The Equalize command automatically adjusts the brightness of colors across the active layer so that the histogram for the Value channel is as nearly flat as possible, that is, so that each possible brightness value appears at about the same number of pixels as every other value. You can see this in the histograms in the example below, in that pixel colors which occur frequently in the image are stretched further apart than pixel colors which occur only rarely. The results of this command can vary quite a bit. Sometimes « Equalize » works very well to enhance the contrast in an image, bringing out details which were hard to see before. Other times, the results look very bad. It is a very powerful operation and it is worth trying to see if it will improve your image. It works on layers from RGB and Grayscale images. If the image is Indexed, the menu entry is disabled.

8.16.2. Exemple de « Égaliser le calque »

Figure 16.149. Image d’origine

Le calque actif et ses histogrammes Rouge, Vert, Bleu avant « Égaliser ».

Figure 16.150. Image traitée

Le calque actif et ses histogrammes Rouge, Vert, Bleu après traitement.

L’étalement des histogrammes crée des vides entre les colonnes de pixels, lui donnant un aspect strié : les couleurs apparaissant fréquemment sont étalées.