The Hidden Power of Photoshop CS: Chapter 2: Color Separations. Pt. 1. By Sybex | 3 | WebReference

The Hidden Power of Photoshop CS: Chapter 2: Color Separations. Pt. 1. By Sybex | 3

The Hidden Power of Photoshop CS: Chapter 2: Color Separations. Pt. 1

RGB Separation to Grayscale

When creating the RGB image from the Prokudin-Gorskii plates in Chapter 1, you saw that scenes can be simplified to grayscale representations of red, green, and blue as tone. Chapter 1 showed you how to put together color from what’s already separated. Taking apart the color is just about as easy! Not only can you use this separation for color correction, but separating layers can also help you create custom black-and-white images.

Separating RGB from a Color Image

Separating the image you put back together in Chapter 1 is an interesting challenge. Depending on your level of expertise and understanding, you may or may not absorb what is going on here right away. You may have to do it a few times before you grasp the details. Being able to separate RGB will help you understand how images go back together again (and how they are sampled by scanners and cameras). It all breaks down to a simple filtering of three colors.

However, users of any level can do this by following the steps outlined here. Once you become familiar with this process, it will help you understand both layers and RGB color. There is an action on the CD that will complete the RGB separation steps for you. You will find the action useful in automating the process, and it can also help by walking you through if you have difficulty with the steps. The action can be used to separate any RGB image into RGB layers.

1. Open the kushbeggi.psd image you saved in Chapter 1 (or kb-L.psd on the CD).

2. Duplicate the background, name the layer Source, and then shut off the view for the Source layer.

3. Change the Background layer to black (to use as your projection screen). To do this, press D to reset to the default colors on the toolbar, and press X to exchange the colors, making black the background color. Then, activate the background by clicking it in the Layers palette, hold down z/Ctrl, and press Delete/Backspace.

4. Create a color adjustment template layer. You will use this layer as a template that you can duplicate so that you don’t have to keep re-creating the adjustment. To make the template, create a Hue/Saturation layer and set it to Hue 120, Saturation 0, and Lightness 0. Change the name of the layer to Hue Adjustment Template. This will not affect the black background but will help you rotate the color around the color wheel at 120? increments.

5. Create the Color Filter layer templates. Again, you will use these as templates that you can duplicate so that you don’t have to re-create color-filled layers:

Figure 2.4 You’ll use these layered components to make some repeated moves and separate out the color components in the next few steps.

6. Duplicate the Source layer, name it Red, and be sure it is at the top of the layer stack as viewed from the Layers palette. Then, duplicate the Color Red layer, move it above the Red layer in the Layers palette, and merge the Color Red Copy into the Red layer. Set the Mode to screen. This will make the layer serve as the red light component.

7. Repeat step 6 using the Color Green and Color Blue layers. Each time, start by duplicating the Source layer. To duplicate, drag the layer to the Create A New Layer button at the bottom of the Layers palette. Name the Source Copy layers Green and Blue in turn. Be sure to pair the Green layer with the Color Green layer and the Blue layer with the Color Blue layer, putting the Color layer above. When you are done, you’ll have a simple separation showing the layers in red, green, and blue colors (see Figure 2.5). View them separately by toggling the layer views. Shut off the view for the Blue and Green layers before continuing.

Figure 2.5 After you complete step 7, the layers should look like this.

8. Convert each of the color layers to grayscale representations:

9. Repeat step 8, using the Green and Blue layers. Each time, shut off the view for the color component you have merged and turn on the view for the color component you are working on; then make the duplicate, apply the Hue Adjustment Template layer, make the second duplicate, apply the adjustment, and merge. When you have finished, the result will look like Figure 2.7.

Figure 2.7 At the top of the stack are Red, Green, and Blue layers that are accurate RGB color component separations.


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

URL: URL: http://webreference.com/graphics/ps1/1