Brightness and contrast controls

This chapter introduces the brightness and contrast controls of video. These operations are affected in the nonlinear domain that is known as gamma-corrected signals. These operations are generally applied to each of the red, green, and blue components simultaneously. The contrast control applies a scale factor—in electrical terms, a gain adjustment—to R'G'B' . components. On processing equipment, it is called video level, and on some television receivers, it is called picture. The contrast control affects the luminance that is reproduced for the reference white input signal; it affects lower signal levels proportionally, having no effect on zero signal. The chapter also discusses the brightness and contrast controls in desktop graphics. In desktop graphics, applications such as Photoshop, image data is usually coded in a perceptually uniform manner, comparable to video R’G’B’ . Photoshop's brightness control is similar to the brightness control of video. Brightness affects an offset between -100 and +100 on the R', G', and B' components.