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Chapter 18. Managing Color from Monitort... > Changing from Additive (RGB) to Subt...

Changing from Additive (RGB) to Subtractive (CMYK) Color

RGB (red, green, blue) is defined as an additive color space. RGB is the color space of computer monitors, televisions, and most PDA's and cell phones with built-in color screens. A monitor uses pixels (small square or rectangular bricks), and each pixel mixes a combination of red, green, and blue to project (additive) a specific color to your eyes. Pixels use (on average) 24 switches to hold color information, and can produce 1 of 16,777,216 separate colors. CMYK (cyan, magenta, yellow, black) is defined as a subtractive color space. CMYK is the color space of high-end inkjet, laser, and professional presses. A press uses plates that define each of the 4 colors; as a piece of paper passes through the press, the colors are applied from each plate. The term subtractive comes from the fact that a piece of paper requires a light source to bounce off the paper, and reflect back up to your eyes. Since a press cannot generate the intense saturation of an electronic pixel, the number of possible colors is reduced into the thousands. However, when used correctly, you can produce some stunning results. It's a simple matter to convert a Photoshop document into the CMYK mode; however, good planning will ensure the colors you want will be the color you get.

Change from RGB to CMYK Color

Open a document.

IMPORTANT You cannot convert a Bitmap or Multi-channel document directly into CMYK mode. Convert a Bitmap image to Grayscale, and then to CMYK; convert a Multi-channel to RGB, and then to CMYK.

Click the Image menu, point to Mode, and then click CMYK.

Photoshop converts the RGB image into CMYK.

If the RGB colors are not supported by the CMYK color space, they will be converted into the closest subtractive color values.



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