main.cpp

#include <stdlib.h>
#include <stdio.h>
#include "cv.h"
#include "highgui.h"

#define IMAGE_WIDTH  640
#define IMAGE_HEIGHT 480
#define S (IMAGE_WIDTH/8)
#define T (0.15f)

void adaptiveThreshold(unsigned char* input, unsigned char* bin)
{
	unsigned long* integralImg = 0;
	int i, j;
	long sum=0;
	int count=0;
	int index;
	int x1, y1, x2, y2;
	int s2 = S/2;

	// create the integral image
	integralImg = (unsigned long*)malloc(IMAGE_WIDTH*IMAGE_HEIGHT*sizeof(unsigned long*));

	for (i=0; i<IMAGE_WIDTH; i++)
	{
		// reset this column sum
		sum = 0;

		for (j=0; j<IMAGE_HEIGHT; j++)
		{
			index = j*IMAGE_WIDTH+i;

			sum += input[index];
			if (i==0)
				integralImg[index] = sum;
			else
				integralImg[index] = integralImg[index-1] + sum;
		}
	}

	// perform thresholding
	for (i=0; i<IMAGE_WIDTH; i++)
	{
		for (j=0; j<IMAGE_HEIGHT; j++)
		{
			index = j*IMAGE_WIDTH+i;

			// set the SxS region
			x1=i-s2; x2=i+s2;
			y1=j-s2; y2=j+s2;

			// check the border
			if (x1 < 0) x1 = 0;
			if (x2 >= IMAGE_WIDTH) x2 = IMAGE_WIDTH-1;
			if (y1 < 0) y1 = 0;
			if (y2 >= IMAGE_HEIGHT) y2 = IMAGE_HEIGHT-1;
			
			count = (x2-x1)*(y2-y1);

			// I(x,y)=s(x2,y2)-s(x1,y2)-s(x2,y1)+s(x1,x1)
			sum = integralImg[y2*IMAGE_WIDTH+x2] -
				  integralImg[y1*IMAGE_WIDTH+x2] -
				  integralImg[y2*IMAGE_WIDTH+x1] +
				  integralImg[y1*IMAGE_WIDTH+x1];

			if ((long)(input[index]*count) < (long)(sum*(1.0-T)))
				bin[index] = 0;
			else
				bin[index] = 255;
		}
	}

	free (integralImg);
}

int main (int argc, char** argv)
{
	IplImage* cvFrame;
	IplImage* binImg;
	int key;

	cvFrame = cvLoadImage("image.bmp", -1);
	binImg = cvCreateImage(cvSize(IMAGE_WIDTH, IMAGE_HEIGHT), 8, 1);

	cvNamedWindow("Input", 1);
	cvNamedWindow("Output", 1);

	adaptiveThreshold((unsigned char*)cvFrame->imageData, (unsigned char*)binImg->imageData);

	cvShowImage("Input", cvFrame);
	cvShowImage("Output", binImg);

	key = cvWaitKey(0);

	return 0;
}