After having read the GIMP Export Image as JPEG section, I still have one understanding issue:
Why am I able to select a higher quality value than the one from original image in the export dialog?
For example, given a
.jpeg image, the quality slider is first set to the default 90. When marking "Use quality settings from original image", the value is set to 75. I can now still select slider values > 75, which creates the impression to raise the quality above original image.
With that assumption in mind (which may be wrong, I am happy to be corrected here), this dialog does not make sense to me. JPEG is a lossy format and an image with lower quality cannot be magically transformed to a higher-detail image. Also, the value seems to indicate some kind of "absolute quality", not a relative one - otherwise the original quality would be 100.
It seems, the biggest source of confusion has been the GIMP tooltip itself for me. Here are some screenshots, to show what I mean:1. This is the default export as jpeg screen with image quality of 90
Quality slider is automatically adjusted to 75 here. Tooltip says, its (almost) same quality, which let me assume, that
- it is an (almost) losless conversion
- 75 is some kind of absolute, computed quality indicator and means 100% quality preserveation in relative terms