Adobe Photoshop CS4 - Manual (Page 280)

273 USING PHOTOSHOP CS4
Selecting and masking
Last updated 1/10/2010
Merge channels
Multiple grayscale images can be combined as the channels of a single image. The images you want to merge must be
in grayscale mode, be flattened (have no layers), have the same pixel dimensions, and be open. The number of grayscale
images you have open determines the color modes available when merging channels. For example, if you have three
images open, you can merge them into an RGB image; if you have four images open, they can become a CMYK image.
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 re-save the file as a DCS EPS file.
1 Open the grayscale images containing the channels you want to merge, and make one of the images active.
You must have more than one image open for the Merge Channels option to be available.
2 Choose Merge Channels from the Channels panel menu.
3 For Mode, choose the color mode you want to create. The number of channels appropriate for the mode appears
in the Channels text box.
4 If necessary, enter a number in the Channels text box.
If you enter a number that is incompatible with the selected mode, Multichannel mode is automatically selected. This
creates a multichannel image with two or more channels.
5 Click OK.
6 For each channel, make sure the image you want is open. If you change your mind about the image type, click Mode
to return to the Merge Channels dialog box.
7 If you are merging channels into a multichannel image, click Next, and select the remaining channels.
Note: All channels of a multichannel image are alpha channels or spot channels.
8 When you have finished selecting channels, click OK.
The selected channels are merged into a new image of the specified type, and the original images are closed without
any changes. The new image appears in an untitled window.
Note: You cannot split and recombine (merge) an image with spot color channels. The spot color channel will be added
as an alpha channel.
Delete a channel
You may want to delete spot or alpha channels you no longer need before saving an image. Complex alpha channels
can substantially increase the disk space required for an image.
❖ In Photoshop, select the channel in the Channels panel and do one of the following:
• Alt-click (Windows) or Option-click (Mac OS) the Delete icon .
• Drag the channel name in the panel to the Delete icon.
• Choose Delete Channel from the Channels panel menu.
• Click the Delete icon at the bottom of the panel, and then click Yes.
Note: When you delete a color channel from a file with layers, visible layers are flattened and hidden layers are discarded.
This is done because removing a color channel converts the image to Multichannel mode, which does not support layers.
An image isn’t flattened when you delete an alpha channel, a spot channel, or a quick mask.