Problem

I'm using OpenCV in Python make a program to crop images into squares.

It draws a square to show the selected area so I have to clear the screen with the image before drawing a new square, but unless I read the image again the code doesn't clear the screen.

This code doesn't work:

# Get Image img = cv2.imread(path,-1) DEFAULT = cv2.imread(path,-1) # Draw Function def draw(event,x,y,flags,param): if event == cv2.EVENT_LBUTTONDOWN: drawing = True # Set initial points ix,iy = x,y elif event == cv2.EVENT_MOUSEMOVE: if drawing == True: # Clear Screen img = DEFAULT # Draw Square if (abs(ix - x) < abs(iy -y)): cv2.rectangle(img,(ix,iy),(y,y),(0,255,0),1) else: cv2.rectangle(img,(ix,iy),(x,x),(0,255,0),1) elif event == cv2.EVENT_LBUTTONUP: drawing = False crop(x,y) 

This one does work:

# Get Image img = cv2.imread(path,-1) # Draw Function def draw(event,x,y,flags,param): if event == cv2.EVENT_LBUTTONDOWN: drawing = True # Set initial points ix,iy = x,y elif event == cv2.EVENT_MOUSEMOVE: if drawing == True: # Clear Screen img = cv2.imread(path,-1) # Draw Square if (abs(ix - x) < abs(iy -y)): cv2.rectangle(img,(ix,iy),(y,y),(0,255,0),1) else: cv2.rectangle(img,(ix,iy),(x,x),(0,255,0),1) elif event == cv2.EVENT_LBUTTONUP: drawing = False crop(x,y) 

Question

How do I make it so I don't have to read the image each time I want to clear the screen?

1 Answer

As @Micka and @Miki suggested I changed DEFAULT = cv2.imread(path,-1) to DEFAULT = img.copy, one thing to note is that you have to do it both ways for it to work (img = DEFAULT won't work because now img has the same pointers as DEFAULT), you have to give a copy of your default image for it to work.

My solution was (it has some extra code and it doesn't work perfectly, but the clearing of the screen does):

import numpy as np import cv2, os, sys, getopt # Global Variables helpMessage = 'Usage:\n\tcrop.py <command> [argument]\n\nCommands:\n\t-h --help\t\tDisplay this help message\n\t-i --image [path]\tInput image\n\t-f --folder [path]\tImage Folder\n\t-r --regex [regex]\tNaming of output files [WIP]\n\t-s --save [path]\tPath to Save' # Arguments pathIMG = '' pathDIR = '' pathSAV = '' regex = '' # Graphical drawing = False # true if mouse is pressed cropped = False ix,iy = -1,-1 # MISC img_index = 0 # Mouse callback function def draw(event,x,y,flags,param): global ix, iy, drawing, img, DEFAULT, cropped cropped = False if event == cv2.EVENT_LBUTTONDOWN: drawing = True ix,iy = x,y elif event == cv2.EVENT_MOUSEMOVE: if drawing == True: img = DEFAULT.copy() cv2.imshow(pathIMG,img) if (abs(ix - x) < abs(iy -y)): cv2.rectangle(img,(ix,iy),(x,y),(0,255,0),1) else: cv2.rectangle(img,(ix,iy),(x,y),(0,255,0),1) elif event == cv2.EVENT_LBUTTONUP: drawing = False crop(ix,iy,x,y) # Get Arguments def getArgvs(argv): try: opts, args = getopt.getopt(argv,"hi:f:r:s:",["help","image=","folder=","regex=","save="]) except getopt.GetoptError: print(helpMessage) sys.exit(2) for opt, arg in opts: if opt in ('-h', "--help"): print(helpMessage) sys.exit() elif opt in ("-i", "--image"): global pathIMG pathIMG = arg #print("img: " + arg) elif opt in ("-f", "--folder"): global pathDIR pathDIR = arg #print("dir: " + arg) elif opt in ("-r","--regex"): global regex regex = arg #print("regex: " + arg) elif opt in ("-s","--save"): global pathSAV pathSAV = arg # Crop Image def crop(ix,iy,x,y): global img, DEFAULT, cropped img = DEFAULT.copy() cv2.imshow(pathIMG,img) if (abs(ix - x) < abs(iy -y)): img = img[iy:y, ix:x] else: img = img[iy:y, ix:x] # Save image def save(crop_img): # Set name name = pathSAV + "img" + str(img_index) + ".png" # Resize dst = cv2.resize(crop_img, (32,32)) # Save cv2.imwrite(name,dst) print("Saved image sucsessfully") # Main Loop def loop(): global img cv2.namedWindow(pathIMG) cv2.setMouseCallback(pathIMG,draw) while (1): cv2.imshow(pathIMG,img) k = cv2.waitKey(1) & 0xFF if (k == 27): print("Cancelled Crop") break elif (k == ord('s')):# and cropped): print("Image Saved") save(img) break print("Done!") cv2.destroyAllWindows() # Iterate through images in path def getIMG(path): global img, DEFAULT directory = os.fsencode(path) for filename in os.listdir(directory): # Get Image Path pathIMG = path + filename.decode("utf-8") print(pathIMG) # Read Image img = cv2.imread(pathIMG,-1) DEFAULT = img.copy() # Draw image loop() return 0 # Main Function def main(): getArgvs(sys.argv[1:]) global img, DEFAULT if (pathDIR != ''): # Print Path print("dir: " + pathDIR) # Cycle through files getIMG(pathDIR) elif (pathIMG != ''): # Print Path print("img: " + pathIMG) # Load Image img = cv2.imread(pathIMG,-1) DEFAULT = img.copy() # Draw Image loop() # Run Main if __name__ == "__main__": main() cv2.destroyAllWindows()