Color Theory Basics - Creating Black with CMY & K

In the color separation process the Black Printer is used to cover up impurities of the CMY inks. Theoretically when Yellow, Magenta & Cyan are added together they create Black. These col-ors of printed ink are supposed to subtract out all the white light on the paper and leave only black. Unfortunately in the real world it does not work this way.

Close examination of CMY printing inks, shows Cyan, Magenta and Yellow are impure or contaminated with other colors. This ink contamination makes it impossible to print a good black with these 3 ink colors.

The main purpose of black ink is to cover up the impurities of these three inks. The black plate adds back contrast to the color reproduction.

Color theory and its practical application

Original photographs or color images like transparencies or reflection art are comprised of continuous tones. To reproduce these continuous tone images they must be broken into tiny dots of different sizes by means of a halftone screen. The halftone screening system is a scheme that produces black and white positive or negative films with dots ranging between 0 to 100 percent. The purpose of the different CMYK halftone dots is to subtract white light and reproduce the neutral gray tones and hues of the original image.

In printing, knowing what size to make halftone dots in order to achieve the tones and hues of the original image is the main skill of reproducing a color image. When the color separa-tion process is properly achieved, that is, the dots are placed correctly in the reproduction, it causes the eye to perceive what the original looks like.

Color Spaces

Color is a perception, but scientific terms and mathematical models allow color to be defined and represented using terms like color spaces and color gamuts. Color spaces are represented in many ways, usually with combinations of three variables, such as:

• Red, Green, Blue - RGB
• Cyan, Magenta, Yellow – CMY
• CIE L* a* b*
• CIE L* c* h* 
• CIEXYZ

What is CIE color?

The Commission International de l’Eclairage or the CIE system defines a color model that provides a standardized mathematical approach for viewing color. It includes viewing and lighting schemes and attempts to describe color the way the human eye perceives it, with-out any color vision defects. That is, if two people are viewing and describing the same color they would identify it with the same numerical value and obtain a visual match.

The CIE system uses three values such as XYZ, RGB, or LAB to numerically identify and map out color gamuts of devices or images. The CIE system is universal and is capable of representing the many different types of color spaces. It is being used more in scanning, color separation programs, PostScript imaging environments and color management systems.

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