[Gimp-developer] jpeg quality factor.

[Guillermo Espertino]

GG:
> Can you clarify where this file is when you do CTRL+S ? You say you 
> open "directly from the camera" , do you mean you are opening a file 
> that is still on the camera ?!
My camera stores the pictures in a Compact Flash card. I use a card reader.
I copy those files to my hard drive, then I open them with gimp (or 
gthumb for viewing.)
 Sometimes I open them directly from the CF card, but it's almost the 
same, it's a storage medium anyway.

> I have not checked the source code but I would expect gimp to retain 
> the existing quality setting of the image defined in the jpeg header, 
> in this case determined by you camera. If you can demonstrate this is 
> not happening it probably needs checking.
That's precisely what I was trying to say.
Is it possible that the quality setting defined in the jpeg header by 
the camera isn't in the IJG scale?
(excuse my ignorance... I don't know how the file is structured).
If that happens, is it possible that Gimp is taking the wrong setting as 
reference from the file?

> If you want to choose a different compression you should be using File 
> | Save As rather than File | Save .
Yes, I'm doing that now. But I learned that in the tough way :-)

> You also say "when I take my image to PS from my camera" , could you 
> me more precise about the operations you are using? Are you opening a 
> file on the camera , are you removing it from the camera and putting 
> it elsewhere with this operation, when you CTRL-S in PS where does it 
> get saved, back to the original file or elsewhere on your disk?
Steps:
1- take the photo.
2- put the  card in the reader and copy the photo to the disk.
3- open it with the image manipulation program
4- save it using CTRL+S

In Gimp, it saves the file directly, without asking for the compression 
setting. Result: an image over-compressed with artifacts. Smaller size 
than the original.
In Photoshop, it shows the quality settings the first time you hit CTRL+S.

> As I said in my last post Øyvind's test shows there is an issue with 
> degradation on multiple resaves , I dont think this caused by 
> 'quality' parameter being changed.
> You may have picked a bug and you are misinterpreting this as a change 
> in the compression.
Yes, I think so. At first I thought it was a quality setting issue, but 
since I learned how the IJG scale works I'm convinced that is a bug or, 
at least, a strange behaviour.

Gez