How to implement LH, HL, HH in DWT of an image ?

I want to implement the subbands without using the built in functions in Matlab

I have calcaluted the LL only but don't know what should be changed to calculate LH, HL, HH subbands

what I have reached so far..

X=double(imread('image.jpg'));
[row,col]=size(X);
Scale_filter = [1/sqrt(2) 1/sqrt(2)]; %Haar scaling filter
Y = conv2(X,Scale_filter(:)','valid'); %filter along the columns
Y(:,end+1) = Y(:,end); % periodically extend the matrix for the next step
Y = Y(:,2:2:end); % downsample along the columns
Y(end+1,:) = Y(end,:); %periodically extend the rows for the next step
Y = conv2(Y',Scale_filter(:)','valid'); % filter along the rows
Y = Y'; 
Y = Y(1:2:end,:)  %downsample

Answer 1

[Dev]

Hi @moustafa abada,

In the code provided above, the Haar wavelet low-pass filter is already computed as ‘Scale_filter’. We also need to compute the high-pass filter to eventually compute the LH, HL and the HH sub-bands. Please refer to the code snippet below as a reference to generate a Haar wavelet high-pass filter-

% High-pass filter 
Wavelet_filter = [-1/sqrt(2) 1/sqrt(2)]; 

After computing the same, we can apply the appropriate convolutions of low-pass and high-pass filters along rows and columns according to the type of filter required. Please refer to a brief overview of the appropriate convolutions below. You can try them in accordance with your code to implement the remaining sub-bands-

• LH: Low-pass filter on columns, high-pass filter on rows.
• HL: High-pass filter on columns, low-pass filter on rows.
• HH: High-pass filter on both rows and columns.

The remaining steps of downsampling and periodic extension in the code provided can be kept the same while implementing these filters.

I hope the above resolve your query.