At first glance, the concept of four-color black and white images would appear contradictory. After all, either you print halftone images in black ink only, or you print them in full color (i.e., cyan, magenta, yellow, and black ink). Or do you?
How about duotones? When you create a duotone, you usually print an image in black and a second color, or you print the image in two PMS colors. When you do this, you create two halftone images with different tone curves (in Photoshop). That is, you focus on a certain portion of the halftone (let’s say midtones and highlights, or quarter-tones and three-quarter-tones. You do this because of the imperfections of printing. Using one custom printing ink and one halftone screen cannot capture the full range of tones from the darkest dark to the lightest light. Something suffers. But each time you add a color (as with a duotone), you can extend the range of tones in the composite halftone image. (This is called increasing the “dynamic range” of the image.)
But that’s a duotone. What about a four-color black and white image?
The same goes for four-color black and white images. If you use cyan, magenta, yellow, and black together, you can (for the most part) capture the full range of color in an image. But if you want an image that stands out because of its simplicity (and a rich, black and white image will definitely stand out in a world of full-color imagery), you can adjust the percentages of the process colors in the halftone to simulate an achromatic (no-color) image.
And given the ability to use each of the process color screens to enhance a specific portion of the tone curve (highlights, quarter-tones, midtones, three-quarter-tones, shadows), you can end up with a deep, rich photograph impossible to create with a single black ink. Or, more precisely, you can hold detail and levels of tonal transition in the deepest shadows, the midtones, and the highlights simultaneously.
But Problems May Arise
As with any truly wonderful artistic technique, this one has dangers as well, namely color shifts or color casts. The success of a four-color black and white image rests on the ability of your commercial printing vendor to hold a neutral gray balance in the image. That is, the image cannot have a color cast, or it will no longer have the characteristic look of a black and white photo.
On press, color casts can occur for a number of reasons. Among these are dot gain. If the halftone dots spread on the press sheet, then the precise balance of the four process colors that yields a true achromatic black will be lost, and the image may tend toward a cyan, yellow, or magenta look.
In fact, it is because of the tendency of neutral grays to shift toward a color tone that such processes as UCR (under color removal) and GCR (gray component replacement) are used to replace a cyan, magenta, and yellow on press with black ink. This stabilizes the overall image color and avoids color casts. In the case of a four-color black and white image, we’re consciously choosing to do the opposite of UCR and GCR. So it’s risky.
In-Line Color Conflicts
Another cause of color casts (in addition to dot gain in one of the process colors, or over or under inking resulting in a color imbalance) is an “in-line conflict.”
An in-line color conflict often occurs in a magazine press signature in which heavy-ink-coverage advertisements, solid colors, and lighter areas of type are distributed across one side of one press signature. To understand this, picture a 16-page signature with four 8.5” x 11” pages across the top of the sheet and four more pages immediately below. On the back there will be eight more pages making a total of 16. This is a traditional 16-page signature.
The individual press sheet travels through the press with the top four pages of the signature going through the inking units first, followed by the four pages immediately beneath them on the flat press sheet. If images on the top four pages use a large amount of a particular process color, it is entirely possible that the pages immediately underneath them (or “in-line” with them) on the 8-page side of the press sheet may be adversely affected by that larger amount of color.
For instance, if a large image on the top left page of the signature requires a large amount of magenta ink, the magazine page immediately below it (i.e., in-line with it) may have a magenta cast as well. If you’re custom printing a four-color black and white image on that particular magazine page within the press form, it may shift from a deep rich black to a rose-tinted warm black. This may be unacceptable.
Fortunately, your commercial printing supplier may suggest putting the four-color black and white image on a different page within the press signature, one that would be less adversely affected by such an “in-line conflict.”
To achieve success with four-color black and white images, the best thing to learn from this discussion is not to avoid four-color black and white images but to involve your custom printing vendor early in the process. Describe your goals. Make sure your printer has done high-end work like this before. And consider attending a press inspection so you will not be unhappily surprised with the final product. After all, on a press inspection, you can identify a color cast and ask the pressman to fix it.
This entry was posted
on Friday, May 23rd, 2014 at 2:13 pm and is filed under Photos.
You can follow any responses to this entry through the RSS 2.0 feed.
Both comments and pings are currently closed.