This distortion is also called differential luminance and is present if luminance gain is affected by luminance levels.

This amplitude distortion is a result of the system’s inability to uniformly process luminance information over the entire amplitude range.

The amount of luminance nonlinearity distortion is expressed as a percentage.

Measurements are made by comparing the amplitudes of the individual steps in a staircase signal as shown. The result is the difference between the largest and smallest steps, expressed as a percentage of the largest step. Measurements should be made at both high and low APL and the worst error should be quoted. In black and white pictures, luminance nonlinearity will cause pictures loss of detail in shadows and highlights which are caused by the crushing or clipping of the white or black portions of the signal. In color pictures, luminance nonlinearity will cause colors in the high luminance portions of the picture to be distorted.