Adobe Photoshop CS5 : Managing Color from Monitor to Print - Changing from Additive (RGB) to Subtractive (CMYK) Color

RGB (Red, Green, and Blue) is defined as an additive color space, in which primary colors are added together to produce other colors. RGB is the color space of computer monitors, televisions, and most PDAs 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 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, and 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 the inks used in printing absorb or “subtract” a portion of the spectrum in order to produce other colors. 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 colors you get.

Change from RGB to CMYK Color

1. Open a document. Important You cannot convert a Bitmap or Multichannel document directly into CMYK mode. Convert a Bitmap image to Grayscale, and then to CMYK; convert a Multichannel to RGB, and then to CMYK.

2. 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.