How to I get a threshold value from looking at histogram

I need to get a threshold value not by looking at the graph I was told there is a way to calculate the threshold value from the histogram, Can someone help me

[Youssef Khmou]

what is the purpose of this threshold ?

[Chok Chuan]

I = imread('Test1.tif'); J=rgb2gray(I); figure; imhist(J);

thresholdValue = 100; bw = J > thresholdValue;

I am currently putting a casual 100 inside after looking at the histogram. I need the threshold value to segment the picture into fore and background. Is the a way to calculate a precise threshold value.

Answer 1

[Youssef Khmou]

Otsu's method exists as built in function with name graythresh, here is an example taken from Mathworks help page :

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

there might be other techniques to choose an adequate threshold.