Gray Scale Conventions

For a single band we typically display the image in shades of gray, with white indicating a large energy returned to the sensor and black no energy. This corresponds with what we see in the visible part of the spectrum (black absorbs all light, white reflects all light), but when we display thermal or microwave energy the image has nothing direct to correlate with what we would "see" with our eyes. By convention, however, some sensors typically display with the colors reversed; thermal weather satellite images represent a prime example. Clouds are cold and emit little infrared radiation, so compared to water or the land surface they should be black. But people would balk at black clouds, so we reverse the color scale. Side scan sonar imagery can be displayed with either convention.

In addition to these conventions, contrast enhancement determines how shades are assigned.


Last revision 11/27/99