To preview exactly which pixels will go to black or white,
press the Alt key (Option on the Mac) as you drag a slider
triangle. When dragging the black triangle, any pixels that
appear black or any color except white (as in the example
at the bottom of this page) will be clipped. When dragging
the white triangle, Photoshop clips the nonblack pixels.- Balance the histogram on the gamma: When position-
ing the gray gamma triangle, think “center of gravity.”
Imagine that you have to balance all the sand in the
histogram on a teetering board that is poised on this
single gray triangle. If you position the gamma properly,
you can distribute the luminosity values evenly across
the brightness spectrum, which generally produces the
most natural results.
Note that these are suggestions, not rules. Clipped colors
can result in interesting effects. An overly dark image may
look great set behind white type. Let these suggestions guide
your experimentation, and you’ll find yourself working more
quickly and effectively in the Levels dialog box.The Nature of Channels 201