Help: What are the differences between lwt2 in previous versions and the current version?

I saw someone using it in MATLAB 2018a with the syntax [CA,CH,CV,CD]=LWT2(img,'haar');. On the official website, I found that after version 2021 it should be written as [CA,CH,CV,CD]=LWT2(img,Wavelet='haar');.

When I ran [CA,CH,CV,CD]=LWT2(img,Wavelet='haar'); in MATLAB 2024a, the CA I got was a double-type 1x1 matrix, which is a single double value.

However, when I ran [CA,CH,CV,CD]=LWT2(img,'haar'); in MATLAB 2018a, the CA was a double-type matrix of size M/2 by N/2, where M and N are the dimensions of img.

why the two CA results are different?

need your help

Thanks

img

lwt2:https://ww2.mathworks.cn/help/wavelet/ref/lwt2.html

code in 2024a:

img=imread('lake.pgm');
img=im2double(img);
[CA, CH, CV, CD] = lwt2(img,Wavelet='haar');
disp(CA);

code in 2018a

img=imread('lake.pgm');
img=im2double(img);
[CA, CH, CV, CD] = lwt2(img,'haar');
disp(CA);

Answer 1

[Hitesh]

Hi @jiang yutong

Starting with MATLAB R2021b, the syntax for the “lwt2”function has been updated. Previously, the "lifewave"object was used, but it has now been replaced by the "liftingScheme"object. To obtain CA as a double-type matrix of size M/2 by N/2, where M and N are the dimensions of “img”, the “liftingScheme”object needs to be passed to the "lwt2"function along with its level.

Kindly refer to the code below:

img=imread('image.bmp');
img=im2double(img);

lScheme = liftingScheme("Wavelet","haar");
[CA, CH, CV, CD] = lwt2(img,LiftingScheme=lScheme,Level=1);
disp(CA);

For more information on "liftingScheme" object and “lwt2” function, refer to below documentation. https://www.mathworks.com/help/wavelet/ref/liftingscheme.html#:~:text=lscheme%20%3D%20liftingScheme(%27Wavelet%27%2Cwname) https://www.mathworks.cn/help/wavelet/ref/lwt2.html#:~:text=lwt2%20input%20syntax%20has%20changed

Hope this clarifies the issue!

[yutong]

Hi Hitesh

Thank you very much！

I think I have already understood the confusion I had before. I am a beginner in MATLAB, and your explanation has given me a deeper understanding of it！