Part 2 - Color 101

Understanding why color proofing is such an arduous task requires at least a basic understanding of how various devices create color. An understanding of the differences between RGB and CYMK color spaces, continuous tones and halftones is also critical, as is understanding the color gamut (the color range) capabilities of various devices.

One of the most basic conflicts that any proofing system must deal with is the difference between additive and subtractive methods of creating color.

Monitors are additive devices, i.e., all displayed colors are composed of combinations of red, green, and blue values. Beginning with all three pixel colors set to 0, the color would be black (actually the "black" displayed is simply the color of the screen.) For a typical 24-bit monitor, each of the three colors can be displayed in 256 levels of intensity, resulting in 16.7 million color combinations. Turning all three colors on at full intensity produces white.

Presses (and printers) are subtractive devices. Most presses use CYMK color space (cyan, yellow, magenta, black). To simplify it, the page starts out white (if you're using white stock) and each ink applied to an area "decreases" the whiteness. In fact, adding CYM produces a fair approximation of black and many early color printers only used those three inks. Adding black to CYM produces "rich" black which is often specified when a page includes a large section of black (typically three square inches or more). A CYMK device can produce only about 4,000 colors by using halftones and ink combinations.

In addition to the huge disparity in color capabilities between a monitor and any press is the the issue of screening or halftoning (sometimes referred to as dithering). As mentioned earlier, each color element in a monitor can vary in intensity. For example, the green element of a pixel can be set at 128, or 50% intensity. This results in a very smooth image without the need for halftones. A press however can't vary an element's intensity--a drop of ink is always 100% intense. To simulate varied intensities, presses use halftones. To achieve a 50% effect, the press would deposit ink on only every other pixel. The two methods are contrasted in the illustration to the left.

Although few high-end proofing device manufacturers would ever admit it, the true challenge of proofing is in realistically downgrading the quality of the monitor display to accurately reflect the relative crudeness of even the best printing press. While it might be tempting to send a stunning proof to a picky client in order to gain approval, it is always a bad idea if you can't deliver that the same thing from your press. It is almost always preferable to promise less than you can deliver with a proof that to set the standard too high.

Jump to part 3 - Analog Proofing