Color Theory - From Monitor to Print
Reproducing all of the colors represented on a computer monitor is more difficult than it seems. We design and view images on computers, then must replicate those designs with screen-printing inks that apply color after a subtractive module.
Monitors transmit color through what’s called additive color synthesis—the method of using two or three distinct stimuli of colored light to create large color ranges. An additive color module is basically RGB (red, green, blue)—or R+G+B = White.
Since printing with light is not possible, however, this is not a likely scenario on a printing press. A subtractive color synthesis is more representative of printing inks. It uses the inks to create color by reflecting some wavelengths of light while absorbing others. According to the subtractive color module of CMY (cyan, magenta, yellow), M+Y=R, C+Y=G and C+M=B.
Color is measured in many ways: RGB, Lab, HSB and so forth. These measurements are based on a pre-defined and dependable standard of color tables. Color separations are made based on this information but, once the screens are on press, the color becomes somewhat less standardized. Advancement in color-separation technology has helped us tremendously in the past 10 years, but this technology is only effective if the printer uses a predictable and balanced ink set, to which the separations may be calibrated.
Color strengths and opacity differences in inks will affect the interplay of blended halftones and the brightness (tint or shade) of a color. These characteristics will even affect each other—the less opaque an ink is, for example, the more it is affected by pigment strength.
These two characteristics of screen-printing inks—color strength and opacity—are frequently ignored, with consequences that may be greater than many printers think.
The importance of equal opacity
Opacity levels between colors on a press run are usually the last things on a printer’s mind. It is very important to consider this characteristic of an ink, though, when a design requires equal blending of multiple colors to achieve secondary and tertiary colors. These blends can fluctuate wildly if one ink has a higher opacity level than the next.
When colors interact, an opaque color will dominate the color shift. But if the inks are all within the same opacity range, the design will have even blends and larger color-gamut capabilities.
Color shifts occur frequently in the average screen-print shop. Despite large investments in artwork, separations, screens and equipment, many printers only consider color hue when they grab ink off the shelf. Many premixed inks are sufficient—if you QC their levels with opacity cards—but the best way to control opacity levels is to create your inks using mixing systems designed for that purpose.
The importance of translucency
Not only are balanced opacity levels important to the printed effect, the overall opacity level of an ink set can affect the outcome of the print. This opacity level becomes most critical on a dark shirt where a white underlay plays a large role in the reproduction of color. The ultimate interaction between the white underlay and the dark shirt is critical for setting the tints and shades of the overprinted color set.
A transparent ink, when used with other transparent inks—such as in four-color process printing—will create a nice, wide gamut on white shirts. This same ink set, though, will be at a disadvantage when called on to overprint a white underbase. The print will have a de-saturation of color because the transparent ink allows an overwhelming amount of white light to reflect back through it.
Opaque inks when used on dark garments may give you the color “pop” for which you are looking, but may overtake an underlay along with any other previously printed colors. This hinders the ability of the white base to control the luminosity and the color blending between hues, and is caused by the over-saturation of color through the lack of white or black influences reflecting through the ink. Though these inks will give you strong, vibrant prints, the lack of total blending of color may flatten the image. Many printers will add extender to an opaque ink to lower its opacity level. This, however, also lowers the pigment load which, in turn, will weaken the color.
So how to strike a good balance? Consider a translucent ink. Translucency, by definition, allows light to pass through the ink film without its being transparent. A good example of translucency is stained glass, as opposed to smoked glass (transparent) and painted glass (opaque). A translucent ink allows a high pigment load for rich color, without compromising the ability of the ink to blend or be affected by the underlying colors. Basically, translucency makes possible a color set that will provide a wide gamut on white shirts as well as a strong, predictable color range on darks.
Separation color reproduction—RGB to HSB
The success of separation technology today is dependent on the reproduction of color. With inks, the colors are represented most closely with the HSB module, in order that the ink is simulated with three characteristics: hue, saturation and brightness (or luminosity). The best chance of simulating this color module is with a translucent set of evenly opaque colors. Though transparent colors will give you good hues and tints, they can fall down when it comes to good saturation and shades on dark garments. Likewise, while opaques will provide good hues and saturation, they can fail in terms of controlling tints and shades. Translucent colors will provide a balance of hue (with clean color), saturation (with pigment strength) and brightness, because the nature of the ink allows the underbase white and the shirt color to affect the tints and shades of the overprinted colors.
If the designer utilizes a saturated color pallet, the underbase white will control the entire brightness range of the design. The printer can then use an ink set that will react much like the colors on his the computer monitor, thus pulling printer and designer onto the same page.
