What are LL,LH,HL,HH in DWT?

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Mihnea Constantin
Mihnea Constantin on 2 Nov 2020
Commented: Dominic Mathew on 17 Mar 2021
Hello everyone, I have a small project where my first step is to decompose an image using DWT. Could anyone help me explain
1:what are LL,LH,HL,HH in DWT?
2: what code do i need to write if I want to do a second level and even third level decompostion to extract the value of LL

Answers (1)

Saurav Chaudhary
Saurav Chaudhary on 5 Nov 2020
DWT is an algorithm used to reduce dimensionality of an image, feature extraction process. DWT algorithm decomposes the image into 4 sub-band (sub-image) ie,LL,LH,HL,HH.
  • LL is the approximate image of input image it is low frequency subband so it is used for further decomposition process.
  • LH subband extract the horizontal features of original image.
  • HL subband gives vertical features .
  • HH subband gives diagonal features .
You can decompose LL band image further, look at the following MATLAB answer to get an idea.https://www.mathworks.com/matlabcentral/answers/163844-how-to-write-matlab-code-for-third-level-dwt
Dominic Mathew
Dominic Mathew on 17 Mar 2021
I had tried to do hyperchaotic image encryption for the decomposed LL image but it is showing error could you explain why and how to resolve it.

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