Adobe Creative Cloud All-in-One For Dummies. Christopher Smith

you don’t edit your images in the Index color mode, but you probably have saved a file in this mode. If you have ever saved a GIF file out of Photoshop, you have experienced working with Indexed color firsthand. Indexed Color mode (see Figure 2-7) uses a color lookup table (CLUT) to create the image from a limited palette of colors. In this example, the flower was set to reduce to 10 colors.

      FIGURE 2-7: Index color uses a limited number of colors to create an image.

      A CLUT contains all colors that make up an image, like a box of crayons used to create artwork. If you have a box of only eight crayons that are used to color an image, you have a CLUT of only eight colors. Of course, your image would look much better if you used the 64-count box of crayons with the sharpener on the back, but those additional colors also increase the size of the CLUT and the file size.

      The highest number of colors that can be in Indexed Color mode is 256. When saving web images, you often have to define a color table in order to keep a file size small. We discuss saving files for the web in Chapter 10 of this minibook.

      

If your image is not in Indexed color, choose Image⇒ Mode⇒ Indexed Color, then, choose Image ⇒ Mode ⇒ Color Table to see the color table making up an image.

      RGB

RGB (Red, Green, Blue) mode, shown in Figure 2-8, is the standard format you work in if you import images from a digital camera or import images from a copier or scanner. For complete access to Photoshop’s features, RGB is the best color mode to work in. If you’re working on images for use on the web, color copiers, desktop color printers, or onscreen presentations, stay in RGB mode.

If you’re having an image printed on a press (for example, if you’re having it professionally printed), it must be separated. Don’t convert images to CMYK mode until you’ve finished the color correction and you know that your color settings are accurate. A good print service may want the RGB file so that it can complete an accurate conversion.

      FIGURE 2-8: RGB creates the image from red, green, and blue.

      CMYK

      CMYK (Cyan, Magenta, Yellow, Black) mode is used for final separations for the press. Use a good magnifying glass to look closely at anything printed in color, and you may see the CMYK colors that created it. A typical four-color printing press has a plate for each color and runs the colors in the order of cyan, magenta, yellow, and then black.

      

Don’t take lightly the task of converting an image into this mode. You need to make decisions when you convert an image to CMYK, such as where to print the file and on which paper stock, so that the resulting image is the best it can be. Talk to your print provider for specifications that are important when converting to CMYK mode.

      LAB color

      The LAB (Lightness, A channel, and B channel) color mode is used by many high-end color professionals because of its wide color range. Using LAB, you can make adjustments to luminosity (lightness) without affecting color. In this mode, you can select and change an L (lightness or luminosity) channel without affecting the A channel (green and red) and the B channel (blue and yellow).

      LAB mode is also good to use if you’re in a color-managed environment and want to easily move from one color system to another with no loss of color.

      

Some professionals prefer to sharpen images in LAB mode because they can select just the Lightness channel and choose Filter ⇒ Sharpen ⇒ Unsharp Mask to sharpen only the gray matter of the image, leaving the color noise-free.

      Multichannel

      Multichannel is used for many things; you can end up in this mode and not know how you got there. Deleting a channel from an RGB, a CMYK, or a LAB image automatically converts the image to Multichannel mode. This mode supports multiple spot colors.

      Bit depth

      You have more functionality in 16-bit and even 32-bit mode. Depending on your needs, however, you may spend most of your time in 8-bit mode, which is more than likely all you need.

      Bit depth, or pixel depth or color depth, measures how much color information is available to display or print each pixel in an image. Greater bit depth means more available colors and more accurate color representation in the digital image. In Photoshop, this increase in accuracy also limits some available features, so don’t use it unless you have a specific request or need for it.

      To use 16-bit or 32-bit color mode, you also must have a source to provide you with that information, such as a scanner or camera that offers a choice to scan in either mode.