Relationship between the Tone Curve and the Histogram of a Photographic Image

This Demonstration shows the effect of tone curve adjustments on a photographic image and its histogram. The tone curve defines the brightness relationship between the input (original) values (on the axis) and output (result) values (on the axis).The histogram displays the tonal distribution of the image. It displays level of brightness on the axis from dark to light. The axis represents the total number of pixels in the image with that level of brightness. Adjust the tone curve by dragging any of the five locators or choosing one of the preset schemes.