Steve on Image Processing

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.

Lowpass:

Bandpass:

Directional:

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.

imshow(imzoneplate(301))

Here's a smaller zone plate image and its horizontal cross-section.

I = imzoneplate(151);
imshow(I)

plot(I(76,:))

Let's zoom in at the edge of the plot.

xlim([140 151])

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.

Get the MATLAB code

Published with MATLAB® 7.14