You can permanently change the tone and visibility of images.
Increasing the brightness lightens the image and can bring out image detail in the shadow areas, although increasing brightness too much can wash out the light areas. Decreasing the brightness darkens the image and can bring out details in the light areas. Likewise, decreasing brightness too much can cause the dark areas can become almost black.
Increasing the contrast makes the differences between dark and light areas more distinct. You can increase contrast in a grayscale image to the point where the image becomes black and white. Decreasing the contrast makes an image that consists mostly of mid-level grays.
In color images, you can adjust the brightness and contrast for individual color channelscolor_channel_1 (red, green, blue, or RGB, which is a combination of the colors). For example, if you choose red and then increase the brightness, you see more reds. In grayscale images, you can adjust only the single channel that represents gray.
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.