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发信人: killest (victor), 信区: Graphics
标  题: PHOTOSHOP(78)-Using Channels and Masks
发信站: 紫丁香 (Sat Apr 25 12:21:01 1998), 转信

Duplicating channels
You can duplicate any channel in the same image,
to a new image, or to any other open image. (You
cannot, however, duplicate a channel to a Bitmap-mode
image.) You may want to duplicate a chan-nel
in the same image to keep a backup if you抮e
going to perform manipulations on a channel. You
may want to duplicate alpha channels to a new
image to keep a library of selections that you can
load into the current image one at a time. This
helps you keep the size of the file smaller to
improve performance.
To duplicate a channel using the Duplicate command:
1 In the Channels palette, select the channel you
want to duplicate.
2 Choose Duplicate Channel from the Channels
palette menu.
3 Type a name for the duplicate channel.
4 For Document, choose a destination. Only
images with the same pixel dimensions as the
current image are available. You can also choose
New to copy the channel to a new image. If you
choose New, type a name for the new image. The
New option creates a single-channel grayscale
image.
5 To reverse the selected and masked areas in the
duplicate channel, select Invert.
6 Click OK.
To duplicate a channel by dragging:
1 In the Channels palette, select the channel you
want to duplicate.
2 Do one of the following: To duplicate a channel into its original image,
drag the channel in the Channels palette into the
image window or onto the New Channel button
(O) at the bottom of the palette. To duplicate the channel into another image,
make sure that the destination image is open; then
drag the channel from the Channels palette into
the destination image window.
Saving and managing channels
As long as you save a file in a format that supports
the image抯 color mode, the color channels will be
preserved. Alpha channels, on the other hand, are
automatically preserved only when you save a file
in the Adobe Photoshop, Adobe Photoshop 2.0
(Macintosh only), TIFF, or Raw formats. Saving in
other formats may cause channel information to
be discarded. See 揂bout file formats� on page 318
for more information.
In addition, you can create a separate new image
for each channel of an original image, and you can
merge channels from separate images into a single
image.
233
Splitting channels into separate images
You can split the various channels that make up an
image into separate images by using the Split
Channels command in the Channels palette menu.
When you choose Split Channels, Adobe Photo-shop
closes the original file and places each chan-nel
into a separate grayscale image window. The
title bar of each window reflects the original image
name along with the channel name (Macintosh)
or abbreviation (Windows). Any changes you抳e
made since you last saved are reflected in the new
images but are lost in the original image.
Note: You can split only flattened images. See 揊lat-tening
all layers� on page 271 for more information.
Merging channels
You can combine channels to form a single image.
For example, some grayscale scanners let you scan
a color image through a red filter, a green filter, and
a blue filter to generate red, green, and blue
images. Merging lets you combine the channels of
a color image that was scanned in this way and save
the image as a single, color image.
The images you want to merge must be in Gray-scale
mode, must have the same dimensions (in
pixels), and must be open. In addition, the num-ber
of grayscale images you have open determines
the available color modes into which you can
merge channels. For example, you can抰 merge the
split channels from an RGB image into a CMYK
Starfish_R.eps
Untitled_1
Starfish_G.eps Starfish_B.eps
CHAPTER 10 234
Using Channels and Masks
image, because a CMYK image requires four chan-nels
and an RGB image contains only three chan-nels.
Note: If you are working with DCS files that have
accidentally lost their links (and so cannot be
opened, placed, or printed), open the channel files,
and merge them into a CMYK image. Then resave
the file as a DCS EPS file.
To merge channels:
1 Open the grayscale images that contain the
channels you want to merge.
2 Make one of the images active.
3 Choose Merge Channels from the Channels
palette menu.
4 For Mode, choose the color mode you want to
create. Image types that aren抰 available are
dimmed. The number of channels appropriate for
the selected image type appears in the Channels
text box.
5 If necessary, enter a number in the Channels
text box.
If you enter a number that is incompatible with the
selected image type, the Multichannel image type
is automatically selected. This creates a grayscale
image, and all color information is lost.
6 Click OK.
7 For each channel, make sure the image you want
is selected. If you change your mind and want to
select a different image type, click Mode to return
to the Merge Channels dialog box.
8 When you have finished selecting the channels,
click OK. If you are merging into a multichannel
image, click Next, and repeat the selection process
for each channel in the image.
Adobe Photoshop merges the selected channels
into a new image of the specified type and closes
the images containing the channels that were
merged without saving them. The new image
appears in an untitled window.
Using masks
You use a mask to isolate an area that you want to
protect from change while you apply color
changes, filters, or other effects to the rest of the
image. Masks are closely related to selection areas.
When you select part of an image, the area that is
not selected is 搈asked� or protected from editing.
You can also create a semitransparent mask that
enables you to partially affect an area of an image.
In our first example, we used a mask to protect the
background as we changed the color of the star-fish.
In the second example, we used a mask to

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※ 来源:．紫丁香 bbs.hit.edu.cn．[FROM: victor.hit.edu.c]

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