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fast wavelet Transformation by using lowpass and highpass

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Jana Kassas
Jana Kassas on 8 Feb 2021
Answered: Pratyush Roy on 17 Feb 2021
hello everyone,
I have to write a function to apply 2D FWT on an image. To do this I should:
  1. apply lowpass in x-direction and seperatly highpass filter also in x-direction
  2. on the 2 resulting images apply the lowpss and seperatly the highpass in y-direction
  3. I will have at the end 4 filtered images
I'm struggeling with applying the filters in one direction. Please help

Answers (1)

Pratyush Roy
Pratyush Roy on 17 Feb 2021
Hi Jana,
The highpass and lowpass functions can be used to perform one dimensional filtering. Let us consider the following snippet:
y = highpass(x,wpass);
Here if x is a matrix, then the function filters each column inependently. To apply filtering across a row, we can take the transpose of the input signal, compute the filtered output and take the transpose of the output again. The following snippet demonstrates the operation.
y_tr = highpass(x',wpass)
y = y_tr';
Similarly, we can perform the operation for lowpass filters.
Hope this helps!

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