Digital Prints

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Mastering Digital Printing
1/2880th of an inch in one horizontal pass. What happens is that different nozzles on the
printhead pass over the same line or row to fill it in. It might require up to eight passes to
print all of the intermediate dot positions and complete the row. This interleaving of dots
is sometimes referred to [in the case of Epson] as ‘weaving.’“ (See Figure 2.8.)
The idea is the same for the other inkjet brands, although each has its own way to arrive
at the maximum resolution numbers. HPs do things like “color layering” to change both
horizontal and vertical resolutions. Canons combine “dot layering” with other factors
including small ink droplets, small nozzle structure, and a small nozzle pitch (the distance
between nozzles on the printhead) to reach high dpi numbers.
What does all this mean? Honestly, not that much. Is 2880 × 1400 really 36 percent
higher—if you simply multiply the two numbers together—than 2400 × 1200 dpi resolution?
I’ve seen outputs from many printers with these stated maximum resolutions, and
I would be hard-pressed to say one is that much better than the other.
The theory is that higher printer resolutions produce finer details and smoother tonal gradations.
This is true up to a point, but you eventually reach a position of diminishing
returns. The negatives of high dpi—slower printing speeds and increased ink usage—eventually
outweigh the positives, especially if you can’t really see the differences. (For more
about this, see “Viewing Distance & Visual Acuity” below.)
When it comes right down to it, the dpi resolution numbers on a spec sheet are irrelevant.
They only tell a very small part of the story, just like the blind men’s elephant. There are
many factors that go into what really counts—the image quality a particular printing device
is capable of producing. Factors like printer resolution, the number of ink colors, the size
of the ink droplets, the precise positioning of the dots, how the inkjet nozzles are arranged
and fire, the order of the colors, the direction of printing, and the screening or dithering
pattern of the image pixels—they all come into play. My advice: Don’t put too much stock
in the dpi numbers alone, and don’t use them to compare printers of different types or
brands. Instead, use dots-per-inch resolution only to weigh different models of the same
brand. Then, at least you’re talking the same language.
Figure 2.8 Multi-pass droplet
offsetting or “weaving” is one factor
affecting an inkjet printer’s addressable
resolution. (Note: the dot sizes and
positions are representative only; actual
printing dots are more variable.)