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Tutorial: Equalize / Homogenize brightness on an image

Written by , translated by devvv · Created on Jan 29, 2011, last updated about 3 years ago CC BY-NC License

Motivation

This technique shows the simulation of a highpass filter in GIMP to influence the brightness of a picture. The aim of this is to get an equal homogenized level of brightness in your image.

Tutorial details

  1. 1

    Homogenizing the brightness

    I’ve opened a simple texture of wood that I want to prepare for making it perfectly seamless. Therefore I have to equalize the brightness of it (you can see that the left part of the image is brighter then the right part).

  2. 2

    To counter that uneven level of brightness you can simulate a highpass filter in GIMP.

    - Duplicate the background layer (the image you want to homogenize).
    - On this duplicate use Filter / Blur / Gaussian Blur. The pixels you enter in this filter determine how big the parts (that need to be homogenzied) should be. In this texture the brigher parts are distributed over a bigger part of the image, therefore I take a larger value – around 20-40 px.
    - Then do an Colors / Invert
    - Colors / Desaturate
    - Set the layers mode to “Overlay”

    By doing this the too bright parts get a little darker and vice versa – thats how the images brightness is equalized.

    Make the effect stronger by just duplicating the “overlay”-layer.

  3. 3

    Here is another example on a (shadowy) photo where I used the same technique to make the too dark parts brighter while the white parts still look white but not “overwhithened”.

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Travis
almost 2 years ago

Thank you so much,
That worked awesome
)

Francois member for over 5 years Francois 10 comments
over 2 years ago

The steps are written in plain English beside the images, lefty.crupps.
Maybe it is too technical for a newbie. You'll find a script that makes it easy if you click the link I posted previously.

lefty.crupps
over 2 years ago

I don't understand, where are the steps? or a video? or anything useful other than the wood image example of before and after, and the before/after shadow example?

Francois member for over 5 years Francois 10 comments rated this topic with 4/5
almost 3 years ago

Useful technique.
A script by Andrew Robinson does exactly the same in less than one second:
http://registry.gimp.org/node/24852
(Andrew has now fixed an issue that caused the script to crash in some cases because he used "1" instead of "image").

UnconventionalT
almost 3 years ago

Why is it that so many people post unhelpful/spiteful comments on this website? It doesn't say much about the comumity as a whole. I for one really enjoyed this tutorial, thanks.
The reason why I like it so much is because you have the finest control you could want over the image, and how it is homogenized.

pevsner
about 3 years ago

There's a "contrast fix" plugin that does similar. Always good to know the theory though.
http://registry.gimp.org/node/182

lylejk
about 3 years ago

GIMP 1.x had a cool filter called Homogenize but they never ported it to GIMP 2.x for whatever reason. I can use various techniques such as this to do this, but I do miss this cool plugin. :)

devvv member for over 7 years devvv 1390 comments
about 3 years ago

what do you mean? what kind of codec? we do not use any codecs on gimpusers.com

gerard82
about 3 years ago

Why do you use a codec that can only be played on proprietary software?
Gimp is opensource (or isn't it?)
Gerard.

Mukesh
about 3 years ago

really useful. Please add a 'tweet this' or 'share of FB' buttons to get across to a larger viewership
Thanks

-Mukesh