The Hidden Power of Photoshop CS: Chapter 2: Color Separations. Pt. 2. By Sybex | 7 | WebReference

The Hidden Power of Photoshop CS: Chapter 2: Color Separations. Pt. 2. By Sybex | 7

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

Lab Color

In the section “Converting to Grayscale from Lab Color,” we looked at taking the tone from an image by separating it from the color. Part of the idea behind this was based on the Lab color model, which treats color separately from tone. Separating tone from color can come in handy when manipulations require that you treat one or the other, rather than both. In CMYK or RGB models, color and tone are essentially inextricable: If you change one of the components, the tone and color of the image are altered. With tone separate from color in Lab, you can make adjustments to the image tone without having the by-product of affecting color change at the same time.

So, say your image is a bit flat (lacks contrast) but you think the color is good. Splitting the image tone (luminosity) from the color allows you to make a curve adjustment to the tone to increase the contrast with no real effect on the color. Lab is also great for making targeted color change (e.g., changing the color of a dress) because it is easier to work on the color in isolation from the tone.

Figure 2.40 You have created five new layers in steps 2 through 6. Before you continue, they need to be in the order shown here.

The conversion to Lab is as simple as choosing Lab mode. Because Lab is able to reproduce more colors than either RGB or CMYK, it can represent all the colors the others can. However, after you make manipulations in Lab, returning an image back to RGB or CMYK will be less friendly to the image information: Some data may be compromised in either case during the conversion. Converting to Lab and back to CMYK will also cause the image to be re-separated, so any changes you have made in customizing separations may be lost. Therefore, it is best to use Lab in correction stages—before targeting your image for CMYK output.

Working separately on color and tone offers distinct advantages when you’re working in layered separation in RGB, Lab, or CMYK. The idea is to create separate layers to carry the image luminosity (or lightness) and another to carry image color (the A and B channel information). Making changes to the Luminosity layer affects only the tone, and changes to the Color layer affect only color as long as those changes are grouped to their target layers.

Let’s take a look at the basics by separating luminosity and color in layers:

1. Open JuliaButterfly.psd.

2. Duplicate the Background and name the layer Color. Change the mode to Color.

3. Duplicate the Color layer and name the layer Luminosity. Change the mode to Luminosity.

4. Activate the Background and create a new blank layer. Name the layer Composite and fill it with gray (50 percent).

5. Duplicate the Composite layer two times. Change the layer copy names to Commit 1 and Commit 2.

6. Move Commit 1 above the Color layer. The Layers palette should look like Figure 2.40.

7. Activate the top layer (press Option/Alt+Shift+] ), link Commit 1, and then press z/Ctrl+E to merge the Luminosity layer with Commit 1. If the Luminosity layer is not the active layer and the layers are not linked, the name can change to Commit 1, rather than retaining the name Luminosity.

Figure 2.41 While not exactly like Lab, which separates two color layers, this setup will give you much of the advantage of Lab color mode without switching to Lab.

8. Change the layer mode of the Luminosity layer to Luminosity. This changes to Normal automatically during the merge.

9. Activate the Color layer (press Option/Alt+[), link to Commit 2, and then merge by pressing z/Ctrl+E. Change the mode of the layer to Color. The result will look the same as the original, but the color will be separated into Luminosity and Color components as in Figure 2.41.

The color dynamic of the Color layer is virtually the same as if you had switched to Lab, except that you won’t adjust the A and B layers separately. In this case, it can actually be an advantage.

If, for example, you have an image with a lot of color noise, you can clear up the problem by just blurring the Color layer—depending on the image, you may be able to blur the Color layer by an almost obscene amount. You can combine the blur effect with specific areas of color noise as applicable. In any case, you can blur and not affect the tone because it is in a separate layer and is self-contained. In other words, the shape of the image will be held by the tone. You will see more of the advantage of this separation when we discuss masking in Chapter 3.

Of course, you can always switch to Lab mode and make corrections to the Lightness channel and blur the A and B color channels to reduce noise. Yet another option is to move to Lab mode and use the Color and Luminosity tool to split luminosity and color within the Lab mode image. This approach may let you handle the desired corrections more easily.

RGBL Hybrid Separation

A hybrid type of separation can be created using luminosity to control tone along with creating an RGB separation for control of color. The result is that you get the simplicity and intuitive arena for color correction and a dynamic control of tone isolated from one another.

All you really have to do is separate RGB in layers and add a luminosity layer to the top of the stack. When you are done, you will have successfully separated color from tone and separated the tone into a light-based representation of colors. This is something that would be very difficult to do using channels alone.

1. Follow the steps to separate RGB channels as layers from the section “Separating RGB from a Color Image” Or play the Split RGB No Stops action.

2. Create a new, blank layer at the top of the layer stack. Name the layer Luminosity, and set the mode to Luminosity.

3. Press z+Option+Shift+E/Ctrl+Alt+Shift+E to merge the visible image into the Luminosity layer.

4. Create a new layer and fill with 50 percent gray (HSB: 0, 0, 50).

5. Move the Luminosity layer above the layer created in step 4, group them, and merge.

6. Set the merged layer mode to Luminosity.

This gives you an image that freezes the current image Luminosity. It allows you to make drastic and controlled changes to the color without affecting the shape of the image. In other words, you can take advantage of and correct the RGB channels by making corrections below the Luminosity layer using curves, for example.

By this point, we have sliced and diced images in innumerable different ways, and this last section shows that you can mix and match color schemes to some extent to take advantage of different theories and separations without necessarily converting the image to a different mode. Being able to extract targets for tone, color, saturation, and different channels gives you greater power over your images in affecting your targeted change. Practice taking your images apart and putting them back together. The better you understand these procedures, the better you can grasp and integrate the chapters to come.

Created: March 11, 2003
Revised: March 1, 2004