Change detection is of great significance in remote sensing. The advent of high-resolution remote sensing images has greatly increased our ability to monitor land use and land cover changes from space. At the same time, high-resolution remote sensing images present a new challenge over other.
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Color Images Another essential ingredient in most remote sensing images is color.While variations in black and white imagery can be very informative, thenumber of different gray tones that the eye can separate is limited toabout 20 to 30 steps (out of a maximum of about 200) on a contrastscale. On the other hand, the eye can distinguish 20,000 or more colortints, enabling small but often important variations within the targetmaterials or classes to be discerned. Since different bands (or wavelengths) have a different contrast,computers can be used to produce a color image from a black and whiteremote sensing data set. Remember, satellites record the reflected and emitted brightness in the different parts of the spectrum, as is demonstrated inthe figure above. Similar to the screen on a color television set, computer screens can display threedifferent images using blue light, green light and red light. Thecombination of these three wavelengths of light will generate the colorimage that our eyes can see. This is accomplished by displaying blackand white satellite images corresponding to various bands in eitherblue, green, or red light to achieve the relative contrast between thebands. Finally, when these three colors are combined, a colorimage—called a 'false color image'—is produced (it's called 'falsecolor' because colors are assigned that we can see and easily interpretwith our eyes). In order to understand what the colors mean in the satellite image, wemust know which band (or wavelength) is used for each of the blue, greenand red parts of the computer display. Without detailed knowledge of howeach band has been changed for contrast and brightness, we cannot besure why the colors are what they are. next:Remote Sensing Methods back:Pixels and Bits | Remote Sensing Introduction and History Radiation Electromagnetic Spectrum Absorption Bands and Atmospheric Windows Spectral Signatures Pixels and Bits Color Images Remote Sensing Methods NASA Remote Sensing Accomplishments References Related Data Sets: Observation Deck |