fast wavelet Transformation by using lowpass and highpass

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

Answer 1

[Pratyush Roy]

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!