BASIC PRINTING INFORMATION

Color Charts & CMYK

 The color system that describes how to combine ink pigments to make colors on a printed page is called CMYK (Cyan-Magenta-Yellow-blacK), this color system starts with white where all light is reflected back from the white paper stock. Printers develop a final color on the page by subtracting color from the reflected light back to your eye. With the color black, the three colors Cyan-Magenta-Yellow make a muddy brown, so blacK is used to make a distinctive black.

            CMYK Color Model                                               RGB Color Model
         
        Subtractive color model                                 Additive color model
          For printed material                                   For computer displays
       Uses ink to display color                             Uses light to display color
 Colors result from reflected light                  Colors result from transmitted light
   Cyan+Magenta+Yellow=Black                          Red+Green+Blue=White                                         

Notice the centers of the two color charts. In the RGB model, the convergence of the three primary additive colors produces white. In the CMYK model, the convergence of the three primary subtractive colors produces black.

In the RGB model notice that the overlapping of additive colors (red, green and blue) results in subtractive colors (cyan, magenta and yellow). In the CMYK model notice that the overlapping of subtractive colors (cyan, magenta and yellow) results in additive colors (red, green and blue).

Also notice that the colors in the RGB model are much brighter than the colors in the CMYK model. It is possible to attain a much larger percentage of the visible spectrum with the RGB model. That is because the RGB model uses transmitted light while the CMYK model uses reflected light. The muted appearance of the CMYK model demonstrates the limitation of printing inks and the nature of reflected light. The colors in this chart appear muted because they are displayed within their printable gamut (see below).

RGB Color

The RGB model forms its gamut from the primary additive colors of red, green and blue. When red, green and blue light is combined it forms white. Computers generally display RGB using 24-bit color. In the 24-bit RGB color model there are 256 variations for each of the additive colors of red, green and blue. Therefore there are 16,777,216 possible colors (256 reds x 256 greens x 256 blues) in the 24-bit RGB color model.

In the RGB color model, colors are represented by varying intensities of red, green and blue light. The intensity of each of the red, green and blue components are represented on a scale from 0 to 255 with 0 being the least intensity (no light emitted) to 255 (maximum intensity). For example in the above RGB chart the magenta color would be R=255 G=0 B=255. Black would be R=0 G=0 B=0 (a total absence of light).

 CMYK or "Process Color"

The CMYK printing method is also known as "four-color process" or simply "process" color. All of the colors in the printable portion of the color spectrum can be achieved by overlapping "tints" of cyan, magenta, yellow and black inks. A tint is a screen of tiny dots appearing as a percentage of a solid color. When various tints of the four colors are printed in overlapping patterns it gives the illusion of continuous tones - like a photograph:

The CMYK model forms its gamut from the primary subtractive colors of cyan, magenta and yellow. When cyan, magenta and yellow inks are combined it forms black - in theory. However, because of the impurities in ink, when cyan, magenta and yellow inks are combined it produces a muddy brown color. Black ink is added to this system to compensate for these impurities.

In the CMYK color model, colors are represented as percentages of cyan, magenta, yellow and black. For example in the above CMYK chart the red color is composed of 14% cyan, 100% magenta, 99% yellow and 3% black. White would be 0% cyan, 0% magenta, 0% yellow and 0% black (a total absence of ink on white paper).

Use RGB For Screen Displays and CMYK For Print

It is important to choose the right color model for the job. If your images will be printed, then convert them to CMYK and manually bring them into gamut before printing. If your images are to be displayed on a computer, then make sure you use RGB color so the full gamut will be available for display. Because both models can be available at the same time while using an application, it is easy to make a mistake and choose the wrong palette or set of color swatches.

Additive vs. Subtractive Color Models

Since additive color models display color as a result of light being transmitted (added) the total absence of light would be perceived as black. Subtractive color models display color as a result of light being absorbed (subtracted) by the printing inks. As more ink is added, less and less light is reflected. Where there is a total absence of ink the resulting light being reflected (from a white surface) would be perceived as white.

Color Gamut and Color "Space"

Each color model has is own gamut (range) of colors that can be displayed or printed. Each color model is limited to only a portion of the visible spectrum. Since a color model has a particular range of available color or gamut, it is referred to as using a "color space". An image or vector graphic is said to use either the RGB color space or the CMYK color space (or the color space of another color model). Some graphic applications present the user with more than one color model for image editing or illustration and it is important to choose the right one for the task. The whole point of this article is to explain the difference between the two color models so you choose the right one for the job. For you work to display at its best, choosing the right color model is critical.

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