Science and Perception

What he also knew is that the conventional Process Color (Cyan Magenta Yellow Black, or CMYK) ink-on-paper color gamut is limited. You cannot reproduce every color that your eye can distinguish using CMYK inks on paper. This is not a matter of perception on the part of a computer operator; it is not a matter of attitude on the part of a printing press operator; it is not a matter of cost and time as presented by a sales representative. It is a matter of science.

You cannot "match" a proof on press (unless it is a press proof made on the same press ... and you probably still can't do it). This, too, is a matter of science.

You cannot "match" what is on the computer screen with a proof nor on press. Again, it is a matter of science.

The degree to which a computer monitor, a digital proof, a press proof, and a finished printed piece "match" is, to some extent, a matter of perception. It is also a matter of calibration and process control throughout the various operations in pre-press, at the supplier(s) to the pre-press house(s), at the paper manufacturer(s), at the ink manufacturer, and on press.

This does not mean that you can never get anything to look good. In fact, how good something looks is a matter of perception on the part of a computer operator; it is a matter of attitude on the part of a printing press operator; it is a matter of cost and time as presented by a sales representative.

No matter what kind of proof you deal with, it does not show you what you will get on press; if calibrated properly, it represents what you can get on press.

Consider photographing a silver vase of red roses on a white cloth.

Light strikes the white cloth. Some of the light is absorbed; the rest is reflected. No particular color is absorbed more than any other; thus it appears white. The reflected light is dispursed by the uneven texture of the white cloth. Thus the cloth does not appear to be a point source of light.

Light strikes the red roses. All of the light except red light is absorbed. A great deal of the red light is absorbed, also. Some red light is reflected back, but it is disbursed by the uneven texture of the rose petals. Thus the roses appear deep red, and not like a point source of light.

Light strikes the green leaves. All of the light except the green is absorbed. A great deal of the green is absorbed, also. Some green light is reflected back, but it is disbursed by the uneven texture of the rose petals. Thus the leaves appear to be deep green, and not like a point source of light

Light strikes the silver vase. Very little of the light is absorbed; a great deal of it is reflected. It is not disbursed, because silver is specular, or mirror-like. Therefore, you see the spot light reflected in the silver vase. It may be distorted, since the silver vase is curved. However, the vase appears to be a point source of light. Light reflected from other objects in the room hits the vase and is reflected, also, so an image of the roses and of the leaves and of the camera is seen in the vase.

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Now all of this reflected light hits the CCD in the camera and creates color values in RGB for each pixel the camera can resolve.

There are color printers, there are really good color printers, there are digital proofers, there are really good digital proofers and there are digital presses (that was in order of the probability that they will accurately represent the finished printed piece, last being highest ... if that is the digital press that will print the final job). Let's assume that you are using a really good digital proofer that has been calibrated to closely match printed pieces.

A digital proof is ink or dye on paper. Light strikes the proof, is selectively absorbed by the ink or dyes, is reflected by the white paper under the ink or dye, goes back through the ink or dye and is selectively absorbed again, and lands in your eye. We are now dealing with reflected light, not transmitted light. We are dealing with CMYK, or the primary subtractive colors, not RGB, the additive transmissive colors of computer monitors. The digital proof cannot look like the image on the monitor. It cannot look like the reflected light of the original photo shoot. You are now dealing with a severely compressed tonal range and colors that have been interpreted by the camera, by the image manipulator, by the digital proofer, and by the paper on which the proof is made.

The digital proofers that use dye sublimation are causing dye to be absorbed into the surface of special paper. This is not ink-on-paper. Therefore it cannot match the ink-on-paper of a printing press. It can look similar to it, but not match it.

The digital proofers that use ink-jet technology put ink on paper. This may seem to be a step in the right direction, but the inks are far less viscous than offset litho inks, the dyes are not necessarily the same as those used by the ink manufacturer for your printer, and the patterns in which the inks are splattered onto the paper are not the same as the patterns of halftone dots or stochastic spots transferred to printing plates.

In most cases, the proofer cannot print on the same paper stock that you will use for the printed piece. Even if it can, the inks are different enough that they will perform differently.

The digital proof can give you a good representation of what a printer should be able to get on press, but it won't match. It can't. It can be very close, but it can't match.

The digital proof made from a calibrated system can allow you to make good, informed color decisions. That is how they should be used.

Various Proofing Problems

We are frequently asked why a CMYK proof doesn't reproduce Pantone Reflex Blue (or any number of other PMS® colors) faithfully. Well, it can't. We are also often asked to choose a color that more accurately represents a PMS color on our press. We can only do so by adding orange, violet, and/or green inks and using a 5, 6, or 7 color separation.

Few digital color printers can print spot colors; they all show CYMK builds of the spot color. If you have a Pantone Process Color Imaging Guide, it shows Pantone Match colors next to the best CMYK screen build they can come up with for it. Many CMYK screen builds are very different from the spot color they are to represent. The same results can be expected with any color printer.

Note: with some digital printers, including ours, you can get custom made matching inks. However, it is normally cost prohibitive for you and the printer unless you will be using the special color on many jobs.

For traditional lithography:

1. Always pick the PMS color you want from the swatch book, not from the computer screen nor from the color printer or digital proofer.
2. Always go to the color OK on press to make the judgement call on what looks best. Even with spot colors there is a reasonable amount of latitude on press with density of solid coverage. And if there are tints and halftones involved, the press operator can vary their outcome tremendously.
3. For digital printing, always pick the color from a CMYK swatch book.

Computer Screens, Digital Proofs and Film Proofs

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