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I read a paper about directional filter bank in image processing and I don't understand clearly about the process. It says they use '2-band structure' like this image:2-band structure

could someone here please explain it to me how this process works? I would like to implement it on python or MATLAB.

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  • $\begingroup$ Could you add a reference to the paper please? Just the figure is a bit short. $\endgroup$ – sansuiso Mar 23 '13 at 22:21
  • $\begingroup$ @sansuiso This is the link to the paper. I hope it can help much. $\endgroup$ – nsrjws Mar 23 '13 at 22:50
  • $\begingroup$ intuitively speaking; this is about separating approximation and details from the signal and the down sampling it to match the actual number of input samples; here approximation means low frequency and detail means high frequency while Q shows the process of down-sampling. The Hw0 and Hw1 are high and low pass filters $\endgroup$ – Sufiyan Ghori Mar 24 '13 at 21:31
  • $\begingroup$ @Effected how does the down-sampling process work? Is it a convolution process? and is the modulation by e is also convolution process too? $\endgroup$ – nsrjws Mar 26 '13 at 0:18
  • $\begingroup$ have a look at what we do when we talk in wavelet domain oi48.tinypic.com/4hruwn.jpg $\endgroup$ – Sufiyan Ghori Mar 26 '13 at 12:40
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Sorry, I couldn't access the paper behing the paywall, so here is an educated guess about the figure that you linked in the question.

  1. $H_0$ is a low-pass filter, while $H_1$ is a high-pass filter. You can note that the union of both domains correctly yield the full bandwidth of the input signal.

  2. These filters are directional, i.e., they operate on different subbands that correspond to a set of orientations. This is shown in the figure by the 1,2,3,4 triangles: each triangle corresponds to a set of low/high-frequency of a given set of orientations. For example, 1 corrresponds to lower frequencies, and the slope of the lines in 1 is positive.

  3. Finally, the directional filter bank consists in two operations: separatig low/high frequencies (the filter bank part) and applying a transfer function that also depends on the orientation of the current frequency (the directional part).

I'm note sure that you can implement the figure from this explanation though. A good starting point now would be for you to look for an example code that does similar things.

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  • $\begingroup$ Thank you for the answer. Does the multiplication by 'e' in the first step mean shifting like fftshift in MATLAB? $\endgroup$ – nsrjws Mar 28 '13 at 1:24

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