On Wed, 2008-10-29 at 21:03 +0100, Claus Berghammer (Bugzilla) wrote:

> But this benchmark represents, what an "average" user notice at first:
> Gimp 2.6 needs much more time, and doesn't deliver that much more
> quality.

Sorry, but your benchmark doesn't show a dramatic slowdown. The impact
is very noticeable when scaling up by a large factor, but that is
already taken care by the proposed patch (that is now in trunk for

Your interpretation of the numbers is somewhat questionable also.
Scaling without interpolation simply had no progress indicator in GIMP
2.4. So that's why you don't notice any progress. The operation still
takes time though. Also GIMP 2.4 did not implement downscaling using
Cubic interpolation, it always used Linear. Now that you know that,
let's look at your numbers again. You will notice that downscaling in
GIMP 2.6 is actually faster than in GIMP 2.4:

  Scale layer from 5000x5000px -> 2500x2500px:

                           GIMP 2.4   GIMP 2.6
  Interpolation: None:         ????       1.54
  Interpolation: Linear:       3.51       2.46
  Interpolation: Cubic:        ----       5.80
  Interpolation: Lanzcos:     22.15      15.12

Let's look at the upscaling operation. The scale factor you tried is
implemented in a two-step scaling in GIMP 2.6. This is addressed by the
patch that I proposed. If you would redo your benchmark with that patch
applied, you would get about the same speed for upscaling in 2.6 than
what you measured for 2.4. Actually I would not be surprised if 2.6
would also perform slightly better here.


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