Adobe 65023809 Printing Guide - Page 61

Color Gamuts A comparison of AdobeRGB (red line), ProPhotoRGB (blue line) and CMYK (dotted line) gamuts to the range of visible light (color shape). RGB The native color mode of images from scanners and digital cameras is RGB (red-green-blue). As humans, we also "think" in RGB, because the color receptors in our eyes process red, green, and blue light to create our view of the world. The gamut of RGB light is somewhat larger than the range of colors that can be printed with CMYK process inks, which is why some vibrant colors in RGB images displayed on a monitor lose richness when printed. This may require some explanation to customers who are disappointed when comparing a printed piece to what they see on their monitor. There are advantages to the large color gamut available in the RGB color mode; if your workflow supports it, keep images in the RGB color mode as long as possible to avoid premature loss of color data. Some color corrections are easier in RGB (such as setting neutral points) and many Photoshop filters do not work in CMYK. CMYK If you prefer to receive CMYK images, but your customer has supplied images in another color space, such as RGB or Lab, you must decide whether to convert the images to CMYK yourself, or rely on the color-conversion function of your RIP. In-RIP color conversions from many vendors are more predictable than in the past, but if you prefer to make your own conversions, it's important to know how to control the conversion to CMYK in Photoshop. When converting between color modes, Photoshop uses the color settings currently in effect. If you have a custom profile for the intended target (such as your press), you should choose that in your color settings. If you prefer to receive CMYK images from your customers, supply them with your preferred settings to ensure that they send images that are appropriate for your workflow. Special case: Screen captures Screen captures benefit from special handling when converting from RGB to CMYK. Create a special Gray Component Replacement (GCR) separation setup that generates a maximum black, replacing all four-color grays and blacks with shades of process black. This prevents small black text (and the gray backgrounds commonly found in software screens) from becoming a fourcolor black, thus minimizing blurring or color casts on press. To create the custom separation setup: 1. Choose Edit > Color Settings. 2. In the Working Spaces area of the dialog box, choose Custom CMYK from the CMYK pop-up menu. 3. In the Custom CMYK dialog box, choose GCR for the Separation Type. 4. For Black Generation, choose Maximum from the pop-up menu. Look closely at the Gray Ramp diagram; wherever the image contains equal levels of red, green and blue (which constitutes a neutral gray in RGB images), those areas will be replaced with shades of black, with no cyan, magenta, or yellow ink in those areas. 5. Type a name for the custom CMYK separation recipe (or accept the name that Photoshop generates for you), and click OK. This returns you to the Color Settings dialog box. Adobe Creative Suite 4 Printing Guide 59