getting started with photoshop - Channels & its features (1)

Duplicating channels

You might duplicate an image's channel to make a backup before editing the channel. Or you might duplicate alpha channels to a new image to create a library of selections to load into the current image one by one--thus keeping the file smaller.

If you are duplicating alpha channels between images, the channels must have identical pixel dimensions.

Note: You cannot duplicate a channel to a Bitmap-mode image.

To duplicate a channel using the Duplicate command:

1. In the Channels palette, select the channel to duplicate.

2. Choose Duplicate Channel from the Channels palette menu.

3. Type a name for the duplicate channel.

4. For Document, do one of the following:

• Choose a destination. Only open images with pixel dimensions identical to the current image are available. To duplicate the channel in the same file, select the channel's current file.
• Choose New to copy the channel to a new image, creating a multichannel image containing a single channel. Type a name for the new image.

5. To reverse the selected and masked areas in the duplicate channel, select Invert.

To duplicate a channel within an image by dragging:

1. In the Channels palette, select the channel you want to duplicate.

2. Drag the channel onto the New Channel button at the bottom of the palette.

To duplicate a channel to another image by dragging or pasting:

1. In the Channels palette, select the channel you want to duplicate.

2. Make sure that the destination image is open.

Note: The destination image does not have to be the same pixel dimensions as the duplicated channel.

3. Do one of the following:

• Drag the channel from the Channels palette into the destination image window. The duplicated channel appears at the bottom of the Channels palette.
• Choose Select > All, then choose Edit > Copy. Select the channel in the destination image and choose Edit > Paste. The pasted channel overwrites the existing channel.

Splitting channels into separate images

You can split the channels of a flattened image into separate images. The original file is closed, and the individual channels appear in separate grayscale image windows. The title bars in the new windows show the original filename plus the channel abbreviation (Windows) or full name (Mac OS). Any changes since the last save are retained in the new images and lost in the original.

Splitting channels is useful when you want to retain individual channel information in a file format that doesn't preserve channels.

Note: Only flattened images can be split. 

To split channels into separate images:

Choose Split Channels from the Channels palette menu.

Merging channels

Multiple grayscale images can be combined into a single image. 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 separate scans into a single, color image.

Note: You can also blend the data in one or more channels into an existing or new channel.

The images you want to merge must be in Grayscale mode, 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, you can't merge the split channels from an RGB image into a CMYK image, because CMYK requires four channels and RGB requires only three.

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 containing the channels you want to merge, and make one of the images active.

You must have more than one image opened for the Merge Channels option to be available.

2. Choose Merge Channels from the Channels palette menu.

3. For Mode, choose the color mode you want to create. If an image mode is unavailable, it is dimmed. 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 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 image type, click Mode to return to the Merge Channels dialog box.

7. If merging into a multichannel image, click Next, and repeat step 6 to select the remaining channels.

Note: All channels of a multichannel image are alpha channels.

8. When you are 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.