Setting quality once for a whole batch of mixed content, so photographs are wasteful while graphics and text come out damaged.
Questions people ask
Quality setting, answered
The follow-up questions people search for once they have the definition.
Is JPEG quality 100 lossless?
No. It applies the gentlest quantisation the encoder offers, but coefficients are still rounded and colour is still converted, so pixels change. Files at 100 are also very large. If you need exact pixels, save PNG, lossless WebP or TIFF instead.
What quality should I use for product listings?
Somewhere in the mid eighties is a sensible default for photographs on a plain background, then confirm by eye at the size buyers will see. Images containing logos or small printed text usually need a higher setting, or a lossless format.
Why did lowering the quality barely shrink my file?
Most likely the file was already compressed at a similar or lower setting, so there is little left for the encoder to discard. Very detailed images also resist compression, since the fine variation is real information rather than redundancy.
Does the quality setting affect image dimensions?
No. It only changes how much detail is discarded within the pixels you already have. Pixel width and height stay the same. To reduce dimensions you need to resize, which is usually the more effective way to cut file size anyway.
Same cluster
More from the glossary
Neighbouring entries, so every term in the set is one hop from every other.
Raster image
A raster image is a picture stored as a grid of coloured pixels, which is how photographs, screenshots and most web images work.
Progressive JPEG
A progressive JPEG stores the image as a series of scans that each add detail, so a rough version of the whole picture appears first and sharpens as more data arrives.
RAW image file
A RAW image file is the unprocessed data a camera sensor recorded, saved before the camera turned it into a finished picture.
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