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Reversible domain shifts are good for more than just elliptical
spheroids. Kai Krause uses Polar Coordinates to illustrate
some very strange stuff, and along those lines, you can do some
interesting blurs in polar coordinates that are difficult to
do otherwise.
Before I begin, a quick note about polar coordinates in
Picture Publisher. To go from rectangular to polar coordinates,
use the "Tunnel" effect. To go from polar to rectangular
coordinates, use "Polar to Rectangular". Further, when you
use "Tunnel", it will put the discontinuity at the top of the
image; when you use "Polar to Rectangular", it expects the
discontinuity to be on the right side. You will need to
rotate your images 90 degrees clockwise prior to using "Polar
to Rectangular" to compensate. Further, Picture Publisher
does not interpolate when it applies these effects, which has
a detrimental effect on picture quality. For these reasons,
I use Photoshop in these examples.
Example 1 Let's take a simple image:  Now use Filter > Distort > Polar Coordinates... and select "Polar to Rectangular". Click OK:  Apply a motion blur (Filter > Blur > Motion Blur...) at 45 degrees, strength 20:  Now convert back, using "Rectangular to Polar", and you'll get a nice spiral blur:  If you don't like the discontinuity at the top (which you probably shouldn't) then I suggest, immediately after the first step, you add some space to the image on either side and paste in extra copies. Then apply your motion blur, and clip the center back out. This has the effect of making the motion blur "wrap" on the edges. Example 2 Go back to our starting image. This time, though, use "Rectangular to Polar". This transforms the image in the other direction:  Now apply a motion blur, this time at 90 degrees, distance 10 pixels:  Use "Polar to Rectangular" to get back to our original shape:  And you have a strange "tangent blur". If you flip the right half of the image before doing anything else, then flip it back when you're done, you can get a nice sweeping curve effect:  Possibilities abound. Try some! |
