Point Image Filter Tool - Before/After Tabs

The Before/After tabs display a histogram representation of the greyscale values of the pixels in the region. The Before tab displays the histogram of the image area prior to being processed, while the After tab displays the histogram of the area post-processing.

The X-axis of the graph represents the total number of greyscale values (0 to 255, or 256 total shades of grey).
The Y-axis of the graph represents the number of pixels at a given greyscale value, and the scale is established by displaying the greyscale value with the greatest number of pixels.
The green vertical line indicates the threshold that is being used to separate the region of the image into black and white pixels; values to the left of the line are considered black and values to the right are considered white.