The tonal range is the change in value from black to white. It is the set of grayscale information in an image. Sometimes tonal range must be adjusted so that images have a full range of values in the shadows, midtones, and highlights.
Adjusting the tonal range addresses these common problems:
The image is too light or too dark. There may be a lot of detail in the light areas or in the shadows that can be made visible or printable through an adjustment.
Contrast is too low or too high. A low-contrast image has a flat tonal range. A ...