8.16. Equalizza

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.

8.16.1. Activating the Command

You can access this command from the main menu through ColorsAutoEqualize.

8.16.2. Esempio di «equalizza»

Figura 16.158. Immagine originale

Immagine originale

Il livello attivo ed i suoi istogrammi di colore rosso, verde e blu, prima del comando «equalizza».

Figura 16.159. Immagine dopo il comando

Immagine dopo il comando

Il livello attivo e i suoi istogrammi rosso, verde e blu, dopo il trattamento.

L'ampliamento dell'istogramma crea degli spazi tra le colonne di pixel, dandone il caratteristico aspetto a strisce: i colori che ricorrono frequentemente vengono allargati.