CMYK simply means cyan magenta yellow and black. These are the colors used to reproduce all colors on a printing press. Photoshop will use this color model when a product is going to be sent to a printer.
Colors that can be produced through cyan magenta yellow and black are much more limited than what can be reproduced on for example, a computer monitor. Therefore Photoshop will greatly limit the range of color that is shown on an image in order for a printer to be able to reproduce it.
How does CMYK Work in Color Reproduction?
Below is a picture of an offset printing press. Notice that there are four main sections of the press. Each prints a different color: Black, Cyan, Magenta, and Yellow. (Technically, black is not a color, but adding black reduces ink consumption, produces better colors, and sharper type).
Now notice this top view of this offset printing press above. Notice the Cyan, Magenta and Yellow in each printing unit.
These four colors can produce a wide range of colors, but not all. The printing press cannot print with RGB, or Red, Green and Blue. Therefore Photoshop must restrict the colors to allow something that the printing press can reproduce.
What range of color does the CMYK allow on an offset printing press?
The illustration below gives an idea of how limited the CMYK color module is. The center of the circle is the least intense and lowest brightness of the color. The outer edge represents maximum brightness and intensity of the color (that’s a simplification, but of course it’s more technical than that).
The problem is that you cannot go beyond the outer circle in terms of brightness.
So some printers will add colors with special pigments to make that circle a little larger. These special inks areb obtained by using pigments that can push the limits of what the normal CMYK color circle above.
For example Rubine red or Reflex blue will produce very intense colors. Offset printers will try and push these limits as much as possible to get closer to the limits of what the naked eye can perceive.
The picture below shows a range or gamut of the colors that can be percieved by the naked eye. The triangle within shows the limitations closer to offset printing. Notice that they eye can percieve colors in the yellow and green range well beyond what can be printed on paper.
CMYK and the “U.S. Web Coated (SWOP) v2” profile
Different printing presses, depending on the type, can push the limits of the CMYK color gamut that can be reproduced. Printers will use higher quality pigments or different processes to push the limits.
What this means is that each each printer will have it’s own unique limitations on the color that it can reproduce.
Since there are so many variables, Photoshop takes one generic profile that fits most printing processes and uses that. Let’s break down it’s name:
U.S. Web Coated (SWOP) v2
U.S. - A standard developed in that fits most commercial printers in the United States
Web - A printing process that is fed by a large roll of paper (as opposed to sheets)
Coated - The paper is coated, as opposed to a matte finish or other (paper makes a big difference)
SWOP - Standard of Web Offset Printing. To see a web offset printing press, click here.
v2 - An improvement over version 1. Embedded profiles preserved for all color modes.
There are of course other profiles, but this is one of the more common generic ones.
What you should do.
If you are seriously going to reproduce your product on a printing press, ask your commercial printer for their own custom CMYK profile. If they take quality seriously, they will have it. You can then follow the instructions suggested in the message above from Photoshop to convert to a profile that matches more closely what your commercial printer can do. They will provide this profile or suggest one of the standard ones provided by Photoshop.
Conclusion
CMYK simply refers to Cyan, Magenta, Yellow and Black. Photoshop uses the CMYK profile conversion to generate a file that can be reproduced by any process that uses printed colors on any substrate. This could be your desktop printer at home, or it may be a commercial printing press - in which case a custom color profile should be used to ensure accurate reproduction.
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