SOI Image Processing 2

### High-Pass Filter

To remove the low-frequency anomaly from the images, a high-pass filter is
constructed in the frequency domain. This filter will attenuate or eliminate
frequencies which are near the center of the transformed image. The shape of
this filter will be a Gaussian surface with its minimum value at the center of
the transformed image. The filter is shown below as an image and as a
surface:

The equation for this filter is

y = 1 - a * exp(-b * radius^2) + a * exp(-b)

where radius is the distance from the center of the transform, and a and b are
two parameters which control the attenuation and the narrowness of the filter.
In the software used, the parameters can be set with sliders. The values of a =
1 and b = 200 were chosen for this filter.

Here is a profile of several filters for different values of a:

Here is a profile of several filters for different values of b:

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Last updated: 11/22/95