Rotate back an image in opencv c++

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I use this code to rotate my image in OpenCV:

// get rotation matrix for rotating the image around its center
Point2f center22(RGBsrc.cols/2.0, RGBsrc.rows/2.0);
Mat rot = getRotationMatrix2D(center22, Angle, 1.0);
// determine bounding rectangle
Rect bbox = RotatedRect(center22,RGBsrc.size(),Angle).boundingRect();
// adjust transformation matrix
rot.at<double>(0,2) += bbox.width/2.0 - center22.x;
rot.at<double>(1,2) += bbox.height/2.0 - center22.y;
Mat dst;
warpAffine(RGBsrc, dst, rot, bbox.size());
imshow("rotated_im", dst);

It works correctly. Now I want to rotate that image back to the original image. When I use the code below, I see the locations of objects in the image are not the same as in the original image. Why is this and how can I rotate my image back?

Point2f center22(RGBsrc.cols/2.0, RGBsrc.rows/2.0);
Mat rot2 = getRotationMatrix2D(center22, -Angle, 1.0);
Rect bbox2 = RotatedRect(center22,RGBsrc.size(), -Angle).boundingRect();
rot2.at<double>(0,2) += bbox2.width/2.0 - center22.x;
rot2.at<double>(1,2) += bbox2.height/2.0 - center22.y;
Mat Rotatedback;
warpAffine(RotatedRGB, Rotatedback, rot2, bbox2.size());
image-rotation opencv image c++
2 Answers

If you add the WARP_INVERSE_MAP flag when calling warpAffine(), it will apply the inverse transform matrix, getting you back to your original image. For example, you should be able to replace the last line of code in your question with something like the following:

warpAffine(RotatedRGB, Rotatedback, rot, RGBsrc.size(), INTER_LINEAR|WARP_INVERSE_MAP);

Note: I haven't tested this code, but I have used WARP_INVERSE_MAP to do the same thing with warpPerspective() and it worked perfectly.

Documentation: https://docs.opencv.org/3.4/da/d54/group__imgproc__transform.html#ga0203d9ee5fcd28d40dbc4a1ea4451983

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