Gimp Script: Histogram Match

My initial test was with the simplest case, having a source histogram that is completely flat. This equates to an perfectly linear incremental histogram. It also happens to be the same as the Gimp command Colour->Auto->Equalize. Or so I though. Initially I was only using the value, but I couldn't match the results of the Equalize function. It was after examining the resultant histograms that I determined that Equalize works independently on each of the RGB channels, so I modified the script to also allow that. Knowing the algorithm worked, I added the option to take the histogram from another image layer, rather than the flat histogram case.

Lastly, I found the gimp histogram function to be quite slow (as every call analyzes the entire image). The solution was to offer a (default) option to re-sample the images first.

City Street

Hillside

On the left are a photo of a city street in Toronto, and one of a hillside in Israel, along with their histograms. On the right is the result of remapping each of them with the other's histogram, also showing the resultant histogram. The hill was mapped using value, and the city street was mapped using independent RGB.

Hillside with City Histogram

City Street with Hillside Histogram

Running the script using the independent RGB options takes the longest, as it has to process each channel independently. Also there is still the occasional full crash of gimp 2.6.4 when running the precompiled windows binary. Running my on compile of 2.6.6 I have not experienced this crash.

EDIT: I forgot to mention the script shows up as Colours->Map->Histogram Match... in the menus!

You can download the an updated version of the script here.