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     <a href="WSfd1234e1c4b69f30ea53e41001031ab64-768da.html"><b>Viewing histograms and pixel values</b></a> 
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                <h1>
                    About histograms
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                <div><p>A <dfn class="term">histogram</dfn> illustrates
how pixels in an image are distributed by graphing the number of
pixels at each color intensity level. The histogram shows detail
in the shadows (shown in the left part of the histogram), midtones
(shown in the middle), and highlights (shown in the right part)
A histogram can help you determine whether an image has enough detail
to make a good correction.</p>
<p>The histogram also gives a quick picture of the tonal range of
the image, or the image <dfn class="term">key type</dfn>. A low‑key image has
detail concentrated in the shadows. A high‑key image has detail
concentrated in the highlights. And, an average-key image has detail
concentrated in the midtones. An image with full tonal range has
some pixels in all areas. Identifying the tonal range helps determine
appropriate tonal corrections.</p>
<div class="fignone"><img alt="" id="ct_01" src="images/ct_01.png" /><div class="figdesc">How to read a histogram </div><br /><dl><dt class="dlterm">A.</dt>
<dd>Overexposed photo</dd><p class="dlseparator"></p><dt class="dlterm">B.</dt>
<dd>Properly
exposed photo with full tonality</dd><p class="dlseparator"></p><dt class="dlterm">C.</dt>
<dd>Underexposed
photo</dd><p class="dlseparator"></p></dl>
</div><div class="para">The Histogram
panel offers many options for viewing tonal and color information about
an image. By default, the histogram displays the tonal range of
the entire image. To display histogram data for a portion of the
image, first select that portion. <div class="tip"><img src="images/tip_help.png" />You can view
an image histogram as an overlay in the Curves dialog box by selecting
the histogram option under Curve Display Options, and in the Curves Adjustment
panel by choosing Curve Display Options from the panel menu, then Histogram. </div></div>
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