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HOWTO: Rotated Halftones in Inkscape

There are a few good tutorials on the web about how to get a (mediocre) halftone screen in Inkscape (1, 2). (The GIMP, by contrast, has a special halftoning plugin that does a nice job. I wish that Inkscape had one of those.)

One thing that none of these tutorials tell you is how to rotate the halftone screen. This turns out to be important, since unrotated screens of different colors do not overlay well.

In this tutorial, I summarize the basic technique for halftoning in Inkscape, and suggest a way to do rotation… The basic technique involves the use of "tiled cloning", available under Inkscape's "Edit" menu. Tiled cloning does what its name implies—it makes many copies of a given image, tiled according to some pattern.

The basic plan is as follows:

  • If you don't have one already, make a greyscale or alpha map that corresponds to how you want your halftoning to look.
  • Make a little dot of the appropriate shape and color to be a halftone dot. Circles are the traditional dot shape.
  • Use tiled cloning to clone the dot over the map. Make sure to bound the area tiled. Pay special attention to the "Trace" tab of "Create Tiled Clones." Set the tiler to use color or opacity of the underlying image as appropriate, and make sure to apply the underlying value to the clones' size.
  • Break the original dot off the clone, and throw it away. Throw the underlying map away. Group the tiled clones. Voilà, halftones.

There's nothing in "Create Tiled Clones" to suggest that you can rotate the tiling; you can rotate the individual tiles, but that doesn't help. What you can do is rotate the map, apply the halftoning, and then rotate the halftoned map back. Use "Object/Transform" and provide an integer rotation, so you can undo perfectly. Sleazy, but it works.

Alternatively, play with the "Shift" values to get an angled effect.

It's not clear what the "Scale" is so useful for.

Have fun! Fob

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