Rotate cv::Mat using cv::warpAffine offsets destination image

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I’ve found a solution that doesn’t involve warpAffine().

But before that, I need to state (for future references) that my suspicion was right, you needed to pass the size of the destination when calling warpAffine():

warpAffine(image, rotated_img, rot_matrix, rotated_img.size());

As far as I can tell, the black border (caused by writing at an offset) drawed by this function seems to be it’s standard behavior. I’ve noticed this with the C interface and also with the C++ interface of OpenCV running on Mac and Linux, using the versions 2.3.1a and 2.3.0.

The solution I ended up using is much simpler than all this warp thing. You can use cv::transpose() and cv::flip() to rotate an image by 90 degrees. Here it is:

Mat src = imread(argv[1], 1);

cv::Mat dst;
cv::transpose(src, dst);
cv::flip(dst, dst, 1);

imwrite("rotated90.jpg", dst);

—-I>

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