Bilinear Interpolation

Bilinear_Interpolation.cpp

for (int i = 0; i < output.rows; i++)
{
	uchar *out_data = output.ptr<uchar>(i);
	for (int j = 0; j < output.cols; j++)
	{
		double ox;
		double oy;
		//Calculate the old point(ox, oy) according to j, i
		//Thus, find a function f:(j, i)->(ox, oy) to get the result like (ox, oy)=f(j, i)
		int x1 = ox < 0 ? 0 : ox;
		int y1 = oy < 0 ? 0 : oy;
		int x2 = x1 + 1 >= WIDTH ? x1 : x1 + 1;
		int y2 = y1 + 1 >= HEIGHT ? y1 : y1 + 1;
		double u = ox - x1;
		double v = oy - y1;

		const uchar *src_data1 = src.ptr<uchar>(y1);
		const uchar *src_data2 = src.ptr<uchar>(y2);

		out_data[3 * j] =
			(1 - u) * (1 - v) * src_data1[3 * x1] +
			u * (1 - v) * src_data1[3 * x2] +
			(1 - u) * v * src_data2[3 * x1] +
			u * v * src_data2[3 * x2];

		out_data[3 * j + 1] =
			(1 - u) * (1 - v) * src_data1[3 * x1 + 1] +
			u * (1 - v) * src_data1[3 * x2 + 1] +
			(1 - u) * v * src_data2[3 * x1 + 1] +
			u * v * src_data2[3 * x2 + 1];

		out_data[3 * j + 2] =
			(1 - u) * (1 - v) * src_data1[3 * x1 + 2] +
			u * (1 - v) * src_data1[3 * x2 + 2] +
			(1 - u) * v * src_data2[3 * x1 + 2] +
			u * v * src_data2[3 * x2 + 2];
	}
}