|Image Processing Toolbox User's Guide|
Compute global image threshold using Otsu's method
computes a global threshold (
level = graythresh(I)
level) that can be used to convert an intensity image to a binary image with
level is a normalized intensity value that lies in the range
graythresh function uses Otsu's method, which chooses the threshold to minimize the intraclass variance of the black and white pixels.
Multidimensional arrays are converted automatically to 2-D arrays using
graythresh function ignores any nonzero imaginary part of
[level EM] = graythresh(I)
returns the effectiveness metric,
EM, as the second output argument. The effectiveness metric is a value in the range [0 1] that indicates the effectiveness of the thresholding of the input image. The lower bound is attainable only by images having a single gray level, and the upper bound is attainable only by two-valued images.
The input image
I can be of class
double and it must be nonsparse. The return value
level is a double scalar. The effectiveness metric
EM is a double scalar.
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.
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