Drawing shapes in images

asked 2014-04-02 07:14:56 -0600

FLY
853 ●3 ●11 ●31

I am trying to draw the circle in the center if the images , like the image below

image description

there may be the images of many shapes/size but i want to draw circle/eclipse every time in the same way.

Below is the code i tried for it

        Mat img = imread ("E:\\test.jpg");
        int center_img = (img.rows*img.cols)/2;
        double radius_img = img.rows/2+img.cols/2;
        circle(img,Point(img.rows/2,img.cols/2), img.rows/2,1, 8,0);
        imshow ("img" , img);
        cvWaitKey(0);

answered 2014-04-02 07:47:12 -0600

Haris

3804 ●3 ●28 ●57

updated 2014-04-02 07:48:34 -0600

Its nothing but you have to draw ellipse() but need to adjust the parameters, like

center=your image centre
axes = Size(img.cols/2,img.rows/2) // width/2 X height/2
angle=0;
startAngle=0;
endAngle=360;

Now draw ellipse using above

ellipse(img,Point(img.cols/2,img.rows/2), Size(img.cols/2,img.rows/2),0,0,360, Scalar(0,0,255), 2, 8,0);

image description

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Can you please tell me about this axes = Size(img.cols/2,img.rows/2) // width/2 X height/2 why we need to use this , whats its actually functionality

FLY ( 2014-04-02 07:53:36 -0600 )edit

It is half of size of ellipse axis, go to docs it's well explained there with picture.

Haris ( 2014-04-02 08:48:22 -0600 )edit

i didn't understand from there thats why i asked here

FLY ( 2014-04-02 12:06:18 -0600 )edit

It is half of the size of ellipse axes, that is the horizontal and vertical lines passing through the centre. If you want to visualize it, just change size to Size(img. cols/4,img.rows/2) and see the major axis of ellipse become(width) reduced.

Haris ( 2014-04-02 13:02:28 -0600 )edit

what if i want to delete the area in the ellipse and make the ellipse covered area transparent

FLY ( 2014-04-30 08:22:37 -0600 )edit

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