Adobe 13101332 - Photoshop - Mac User Manual page 275

Adobe Photoshop Help
Using Help | Contents
3 For Channel, choose the spot channel from step 1, and click OK.
4 To create a trap when knocking out the underlying color, choose Select > Modify >
Expand or Contract, depending on whether the overlapping spot color is darker or lighter
than the spot color beneath it. For more information on trapping, see
traps" on page 479.
5 In the Channels palette, select the underlying spot channel that contains areas you
want to knock out. Press Backspace (Windows) or Delete (Mac OS).
This method can be used to knock out areas from any channels under a spot color,
such as the CMYK channels.
6 If a spot color in one channel overlaps more than one other spot color, repeat this
process for each channel that contains areas you want removed.
Using channel calculations to blend layers and channels
(Photoshop)
You can use the blending effects associated with layers to combine channels within and
between images into new images using the Apply Image command (on single and
composite channels) and 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 from 0 (off or black) to 255 (on or white).
•
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. (See
resolution" on page 65
Using 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).
To use the Apply Image command:
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.
Using Help | Contents
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for information on adjusting an image's pixel dimensions.)
| Index
Using Channels and Masks
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"Creating color
"Changing image size and
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