Connect new point to the previous point on a image with a straight line in Opencv-Python

OpenCV-Python is a library of Python bindings designed to solve computer vision problems. Let’s see how to Connect a new point to the previous point on an image with a straight line.

Step 1: Draw points on image:

On a image we can mark points using cv2.circle( ) method. This method is used to draw a circle on any image.

Syntax: cv2.circle(image, center_coordinates, radius, color, thickness)

Parameters: This method will take the following parameters:

image: It is the image on which circle is to be drawn.

center_coordinates: It is the center coordinates of the circle. The coordinates are represented as tuples of two values i.e. (X coordinate value, Y coordinate value).

radius: It is the radius of the circle.

color: It is the color of the borderline of the circle to be drawn. For BGR, we pass a tuple. eg: (255, 0, 0) for blue color.

thickness: It is the thickness of the circle borderline in px. The thickness of -1 px will fill the rectangle shape by the specified color.

Return: It returns an image with a circle drawn on it.

Step 2: Joining two points through a straight line:

We can join two points on an image using the cv2.line() method. This method is used to draw a line on any image.

Syntax: cv2.circle(image, center_coordinates, radius, color, thickness)

Parameters: This method will take the following parameters:

image: It is the image on which circle is to be drawn.

center_coordinates: It is the center coordinates of the circle. The coordinates are represented as tuples of two values i.e. (X coordinate value, Y coordinate value).

radius: It is the radius of the circle.

color: It is the color of the borderline of the circle to be drawn. For BGR, we pass a tuple. eg: (255, 0, 0) for blue color.

thickness: It is the thickness of the circle borderline in px. The thickness of -1 px will fill the rectangle shape by the specified color.

Return Value: It returns an image with a line drawn on it.

Below is the implementation:

Python3

# importing required packages 
import cv2 
import numpy as np 
  
# mouse call back function 
def click_event(event, x, y, 
                flags, params): 
    
    # if the left button of mouse  
    # is clicked then this  
    # condition executes 
    if event == cv2.EVENT_LBUTTONDOWN: 
        
        # appending the points we 
        # clicked to list 
        points.append((x,y)) 
          
        # marking the point with a circle 
        # of center at that point and  
        # small radius 
        cv2.circle(img,(x,y), 4,  
                   (0, 255, 0), -1) 
          
        # if length of points list  
        # greater than2 then this 
        # condition executes 
        if len(points) >= 2: 
            
            # joins the current point and 
            # the previous point in the 
            # list with a line 
            cv2.line(img, points[-1], points[-2], 
                     (0, 255, 255), 5) 
              
        # displays the image 
        cv2.imshow('image', img) 
          
# making an black image 
# of size (512,512,3) 
# create 3-d numpy  
# zeros array 
img = np.zeros((512, 512, 3), 
             np.uint8) 
  
# decalre a list to append all the  
# points on the image we clicked  
points = [] 
  
# show the image 
cv2.imshow('image',img) 
  
# setting mouse call back 
cv2.setMouseCallback('image', 
                     click_event) 
  
# no waiting 
cv2.waitKey(0) 
  
# To close the image 
# window that we opened 
cv2.destroyAllWindows()

My Personal Notes

Python3

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