本节实现的是使用OpenCV里自带的函数，绘制直线、长方形、圆形和椭圆。

• 绘制直线
• 绘制长方形
• 绘制圆形
• 绘制椭圆
• 添加文字

实现过程

引用与创建空图

不再赘述，代码如下。

import cv2  
import numpy

# empty image
img = np.zeros((512, 512, 3), np.uint8)

绘制直线

使用opencv自带的line()函数绘制一条对角线，其声明如下：

cv2.line(img, pt1, pt2, color[, thickness[, lineType[, shift]]])

其中各种参数的意义如下：

• img – Image.
• pt1 – First point of the line segment.
• pt2 – Second point of the line segment.
• color – Line color.
• thickness – Line thickness.
• lineType – Type of the line:

• shift – Number of fractional bits in the point coordinates.

在本文中，我绘制的直线从(0,0)到(511,511)，线的颜色为蓝色(255,0,0)，粗细为10，其他参数省略。

# draw a line
cv2.line(img, (0,0), (511,511), (255, 0, 0), 10)

绘制矩形

利用opencv自带的rectangle()函数可以绘制一个长方形，其声明如下：

cv2.rectangle(img, pt1, pt2, color[, thickness[, lineType[, shift]]]) 

其中各种参数的意义如下：

• img – Image.
• pt1 – Vertex of the rectangle.
• pt2 – Vertex of the rectangle opposite to pt1 .
• rec – Alternative specification of the drawn rectangle.
• color – Rectangle color or brightness (grayscale image).
• thickness – Thickness of lines that make up the rectangle. Negative values, like CV_FILLED , mean that the function has to draw a filled rectangle.
• lineType – Type of the line. See the line() description.
• shift – Number of fractional bits in the point coordinates.

本文中绘制一个长方形从(0,0)到(255,255)，设置线的颜色为绿色(0,255,0)，线的粗细为5，其他参数默认，如下：

# draw a rectangle
cv2.rectangle(img, (0,0), (255,255), (0, 255, 0), 5)

绘制圆

opencv里自带的circle()函数可以绘制以一个点为圆心特定半径的圆，其函数的声明如下：

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

其中各个参数的意义如下：

• img – Image where the circle is drawn.
• center – Center of the circle.
• radius – Radius of the circle.
• color – Circle color.
• thickness – Thickness of the circle outline, if positive. Negative thickness means that a filled circle is to be drawn.
• lineType – Type of the circle boundary. See the line() description.
• shift – Number of fractional bits in the coordinates of the center and in the radius value.

本文中绘制的圆的圆心为(255,255)，半径为127，线的颜色为红色，线的粗细为8，如下：

# draw a circle
cv2.circle(img, (255, 255), 127, (0, 0, 255), 8)

绘制椭圆

调用ellipse()函数绘制椭圆，其声明为：

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

其中各个参数的意义如下：

• img – Image.
• center – Center of the ellipse.
• axes – Half of the size of the ellipse main axes.
• angle – Ellipse rotation angle in degrees.
• startAngle – Starting angle of the elliptic arc in degrees.
• endAngle – Ending angle of the elliptic arc in degrees.
• box – Alternative ellipse representation via RotatedRect or CvBox2D. This means that the function draws an ellipse inscribed in the rotated rectangle.
• color – Ellipse color.
• thickness – Thickness of the ellipse arc outline, if positive. Otherwise, this indicates that a filled ellipse sector is to be drawn.
• lineType – Type of the ellipse boundary. See the line() description.
• shift – Number of fractional bits in the coordinates of the center and values of axes.

本文绘制了一个完整的椭圆，中心在(255,255)，长轴150，短轴75，旋转0°，起始角度0°，终止角度360°，线的颜色为黄色(0,255,255)，粗细为1。

# draw a ellipse
cv2.ellipse(img, (255, 255), (150, 75), 0, 0, 360, (0, 255, 255), 1) 

添加文字

opencv里的自带函数putText()可以在图像上加上文字，其声明如下：

cv2.putText(img, text, org, fontFace, fontScale, color[, thickness[, lineType[, bottomLeftOrigin]]])

各个参数的意义如下：

• img – Image.
• text – Text string to be drawn.
• org – Bottom-left corner of the text string in the image.
• font – CvFont structure initialized using InitFont().
• fontFace – Font type. One of FONT_HERSHEY_SIMPLEX, FONT_HERSHEY_PLAIN, FONT_HERSHEY_DUPLEX, FONT_HERSHEY_COMPLEX, FONT_HERSHEY_TRIPLEX, FONT_HERSHEY_COMPLEX_SMALL, FONT_HERSHEY_SCRIPT_SIMPLEX, or FONT_HERSHEY_SCRIPT_COMPLEX, where each of the font ID’s can be combined with FONT_ITALIC to get the slanted letters.
• fontScale – Font scale factor that is multiplied by the font-specific base size.
• color – Text color.
• thickness – Thickness of the lines used to draw a text.
• lineType – Line type. See the line for details.
• bottomLeftOrigin – When true, the image data origin is at the bottom-left corner. Otherwise, it is at the top-left corner.

本文在图像上显示OpenCV这几个字，如下：

font=cv2.FONT_HERSHEY_SIMPLEX
cv2.putText(img,'OpenCV',(10,500), font, 4,(255,255,255),2)

显示图像

显示最终绘制完的图像：

# show image
cv2.imshow("shape", img)

cv2.waitKey(0)
cv2.destroyAllWindows()

源代码

整个程序的源代码如下：

# created by Huang Lu
# 27/08/2016 17:59:31  
# Department of EE, Tsinghua Univ.

import cv2
import numpy as np

# empty image
img = np.zeros((512, 512, 3), np.uint8)

# draw a line
cv2.line(img, (0,0), (511,511), (255, 0, 0), 10)

# draw a rectangle
cv2.rectangle(img, (0,0), (255,255), (0, 255, 0), 5)

# draw a circle
cv2.circle(img, (255, 255), 127, (0, 0, 255), 8)

# draw a ellipse
cv2.ellipse(img, (255, 255), (150, 75), 0, 0, 360, (0, 255, 255), 1)

# add text
font=cv2.FONT_HERSHEY_SIMPLEX
cv2.putText(img,'OpenCV',(10,500), font, 4,(255,255,255),2)

# show image
cv2.imshow("shape", img)

cv2.waitKey(0)
cv2.destroyAllWindows()

也可以参考我的GitHub上的，点击这里。

运行结果

在命令行进入该源程序所在目录后，运行python main.py后即可显示结果。显示结果如下：

参考

• http://docs.opencv.org/2.4/modules/core/doc/drawing_functions.html
• OpenCV-Python-Toturial-中文版.pdf
• https://github.com/hlthu/Python-OpenCV-Learn/tree/master/Draw_Shape/