The Hidden Power of Photoshop CS: Chapter 2: Color Separations. Pt. 2. By Sybex | 2 | WebReference

The Hidden Power of Photoshop CS: Chapter 2: Color Separations. Pt. 2. By Sybex | 2

The Hidden Power of Photoshop CS: Chapter 2: Color Separations. Pt. 2

Printing Duotones

When trying to print your duotone, one of several things will happen, depending on the equipment you are using to print and the expertise/experience of the prepress people you are dealing with. Your duotone and spot color channel files might be acceptable as is for PostScript processing, but not for printing to a home ink-jet printer. You would usually just save the file as an EPS (perhaps a DCS, or Desktop Color Separation, for the spot color channel type), insert that file into your layout, and print. Files created with separations as layers will need to be converted by moving the layers to spot channels, or possibly by creating separate plates—the latter option may be less desirable.

However, there are times when you will want to convert the Duotone mode file to spot color channels to separate EPS or TIFF, so you can use the channels from that file as you would with a manually created duotone. Just flattening the file and sending it to your home ink-jet is not what you want to do after you’ve gone to the trouble of keeping the information separated. It is most likely that the file will be converted and re-separated on-the-fly (with your home printer, and a number of other digital processes), and the result may be anything from simply unexpected to a real disaster.

What you actually have by the time you are done with either of the manual procedures as described is a bona fide duotone separation: two tones of ink, not necessarily the equivalent of the RGB or CMYK process. This is different from a Duotone mode file, which applies what are essentially transfer functions to the reference tone for the image. If you flatten the manual duotone images and change to CMYK or RGB, the color for the manual-layered duotone and Photoshop duotone will be converted to that mode rather than handled as a true duotone. If you attempt to print the manual file to a home printer with spot color channels, you may get a conversion (to RGB and back to CMYK!) or nothing at all (because the additional color channels may not be recognized). Treating the image as a true duotone will help you get the best duotone results. This generally means using the inks/channels separately and applying them in the intended colors on a press that can handle custom color.

When printing any of these duotones, you can best handle the duotone color information by splitting it out into different channels, or representations of ink intensity. The separated channels can then be recombined into a CMYK, RGB, or grayscale image as spot colors or existing tones (e.g., K in CMYK), or can be colored and used with a home ink-jet printer in a multiple-pass technique that imitates press processing. While the Duotone mode file and the spot channel duotone are really press ready, the layered duotone will require adjustment in order to be used as a true duotone. On the other hand, trying to print spot color won’t be good for all situations, such as home printing on an ink-jet. We’ll look at both options more closely in the following sections. First let’s make sure you can separate the ink tones from the image.

Table 2.1 attempts to clarify just what you can use your duotones for. If a file is “Press Ready,” it means that you can send it to process with spot color as is; if it is “Home Printer Ready,” it means that the file can be sent to your home printer as is but that you should expect a CMYK result rather than spot color one.

Table 2.1 Uses for Duotones.

Creating the Duotone Channels

Depending on whether you used the layer method or Photoshop Duotone to create the duotone information, you will have to extract the channel information differently. Having to separate out the channels doesn’t apply to the channel method since the channels are already created, but you may still want to separate the channels to make prints at home. The goal here is to isolate the channels in their own images so that you can combine them however you’d like. Creating a separate image for each channel gives you many options for combining the information and allows you to combine multiple channels—perhaps separated using different methods. This may also create options for adjusting tone and can help with management of non-duotone spot colors that you might use in files.

If you created the duotone using the layer method, extracting the channels is fairly straightforward. You can do this by merging the curve adjustments with the duotone layers, and then duplicating each duotone layer to a new image (using the Duplicate Layer command and targeting a New image). The new image will be in the same mode as the original file; you can change it to grayscale, if necessary. You’ll have one image for each channel you extract. You may want to attach names to the layers as they are duplicated to the new image so that you know which is which.

In order to extract channels from a duotone created with the Duotone tool, the best and easiest result is typically obtained by changing to Multichannel mode. Doing this will apply the curves and create a single channel for each ink during the conversion. After the Multichannel file is created, use the Split Channels command on the Channels palette pop-up menu to create separate channels. When the channels separate, Photoshop will name the new image “[file name]. [channel name],” which should help you keep track of what the images represent.

Creating separate images for channels from duotones made using the channel method is the easiest of the bunch: just choose Split Channels from the Channels palette pop-up. This step isn’t necessary for printing this type of file with spot colors on press. However, there may be other instances in which you will want to revert to manual control of the channels—such as when you are repurposing the file to print to a home ink-jet.

With the channels separated into individual files, you can combine them in different ways to print as spot color or to make separated prints at home with the multipass method.

Duotone Prints as Spot Color

Part of the trick of successfully using duotone color is incorporating it correctly into image files. Duotone information can be compiled into a single file to print as spot color, or as part of existing color spaces. For example, if you had a duotone created from black and cyan, you could combine the duotone channels into a CMYK image as the Cyan and Black channels. If the colors don’t correspond to a process color, you can incorporate them as spot color.

With the duotone channel files open, you can quickly incorporate them into a single image file. The following steps assume you are still working with the wagontrain.psd example and that you have converted the channels to separate files.

1. Open a new image in Grayscale mode and make it the same size as the originals. Do this quickly by selecting All and copying one of the originals and then opening a new document; Photoshop will size the image to those dimensions for you.

2. Choose Merge Channels from the Channels palette pop-up menu.

3. When the Merge Channels dialog box opens, choose Multichannel and set the number of channels to 3: one for the grayscale channel, and one each for the duotone colors.

4. Assign the image you created in step 1 to the grayscale channel and the duotones to the other spot color slots (see Figure 2.22). Click OK.

Figure 2.22 Because the new image is blank, assigning it to the grayscale channel will not affect the duotone result.

Figure 2.23 Converting to Grayscale from Multichannel allows you to save the file and spot channels in a broadly supported file type.

5. Open the Channels palette and double-click the Alpha 2 thumbnail. This will open the Channel Options dialog box.

6. Change the Color Indicates selector to Spot Color, change the Opacity setting to 0%, and specify a color that matches the color selected for the duotone channel. You assign the color by clicking the swatch to open the Color Picker.

7. Repeat step 6 for the Alpha 3 channel.

8. Click on Alpha 1 in the Channels palette and change the image mode to Grayscale. As a result, Photoshop names and incorporates the spot color channels correctly in the new file (see Figure 2.23).

If saved in a format that allows and recognizes additional color channels (TIFF or EPS), the file will carry the information to a layout program that can recognize spot color, and will print separated spot color plates when sent to print in a PostScript workflow.

Created: March 27, 2003
Revised: March 1, 2004