C++ 双线性插值缩放图像

缩放灰度图

cv::Mat bilinear(cv::Mat src, int row, int col){
int rows = src.rows, cols = src.cols;
cv::Mat dst(row, col, src.type());
for(int i = 0; i < row; ++i) {
//以ptr的方式访问dst的数据
uchar *p = dst.ptr<uchar>(i);
//使两个图像的几何中心重合，采样更合理
float x = (i+0.5)*rows/row-0.5;
int fx = (int)x;
//x为坐标的小数部分
x -= fx;
//以整数计算速度更快
short x1 = (1.f-x)*2048;
short x2 = 2048 - x1;
for(int j = 0; j < col; ++j) {
//trick
float y = (j+0.5)*cols/col-0.5;
int fy = (int)y;
y -= fy;
//trick
short y1 = (1.f-y)*2048;
short y2 = 2048 - y1;
//结果右移22位抵消2048的平方
p[j] = (src.at<uchar>(fx,fy)*x1*y1 + src.at<uchar>(fx+1,fy)*x2*y1
+src.at<uchar>(fx,fy+1)*x1*y2 + src.at<uchar>(fx+1,fy+1)*x2*y2) >> 22;
}
}
return dst;
}