# what is 2D otsu algorithm and how to implement it

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hend on 20 Aug 2014
Commented: Image Analyst on 9 Jan 2021
I'm a little confusing about what does 2D-Otsu mean? and how to implement it? I didn't find enough information about it in the site. and I hope anyone can help me

Image Analyst on 20 Aug 2014
It's a thresholding method. It's implemented in the Image Processing Toolbox function graythresh(). In most cases I find it to be sub-optimal. It's best for images with a nice bimodal histogram, like you'd get with a light part/object/region on a uniform background. For anything complicated it's not so great and you'd need to write a custom thresholding algorithm.
Image Analyst on 9 Jan 2021
I don't know that method. Exactly what spatial relationship does it look at and what does it do with those? So I guess you're saying this is neither a global Otsu threshold over the whole image, nor a spatially adaptive one that computes the threshold based on a scanning 2-D window. But I don't know what other kinds of Otsu there are.
Personally I find Otsu not as useful as triangle thresholding, which I attach code for. This is because often/usually you don't have nice bimodal histograms and usually what I see are skewed unimodal histograms which the triangle threshold is perfect for.

William Frane on 20 Aug 2014
Edited: William Frane on 20 Aug 2014
Otsu's method (as it's more commonly known) is an image thresholding method used to convert a grayscale image to a binary one. MATLAB's graythresh() function (see this page) is an implementation of Otsu's method. If you're curious about the actual algorithm, it's described in the appropriate Wikipedia article.
Also, just a side note: the MATLAB documentation page for graythresh() that I linked to above was the first result for a Google search of the string matlab otsu algorithm, so don't hesitate to check Google for queries such as this; there's often useful information already available.
Lars Abrahamsson on 9 Jan 2021
But the question was about 2-dimensional Otsu. That is not included in Matlab and has to be written manually, I think.

Meshooo on 21 Aug 2014
Edited: Walter Roberson on 9 Jan 2021
Otsu method is a well-known thresholding method. In other words, it can find the threshold value to convert your image to two levels (bilevels) 0 and 1.
This work was published lone time ago in 1979.
[1] Otsu, N., "A Threshold Selection Method from Gray-Level Histograms," IEEE Transactions on Systems, Man, and Cybernetics, Vol. 9, No. 1, 1979, pp. 62-66.