histogram

Definition: Statistical graphical representation showing the relative numbers of a variable or part of a range of variables e.g. population of pixels with a certain value: the taller the column at a certain value, the more pixels have that value, the width of the column representing the range of values being counted. * Usually arranged so the left is the shadow end (low light) and highlight is to the right.
Meeting on the level
In image manipulation, histograms are used to analyse overall brightness distribution of an image e.g. if all columns are roughly the same height, there is an even distribution of light values; if the columns over dark values are much higher than the rest, most of the pixels are dark; a distribution with many gaps -- like a comb that has been to the wars -- is usually caused by poor scanning or results from someone playing around excessively with software brightness/contrast adjustment. The histogram display has become one of the essential tools of digital photography: it's worth being confident about reading the display.

Related Terms: levels

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