Adobe 13101332 User Guide - Page 88

Adobe Photoshop Help Using Help | Contents | Index Working with Color Back 88 Although RGB is a standard color model, the exact range of colors represented can vary, depending on the application or display device. Photoshop's RGB mode varies according to the working space setting that you have specified in the Color Settings dialog box. (See "About working spaces" on page 106.) CMYK model The CMYK model is based on the light-absorbing quality of ink printed on paper. As white light strikes translucent inks, certain visible wavelengths are absorbed while others are reflected back to your eyes. In theory, pure cyan (C), magenta (M), and yellow (Y) pigments should combine to absorb all light and produce black. For this reason these colors are called subtractive colors. Because all printing inks contain some impurities, these three inks actually produce a muddy brown and must be combined with black (K) ink to produce a true black. (K is used instead of B to avoid confusion with blue.) Combining these inks to reproduce color is called four-color process printing. The subtractive (CMY) and additive (RGB) colors are complementary colors. Each pair of subtractive colors creates an additive color, and vice versa. Subtractive colors (CMYK) CMYK mode In Photoshop's CMYK mode, each pixel is assigned a percentage value for each of the process inks. The lightest (highlight) colors are assigned small percentages of process ink colors, the darker (shadow) colors higher percentages. For example, a bright red might contain 2% cyan, 93% magenta, 90% yellow, and 0% black. In CMYK images, pure white is generated when all four components have values of 0%. Use the CMYK mode when preparing an image to be printed using process colors. Converting an RGB image into CMYK creates a color separation. If you start with an RGB image, it's best to edit first and then convert to CMYK. In RGB mode, you can use the Proof Setup commands to simulate the effects of a CMYK conversion without changing the actual image data. (See "Soft-proofing colors" on page 113.) You can also use CMYK mode to work directly with CMYK images scanned or imported from high-end systems. Although CMYK is a standard color model, the exact range of colors represented can vary, depending on the press and printing conditions. Photoshop's CMYK mode varies according to the working space setting that you have specified in the Color Settings dialog box. (See "About working spaces" on page 106.) Using Help | Contents | Index Back 88