graythresh

Global image threshold using Otsu's method

Syntax

level = graythresh(I)
[level EM] = graythresh(I)

Description

level =
graythresh(I) computesa global threshold (level) that can be used toconvert an intensity image to a binary image with
im2bw. level isa normalized intensity value that lies in the range
[0, 1].

The graythresh function uses Otsu's method,which chooses the threshold to minimize the intraclass variance ofthe black and white pixels.

Multidimensional arrays are converted automatically to 2-D arraysusing reshape. The
graythresh functionignores any nonzero imaginary part of I.

[level EM] =
graythresh(I) returnsthe effectiveness metric, EM, as the second outputargument. The effectiveness metric is a value in the range [0 1] thatindicates the effectiveness of the thresholding of the input image.The lower bound is attainable
only by images having a single graylevel, and the upper bound is attainable only by two-valued images.

Class Support

The input image I can be of class uint8, uint16,
int16, single,or double andit must be nonsparse. The return value
level isa double scalar. The effectiveness metric EM isa double scalar.

Examples

I = imread('coins.png');
level = graythresh(I);
BW = im2bw(I,level);
imshow(BW)

See Also

im2bw

Reference

[1] Otsu, N., "A Threshold Selection Methodfrom Gray-Level Histograms,"
IEEE Transactions on Systems,Man, and Cybernetics, Vol. 9, No. 1, 1979, pp. 62-66.