Mat rotation center

asked 2016-09-14 05:04:46 -0600

Hi, I'm rotating the 10x1 image by specifying center at 5,0:

[255, 255, 255, 255, 255, 255, 255, 255, 255, 255]

int size = 10;
Mat test = Mat::zeros(Size(size, 1), CV_8U);
line(test, Point(0, 0), Point(size, 0), Scalar(255));

Mat rot = getRotationMatrix2D(Point(test.cols/2, test.rows/2), 90, 1);
Mat dest;
warpAffine(test, dest, rot, Size(size, size));

imshow("Source", test);
imshow("Result", dest);

I assume that result will be the vertical line at center of 10x10 Mat, but it is shifted and cropped to the top:

[  0,   0,   0,   0,   0, 255,   0,   0,   0,   0;
   0,   0,   0,   0,   0, 255,   0,   0,   0,   0;
   0,   0,   0,   0,   0, 255,   0,   0,   0,   0;
   0,   0,   0,   0,   0, 255,   0,   0,   0,   0;
   0,   0,   0,   0,   0, 255,   0,   0,   0,   0;
   0,   0,   0,   0,   0, 255,   0,   0,   0,   0;
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0;
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0;
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0;
   0,   0,   0,   0,   0,   0,   0,   0,   0,   0]

I'm trying to understand why it happens?

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Thanks! I expected that rotation will be centered in resulting mat, but now I see it couldn't without explicitly specified offset:

Mat rot = getRotationMatrix2D(center, 90, 1);
rot.at<double>(0, 2) += 0; // x
rot.at<double>(1, 2) += size/2; // y

tischenkoalex ( 2016-09-14 14:07:20 -0600 )edit

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