If the histogram doesn't extend all the way across the full width of the histogram area, then your image has a limited brightness range (Figures 6.73 and 6.74). When that's the case, you can usually move the upper-right and lower-left points on a curve toward the middle, which will widen the histogram (Figures 6.75 to 6.77). As you do, keep an eye on the histogram. Most images will look their best when the histogram extends all the way across the area available, without producing any tall spikes on either end.
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