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发信人: killest (矛盾), 信区: Graphics
标  题: PHOTOSHOP(92)-Using Layers
发信站: 紫丁香 (Tue Apr 28 20:38:15 1998), 转信

Calculations blending options
The following is a brief description of some Calcu-lations
blending options. For a description of the
remaining blending options, see 揝electing a
blending mode� on page 208.
Lighter Compares the brightness values of the cor-responding
pixels in two channels and displays the
lighter of the two. With two single-channel files,
such as grayscale files, using Lighter simply retains
the lighter values from both files. In composite
color images, Lighter compares the brightness
value in each set of color channels and then com-bines
the lighter values into one channel. In this
case, the colors in the resulting image may be very
different from the colors in either source channel.
Add Adds the pixel values in two channels. This is
a good way to combine nonoverlapping images in
two channels.
Because higher pixel values represent lighter col-ors,
adding channels with overlapping pixels light-ens
the image. Black areas in both channels remain
black (0 + 0 = 0). White in either channel results in
white (255 + any value = 255 or greater).
The Add option divides the sum of the pixel values
by the Scale amount and then adds the Offset value
to the sum. For example, if you wanted to find the
average of the pixels in two channels, you would
add them, divide by 2, and enter no Offset value.
The Scale factor may be any number between
1.000 and 2.000. Entering a higher Scale value
darkens the image.
The Offset value lets you lighten or darken the pix-els
in the destination channel by any brightness
value between +255 and �255. Entering a negative
Offset value darkens the image even more. Enter-ing
a positive Offset value lightens the image.
Subtract Subtracts the pixel values in the source
channel from the corresponding pixels in the tar-get
channel. As with the Add option, the result is
then divided by the Scale factor and added to the
Offset value.
The Scale factor may be any number between
1.000 and 2.000. The Offset value lets you lighten
or darken the pixels in the destination channel by
any brightness value between +255 and �255.
CHAPTER 11 276
Using Layers

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Graphics 版 (精华区)