Additive Color

Color reproduction on the computer monitor (and on television) is achieved by combining Red, Green, and Blue light (RGB) in varying levels to produce a full color image. Red, green, and blue are the primary colors of white light and they cannot be produced by the combination of any other colors. When they are combined full strength, they will produce white light. The combining of red, blue and green colors is known as the "Additive Color Process", because when the colors of light are combined with one another, or added together, the result is an increase in light intensity. If none of the additive primaries are present, the color is perceived as black.
When two primary colors of light are combined, a secondary color is produced. The secondary colors of light are Cyan, Magenta, and Yellow (CMY). The secondary light colors are also the primary colors of the "Subtractive Color Process". The process of combining cyan, magenta and yellow colors is used to reproduce color for printed media

Color Gamut
The color gamut refers to the range of colors that can be viewed, displayed, or printed. The items in the list below are arranged from the greatest to the least in terms of the range of colors that each is able to reproduce:

• Human Eye
• Photographic Film
• Television or Computer Monitor
• Digital
• Printing Equipment
• Offset Printing

Defining Color
The following are the properties that are used to define color:

• Hue: is used to describe the name of a color such as red, orange, violet, or blue.
• Value: describes the lightness or darkness of the color. Value is also known as tone, tone value, or lightness.
• Saturation: describes the intensity of the color such as bright or dull. Saturation is also known as intensity or chroma. It is important to remember that a color that has a very intense or bright level of saturation may not necessarily be very light in value just as a very dull color may not necessarily be very dark in tone or value.

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Color

Color Conversion
The color gamut of RGB is broader than CMYK and the file size is smaller as well, but CMYK is the better choice for documents that will be used on the Web and for print. CMYK documents work well enough in the RGB environment, but RGB doesn't work as well in the CMYK environment.

Trapping
Trapping can help compensate for registration problems by slightly expanding one color into another and eliminating the gaps and color shifts between colors. PDF stores the trapping instructions in such a way that the trapped images will look the same on any computer and also when the images are output.

For trapping to be effective, it must compensate for less than perfect registration without forming noticeable lines of unrelated color around objects caused by the overprint. Process colors that share a sufficient percentage of common colors do not require trapping, because any registration problems will reveal a color that is similar to each of the adjacent colors. An example of where trapping would not be necessary would be a printed item containing mostly reds and oranges. If the object on such a page were not in perfect register, the result would not be visually distracting because the colors in the gaps and overprinted areas would be similar to any adjacent colors.

The sequence in which the process colors are printed also influences ink trapping. For standard four color printing, the correct sequence to print the process colors are black, cyan, magenta, and finally yellow. Printing in the correct sequence will help ensure the best results. A change in the standard sequence will result in a change in the ink trapping characteristics.

Color Management
Device color spaces refer to the color space of the input device such as a scanner and the color space of the output device such as a printer. Data that is scanned may not display the same colors on a monitor and a printer, so a color management system is necessary. There are many differences between color profiles, so there is no guarantee that colors will be consistent throughout the workflow.

The ICC (International Color Consortium) was developed to set standards for device independent color. ICC profiles are electronic files that describe all of the color characteristics of a device. They can be either generic for a certain device such as a scanner or a monitor or they can be customized with profile generation tools. Color profiles are important because the color spaces of devices such as scanners, monitors, printers, presses, and digital cameras vary greatly.

PDF is able to support objects that are specified in different device dependent, device independent, or special color spaces. Acrobat supports Adobe Color Engine (ACE) and ICC Color Management that are in Photoshop and Illustrator. Displaying and printing color documents is more consistent. InDesign does not support this.

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Spot Color

The colors used on spot color proofs are also known as "matched" colors, special colors, or by one of the brand names "Pantone" or "PMS" colors. Spot colors are printed from a single ink on a separate printing unit of the press. Spot colors can be standard, pastel, fluorescent or metallic colors. Several colors can be printed in select areas to create two, three or more color jobs. Spot colors can be used on may types of jobs, such as business cards, letterheads, forms, brochures and direct mail pieces.

There are several variables involved with spot colors. A few manufacturers create color guides such as binders, chips, and fan books to show the spot colors and the equivalent process colors. It is important to realize that the color guides fade over time and the paper may change colors so check the date of your guide and replace it periodically.

When you choose the spot color on the monitor, remember that it is simulated in RGB, and not as the spot color or CMYK. Be sure to tear off a chip from the guide and include it with the job.

Remember that if you are trying to match a spot color with process colors, very few colors will match. Many spot colors are outside of the color gamut of process inks. The paper stock that is used for the job will also provide different results than expected. The use of varnishes or coatings can also change the appearance of the color.

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