With OpenCV, it’s easy to rotate an image by code.

This is Lena:

Now, I want to rotate this picture 30 degree like this:

Here is the code:

``` cpp Rotate Lena 30 Degrees #include #include #include #include #include

//Created by Leon //http://leons.im //20, Mar, 2011

#define PI acos(-1) int main() { IplImage* img = 0; int height,width,step,channels; uchar *data, *result; int i,j,k,t,x,y; double angle = PI / 6; double cosa, sina; cosa = cos(angle); sina = sin(angle);

// load an image img=cvLoadImage(“lena.bmp”); if(!img){ printf(“Could not load image filen”); exit(0); }

// get the image data height = img->height; width = img->width; step = img->widthStep; channels = img->nChannels; data = (uchar *)img->imageData; result = (uchar *)malloc(height * step); printf(“Processing a %dx%d image with %d channelsn”,height,width,channels);

// create a window cvNamedWindow(“mainWin”, CV_WINDOW_AUTOSIZE); cvMoveWindow(“mainWin”, 100, 100);

// invert the image for(i=0;i<height;i++) { for(j=0;j<width;j++) { x = (j - width / 2) * cosa - (i - height / 2) * sina + width / 2; y = (j - width / 2) * sina + (i - height / 2) * cosa + height / 2; for(k=0;k<channels;k++) { t = y * step + x * channels + k; if (t >= 0 && t < height * step){ result[i * step + j * channels + k] = data[t]; } } } }

for (i = 0; i < height * step; ++i) {
	data[i] = result[i];
}   // show the image   cvShowImage("mainWin", img );

// wait for a key cvWaitKey(0);

// release the image cvReleaseImage(&img ); return 0; } ```

Here is my Makefile on Linux:

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CC = g++
CFLAGS = `pkg-config --cflags opencv` `pkg-config --libs opencv`

hello : hello-world.cpp
	PKG_CONFIG_PATH=/usr/local/lib/pkgconfig &&
	export PKG_CONFIG_PATH &&
	$(CC) $(CFLAGS) hello-world.cpp -o hello

You may change the angle to rotate to any degree you like. As you can see, the picture rotated is aliasing, so if anyone knows how to anti-aliasing, please tell me.