Channel Calculations; Blending Layers And Channels; To Use The Apply Image Command - Adobe PHOTOSHOP CS2 User Manual

See also
"Creating color traps" on page 724

Channel calculations

Blending layers and channels

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
palette—Add and Subtract. Although it's possible to create new combinations of channels by copying channels into
layers in the Layers palette, you may find it quicker to use the calculation commands to blend channel information.
The calculation commands perform mathematical operations on the corresponding pixels of two channels (the
pixels with identical locations on the image) and then combine the results in a single channel. Two concepts are
fundamental to understanding how the calculation commands work.
Each pixel in a channel has a brightness value. The Calculations and Apply Image commands manipulate these
•
values to produce the resulting composite pixels.
These commands overlay the pixels in two or more channels. Thus, the images used for calculations must have the
•
same pixel dimensions.

To use the Apply Image command

The Apply Image command lets you blend one image's layer and channel (the source) with a layer and channel of the
active image (the destination).
1 Open the source and destination images, and select the desired layer and channel in the destination image. The
pixel dimensions of the images must match for image names to appear in the Apply Image dialog box.
Note: If the color modes of the two images differ (for example, one image is RGB and the other is CMYK), you can copy
a single channel to another channel between images, but you cannot copy a composite channel to a composite channel in
another image.
2 Choose Image > Apply Image.
Choose the source image, layer, and channel you want to combine with the destination. To use all layers in the
3
source image, select Merged for Layer.
4 To preview the results in the image window, select Preview.
To use the negative of the channel contents in the calculation, select Invert.
5
For Blending, choose a blending option.
6
For information on the Add and Subtract options, see "About the Add and Subtract blending modes" on page 447.
For information on other blending options, see "List of blending modes" on page 487.
7 Enter an Opacity value to specify the effect's strength.
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User Guide