What does the JPEG quality setting in Photoshop actually change?
Asked 8/3/2014
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When saving a photo as JPEG in Photoshop, there is a quality setting. Lower values make the file smaller, while higher values make it larger. In many cases, especially at normal viewing sizes, the image can look almost the same.
What does this quality option really do, and when does it matter?
Originally by user21734. Source · Licensed CC BY-SA 4.0
user21734
12y ago
2 Answers
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You say "if we try to zoom in the images saved in different quality values, there is no difference", but, actually, that's just because you're not looking closely enough, or don't know what to look for. If you choose an extreme value (very low) the difference should be obvious. At higher settings, it's more tricky, but usually there's a difference there too even if it's harder to detect by eye.
Take a look at What are jpeg artifacts and what can be done about them? for the result of JPEG compression, which will be more apparent at lower quality levels, and Is it worth using Pentax's Premium JPEG quality setting? for some additional examples.
Originally by user1943. Source · Licensed CC BY-SA 4.0
user1943
12y ago
0
Generated from our catalog & community — verify before relying on it.
The JPEG quality setting controls how much compression is applied to the image.
Higher quality = less compression, larger file, fewer visible compression artifacts. Lower quality = more compression, smaller file, more image damage.
The reason you may not notice a difference is that at moderate or high settings, JPEG losses can be subtle and may only show up when you inspect fine detail, edges, smooth gradients, or areas with repeated editing/saving. At very low settings, the artifacts become obvious.
So the setting exists to balance image quality against file size. Use a higher setting when you want to preserve detail and avoid artifacts; use a lower setting when smaller files matter more and some loss is acceptable.
In short: the files are not identical—JPEG is a lossy format, and the quality option determines how much visual information is discarded to reduce size.
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