OpenCV python: How do I draw a line using the gradient and the first point?

问题

I am trying to draw a line using a live feed with opencv. I am using one frame and storing the x,y coordinates. I use the next frame's x,y coordinate of the point to work out the gradient ((y2-y1)/(x2-x1)). I want to draw a straight line from the first coordinate straight through the second and continue past which would draw a trajectory. I can currently draw a straight line between the two points using cv2.line(). My code is below. Any suggestions would be wonderful! Thank you

import numpy as np
import math
import matplotlib.pyplot as plt

lower_red = np.array([-10,160,160])
upper_red = np.array([10,255,255])

oX, oY = 0,0

cap = cv2.VideoCapture(0)
if not cap.isOpened():
    print("Cannot open camera")
    exit()
while(1):
    ret, frame = cap.read()
    if not ret:
        print("Can't receive frame (stream end?). Exiting ...")
        break

    hsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)
    mask = cv2.inRange(hsv, lower_red, upper_red)
    #ret, thresh = cv2.threshold(mask, 80, 255, cv2.THRESH_BINARY)
    contours, _ = cv2.findContours(mask, cv2.RETR_TREE, cv2.CHAIN_APPROX_NONE)

    if len(contours) != 0:
        c = max(contours, key = cv2.contourArea)
        x1, y1, w, h = cv2.boundingRect(c)
        x2, y2 = x1 + w, y1 + h
        cv2.rectangle(frame, (x1, y1), (x2, y2), (0, 255, 0), 2)
        x3, y3 = round((x1+x2)/2), round((y1+y2)/2)
        cv2.circle(frame, (x3,y3), 4, (255,0,0), 2)
        #print(x3, y3)

        if oX and oY != 0:
            try:
                angle = (x3-oX)/(y3-oY)
                cv2.line(frame,(oX,oY),(x3, y3),(0,255,255),2)
            except ZeroDivisionError:
                oX, oY = x3, y3

    oX, oY = x3, y3

    cv2.imshow('frame', frame)
    cv2.imshow('mask', mask)


    if cv2.waitKey(1) == ord('q'):
        break
# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()

回答1:

Found a solution from this answer which was in c, Converted to python and modified for your usecase.

Solution to draw infinte line in image given two points.

def slope(x1,y1,x2,y2):
    ###finding slope
    if x2!=x1:
        return((y2-y1)/(x2-x1))
    else:
        return 'NA'

def drawLine(image,x1,y1,x2,y2):

    m=slope(x1,y1,x2,y2)
    h,w=image.shape[:2]
    if m!='NA':
        ### here we are essentially extending the line to x=0 and x=width
        ### and calculating the y associated with it
        ##starting point
        px=0
        py=-(x1-0)*m+y1
        ##ending point
        qx=w
        qy=-(x2-w)*m+y2
    else:
    ### if slope is zero, draw a line with x=x1 and y=0 and y=height
        px,py=x1,0
        qx,qy=x1,h
    cv2.line(image, (int(px), int(py)), (int(qx), int(qy)), (0, 255, 0), 2)

you can replace (px,py) with (x1,y1) or (qx,qy) with (x2,y2) according to your usecase.

来源：https://stackoverflow.com/questions/59578855/opencv-python-how-do-i-draw-a-line-using-the-gradient-and-the-first-point

标签

python

OpenCV

line

opencv-python