Last year I posted a few times about the "Jähne test pattern," something that readers then told me was called a zone plate. This is a radial sinusoid pattern with low frequency in the middle of the image and high frequency toward the edges.
In my 02-Jul-2012 post, Filtering fun, I used the zone plate image to illustrate the effects of different kinds of frequency-selective filtering.
Last week I submitted a function called imzoneplate to the MATLAB Central File Exchange.
I resisted the urge to give imzoneplate a lot of optional parameters. Instead there's only one, the size of the image.
Here's a smaller zone plate image and its horizontal cross-section.
I = imzoneplate(151); imshow(I)
Let's zoom in at the edge of the plot.
You can see that, with the parameters I've chosen for imzoneplate, the sinusoidal period decreases to about 3 samples at the edge of the image.
Be sure to download imzoneplate and give it a try. Post a comment here if you have a particular application for it.
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