Algorithm used to implement the function qtdecomp?

Joe
2025 2 18
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更新时间：2025 2 19
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I am wondering if anyone is familiar with the algorithm used to implement the qtdecomp function in the image processing toolbox. I am working on my masters thesis and am trying to compare results of my proposed algorithm vs other existing algorithms and the qtdecomp function was a useful tool for early simulation results and I am wanting to be as accurate as possible when comparing my results.

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Mike Croucher
Mike Croucher 2025-2-18
编辑：Mike Croucher 2025-2-19

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There is a description of the algorithm on the documentation page qtdecomp. It says
"The qtdecomp function divides a square image into four equal-sized square blocks, and then tests each block to see if it meets some criterion of homogeneity. If a block meets the criterion, it is not divided any further. If it does not meet the criterion, it is subdivided again into four blocks, and the test criterion is applied to those blocks. This process is repeated iteratively until each block meets the criterion. The result can have blocks of several different sizes."
In the comments section you asked about the homogeneity criteria. I asked internally and the default is simply to test if they are all exactly equal. This is also mentioned in the doc. It depends on the syntax used:
S = qtdecomp(I) performs a quadtree decomposition on the grayscale image I and returns the quadtree structure in the sparse matrix S. By default, qtdecomp splits a block unless all elements in the block are equal.
Then for threshold
S = qtdecomp(I,threshold) splits a block if the maximum value of the block elements minus the minimum value of the block elements is greater than threshold.
You can come up with your own function to determine if a block should be split or not:
S = qtdecomp(I,fun) uses the function fun to determine whether to split a block.
Does that help?

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Joe
Joe 2025-2-18
Ya the description gives a general overview of quadtree decomposition. I guess my question is more specifically about the line "meets some criteria of homogeneity." How is homogeneity determined with this function? Does it use a mean square error critreia with a fixed threshold (my current assumption since one of the function paramaters is a threshold) or does it use some other homogeneity critreia?
Mike Croucher
Mike Croucher 2025-2-18
I'll ask internally and see what I can find
Joe
Joe 2025-2-18
That would be fantastic, thank you!
Joe
Joe 2025-2-19
That is super helpful, thank you!

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