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Op Art Hacks using Photoshop

Representing shades of gray using only black-and-white

To print continuous tone images, such as photographs, using black-and-white printing, some form of shading technique is needed. Nowadays, halftoning is the most common method. If you look very closely at a half-toned image, you'll see that it is composed of dots of solid color on a grid. The illusion of gray is created by varying the size of the dots. If the grid is fine enough (or the observer is far enough away), the observer's eye is fooled into seeing shades of gray, rather than a grid of dots.

For most desktop publishers, this process doesn't require much attention from the document designer. It's just one of the things the printing software does. However most illustration, photo manipulation and page layout programs do give you some control over the halftoning process for them that wants it. Of course, Photoshop lets you control your halftones, so let's have some fun!

Making an Op Art Sphere

  1. Create a dark radial gradient. Note: histogram cover roughly the bottom third of the range from black to white.
  2. Convert to bitmap mode with halftone option and frequency: 1 lines/inch, angle: 45, shape: round
  3. Convert back to grayscale
  4. Pinch -40%
  5. Cleanup by bluring and reducing the image size to get nice smooth anti-aliased edges

Making Zebra Stripes

If we make our halftone using lines of varying thickness instead of dots of varying radii, we get stripes. Adding a little wiggle to those stripes with Photoshop's Wave... filter gets us zebra stripes or flames.

  1. Choose a starting image. Transitions from light to dark lead to variations in stripe thickness. For example, create a ramp, like the one below left.
  2. Convert it to bitmap mode with halftone option and frequency 2 lines/inch, angle: -27, shape: line (below center)
  3. Apply the Waves... filter (below right)
  4. Clean up as before

Here's a little puzzle for you: what did I do to the linear gray ramp to bow the stripes? Send me email.

With a little more work (and a friend with a nice picture of her legs), you can create images like this:

Edited 8 Jan 2004 by John D. Corbett
Copyright © 2004 John D. Corbett