Most printers are CMYK printers; in other words, they only have cyan, magenta, yel-
low, and black (K) inks. To print all the colors of the rainbow, they must combine
dots and simulate colors. This technique of halftoning (similar to the printing press)
tricks the eye into seeing a specific color. Its this combination of inks that generates
the dpi numbers you see in advertisements.
To create a specific color such as green, for example, a CMYK printer must combine
several colors and drop them onto the same tiny spot. The printer will lay down a
little cyan and a little yellow in a specific area (see Figure 18.2). It will then lay
down some black if the color was the least bit dark. All of these spots are printed
near each other to fool the eye into seeing the color green for this specific pixel.CHAPTER 18 PRINTERS AND PRINTER RESOLUTION 271FIGURE 18.2
Close-up of an
inkjet print.
Notice the small
dots, which are
laid up to create
specific colors.
Pixels per inch is the number of pixels that will be printed per inch. Select View,
Image Size in Photoshop or Image, Resize, Image Size and check the ppi rating for
your image. Inkjet printers are good for around 150–300 pixels per inch; high-end
photo inkjets can handle 400 pixels per inch.
For example, a 3:1, 5:1, or even 7:1 relationship is necessary to create the color
green depending on the number of separate inks in a printer. It takes multiple spots
(dots) per pixel location on a printer to create the color intended for that pixel. For
this reason, the dpi rating you see in printer advertisements should be divided by the
number of inks to obtain a rough estimate of printed ppi (pixels per inch). Today’s
modern photo printers can accept high ppi ratings, but the human eye cannot per-
ceive much beyond 16 pixels per millimeter. For this reason, the maximum ppi rat-
ing for an image should be around 360 or some number divisible by your printer’s
advertised dpi resolution.