A special filter sometimes also called a “diff step” filter that is used to measure luminance nonlinearity. When this filter is used with a luminance step waveform (see the waveform discussed in the Luminance Nonlinearity discussion), each step on the waveform is translated into a spike that is displayed on the waveform monitor. The height of each spike translates into the height of the step so the amount of distortion can be determined by comparing the height of each spike. Refer to the figure below.