8.11. Stretch Contrast

The Stretch Contrast command automatically stretches the histogram values in the active layer. For each channel of the active layer, it finds the minimum and maximum values and uses them to stretch the Red, Green and Blue histograms to the full contrast range. The bright colors become brighter and the dark colors become darker, which increases the contrast. This command produces a somewhat similar effect to the Normalize command, except that it works on each color channel of the layer individually. This usually leads to color shifts in the image, so it may not produce the desired result. Stretch Contrast works on layers of RGB, Grayscale and Indexed images. Use Stretch Contrast only if you want to remove an undesirable color tint from an image which should contain pure white and pure black.

This command is also similar to the Color Balance command, but it does not reject any of the very dark or very bright pixels, so the white might be impure.

8.11.1. Activate the Command

  • This command can be accessed from an image menubar as ColorsAutoStretch Contrast.

8.11.2. Stretch Contrast Example

Figure 15.139. Original image

Original image

The layer and its Red, Green and Blue histograms before Stretch Contrast.

Figure 15.140. Image after the command

Image after the command

The layer and its Red and Green and Blue histograms after Stretch Contrast. The pixel columns do not reach the right end of the histogram (255) because of a few very bright pixels, unlike White Balance.

Histogram stretching creates gaps between the pixel columns, giving it a stripped look.