Using Channel Calculations To Blend Layers And Channels - Adobe PHOTOSHOP 5.0 User Manual

Use the Underlying sliders to specify the range of
•
pixels in the underlying visible layers that will
blend in the final image. Blended pixels are
combined with pixels in the active layer to produce
composite pixels, while unblended pixels show
through overlying areas of the active layer. For
example, if you drag the black slider to 19, pixels
with brightness values lower than 19 will remain
unblended and show through the active layer in
the final image.
Using channel calculations to
blend layers and channels
You can use the blending effects associated with
layers to combine channels within and between
images into new images using the Calculations
command (on single channels only) and the Apply
Image command (on single and composite
channels). These commands offer two additional
blending modes not available in the Layers palette:
Add and Subtract. Although it's possible to
combine channels into new combinations by
copying channels into layers in the Layers palette,
you may find it quicker to use the calculations
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 under-
standing 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 manip-
ulate these values to produce the resulting
composite pixels.
These commands overlay the pixels in two or
•
more channels. Thus, the images used for calcula-
tions must have the same pixel dimensions. For
information on adjusting an image's pixel dimen-
sions, see "Changing image size and resolution" on
page 46.
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:
Open the source and destination images, and
1
make active the desired layer and channel in the
destination image.
Pixel dimensions must match for the image names
to appear in the Apply Image dialog box.
Note: If the color modes of the two images differ (for
example, an RGB and a CMYK image), you can
copy a single channel to another channel, but you
cannot copy a composite channel to another image's
composite channel in another image.
Choose Image > Apply Image.
2
Choose the source image, layer, and channel you
3
want to combine with the destination. To use all
layers in the source image, select Merged for Layer.
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User Guide