Watkins Printing - Support: Process and Spot Color

Watkins Printing
110 West 1200 South
Logan, Utah 84321

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Process and Spot Color

Color Models and Gamuts

There are two basic ways to reproduce color. Additive and subtractive.
The additive system uses light emitted from a source, before it is reflected by any object. Light of a specific color can be produced by directing white light through filters. To reproduce the spectrum of colors using the additive system, the three primary additive colors are used: red, green and blue. By mixing these in various amounts, the secondary additive colors can be produced: cyan, magenta and yellow. Television screens and computer monitors employ additive color methods. The more light added, the brighter the overall color, with white as a peak value.
The subtractive system uses colorants such as pigment or dye and an object that reflects light; the paper surface in printing for example. Light of specific colors is absorbed by pigmentation and ink, and the resulting apparent color is that which is reflected (not absorbed). To reproduce the spectrum of colors using the subtractive system on a printing press, the three primary subtractive colors are used: cyan, magenta and yellow. In theory, overprinting cyan, magenta and yellow absorbs all portions of white light to produce black, however in reality a muddy brown is produced. Therefore a fourth ink, black (designated 'K' to avoid confusion with blue 'B'), is added to both accomodate for impurities in inks, and add depth to shadow areas and enhance detail in images. Mixing these colors in varying amounts produces the secondary subtractive colors red, green and blue. The more ink or pigment added, the darker the overall color, with black as a peak value.
No color reproduction system can reproduce the entire range of colors we see in nature. Each system has its limitations or range of colors it can produce. This is called gamut. The gamut of colors that photographic film can reproduce is greater than the gamut of colors that can be reproduced with process color on a printing press. The gamut of computer monitors contains not only more, but different colors than that of either film or process color.

Human eye: billions of colors

Computer monitor: 16 million

Photographic film: 10-15 thousand

Process color (CMYK): 5-6 thousand

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Ink Selection

Spot colors are reproduced using pre-mixed inks, while process colors are reproduced with cyan, magenta, yellow, and black inks. Spot colors have a vast library of colors to select from, but require a complete separation and pass through a press to print. While spot inks are nearly opaque, process inks are translucent. This allows mixing of process inks to produce a variety of colors, while spot colors are mostly intended to stand alone.
Use spot colors when

You need three or fewer colors;

You will not be printing photographs in full color;

You want to print special colors using inks such as varnishes, metallics, fluorescents, or pearlescents;

You need to print logos or other elements that require precise color matching.

Use process colors when

You need more than three colors;

You want to print full color photographs.

Use spot and process combined when

You need both full color photographs and precise color matching of graphic elements;

You require more colors than available by four-color process alone.

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Halftones

Photographs are continuous tone or have solid colors continuously. Printing ink, black for example, is always black. It is not possible to print various shades of black using solid ink without making a halftone.* A halftone is a series of dots of various size to simulate the effect of darker and lighter areas. Smaller halftone dots make up lighter areas of an image while larger halftone dots make up dark areas. Halftones are created when printing separations to film or even composite proofs to a laser printer. If you examine a 'gray' area closely, you will find that it is made up of a series of small black dots.
* FM or stochastic screening is a method of printing various shades by adjusting the distance between dots rather than the size of dots, which technically is not a halftone.

Process color halftones are made of four separations, or plates, that represent the four process colors. Each is printed at a different angle to avoid unwanted moirè patterns.

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Trapping

To print a piece as it was designed, each ink must be printed in register--or exactly aligned with one another. If one or more inks prints out of registration, visible white gaps or unwanted colors may appear. To compensate, trapping was developed to slightly overprint common edges of inks to minimize the visual impact of slightly misregistered pages.

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