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

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

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

This book excerpt is from "The Hidden Power of Photoshop CS: Advanced Techniques for Smarter, Faster
Image Processing."
ISBN 0-7821-4255-9. All rights reserved. Chapter 2: Color Separations. , is posted with permission from Sybex.

Duotones via Spot Color Channels

A second way to achieve manual duotoning is to create the effect using spot color channels. This creates an image with the spot color built in, and essentially it will be press ready as a separation. In the following techniques you will use both the manual layer method just described in the previous section and Photoshop’s duotone interface to create duotone results.

1. Open the wagontrain.psd from the CD.

2. Change the mode from RGB to Grayscale. You can also use other means for conversion, but since the image is already grayscale, the difference in the conversion shouldn’t matter.

3. Duplicate the Gray channel.

4. Double-click the Gray Copy channel to open the Channel Options dialog box. Change the options to Spot Color, 0% Solidity, and pick your spot color from the Color Picker. The dialog box should look like the one shown in Figure 2.20. We’ll use Pantone 472 for the spot color in this case to get something of a sepia tone; the name of the channel automatically changes to the pantone selected.

5. Repeat steps 3 and 4, creating a second color channel with the same settings: Spot Color and 0% Solidity. We’ll use black for the second color; you can use a Pantone black, or set the Color Picker to 0, 0, 0 in RGB and Photoshop will change the channel name to Black.

6. Click on the background layer to be sure it is active, press D to set the default colors (white in the background), select all (press z/Ctrl+A), and then press the Delete key. This will clear the original image and the gray channel.
7. Make the Pantone 472 and Black channels visible by clicking in the visibility box on the Channels palette to turn on the Adobe eye for each. This will show a preview of the duotone.

8. Make curve adjustments as desired to each of the channels. To make the adjustment, click once on a channel to activate it, then select Image ‘ Adjustments ‘ Curves, or press z/Ctrl+M. The dialog box will appear.

Figure 2.20 The Channel Options dialog box allows you to change the behavior of individual channels in the Channels palette. Changing the Color Indicates option from Masked Areas to Spot Color tells Photoshop to handle the channel like a color.

While this technique offers immediate feedback in the previews and a finished format, there is a drawback to not being able to adjust the curves more fluidly; changes you make with the curves are more or less a one-shot-deal in that they affect the channels directly. The previous layer technique allows you to return to curves as often as you’d like before committing any changes.

It is possible to combine these techniques somewhat so that you use the adjustability of the layer technique and the final format advantage of the channel technique. If you start with the layer technique to create the curves, you can later apply those curves settings to the duotone channels. Try this:

1. Run through the steps for creating a manual duotone. Use the Duotone Layer Setup action in the The Hidden Power Tools to speed you through this step.

2. Save the curve settings by double-clicking the curve adjustment layers in turn to open the Curves dialog box, and then click the Save button to save the settings to a file. Save the file in a place you will find easy to get to, using a name that makes sense. For example, you might want to save to a Curves folder that you create in the Presets folder in the Photoshop program file directory. If you name the files Pantone 472 and Black and date them, you can locate the right curves. These curve files will have an .acv extension appended to them during saves.

3. Click the original History state (Open) or initial snapshot in the History palette. This will return the image to the original state.

4. Set up the duotone channels using the Duotone Channels Setup action in the Hidden Power Tools. This will do the basic setup described in steps 1 through 7 in the previous procedure.

5. Instead of making curve adjustments by following the instructions in step 8, load the curve settings saved in step 2. To load these settings, click on a channel once to activate it, choose Curves (press F/Ctrl+M), click the Load button in the Curves dialog box, and select the curve you saved for the active channel.

These steps allow you to make custom adjustments to the curves before you make the spot channels. In other words, you can play freely with the curves to get the settings right and using the on-screen previews, and then save the settings to apply them to the spot channels.

There will be several problems here as well. The first is that the color in RGB layers may be slightly different than the PMS color. This can be due to color settings or conversions. However, you are more likely to get a satisfactory result from combining the methods than you can trying to get it perfect in one shot.

Using Photoshop’s Duotone Interface

You can change a grayscale image directly into a duotone format using Photoshop’s Duotone interface. This dialog box, shown in Figure 2.21, opens when you convert a grayscale image to Duotone mode.

To create a basic conversion using the Duotone interface:

1. Choose Image ‘ Mode ‘ Duotone. This command will be available only from Grayscale mode or Duotone mode. The dialog box opens with either the current (when the image is already duotone) or previously used settings.

2. Choose a setting from the Type drop-down list. This can be Monotone (one color), Duotone (two colors), Tritone (three colors), or Quadtone (four colors). Choose the setting based on the number of colors you expect to apply. After you make the selection, the views will activate for the number of colors you selected.

3. Click the color swatch for each of the colors in turn and choose the color from the Color Picker. For this example, choose the same colors as in the previous example: Pantone 472 and Black.

4. Click the Curve boxes in turn and set the curves as appropriate for the color application. To do this with the same settings as the previous examples, load Duotone_black.acv for the Black ink and Duotone_P472.acv for the Pantone 472 ink from the Hidden Power Tools.

5. Accept the changes by clicking OK.

Figure 2.21 Photoshop’s Duotone dialog box allows you to assign color and curve application based on the original tone, but does it all in a one-layer image.

If you don’t like the idea of fiddling with layers as in the manual method, this can prove less troublesome, but it also can offer fewer options and opportunities for making changes and controlling the result because of the inherent limitations of the mode and the lack of channels. Therefore, it may actually prove harder to use for advanced applications. For example, if you want to adjust spot color density with a brush or add spot color type, these files can prove difficult to manipulate.

Files created using the Duotone interface may appear different (on screen and in print) than those created using the manual technique—even when exactly the same settings are used for colors and curves. The difference depends on the color-management settings you are using—specifically the dot gain settings, which tell Photoshop how much a printed dot can be expected to expand on press. The result may be better or worse depending on the process.

The Curves dialog box you use when working with duotones is somewhat different than the Curve dialog box used in image adjustment. This is because the behavior is more akin to using Transfer Functions, affecting the ink, rather than technically changing the stored values for the pixels in the image. You are somewhat more limited in the number of curve points that can be placed; there are 13 positions. Curves you load that were saved from adjustment curves will be transcribed.

The Overprint Colors dialog box is a means of adjusting the preview to fit the inks you are using. If, for example, you are using a metallic ink that has 100 percent solidity and will overprint even black ink, you can adjust the overprint mix of black and the metallic ink to look more like the metallic. Of course, this has its own problems since the metallic will not represent well on an RGB screen. Do not make changes to the Overprint settings unless you have tested the output and know the result. Any changes in the overprint settings do not affect the printed outcome—changes here affect image preview only.

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