Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
More than one image is compared in methods employing variance. Note the upper series of pixels (intersected by the yellow arrow); even though they are brighter than the background they do not vary among the images. The red arrow bisects pixels that in aggregate have the same mean value as the pixels bisected by the yellow arrow but show variability from one image to the next.
