Digital Prints

as each dot or spot having its own address on the paper, and all this is measured in dots
per inch (dpi). (Imaging scientists actually have other ways of talking about resolution,
too, but I’ll leave the arcane terms and definitions to them.)
Do you know the story of the blind men and the elephant? Six blind men encountered an
elephant for the first time. Each touched a separate part of the beast and was then asked to
describe the whole animal. They did so but in very different ways. The elephant was either
like a snake, a wall, a spear, a fan, a tree, or a rope depending on which blind man spoke.
And so it is with “addressability” and dots per inch. Those numbers you see listed on every
print device’s spec sheet and in every advertisement only give you part of the picture. And
each print-device manufacturer talks about it differently.
Take inkjet printers. The Epson Stylus Pro 4000 printer’s maximum resolution is listed
as 2880 × 1440 dpi (Note: virtually all digital-printing devices have multiple modes that
allow for more than one resolution setting; naturally, only the maximum is advertised.
The smaller the resolution numbers, the faster the printing, but the lower the image quality).
The maximum resolution on the HP Designjet 130 is 2400 × 1200 dpi. For the
Canon i9900, it’s 4800 × 2400 dpi.
So what do these numbers mean? The 2880 (or 2400 or 4800) refers to the horizontal axis
and is the maximum number of dots the printer can cram into one inch across the paper,
or in the direction of the printhead’s travel (see Figure 2.7). The other number (720, 1200,
or 1440) is the maximum number of dots the printer can place in one inch down the paper
(in the direction of the paper feed).Keep in mind that these are not separate little dots
standing all alone; they are frequently overlapping or overprinting on top of each other.
Why are the horizontal numbers usually higher? Because it’s a lot easier to position the
printhead precisely than it is to position the paper precisely. As software developer Robert
Krawitz explains it, “The printhead typically doesn’t actually lay down a dot every
Chapter 2 ■ Understanding Digital Printing 45
Figure 2.7 Inkjet printers have the
higher-resolution numbers in the
horizontal or printhead-travel
direction.
Printer image courtesy of Hewlett-
Packard Company