CLAHE GIMP plugin

Nicolas · August 6, 2026, 9:44pm

Hi! I just made a GIMP 3 plugin for CLAHE contrast at multiple scales :

Small scales bring up details while large scale increase global contrast.

Here is an example: original, CLAHE at scale 1/2 and CLAHE at scale 1/32

I hope this may be of some use, feedback welcome!

afre · August 6, 2026, 10:49pm

@Nicolas Welcome to the forum and thanks for sharing. I know there are some multiscale CLAHE papers out there. Maybe you could consider, experiment with and implement some of their findings.

LaurentFromSF · August 7, 2026, 12:46am

I have been using CLAHE in medical imagery thanks to its ability to “reveal” potential bad stuff. I did not know that it could be also interesting in digital photography… TIL

For the curious folks, here is my implementation (with plenty of room for improvements and some limitations)

github.com/LaurentInSeattle/Lyt.Framework

Lyt.ImageProcessing/Algorithms/ContrastEqualization/Clahe.cs

main

namespace Lyt.ImageProcessing.Algorithms.ContrastEqualization;

using Lyt.Framework.Interfaces.Profiling;

/*
CLAHE, standing for Contrast Limited Adaptive Histogram Equalization, is an image processing technique that 
enhances image contrast by dividing an image into smaller regions, calculating a histogram for each region, 
and then applying a clipped and redistributed histogram equalization to each region. 
Unlike traditional histogram equalization, CLAHE limits the amount of contrast amplification 
to avoid noise amplification in homogeneous areas. It is widely used in applications like enhancing foggy images, 
improving medical images for diagnosis, and strengthening details in low-light conditions.  

How CLAHE Works

1. Tile Generation:
The input image is divided into a grid of smaller rectangular regions called tiles or bins. 

2. Histogram Equalization per Tile:
A histogram is computed for each individual tile.

This file has been truncated. show original

Reptorian · August 7, 2026, 2:31am

This is something I wanted to implement in G’MIC, but couldn’t. Great job.

David_Tschumperle · August 7, 2026, 7:47am

It’s already implemented in G’MIC, with filter : Details / Equalize Local Histogram.
Maybe not exactly the same, but very similar probably.

It basically does this:

$ gmic sp colorful +apply_tiles \"equalize 256 n 0,255\",32,32,1,50%,50% blend alpha,0.5

iarga · August 7, 2026, 9:33am

Thank you. It is working in GIMP 3.2.Windows. Installing NumPy was a bit tricky. But with instructions from chatGPT, I managed to do it. Thank you.

There might be some room for an additional feature: namely running CLAHE separately for each color channel. This way, you can also perform color correction at the same time.

David_Tschumperle · August 7, 2026, 10:07am

To be perfectly honest, I’m a little put off by the fact that you have to install NumPy and Python (which together easily weigh in at 200 Mb) just to get a local histogram equalization filter in GIMP. We’re really in the era of software bloat…

This thought isn’t directed at @Nicolas at all.

Having gotten my start in computer science by creating like 4KB demos on the Amstrad CPC in Z80 assembly language, I have to admit that it still strikes me as odd to see the monstrosities (in terms of size) resulting from the use of Python nowadays.

I guess that’s what they call “progress”!

Reptorian · August 7, 2026, 1:41pm

It’s not the same. I get some idea though.