Created attachment 169507 [details]
Patch that introduces the optimization

Hi,

As a part of my student project for "Optimizing Open-Source Applications" at
Warsaw University I have speed up despeckle plug-in for gimp.

Original version of the plugin run 56seconds for 1024x768 image with
despeckle radius 30 and adaptive flag turned off (on my Intel Macbook
2.1GHz). My optimized version with the same settings completes the task in
3.5 seconds with the same image quality.

I'm attaching patch to this bug report but the whole file can be downloaded from here
http://students.mimuw.edu.pl/~pz248275/despeckle.c
http://students.mimuw.edu.pl/~pz248275/0001-Included-optimized-version-of-despeckle-plug-in.patch

There is also a thread on gimp-developer@lists.xcf.berkeley.edu "Optimized Despeckle plug-in" regarding this change (https://lists.xcf.berkeley.edu/lists/gimp-developer/2010-July/025015.html)

Optimization will not pass simple golden image tests against the non-optimized version because of the nature of the filter itself (filter sorts pixels based on their luma and takes a pixel that falls into median luma bucket, since there can be several pixels that fall into the same luma bucket, the resulting pixel might differ).

Hope the enchantment will be useful.

Regards,
Przemyslaw Zych