Feczak Szabolcs <[EMAIL PROTECTED]> writes:

> Changing the color balance/brightens-contrast/ color curves are
> significantly slower in gimp vs. photoshop on the same machine.  The
> problem is not the processing time alone, but the preview takes the
> same amount of time as the final processing.  I have relized, that
> gimp calculates all the data in preview mode as I would have pressed
> the ok button.

Very well spotted.

> I have Also noticed, that during the process it divides the picture
> into smaller squares top-down, and the change takes effect
> continously in these squares (in preview mode also). Photoshop also
> uses these squares, but it uses only about 6/picture while gimp is
> using much-moch more smaller (I couldn't count). I think this is the
> source of the difference in the preview processing time."

I don't think the number of tiles makes any difference. The problem is
indeed that the preview is implemented by doing the color
transformation on the full-size image data.

> I think if it is not solved, maybe preview should be done through
> sdl or xvid or whatever instantly (but maybe the videocard controll
> gives slightly different result than the later calculated image
> after OK button...)

Sorry, SDL or similar approaches are not an option here. Not only
would they be highly unportable, there's also no way to ensure that
the result matches the actual color transformation you want to

> Other good idea came from my friend: creating a smaller image in
> memory, which has the resolution of the screen and calculating the
> preview on that image.

That is obviously the approach that should be taken.

> So long Im not into C programming so much, so I can't work it out
> within a reasonable time, but please let me know if you are willing
> to do some improvements like this, since at the moment this slowness
> on previews holds us back from changeing. If we can change of course
> we can make some donations to the community.

AFAIK, there are no plans to do such an improvement. Considered that
we still lack some funding for our developers conference this summer,
perhaps we could be persuaded to give it a try.

Gimp-developer mailing list

Reply via email to