Histograms

The Histogram is one of the key tools in digital imaging. It provides a graph of the density values of an image. The Histogram shows the number of pixels at each particular density value. The left-most point of the Histogram is pure black (very dense), the midpoint gray, and the right-most point pure white (no density). A big peak in any of these regions means the image has lots of pixels at this density; an open gap in the Histogram means there are no pixels at this density.

Use the distribution of the Histogram to determine the overall exposure of an image. The rule of thumb is that an image looks best if it contains values at both the dark and light ends. Without some dark and light values, the image may lack contrast and appear flat. If you have a strong peak at the bright or dark end of the Histogram, it's possible your image is over or underexposed. Much depends on the individual image and personal aesthetic.

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A flat Histogram A Histogram with A Histogram that may without contrast good contrast be underexposed

A flat Histogram A Histogram with A Histogram that may without contrast good contrast be underexposed

The Histogram is also used to depict the smoothness of tones of an image. The illustration below shows from left to right:

1 A smooth Histogram representing an image with a full range of tones. You can edit this image extensively without concern.

2 A Histogram with a few strong spikes or gaps representing an image with some gaps in tone. You need to be careful about heavily editing this image.

3 A Histogram with a comb-like appearance representing an image with sparse tones. This image may appear blotchy or posterized especially when printed.

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A smooth Histogram A Histogram A comb-like with some spikes Histogram may print and gaps poorly

A smooth Histogram A Histogram A comb-like with some spikes Histogram may print and gaps poorly

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The Histogram palette provides a real-time Histogram of the active image as it is being edited. Typically it docks behind the Navigator palette, click on the Histogram tab to bring it forward. Here are a couple of tips to keep in mind when using this tool: First, make the Histogram display as large as possible. Do this by opening the Histogram palette menu and selecting "Expanded View." Second, the Histogram palette uses cached data to update the Histogram in real-time, but this cache quickly gets out of date and inaccurate. When this happens, Photoshop displays a cached data warning icon. Click on this icon to update the palette and get an accurate Histogram.

Finally, the Histogram immediately shows the effects of an adjustment on the image. New adjustments made to the image appear in black overlaying the old ones which appear in gray. This real-time feedback allows for quick decisions on how much to edit your image.

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[ Niuqitor Info t Histogtim

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Source! [Entire Image

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