The C++ Augmented Reality Toolkit

Appendix A - Sample Otsu Thresholding C++ Code

// NOTE: Creation of histogram[256] not shown



float  w = 0;                // first order cumulative

float  u = 0;                // second order cumulative

float  uT = 0;               // total mean level



int    k = 255;              // maximum histogram index

int    threshold = 0;        // optimal threshold value



float  histNormalized[256];  // normalized histogram values



float  work1, work2;		// working variables

double work3 = 0.0;

	



// Create normalised histogram values

// (size=image width * image height)

for (int I=1; I<=k; I++) 

histNormalized[I-1] = histogram[I-1]/(float)size;





// Calculate total mean level

for (int I=1; I<=k; I++) 

uT+=(I*histNormalized[I-1]);





// Find optimal threshold value

for (int I=1; I<k; I++) {

    w+=histNormalized[I-1];

    u+=(I*histNormalized[I-1]);

    work1 = (uT * w - u);

    work2 = (work1 * work1) / ( w * (1.0f-w) );

    if (work2>work3) work3=work2;

}



// Convert the final value to an integer

threshold = (int)sqrt(work3);