Python OpenCV using Notes (ii) (Simple geometric image drawing)

Simple geometric images typically include points, lines, matrices, circles, ellipses, polygons, and so on. First of all, recognize OpenCV's definition of pixel points.

A pixel of an image has 1 or 3 values. Grayscale image has a gray value, the color image has 3 values to form a pixel value. They show a different color.

Then there is a little talent to make up a variety of polygons.

(i) Draw a line first

Function: Cv2.line (img,point pt1,point pt2,color,thickness=1,line_type=8 shift=0)
The representative with the value has a default value. You don't have to. Can see that this function mainly accepts the coordinates of the number of two points, the color of the line (color Image color is a 1*3 array) such as the following:

import cv2importas npfromimportas pltimg = np.zeros((512,512),np.uint8)#生成一个空灰度图像cv2.line(img,(0,0),(511,511),255,5)plt.imshow(img,‘gray‘)

import cv2importas npfromimportas pltimg = np.zeros((512,512,3),np.uint8)#生成一个空彩色图像cv2.line(img,(0,0),(511,511),(155,155,155),5)plt.imshow(img,‘brg‘)

(ii) Draw a rectangle

Functions: Cv2.rectangle (IMG, (380,0), (511,111), (255,0,0), 3), the two points of the rectangle (upper-left corner and lower-right corner) need to be determined. Color, the type of line (not set to default).
For example:

import cv2importas npfromimportas pltimg = np.zeros((512,512,3),np.uint8)#生成一个空彩色图像cv2.rectangle(img,(20,20),(411,411),(55,255,155),5)plt.imshow(img,‘brg‘)

(iii) Draw round

Drawing a circle is also very easy, just need to determine the center and radius, function:
Cv2.circle (IMG, (380,0), 63, (255,0,0), 3), for example:

import cv2importas npfromimportas pltimg = np.zeros((512,512,3),np.uint8)#生成一个空彩色图像cv2.circle(img,(200,200),50,(55,255,155),1)#改动最后一个參数plt.imshow(img,‘brg‘)

import cv2importas npfromimportas pltimg = np.zeros((512,512,3),np.uint8)#生成一个空彩色图像cv2.circle(img,(200,200),50,(55,255,155),8)#改动最后一个參数plt.imshow(img,‘brg‘)

(d) Draw an ellipse

The

Ellipse is more complex, involving the long axis short axis, ellipse center, rotation angle, and so on, see the introduction of OPENCV reference manual:

Image for example:

Example:

import  cv2import  numpy as  npfrom  Matplotlib import  pyplot as  pltimg = Np.zeros (( Span class= "Hljs-number" >512 , 512 , 3 ), np.uint8)  #生成一个空彩色图像  cv2.ellipse (img, 256 , Span class= "Hljs-number" >256 ), (150 , 100  ), 0 , 0 , 180 , Span class= "Hljs-number" >250 ,-1 )  #注意最后一个參数-1, Indicates that the image is populated and is not populated by default, assuming that the ellipse outlines only the  plt.imshow (img,)  

Python OpenCV using Notes (ii) (Simple geometric image drawing)