Creating a Halftone Pattern for Print *and* Web

A while back, I posted a piece by member Christ Hart, who shared his process for creating halftones for his comic. Halftones are greys that are created by small, solid black dots (or sometimes lines or other shapes). A halftone closely replicates the type of gray that was achieved by using Zip-a-tone.

Why halftones?

Why use a halftone? Well, back in the day, photostat machines were geared at creating image of straight black and white -- with no grays -- for reproduction. It photographed better and it printed more easily. And so a few industrious folks realized that one could simulate a continuous gray tone by breaking the area into a series of solid black dots.

And that's what a halftone is -- a mass of dots, arranged in rows that fool our naked eyes into seeing a contunuous gray tone.

The more dots, the more detail was possible. That's called resolution. We still talk about resolution in terms of DPI (Dots Per Inch) rather than the more accurrate PPI (pixels per inch). Likewise, the closer together we arrange those dots, the less our nakes eyes are able to perceive them as rows of dots. That's called Line Per Inch (LPI).

Now, here's the rub. As great as this system was, it had one fatal flaw: Reducing the size of a halftone image brought some dots closer to dots in other rows (and increased the spacing between other dots and the dots in neighboring rows). Now, our eyes can be easily fooled into see gray, but they're fantastic at seeing patterns. And once those dots aren't evenly spaced anymore, they create patterns. They're called moiré patterns, and they're distracting as heck.

You can decrease the likelihood of creating a moiré patten by adding more space between the rows of dots -- in other words, decreasing the LPI. The more space, the harder it is to form patterns.

The guide Chris posted was decidedly aimed at getting good results in print, but getting that result to transfer to the Web is pretty complicated.

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