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Working with Color in Photoshop

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This sample chapter teaches additive and subtractive color correction with image variations and color balance, global color correction with Levels and Curves, selective and interchannel color correction, and correcting color temperature problems.
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We are very sensitive to color, and our eyes are tremendous tools to see and compare color. The emotional and subliminal importance of color in our world cannot be denied. For retouchers, being sensitive to color values can make the difference between a so-so print and a print that looks as vibrant as the memories it represents.

The importance of color challenges us to work with our visual memory in combination with the best that Photoshop has to offer: Adjustment Layers, the Info palette, the Histogram dialog box, painting and selection tools, and Blending Modes. In this chapter, you work with color images to learn

  • Additive and subtractive color correction with image variations and color balance

  • Global color correction with Levels and Curves

  • Selective and interchannel color correction

  • Correcting color temperature problems

Many of the tools and techniques used to improve tone, contrast, and exposure discussed in Chapters 2, "Improving Tone and Contrast," and 3, "Exposure Correction," serve as the foundation for working with color. I highly recommend that you review those two chapters before diving into the wonderful world of color.

Color Essentials

There are two types of color in the world: additive and subtractive. In the additive world, a light source is needed to create color. When the primary colors (red, green, and blue) are combined, they create white, as shown in figure 4.1. You monitor is an example of additive light.

In the subtractive world, color is determined by the absorption of light. When the secondary colors—cyan, magenta, and yellow—are combined, they create black-brown, as shown in figure 4.2. Printing ink on paper is an example of subtractive color. In creating inks for print, impurities in the pigments result in a muddy black-brown when cyan, magenta, and yellow are combined. To achieve rich shadows and pure blacks, black is added to the printing process, which also cuts down on the amount of the more expensive color inks used.

Figure 4.1 The additive color space is formed by the red, green, and blue primary colors.

Figure 4.1

Figure 4.2Figure 4.2 The subtractive color space is formed by the cyan, yellow, and magenta primary colors.

Combining additive primaries yields the subtractive primaries, and combining the subtractive primaries creates the additive primaries. For the retoucher, understanding this opposite relationship can be very useful when identifying and correcting color problems. For example, if an image is too blue, you have two ways to approach the problem: either increase yellow (which is the opposite of blue to neutralize blue) or decrease the blue in the image. Both yield the same result: an image with less blue.

In digital imaging, the four most prevalent color modes are RGB, CMYK, Lab, and HSB:

  • RGB is the additive color space that monitors, scanners, digital cameras, and color slide film originals work or exist in. The advantages to color correcting and retouching in RGB include these: smaller file sizes; equal values of red, green, and blue will always result in a neutral color; and a larger RGB color space allows the file to be converted into multiple gamuts and repurposed for multiple final output destinations.

  • CMYK (cyan, magenta, yellow, and black) is the subtractive color mode. Many people (especially people with prepress or printing experience) prefer doing color correction and retouching in CMYK because they are more comfortable with CMYK color values, and editing colors that are in the same gamut as your printer can help avoid unhappy surprises after the ink hits the paper.

  • Lab is a three-channel color mode in which the black and white L (luminosity) channel information has been separated from the color information. The "a" channel carries red to green, and the "b" channel carries blue to yellow information, and it can range from +128 to –128. Lab is a device-independent color space used by color management software and by Photoshop when converting RGB files to CMYK. Color correcting in Lab is a delicate task, because the slightest move on the "a" or "b" channels can result in a very strong color shift. On the other hand, Lab is a useful color mode when you are adjusting exposure or cleaning up color artifacts from digital camera files, as discussed in Chapter 5, "Dust, Mold, and Texture Removal."

  • HSB stands for hue, saturation, and brightness. Hue refers to the color, brightness refers to the amount of light in the color, and saturation determines the amount of color. You can take advantage of HSB to emphasize or de-emphasize color in portrait retouching, as shown in Chapter 10, "Glamour and Fashion Retouching."

Each color mode has numerous pros and cons, all of which have been described in detail in Real World Photoshop by David Blatner and Bruce Fraser (Peachpit, 2002), Professional Photoshop by Dan Margulis (Wiley, 2002), and Photoshop Color Correction by Michael Kieran (Peachpit, 2002). Rather than reworking information that is well explained by these digital maestros, I propose we learn how to identify and correct colorcasts in antique and contemporary photographs.

Are All Color Casts Evil?

There are only two types of color casts in the world: those that accentuate the image and those that detract from the image. Positive color casts include the golden tones of the early morning or the cool blue cast on a late winter afternoon (see figure 4.3), the warm color created by candlelight, and the color tones created when the photographer filters the lens or light to create or accentuate the color atmosphere. Undesired color casts occur if the photographer used the wrong color film to take a picture, the picture has faded over time, light has leaked into the camera, a scanner introduces a color cast, or an undesired color is being reflected into a photograph (as the blue carpet is doing to the fur of the white cat in figure 4.4).I'm sure you've seen pictures taken in a stadium or in an office in which the color temperature of the light doesn't match the color balance of the film used. The orange, red, or green color casts introduced by using the wrong color film or not compensating for the light temperature with photographic filters are both what I would categorize as undesired. Another example of an undesired color cast occurs when sunlight is filtered through green tree leaves and the people in the picture look slightly Martian-like.

Figure 4.3Figure 4.3 Taken on a late winter afternoon, the blue light striking the buildings in New York adds to the mood of the image.

Figure 4.4Figure 4.4 This is an example of an undesired color cast. The blue carpet the cat is laying is adding a blue tinge to the cat's white fur.

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