The Hidden Power of Photoshop CS: Chapter 2: Color Separations. Pt. 1. By Sybex | 4
The Hidden Power of Photoshop CS: Chapter 2: Color Separations. Pt. 1
Adding Color to the RGB Separation
At this point in the example, you have filtered out the color channels. To complete the process and add back the color, you can clean up the template layers you won’t need anymore, and then use the Color Red, Color Green, and Color Blue layers to re-color the image, as we did in Chapter 1. Follow these steps:
1. Throw out the Source and Hue Adjustment Template layers by dragging them to the Trash icon at the bottom of the Layers palette.
2. Change the mode of the Red, Green, and Blue layers to Screen. When you are done, leave the Red layer active.
3. Move the Color Red layer above the Red layer; then group them by pressing z/Ctrl+G.
4. Move the Color Green layer above the Green layer; then group them.
5. Move the Color Blue layer above the Blue layer; then group them. The layers should look like they do in Figure 2.8.
Figure 2.8 The image will be re-created in full color, in essence, projected as light onto the black background screen.
Can you accomplish this in other ways? Sure. You can copy the channels into layers and apply fill color to accomplish the same result. But what’s pretty interesting is that the result is exactly the same. This process should show light theory applied to make your separation into RGB. The Split RGB action provided with the Hidden Power Tools on the CD executes the steps just described.
That may seem like a lot of work, so what does it get you? Flexibility. Now you can use channels and control them using layer properties in a way that is more intuitive than working with them in separate palettes. This approach offers many opportunities for color and tone correction and conversion based on additive light theory.
Earlier we were looking at some simple conversions of the pumpkin into grayscale. Open the Pumpkin.psd image again and run the Split RGB action. If you look at the separations as grayscale (to do this, shut off all the layer views except the channel you want to view), the green channel will be most like the tone as you might expect it to look in a black-and-white image. Red tends to look more like infrared and the blue like ultraviolet. Green, being closer to the center of the range of visible light, often looks most like you expect tone, but matching this up to a luminosity or brightness extraction will often reveal some pretty steep differences.
This look at extracting the RGB tone is all well and good, but it tells only part of the story. Another advantage of the separation to gray components is that you can also mix the channels using layer properties to achieve still other results. How you choose the
combinations depends on the image. Having the channels as separate layers allows you to enhance and customize the conversions. Your choice may be based on theory or experimentation.
For example, going back to the kushbeggi.psd image you just finished separating,
shut off the color fill layers, and change the settings for the Blue, Green, and Red layers as follows:
• Blue layer: Opacity: 100%; Mode: Normal
• Green layer: Opacity: 30%; Mode: Normal (this blends in 30 percent of the Green layer)
• Red layer: Opacity: 30%; Mode: Normal (this will blend back 30 percent of the Red layer)
This is yet another representation of the black-and-white conversion. Now try this: Activate the Green layer, set the opacity to 0%, click in the Opacity field on the Layers palette, hold down the Shift key, press the Up arrow on the keyboard. Press the Up arrow again. This will increase the opacity of the Green layer in increments of 10 percent. Keep doing this while watching what is happening on screen—and take snapshots when the opacity of the Green layer is at 30, 60, and 90 percent. Then click the snapshots in turn to view the differences. Each should have its own interest and appeal—though each is a very different result based on the tone of the image. See Figure 2.9.
If you see how easily different tone separations can be combined, the possibilities move exponentially from here. For example, you can mimic infrared effects by manipulating channels and how they go together:
1. Open the sheep.psd image from the CD.
2. Duplicate the background and name the new layer Color Shift.
3. Create a Hue/Saturation adjustment layer, and load Infrared.ahu from the Extras folder (or enter the Hue/Saturation values shown in Figure 2.10).
4. Group the Hue/Saturation adjustment layer and the Color Shift layers. Set the layer mode of the Hue/Saturation adjustment layer to Color, then merge the Hue/Saturation layer with the Color Shift layer. This targets the change to the color only.
Figure 2.9 These two series show examples of mixing channel tone in layers to get different grayscale results.
5. Change the Advanced Blending Channel of the Color Shift layer to R (shut off the G and B Channels checkboxes in the Layer Styles dialog box) to keep the change targeted to the color. Change the Mode to Color and then use Gaussian Blur to soften the color a little (say 5 pixel radius).
6. Flatten the image and play the Split RGB No Stops action.
7. Shut off the view for the Red layer and the Green layer, and throw out the Color layers (Color Red, Color Blue, and Color Green) by dragging them to the trash.
8. Hold down the z/Ctrl key and click the blue channel in the Channels palette (any of the channels will actually do). This loads the light portion of the blue channel as a selection.
Figure 2.10 Loading the Hue/Saturation setting makes an adjustment to shift cyans, greens and yellows toward red. Look at the preview bar at the bottom of the palette to see the effect. It should show yellow, green, and cyan (upper bar) shifting toward red (lower bar).
9. Duplicate the background, name it Blue Mask, and move it above the Red layer.
This will be used in the next steps to create a mask to darken blues in the image.
10. Invert the selection created in step 8 (press z/Ctrl+Shift+I). This makes a selection
of the dark portion of the original blue channel.
11. Delete the selected area (press Backspace/Delete), and change the layer mode to Multiply. This leaves the more intensely blue areas of the shifted color by removing the dark areas of the blue channel.
12. Duplicate the Red layer, change the mode to Normal, name it Black Blues, and drag it above the Blue Mask layer.
13. Group the Black Blues and Blue Mask layers. This uses the red content masked by the blue to darken bluer areas of the image; this targets the darkening to areas which are not red or bright but have strong blue components.
14. Duplicate the Red layer, name it Infrared Glow, and drag it to the top of the layer stack.
15. Hold the z/Ctrl key and click the red channel in the Channels palette (again, any of the channels will do).
16. Invert the selection and delete. This will leave just the highlights.
17. Deselect (press z/Ctrl+D), then blur using Gaussian Blur (3–10 pixels). Set the mode to Screen.
18. Turn on the view for the Red layer.
Figure 2.11 A more traditional conversion using Luminosity is shown here in comparison to a more radical mock infrared conversion.
The result of these steps mimics a type of infrared black-and-white. Since infrared film (properly filtered) is sensitive to red and infrared light, the idea of the conversion is to play up the red response of the capture, while choking the blue image area (steps 4–8), and adding a characteristic infrared glow in bright spots (steps 9–12). Steps 2–5 shift the gamut of yellows, greens, and cyan toward the red spectrum in an attempt to mimic infrared’s tendency to make foliage glow. As you can see in Figure 2.11, the effect is noticeably different from a conversion based on Luminosity.
There are other means of improving the result (such as adding film grain), ways to accomplish similar results, and ways to mimic other specific film types according to their response (different black-and-white or infrared films). While this mock infrared will never be exactly like real infrared (infrared light is not stored separately on color film or in RGB images, after all), this should give you an idea of how far you might take conversions. I have included an Infrared action with the Hidden Power Tools so you can experiment with, and re-create, this series of steps.
This type of mixing of channels is what happens (to a lesser degree) when you use the Channel Mixer function. The Channel Mixer can help you achieve similar results, but using the tool will not allow you the same flexibility you achieve working with the results as layers, where you are afforded the luxury of modes, opacities, and selective custom (rather than channel-based) masking.
When scanning color images to turn them to black-and-white, you may be tempted
to scan to grayscale. This offers only one possible grayscale result. Pouring through these options—both simple and complex—it should becomes obvious that there may often be good reason to consider scanning images that you plan to use in grayscale as RGB first. This will allow you some additional freedom to experiment to get the best black-and-white result.
As we’ve seen, extracting image tone from color can be complex, and can be much more of an art than science. Considering that tone is the basis of digital color representation, the complexity of your digital images increases exponentially when you’re working with color. To achieve a result, you need to have control over two, three, or more color components in your image to represent the color, and you need to be able to balance the color and tone. Let’s now look at how the complexity builds by adding color to tone.
Created: March 27, 2003
Revised: March 1, 2004
URL: URL: http://webreference.com/graphics/ps1/1