How to get threshold value from histogram?

Question

I\'m writing an Android app in OpenCV to detect blobs. One task is to threshold the image to differentiate the foreground objects from the background (see image).

It wo

Answer 1

The following is a C++ implementation of Abid's answer that works with OpenCV 3.x:

// Convert the source image to a 1 channel grayscale:
Mat gray;
cvtColor(src, gray, CV_BGR2GRAY);
// Apply the threshold function with the CV_THRESH_OTSU setting as well
// You can skip having it return the value, but I include it for showing the
// results from OTSU
double thresholdValue = threshold(gray, gray, 0, 255, CV_THRESH_BINARY+CV_THRESH_OTSU);
// Present the threshold value
printf("Threshold value: %f\n", thresholdValue);

Running this against the original image, I get the following:

OpenCV calculated a threshold value of 122 for it, close to the value Abid found in his answer.

Just to verify, I altered the original image as seen here:

And produced the following, with a new threshold value of 178: