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Color histogram
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<p>In <a href="/facts/Image_processing/zenalNCf">image processing</a> and <a href="/facts/Photography/ezLPT43M">photography</a>, a color histogram is a representation of the distribution of colors in an <a href="/facts/Image/fY9DudpT">image</a>. For digital images, a color histogram represents the number of <a href="/facts/Pixel/UzwBvXBV">pixels</a> that have colors in each of a fixed list of color ranges that span the image's <a href="/facts/Color_space/zFvEyfHv">color space</a> (the set of all possible colors). </p><p>A color histogram can be built for any kind of color space, although the term is more often used for three-dimensional spaces such as <a href="/facts/RGB_color_space/00Q0tTS5">RGB</a> or <a href="/facts/HSV_color_space/opaXI7FM">HSV</a>. For <a href="/facts/Monochromatic_image/Tjb9kR8v">monochromatic images</a>, the term intensity histogram may be used instead. For multi-spectral images, where each pixel is represented by an arbitrary number of measurements (for example, beyond the three measurements in RGB), a color histogram is <i>N</i>-dimensional, with N being the number of measurements taken. Each measurement has its own wavelength range of the light spectrum, some of which may be outside the visible spectrum. </p><p>If the set of possible color values is sufficiently small, each of those colors may be placed on a range by itself; then the histogram is merely the count of pixels that have each possible color. Most often, the space is divided into an appropriate number of ranges, often arranged as a regular grid, each containing many similar color values. A color histogram may also be represented and displayed as a smooth <a href="/facts/Function_(mathematics)/CdReEKCh">function</a> defined over the color space that approximates the pixel counts. </p><p>Like other kinds of <a href="/facts/Histogram/oMmvqGEA">histograms</a>, a color histogram is a <a href="/facts/Statistic/av21WaMK">statistic</a> that can be viewed as an approximation of an underlying continuous <a href="/facts/Frequency_distribution/5WA78UDy">distribution</a> of color values. </p>