OpenCV: how to rotate IplImage?

Question

I need to rotate an image by very small angle, like 1-5 degrees. Does OpenCV provide simple way of doing that? From reading docs i can assume that getAffineTransform() should be involved, but there is no direct example of doing something like:

IplImage *rotateImage( IplImage *source, double angle); 

Answer 1

If you use OpenCV > 2.0 it is as easy as

using namespace cv;  Mat rotateImage(const Mat& source, double angle) {     Point2f src_center(source.cols/2.0F, source.rows/2.0F);     Mat rot_mat = getRotationMatrix2D(src_center, angle, 1.0);     Mat dst;     warpAffine(source, dst, rot_mat, source.size());     return dst; } 

Note: angle is in degrees, not radians.

See the C++ interface documentation for more details and adapt as you need:

• getRotationMatrix
• warpAffine

Answer 2

Edit: To down voter: Please comment the reason for down voting a tried and tested code?

#include "cv.h" #include "highgui.h" #include "math.h" int main( int argc, char** argv ) {     IplImage* src = cvLoadImage("lena.jpg", 1);         IplImage* dst = cvCloneImage( src );      int delta = 1;     int angle = 0;     int opt = 1;   // 1： rotate & zoom                // 0:  rotate only     double factor;     cvNamedWindow("src", 1);     cvShowImage("src", src);      for(;;)     {     float m[6];     CvMat M = cvMat(2, 3, CV_32F, m);     int w = src->width;     int h = src->height;      if(opt)           factor = (cos(angle*CV_PI/180.) + 1.05) * 2;     else          factor = 1;     m[0] = (float)(factor*cos(-angle*2*CV_PI/180.));     m[1] = (float)(factor*sin(-angle*2*CV_PI/180.));     m[3] = -m[1];     m[4] = m[0];     m[2] = w*0.5f;       m[5] = h*0.5f;        cvGetQuadrangleSubPix( src, dst, &M);     cvNamedWindow("dst", 1);     cvShowImage("dst", dst);     if( cvWaitKey(1) == 27 )         break;     angle =(int)(angle + delta) % 360;     }          return 0; } 

UPDATE: See the following code for rotation using warpaffine https://code.google.com/p/opencvjp-sample/source/browse/trunk/cpp/affine2_cpp.cpp?r=48

#include <cv.h> #include <highgui.h>  using namespace cv;  int main(int argc, char **argv) {   // (1)load a specified file as a 3-channel color image,   //    set its ROI, and allocate a destination image   const string imagename = argc > 1 ? argv[1] : "../image/building.png";   Mat src_img = imread(imagename);   if(!src_img.data)     return -1;   Mat dst_img = src_img.clone();    // (2)set ROI   Rect roi_rect(cvRound(src_img.cols*0.25), cvRound(src_img.rows*0.25), cvRound(src_img.cols*0.5), cvRound(src_img.rows*0.5));   Mat src_roi(src_img, roi_rect);   Mat dst_roi(dst_img, roi_rect);    // (2)With specified three parameters (angle, rotation center, scale)   //    calculate an affine transformation matrix by cv2DRotationMatrix   double angle = -45.0, scale = 1.0;   Point2d center(src_roi.cols*0.5, src_roi.rows*0.5);   const Mat affine_matrix = getRotationMatrix2D( center, angle, scale );    // (3)rotate the image by warpAffine taking the affine matrix   warpAffine(src_roi, dst_roi, affine_matrix, dst_roi.size(), INTER_LINEAR, BORDER_CONSTANT, Scalar::all(255));    // (4)show source and destination images with a rectangle indicating ROI   rectangle(src_img, roi_rect.tl(), roi_rect.br(), Scalar(255,0,255), 2);    namedWindow("src", CV_WINDOW_AUTOSIZE);   namedWindow("dst", CV_WINDOW_AUTOSIZE);   imshow("src", src_img);   imshow("dst", dst_img);   waitKey(0);    return 0; }