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Figure 17-13: Comparing the before (top row) and after (bottom row) of a +120-degree Hue shift, youll see that the red and green channels are identical, as are the green and blue channels and the blue and red channels.Note
As long as you select only the Master option and edit only the Hue value, Photoshop retains all colors in an image. In other words, after shifting the hues in an image +60 degrees, you can later choose Hue/Saturation and shift the hues 60 degrees to restore the original colors.Changing saturation levels When I was a little kid, I loved watching my grandmothers television because she kept the Color knob cranked at all times. The images leapt off the screen, like they were radioactive or something. Way cool. Well, the Saturation option works just like that Color knob. I dont recommend that you follow my grandmothers example and send the saturation through the roof for every image, but the option can prove helpful for enhancing or downplaying the colors in an image. If the image looks washed out, try adding saturation; if colors leap off the screen so that everybody in the image looks like theyre wearing neon makeup, subtract saturation.Note
Just as the Saturation option works like the Color knob on a TV set, the Hue value serves the same purpose as the Tint knob, and the Lightness value works like the Brightness knob. So you see, your mother was quite mistaken when she told you that sitting on your butt and staring at the TV wasnt
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Part V: Color and Output
going to teach you anything. Little did she know, you were getting a head start on electronic art. Figure 17-14 shows the same +120-degree Hue shift with Saturation values of 20 percent (top row) and 60 percent (bottom row). As you can see, increasing the Saturation has the effect of heightening the contrast of the color channels. The middle-left example of Color Plate 17-3 shows a Saturation
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value of 40 percent.
Figure 17-14: The difference between a Saturation increase of 20 percent (top row) and 60 percent (bottom row) on a channel-by-channel basis.
Now that we have some idea of how the Hue and Saturation parameters work, lets try applying them to the practical goal of trying to give my Little Puppet Friend a slightly rosier glow. The first thing you need to know is that if you adjust the Hues of an image with any Edit option other than Master, the musical chairs metaphor mentioned earlier breaks down a little. All pixels that correspond to the selected color range move while pixels outside the color range remain seated. The pixels that move must sit on the non-moving pixels laps, meaning that you sacrifice colors in the image.
For example, in the middle-right image of Color Plate 17-3, I switched the Edit menu from Master to Cyans and then performed my Hue shift and Saturation increase, and then repeated this with Edit set to Blues. All pixels that fell in the cyan and blue ranges shifted to new hues; all non-cyan and non-blue pixels remained unchanged. Although the effect is subtle, my Little Puppet Friend does appear a little rosier than in the upper-left image. Then again, so do the blues in my shirt.
The Saturation option is especially useful for toning down images captured with lowend scanners and digital cameras, which have a tendency to exaggerate certain colors. Back in the early years, I used to work with an Epson scanner that would digitize flesh tones in varieties of vivid oranges and red. For the life of me, I couldnt figure out how to peel the colors off the ceiling until I tried the Saturation option in the Hue/Saturation dialog box. By selecting the Red color range and dragging the slider down to about 50, I was usually able to eliminate the problem, and so can you.Correcting out-of-gamut colors Another common use for the Saturation option is to prepare RGB images for process- color printing.
As I explained in Chapter 4, many colors in the RGB spectrum are considered out-of-gamut, meaning that they fall outside the smaller CMYK color space. Photoshop provides a means for recognizing such colors while remaining inside the RGB color space. Choose View® Gamut Warning or press Ctrl+Shift+Y(z -Shift-Y on the Mac) to color all out-of-gamut colors with gray (or some other color that you specify using the Preferences command). The pixels dont actually change to gray; they just appear gray on-screen as long as the command is active. To turn View® Gamut Warning off, choose the command again.
How do you eliminate such problem colors? Well, you have three options:
Let Photoshop take care of the problem automatically when you convert the image by choosing Image® Mode® CMYK Color. This tactic is risky because Photoshop simply cuts off colors outside the
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575 Photoshop CS Bible @Team LiB
gamut and converts them to their nearest CMYK equivalents. What was once an abundant range of differently saturated hues becomes abruptly flattened, like some kind of cruel buzz haircut. Choosing View® Proof Setup® Working CMYK gives you an idea of how dramatic the buzz can be while permitting you to continue working in the RGB color space. Sometimes the effect is hardly noticeable, in which case no additional attention may be warranted. Other times, the results are disastrous. Another method is to scrub away with the sponge tool. In Chapter 5, I discussed how much I dislike this alternative, and despite the passage of a dozen chapters, I havent changed my mind. Although it theoretically offers selective control you just scrub at areas that need attention until the gray pixels created by the Gamut Warning command disappear the process leaves too much to chance and frequently does more damage than simply choosing Image® Mode® CMYK Color.