OpenCV defocus blur with custom kernel? - opencv

Question

I would like to simulate defocus blur, the intensity for each pixel in an image is:
1/(pi*r^2) for a given radius r, if the pixel is within sqrt(x^2+y^2) and 0 if not
(see code for better explanation)
This gives a blur/convolution kernel in a circular shape.
I tried to do this in opencv bu had no luck: opencv just "pixelizes" the edges of my image:
testimage http://www.bilderkiste.org/show/original/1131895735815/test_out.jpg
I can't really figure out why this is happening, here's my code so far:
//includes. then:
using namespace std;
#define KERNELLENGTH 3
#define PI 3.14159265
int main() {
IplImage *src = 0;
IplImage *dst = 0;
src = cvLoadImage("test.bmp"); //create image matrixes..
dst = cvLoadImage("test.bmp"); //
CvMat *filter;
double kernel[KERNELLENGTH * KERNELLENGTH]; //create an appropriate kernel
int r = KERNELLENGTH / 2; //calculate the radius
double value = 1 / (PI * KERNELLENGTH * KERNELLENGTH / (4 * r)); //calculate the defocus blur value
cout << "Kernel:" << "\n";
for (int x = 0; x < KERNELLENGTH; x++) //calculate kernel (seems to work right!)
{
for (int y = 0; y < KERNELLENGTH; y++) {
if (sqrt((x - KERNELLENGTH / 2) * (x - KERNELLENGTH / 2) + (y
- KERNELLENGTH / 2) * (y - KERNELLENGTH / 2)) <= r) {
kernel[y * 4 + x] = value; //Wert zuweisen
cout << value << "\t";
} else
cout << 0 << "\t";
}
cout << "\n";
}
filter = cvCreateMatHeader(KERNELLENGTH, KERNELLENGTH, CV_32FC1);//create the filter
cvSetData(filter, kernel, KERNELLENGTH * sizeof(kernel[0]));//link kernel and filter
cvFilter2D(src, //convolve filter and src, save to dst
dst, filter, cvPoint(-1, -1));
cvSaveImage("test_out.bmp", dst); //save dst on disk
cvReleaseImage(&src);
cvReleaseImage(&dst);
return 0;
}
I would really appreciate some help with this, thanks!

Answer 1

It seems the problem is in #define KERNELLENGTH 3, as you get KERNELLENGTH / 2 == 1 and the kernel is 3-by-3 something, which I wouldn't call a proper defocus disk.
Have you tested with e.g. #define KERNELLENGTH 10?