What is a histogram?
What is a histogram?
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A histogram is a graphical representation of the distribution of pixels in an image. It displays whether the image has details in the shadows (left side of the histogram), midtones (middle of the histogram), or highlights (right side of the histogram). The scale of the histogram is 0 - 255 (left to right), where 0 determines black and 255 determines white.
A histogram is used to evaluate an image. An overexposed photograph has data concentrated to the right side in the histogram. When the concentration of data is to the left, the photograph is underexposed; and when the concentration is in the midtones, the photograph is properly exposed.
A histogram also gives a picture of the image key type. When data is concentrated to the right in the histogram, it indicates that the image is a high-key image. A low-key image produces a histogram with data concentrated to its left, and an average-key image produces a histogram with data concentrated in the midtones.
A quick review of a histogram gives an idea of the tonal range of the image. When a number of pixels are spread in all areas, the image is said to be with full tonal range.
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