Automatic Generation of Gauss Filter

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Formula


H(i,j) = (1 / 2pi sigma^2) e^{[(i-k-1)^2 + (j-k-1)^2] / (2*sigma^2)}

The size of the filter is 2k+1 and (i, j) represents a position in the coordinate. The origin of coordinate is the central position of the filter. Pi is circumference ratio and sigma is standard deviation.

Code

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ElementType** malloc2DArray(int nRow, int nColumn)
{
	ElementType **filter = (ElementType**)malloc(sizeof(ElementType*)*nRow);
	for (int y = 0;y < nRow;y++) {
		*(filter+y) = (ElementType*)malloc(sizeof(ElementType)*nColumn);
	}
	return filter;
}
ElementType** makeGaussianFilter(int size, ElementType sigma)
{
	ElementType** filter = malloc2DArray(size, size);
	int center = (size - 1) / 2;
	ElementType sum = 0;
	ElementType x2 = 0;
	ElementType y2 = 0;
	for (int y = 0;y < size;y++)
	{
		x2 = pow(ElementType(y-center), 2);
		for (int x = 0;x < size;x++)
		{
			y2 = pow(ElementType(x-center), 2);
			*(*(filter+y)+x) = exp(-(x2+y2) / (2*sigma*sigma));
			sum += *(*(filter+y)+x);
		}
	}
	if (0.0 != sum)
	{
		for (int y = 0;y < size;y++)
		{
			for (int x = 0;x < size;x++) {
				*(*(filter+y)+x) /= sum;
			}
		}
	}
	return filter;
}
ElementType* GaussianFilter(int size, ElementType sigma)
{
	if (!(size%2)) {
		size += 1;
	}
	ElementType **filter2D = makeGaussianFilter(size, sigma);
	ElementType *filter = (ElementType*)malloc(sizeof(ElementType)*size*size);
	for (int y = 0;y < size;y++)
	{
		for (int x = 0;x < size;x++) {
			*(filter+y*size+x) = *(*(filter2D+y)+x);
		}
	}
	return filter;
}