If an image has many pixels that are approximately the same color or shade, you can equalize the image to bring out more detail.
Equalization makes the darkest pixels darker and the lightest pixels lighter, then reassigns the remaining pixels to the colors in between. This is also known as a non-linear contrast stretch.
You can limit the effect of brightness or contrast changes to a portion of the image called a sub-region. If the image palette is Index Color (8-bit), you can alter the palette of the image to include the new colors.