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In Photoshop, while saving an image as JPEG, there is an Image Option called Quality.

Increasing or decreasing the value, only increases or reduces the size of the JPEG file.

If we try to zoom in the images saved in different quality values, there is no difference.

Then why there is Quality option? What is the real use and need of this option?

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  • \$\begingroup\$ Take two qualities as different layers, chose difference, then adjust contrast and have a look \$\endgroup\$
    – PlasmaHH
    Commented Aug 3, 2014 at 20:05
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    \$\begingroup\$ Make sure you are looking at the saved images after you close your original image. You'll see the difference, then. \$\endgroup\$
    – B Shaw
    Commented Aug 3, 2014 at 21:26

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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.

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