“Reflective symmetry” is a measure of light amplitude in the endoscope’s field of view.
This value is important in that it quantifies the effective distribution of light.
By employing five magnitude comparators, it is possible to transform the continuous
illumination pattern into five annular rings of decreasing grayscales. The pattern of gray
rings produced by this test should be nearly centered on the image. The pattern is circular
for zero-degree endoscope tip angles and sometimes is elliptical for angled endoscope
tips. A histogram graphs the number of pixels from each comparator output (light intensity).
For each “ring” that is displayed in the filtered image, the user can see graphically
how many pixels exist for each band of intensity. In order to pass this test, the “percent
bright area” is required to be greater than or equal to 50% of the maximum brightness.
The following equation defines how percent bright area is calculated. “Gray 1” and “Gray
2” refer to the two brightest (i.e., innermost) rings.