I'm noticing big differences between jpeg files from gimp and photoshop.
The same image exported as jpeg with the same quality factor (let's take 
75% as an example) gives very different results in both programs.
In my tests, Photoshop image has better image quality, but its size  is 
75 KB.
Gimp image shows lots of artifacts and its quality is lower, but its 
size is 35 KB.
Doing more tests I found that the factor 75% of Photoshop is equivalent 
to the 93% in gimp. Conclusion: Both programs calculate the compression 
ratio differently.
I'd like to know how the compression factor is set (if gimp or the jpeg 
library manages that).
Most people consider Photoshop as a industry standard (which is not, but 
is a de facto standard) so I'd like to know which program isn't working 
as it should (I mean, if the qualiy factor is 80%, and the compression 
algorythm is the same, it sounds ilogical to get different results).
I'm worried about that, because one who cames from photoshop to gimp may 
thing that Gimp jpg files have "less quality" than photoshop ones.
In my personal experience, I find the default compression quality of the 
jpeg in Gimp to be very destructive. And I don't know if it happens 
because gimp uses the compression factor from the file and recompresses 
to its own equivalent.
Trying to be more specific: If I open an image from my digital camera 
with gimp, adjusts its levels or curves, and re-save it, the saved image 
is very deteriorated. If I do the same with Photoshop that doesn't happen.
I think it's problem, but let me know if I'm wrong. At least I know that 
I must re-save images from other sources using a higher quality factor.

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