Comparison betweens resize/interpolation algorithms

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Hello, I'm trying to evaluate nearest, bilinear and bicubic interpolation algorithms from the resize function but all my images are exactly the same.

Can anyone help me?

Mat img; 
Mat img2;

img = imread("face2.png", IMREAD_UNCHANGED);

Size size(720,1080);

vector<int> com_param;
com_param.push_back(CV_IMWRITE_JPEG_QUALITY);
com_param.push_back(9);
cv::resize(img, img2, size, cv::INTER_NEAREST);
imwrite("nearest.jpg",img2,com_param);
cv::resize(img, img2, size, cv::INTER_NEAREST);
imwrite("bilinear.jpg",img2,com_param);
cv::resize(img, img2, size, cv::INTER_NEAREST);
imwrite("cubic.jpg",img2,com_param);