CODEWITHSUNDEEP
pythonglobal-variables
Larrea
Larrea

Reputation: 21

How can I assign to a global variable from inside a function? How do I reset a painted-over image with CV2?

I'm working on a small program that open an image and lets the user click on points to draw lines.

import datetime
import cv2 
import numpy

clicked = False

path = "files/file1.png"
coordinates = {'x':[],'y':[]}
def onMouse(event, x, y, flags, param):
 global image
 global clicked
 if event == cv2.EVENT_LBUTTONUP:
    coordinates['x'].append(x)
    coordinates['y'].append(y)
    clicked = True
    if (len(coordinates['x'])> 1 ):
        print("debug drawing line")
        cv2.line(image, (coordinates['x'][-2],coordinates['y'][-2]), (coordinates['x'][-1],coordinates['y'][-1]),(255,0,0),1)
  
    print('debug drawing point')
    cv2.circle(image,(coordinates['x'][-1],coordinates['y'][-1]), 3,(255,0,255),3)

def saveImage():
    xmin, xmax = min(coordinates['x']),max(coordinates['x'])
    ymin, ymax = min(coordinates['y']),max(coordinates['y'])
    nombre = datetime.datetime.strftime(datetime.datetime.now(),'%Y-%m-%d-%H-%M-%S')
    cv2.imwrite(f'files/Result-{nombre}.png',image[ymin:ymax,xmin:xmax])

image = cv2.imread(path) 
cv2.namedWindow("Display", cv2.WINDOW_AUTOSIZE) 
cv2.setMouseCallback('Display', onMouse)

active = True
while active: 
    cv2.imshow('Display', image)
    key = cv2.waitKey(1)
    if key == ord('q'):
         cv2.destroyAllWindows()
         active = False
    if key == ord('s'):
        saveImage()
        cv2.destroyAllWindows()
        active = False

The program opens an Image with cv2. The main loop consists of waiting for the user key input, Q to quit the program or S to save the image. When the user clicks on a point on the image, we paint a point on the image, and after the first point, we paint lines between the points.

I'm trying to add a codeblock to reset the image like this

if key == ord('r'):
        resetImage()

def resetImage():
    print('Debug: reset Image')
    coordinates['x'].clear()
    coordinates['y'].clear()
    # image = cv2.imread(path)   
    # cv2.destroyAllWindows()

This has a result but obviously it's not what I'm looking for.

Upvotes: -4

Views: 97

Answers (1)

Larrea
Larrea

Reputation: 21

The issue was that I was trying to access a global variable the wrong way. I solved it like this:

def resetImage():
    global image
    print("Debug: reset Image")
    coordinates["x"].clear()
    coordinates["y"].clear()
    newImage = cv2.imread(path)
    image = newImage.copy()

Upvotes: 0

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