False-color image
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A false-color or pseudo-color image is a color image derived from a grayscale one by mapping each pixel value to a color according to a table or function. A familiar example is the encoding of altitude in physical relief maps, where negative values (below sea level) are usually represented by shades of blue, and positive values by greens and browns.
Although false-coloring does not increase the information contents of the original image, it can make some details more visible, by increasing the distance in color space between successive gray levels.
More importantly, false-coloring allows the visual comparison of pixel values between non-adjacent regions of the image. This is not possible when the image is displayed in shades of gray, because our eye sees intensity changes rather than intensity values --- so that the same gray level will appear darker or lighter depending on its surround. For this reason, the altitude scale in a relief map would be mostly useless if it was displayed in shades of gray. Hues, in contrast, are perceived in a more "absolute" fashion. So, in a false-color relief map, there is little danger of confusing negative altitudes with positive ones; and the relative altitude of two mountains is clearly perceived, even if they lie at opposite ends of the map.
False-color images are also frequently used for viewing satellite images, such as from weather satellites, the Hubble Space Telescope, and the Cassini-Huygens space probe's images of the rings of Saturn.