QUESTION:
Viewing the images that came down from Pathfinder, we saw histograms in the
lower, left-hand corner.  What exactly does that information represent and
how do you use it?

ANSWER from Justin Maki on November 16, 1997:
The histogram is generally used to assess the exposure characteristics of
the image.  If the image is exposed properly, the histogram is a nice
bell-shaped (sort of) curve. If the image is overexposed then the histogram
is assymetric (all bunched up on the right side).  Similarly, if the image
is underexposed, the histogram is bunched up on the left.

So, in a nutshell, it's a quick way to assess the quality of an exposure.