Levels
From OSP Wiki
This tutorial was last tested for the Gimp 2.4.5
Overview
Various man made and natural factors contribute to a photo looking "flat". This means that there are no real blacks or whites in your photo. It means that your image is not taking advantage of the full range of colours available.
This tutorial is how to fix that, it is simple, quick and one of the first skills you should learn when post processing photos.
The first image here is the original, the second one has had it's levels adjusted.
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| Before | After |
I will be using the original photo on the left than can be downloaded here.
Prerequisites
An understanding of what histograms mean.
Each photo is made up of multiple pixels, millions of them, each pixel has a brightness level. The histogram adds up those pixels that are black (brightness level 0) then brightness level 1 etc, all the way up to brightness level 255 (white). The histogram shows you this information as a graph.
Steps
- Go to <Image> -> Layer -> Colors -> Levels (or select the Levels tool and click on the image)
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- Adjust the lower limit so that the arrow is at the start of the graph. This will mean the pixels at that point will be black. In this photo there were no pixels darker than 39 so that is where the slider is moved to.
- Doing the same thing at the white end means the pixels at level 213 become the white pixels instead of being greyish.
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- When you click the "Ok" button GIMP will stretch out the brightness levels of the pixels so they have all 256 levels instead of only 174. They go all the way from pure black to pure white.
Below is what the histogram looks like after the levels adjustment, as you can see it is the same basic shape but spread out and has some gaps.
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