What is the formula for the contrast of a grating?

The formula for contrast in the context of a grating is based on the relationship between the maximum and average luminance levels. The correct expression calculates contrast as the difference between the maximum luminance (Lmax) and the average luminance (Lavg), divided by the average luminance. This approach captures how much the maximum luminance differs from the average, relative to the average itself.

When we use this formula, we see that contrast reflects the visibility of the pattern formed by the grating. A higher contrast value indicates a more apparent distinction between light and dark areas, thereby enhancing the visibility of the grating. This is crucial in visual perception because greater contrast can lead to improved detection and differentiation of visual stimuli.

By dividing by the average luminance, this formula accounts for variations in brightness and allows for a standard measure of contrast that is independent of absolute luminance levels. This is particularly useful in fields like visual optics and psychophysics, where understanding the perception of contrast is vital.