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Smoothing Through Lowpass Filters |
Brought to you by Team Phantom
Cruiser and the Power of Steam
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| Top: Original image. Bottom: Image filtered with
5th order Butterworth lowpass filter, normalized cutoff frequency .3 |
But there are frequency domain filters that we can
apply to the image without artifacting. Here we've created an
equiradial 5th order lowpass Butterworth filter. As with a one
dimensional Butterworth filter, this filter does not create ringing in
the image, and so we can now start to examine the actual effects of lowpass
filtering on an image.
As expected, when the car is multiplied in the
frequency domain by the lowpass filter seen here to the right, it
serves to smooth the image and blur out the sharply defined lines. In this way, a low pass filter can be used to create
a blur effect on an image. When used subtely, this can have the
effect of smoothing out high frequency noise in an image, such as dust
or film grain. When used more grossly it can be used for general blur
or, if the distribution of the filter around the DC is elliptical
rather than circular, can create the effect of a directional motion
blur.
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