opencv draw ellipse

To draw an ellipse using opencv in the Python environment, you need to use the cv2.ellipse() function.

The following sample program is to use this function to draw a white ellipse with a center at (260,240), a major axis 170, a minor axis 130, and a line width of 3 on a black background.

import cv2
import numpy as np
 
img=np.zeros((512,512,3),np.uint8) #设置背景
cv2.ellipse(img, (260, 240), (170, 130), 0, 0, 360, (255, 255, 255), 3) #画椭圆
cv2.imshow("test",img) #显示
cv2.waitKey(0) #按下任意键退出
cv2.destroyAllWindows()

The cv2.ellipse() function is more complicated. The parameters involved are described in detail below:

Function prototype:

cv2.ellipse(img, center, axes, angle, startAngle, endAngle, color, thickness, lineType, shift) 

The meaning of each parameter is as follows:

img: the image to be drawn

center: the coordinates of the center point of the ellipse

axes: ellipse size (ie long and short axis)

angle: rotation angle (clockwise)

startAngle: the starting angle of drawing (clockwise)

endAngle: the end angle of drawing (for example, drawing the entire ellipse is 0,360, drawing the lower half of the ellipse is 0,180)

color: line color (BGR)

thickness: thickness of the line (default = 1)

lineType: line type (default value=8)

shift: the precision of the center coordinate point and the number axis (default value=0)

By the way, introduce several commonly used drawing functions:

1. Draw a straight line cv2.line()

cv2.line(img, Point pt1, Point pt2, color, thickness=1, line_type=8, shift=0)

pt1 and pt2 respectively represent the two end points of the straight line.

2. Draw a rectangle cv2.rectangle()

cv2.rectangle(img, Point pt1, Point pt2, color, thickness=1, line_type=8, shift=0)

pt1 and pt2 respectively represent the upper left corner and the lower right corner of the rectangle.

3. Draw a circle cv2.circle()

cv2.circle(img, center, radius, color, thickness, lineType, shift) 

center, radius represents the center and radius of the circle.