Performing Channel Operations


You can perform several operations within the Channels palette that change the structure of the document. Some of these operations produce shifts in the color mode, and some disperse the channels into several documents.

Note  

Because of the radical changes to the color information, it is always a good idea to make a copy of the document before implementing most of these channel operations. To duplicate the document, choose Image Duplicate.

Duplicating Channels

When you duplicate a targeted channel, you get an exact copy of it in the Channels palette. You should duplicate the channel if you want to experiment with modifying it by painting, applying a filter effect, or using any other editing function. Also duplicate the channel if you want to invert it and save it for alterations, as seen in Hands On 4, Channels. Click the arrow in the upper-right corner of the Channels palette and scroll down to the Duplicate Channel command.

Note  

The Duplicate Channel option will be dimmed if the composite channel is targeted, because you can duplicate only one channel at a time.

A fast way to duplicate a channel is to drag it to the New Channel icon at the bottom of the Channels palette.

Deleting Channels

You can delete a targeted channel from the document by choosing Delete Channel from the palette pull-down menu. You can delete alpha channels and maintain the integrity of the image, but when you delete color channels, the color mode of the image will change to Multichannel (see the section titled Using Multichannel later in this chapter). If you delete the red channel of an RGB image, for example, the remaining color channels will convert to magenta and yellow. (Multichannel documents always default to CMYK descriptions.) You cannot delete the composite channel.

A fast way to delete a channel is to drag it to the Delete Current Channel icon (the trash icon) at the bottom of the Channels palette.

Splitting Channels

Photoshop can split a document s channels into independent grayscale documents. The title of each window is automatically appended to the channel s color name as a suffix in the image title bar at the top of the window. For example, a CMYK document named Box will be divided into four channels: Box_C, Box_M, Box_Y, and Box_K. Alpha channels will be converted to separate grayscale documents. This option is useful as a first step in redistributing channels or for making a single document out of the channels information. This is not a process you ll use every day, unless you re a printer who needs to isolate the color information to a single document or you have very specialized needs to analyze the channel information. The new documents are not automatically saved, so you should save them to your hard disk.

To split a channel, first flatten the image. Choose Split Channels from the Channels Palette menu. When you perform this operation, the original document is automatically closed.

Merging Channels

Separate channels can be merged into a single Multichannel document by choosing Merge Channels from the Channels Palette menu. The images must be open, grayscale, and the exact same height, width, and resolution. A dialog box appears that enables you to assign a color mode to the image, based on the number of images open. Three open images will produce an RGB, Lab, or Multichannel image; four open images will produce a CMYK or Multichannel image. Click OK and another dialog enables you to determine the distribution of the color channels. You can create some rather surprising color distortions by switching color information between channels.

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Note  

One of the most common uses for the Merge Channels command is for recombining EPS DCS files. Prepress users have to recombine an EPS DCS 1 or 2 file that has lost the composite preview file, which links the separations. A new EPS DCS file can be created that includes the composite preview file and the high-resolution separations.

Using Multichannel

You can divide an image s channels into an individual series of channels. When you choose Image Mode Multichannel, the new channels lose their color relationships to each other and appear as individual grayscale channels within a single document. There is no composite channel. This can be useful if you want to separate the color information of a composite channel such as a Duotone, Tritone, or Quadtone and view the color information of each ink color separately. (Chapter 18 goes into more detail on image features such as Duotones and spot colors.) The Multichannel operation converts the red, green, and blue channels on RGB images into separate cyan, magenta, and yellow channels within the same document.

Mixing Channels

The Channel Mixer is a Photoshop feature that enables you to adjust the color information of each channel from one control window. You can establish color values on a specific channel as a mixture of any or all of the color channels brightness values. The Channel Mixer can be used for a variety of purposes, including:

  • Creating an optimal grayscale image from an RGB or CMYK file

  • Making a high-quality sepia tone from a CMYK or RGB file

  • Converting images into alternative color spaces

  • Swapping color information from one channel to another

  • Making creative color adjustments to images by altering the color information in a specific channel

To learn how to use the Channel Mixer, see Chapter 16, Adjusting Tonality and Color.

Using Spot Color Channels

The spot channel features in the Channels Palette pull-down menu are used to create images that are output to film for printing on printing presses. They are most frequently applied to grayscale images for two- and three-color print jobs. They are also used on four-color process (CMYK) images when additional areas of solid rich color, varnishes, and special inks are specified. Spot colors are usually printed with PANTONE or other custom color inks. See Chapter 18 to learn how to work with spot colors.




Photoshop CS Savvy
Photoshop CS Savvy
ISBN: 078214280X
EAN: 2147483647
Year: 2004
Pages: 355

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