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.
• Create a blank layer named Color Red and fill it with pure red (255,
0, 0). Change the Mode of the Color Red layer to Multiply.
• Duplicate the Color Red layer, and rename it Color Green.
• Duplicate the Hue Adjustment Template layer and move it above
the Color Green layer. This will change the effect of the layer from red to green.
• Merge the Hue Adjustment Template layer with the Color Green layer by pressing F/Ctrl+E.
• Duplicate the Color Green layer, and name it Color Blue.
• Duplicate the Hue Adjustment Template layer, and drag it above the Color Blue layer. This will change the effect of the layer to blue.
• Merge the adjustment layer. At this point, your layers should look like they do in Figure 2.4.
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:
• Start with the Red layer. Duplicate this layer (leave the name Red Copy
since it will be temporary).
• Duplicate the original Hue Adjustment Template layer and drag it above the Red Copy layer. This will turn the Red Copy layer green (note the similarity to step 5). Commit the change by merging the Hue Adjustment Template layer with the Red Copy layer.
• Duplicate the Red Copy layer (now actually green in color from the 120? color rotation).
• Duplicate the original Hue Adjustment Template layer and drag it above the new duplicate (you may need to resize the Layers palette to do this). This will turn the Red Copy 2 layer blue.
• Merge the adjustment layer with the Red Copy 2 layer to commit the change.
• Link the Red, Red Copy, and Red Copy 2 layers (click the Link box as shown in Figure 2.6), click the Red layer to activate it, and choose Merge Linked from the Layers menu (or press F/Ctrl+E). This will merge the layers into a single Red layer as grayscale.
Figure 2.6 Link the layers prior to merging.
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