How to draw a rounded rectangle (rectangle with rounded corners) with OpenCV?

问题

How can I draw a rectangle with rounded corners in OpenCV? I know that the functions ellipse() and line() can be simply put together to draw it. I just wonder if someone has done it before and has put it in a proper function so I can use it? Ideally the corner radius is to calibrate in a parameter.

I searched a lot for that, but it seems no one had that problem before. If no one has such I function I will probably post my own solution here in a few days.

回答1:

I realized, this is much easier that I thought. Here is my function. I hope it is helpful for someone.

/**
 * Draws a rectangle with rounded corners, the parameters are the same as in the OpenCV function @see rectangle();
 * @param cornerRadius A positive int value defining the radius of the round corners.
 * @author K
 */
void rounded_rectangle( Mat& src, Point topLeft, Point bottomRight, const Scalar lineColor, const int thickness, const int lineType , const int cornerRadius)
{
    /* corners:
     * p1 - p2
     * |     |
     * p4 - p3
     */
    Point p1 = topLeft;
    Point p2 = Point (bottomRight.x, topLeft.y);
    Point p3 = bottomRight;
    Point p4 = Point (topLeft.x, bottomRight.y);

    // draw straight lines
    line(src, Point (p1.x+cornerRadius,p1.y), Point (p2.x-cornerRadius,p2.y), lineColor, thickness, lineType);
    line(src, Point (p2.x,p2.y+cornerRadius), Point (p3.x,p3.y-cornerRadius), lineColor, thickness, lineType);
    line(src, Point (p4.x+cornerRadius,p4.y), Point (p3.x-cornerRadius,p3.y), lineColor, thickness, lineType);
    line(src, Point (p1.x,p1.y+cornerRadius), Point (p4.x,p4.y-cornerRadius), lineColor, thickness, lineType);

    // draw arcs
    ellipse( src, p1+Point(cornerRadius, cornerRadius), Size( cornerRadius, cornerRadius ), 180.0, 0, 90, lineColor, thickness, lineType );
    ellipse( src, p2+Point(-cornerRadius, cornerRadius), Size( cornerRadius, cornerRadius ), 270.0, 0, 90, lineColor, thickness, lineType );
    ellipse( src, p3+Point(-cornerRadius, -cornerRadius), Size( cornerRadius, cornerRadius ), 0.0, 0, 90, lineColor, thickness, lineType );
    ellipse( src, p4+Point(cornerRadius, -cornerRadius), Size( cornerRadius, cornerRadius ), 90.0, 0, 90, lineColor, thickness, lineType );
}

回答2:

Here's a Python implementation(in case anyone was looking for one): it draws a rounded corner (of random radius and line thickness --- change that if you want) border around an image:

def addRoundedRectangleBorder(img):
    height, width, channels = img.shape

    border_radius = int(width * random.randint(1, 10)/100.0)
    line_thickness = int(max(width, height) * random.randint(1, 3)/100.0)
    edge_shift = int(line_thickness/2.0)

    red = random.randint(230,255)
    green = random.randint(230,255)
    blue = random.randint(230,255)
    color = (blue, green, red)

    #draw lines
    #top
    cv2.line(img, (border_radius, edge_shift), 
    (width - border_radius, edge_shift), (blue, green, red), line_thickness)
    #bottom
    cv2.line(img, (border_radius, height-line_thickness), 
    (width - border_radius, height-line_thickness), (blue, green, red), line_thickness)
    #left
    cv2.line(img, (edge_shift, border_radius), 
    (edge_shift, height  - border_radius), (blue, green, red), line_thickness)
    #right
    cv2.line(img, (width - line_thickness, border_radius), 
    (width - line_thickness, height  - border_radius), (blue, green, red), line_thickness)

    #corners
    cv2.ellipse(img, (border_radius+ edge_shift, border_radius+edge_shift), 
    (border_radius, border_radius), 180, 0, 90, color, line_thickness)
    cv2.ellipse(img, (width-(border_radius+line_thickness), border_radius), 
    (border_radius, border_radius), 270, 0, 90, color, line_thickness)
    cv2.ellipse(img, (width-(border_radius+line_thickness), height-(border_radius + line_thickness)), 
    (border_radius, border_radius), 10, 0, 90, color, line_thickness)
    cv2.ellipse(img, (border_radius+edge_shift, height-(border_radius + line_thickness)), 
    (border_radius, border_radius), 90, 0, 90, color, line_thickness)

    return img

来源：https://stackoverflow.com/questions/18973103/how-to-draw-a-rounded-rectangle-rectangle-with-rounded-corners-with-opencv