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Printing Color Models in Desktop Publishing

There are two basic models used in DTP (Desk Top Publishing) software for specifying color. They are called spot color and process color. Spot color is a way of specifying that one or more pre-mixed ink colors be used on a printed piece. Each spot color is a different ink on the press. Process color is a special process used to create a wide variety of colors with only four standard inks: cyan, magenta, yellow, and black (commonly called CMYK.) Not all colors can be reproduced using process colors. Many colors such as metallic colors have no process equivalent. This is why spot colors are often added to a design even when the job requires four color process inks for color photos.

The process and spot color models arise from the two basic methods of creating colors on a printing press. When a press operator is preparing the press for a press run, he or she loads the rollers on the press with ink. Each roller assembly is loaded with a different color. As each piece of paper is fed through the press, it passes through each of the roller assemblies and is imprinted with each color in succession. Usually, one of the inks is black.

Often, one or more spot colors are added to enhance the design. If a color photo is used, then four of the roller assemblies are loaded with the colors cyan, magenta, yellow, and black. These four process ink colors are printed on top of each other in varying amounts to create all the possible process colors. Printing inks are typically semi-transparent so that overlaying colors result in a third color. For example, cyan and yellow will produce green, magenta and yellow produce red. By using spot color inks and the four basic process component inks, a press operator can reproduce designs that range from simple black only jobs to full color reproductions. Understanding how colors are put down by the presses is important for understanding how color works in your designs and how to correctly specify colors, whether spot or process, in your DTP software.

Spot Colors

Spot colors are simply colored inks. The range of ink colors available and means for specifying these inks depends on the color system used by your printer. Printing Services uses the Pantone color system. There are over a thousand colors available in the Pantone color system. Each color is specified with a label which usually takes the form:

PANTONE xxxx CVC

The xxxx is usually a number in the hundreds but can be in the thousands. A Pantone color can also have a label like PANTONE Reflex Blue CVC. All designers should definitely have a current version of a PANTONE MATCHING SYSTEM color guide. These are the best way to see what the ink you choose is going to look like once it is printed; choosing the color by its appearance on your computer screen is unreliable and inaccurate.

Process Colors

Unlike Spot colors, which use a different pre-mixed ink for each printed color, Process color is a system of using four standard inks and mixing them on the press to create a wide spectrum of different colors. The inks used are Cyan, Magenta, Yellow, and Black (CMYK.) One of the most common uses for process color is for color photograph reproduction. The color images are broken down by software into their CMYK components, and each component layer is imaged to a separate piece of film. When the CMYK plates are printed on top of each other, the color photo reappears in full color. Pantone colors can also be built out of process colors. For example, your job may call for four color process and one spot color. It may turn out that the spot color is easily reproducible with process colors. You could save some money if you designed your piece using four color process builds for everything instead of adding a fifth color. Please discuss these issues with a CSR and decide on your color scheme before you spend a lot of time creating the electronic files.

Their are several limitations on what can be simulated with process colors. Many Pantone colors are simply not reproducible with process colors. Since process colors use Cyan, Magenta, Yellow, and Black to create the other colors, you can imagine you would have more success simulating colors that are close to one of these colors to start with. Cyan and Magenta make a dark purple, Magenta and Yellow make a red, Cyan and Yellow make a green. But these builds tend to be very dark, and a little dull.

Confusing Spot and Process Colors

Since each spot color results in a different piece of film when the job is sent to the image setter, it is critical that the colors be specified correctly in all your software packages and graphics. One common mistake is to confuse spot color definitions and process color definitions. You have to explicitly tell the software one way or the other. People often just go into the color definition window and make a new color without considering whether it is a spot or process, and the result is the color is set to whatever the default for the software was. Your odds are not good for ending up with the correct default; less than 50:50 since there are often more choices available.

Tints

Besides specifying a spot or process color, you can also make an object’s line or fill a tint of some other color, either spot or process. Tints are expressed in percentages from 0 to 100. A 50% tint of PANTONE 128 CVC will produce a 50% halftone screen for that ink in the specified areas.

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