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                <h1>
                    Blending layers and channels
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                <div><p>You
can use the blending effects associated with layers to combine channels within
and between images into new images. You can use either the Apply
Image command (on single and composite channels) or the Calculations
command (on single channels). These commands offer two additional
blending modes not available in the Layers panel—Add and Subtract.
Although it’s possible to create new combinations of channels by
copying channels to layers in the Layers panel, you may find it
quicker to use the calculation commands to blend channel information. </p>
<p>The calculation commands perform mathematical operations on the
corresponding pixels of two channels (the pixels with identical
locations in the image) and then combine the results in a single
channel. Two concepts are fundamental to understanding how the calculation
commands work.</p>
<ul><li><p>Each pixel in a channel has a brightness value. The Calculations
and Apply Image commands manipulate these values to produce the
resulting composite pixels. </p>
</li>
<li><p>These commands overlay the pixels in two or more channels.
Thus, the images used for calculations must have the same pixel
dimensions.</p>
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