how otsu multithresh works?

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mo ma
mo ma on 20 Aug 2013
hello can anyone explain me how otsu multithresh works?

Answers (2)

Amith Kamath
Amith Kamath on 22 Aug 2013
From http://en.wikipedia.org/wiki/Otsu%27s_method, the algorithm assumes that the image to be thresholded contains two classes of pixels or bi-modal histogram (e.g. foreground and background) then calculates the optimum threshold separating those two classes so that their combined spread (intra-class variance) is minimal.
MULTITHRESH can accept another argument that decides how many such classes of pixels are needed, so that you can segment the image over multiple levels.
http://www.mathworks.com/help/images/ref/multithresh.html#btksdqr-1 shows some examples using MULTITHRESH and IMQUANTIZE which may be instructive.

Anand
Anand on 22 Aug 2013
Look at the paper referenced in the documentation page for multithresh. The link is below:
Specifically, look at section III.B for an explanation.
The basic idea is to find the two thresholds that maximize between class variance over the gray levels in the image. A search-based optimization is used (fminsearch) to determine the two thresholds. The best way to understand is by looking at lines 141-155 in multithresh.
>>edit multithresh

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