Multitone Images

In the old tale of the four blind men and the elephant, each man describes the animal according to the piece he's experienced. "It's a snake-like creature with wrinkled skin," says one, holding the trunk.

"No, it's a hairy animal with giant wings," says another, feeling the ear.

Printing a grayscale image is similar to this experience. Printing presses are powerful and delicate instruments, but depending on the press, the operator, the ink, and the paper, they're often limited to printing far fewer than the 256 shades of gray you can theoretically achieve with an 8-bit image. So after you've gone through a lot of trouble adjusting tone, those tones are pummeled when the image is slapped onto paper. In other words, the final printed result is only a fraction of the whole image, and the viewer is blind to the richness of the original.

There are ways, however, to coax more gray levels, more detail, and more depth out of a printed image. Printers have traditionally tackled this problem by printing the grayscale image more than once, each time with a different-colored ink. These are called duotones, tritones, and quadtones (depending on the number of inks you use). When talking about the genre as a whole, we call these multitones, because we're too lazy to keep typing "duotones, tritones, and quadtones." Remember, multitones differ from color images in that they almost always represent an underlying neutral, grayscale image.

Expanding the Tonal Range

While they're often used to colorize grayscale images, the original goal of multitones was to expand the tonal range of the image. For instance, a 50-percent tint in gray ink may be lighter than an 11-percent spot of black ink; so an 11-percent spot of the gray ink is far lighter than the tonal range of black ink can achieve. If you print black ink in the shadows and gray ink in the highlights, you can achieve more levels of highlight grays.

On the other end of the spectrum, we usually think of 100-percent black ink as solidyou can't get darker than that. But in reality, printing 100-percent black on top of 100-percent gray results in a darker, richer, denser black. Therefore, by adding the gray in the shadows, you expand the tonal range of the image even further toward real black.

Adding an ink is like listening to two of the blind men instead of just one; you get that much more information and can see the whole of the image that much more clearly.

Colorizing Images

When most designers think about duotones, they don't think about expanding tonal range; they think about colorizing grayscale images. For instance, many newsletters are printed with two inksblack and some Pantone color. When given the opportunity to print with a second ink, many designers immediately think, "Oh, I can give some color to my grayscale images by making them duotones."

There's nothing wrong with colorizing a grayscale image. But colorizing images without thinking about the expanded tonal range usually looks pretty bad. In this chapter we talk about both, and how they relate to one another.

Tip: Dumb, Fast Duotones

If we didn't know how hectic life can get in a production setting, we would hardly believe how many people (printers, especially) still use the flat-tint duotone trick. The idea is that you can fake a duotone by laying a flat tint behind the grayscale image. For example, let's say you want to add some blue to a grayscale image. To fake the duotone look, you could lay down an 11-percent tint of magenta or PMS 485 behind the entire image (see Figure 10-5), and set the image to overprint in your page-layout program.

Figure 10-5. Fake versus real duotones

Note that this really is an old printer's trick, and it doesn't look very good. Since you're making no allowance for the tonal shift, fake duotones are often too dark and muddy. Photoshop makes creating real duotones so easy that faking it is hardly worth the effort. It's faster, but it's not that much faster.