如何使用opencv python在运行时在图像上添加文本

Question

I want to add text on my image or you can say type on an image at run-time. That means after running the application when an image is displayed, by pointing using mouse on image we able to type text on it.

I did that partially using mouse event in opencv python. Now what I want is, I want to do two things,

1. Delete the text using backspace or delete key.

2. Show the blinking cursor, so one can see where text is getting typed.

Please tell me how can I do that. or anything alse is needed for that in python.

here is my code you can test it. Just point any where on image using left click and start typing.

xi, yi = -1,-1 # set default position

def take_posi(event, x, y,flags, param):
    global xi, yi
    if event == cv2.EVENT_FLAG_LBUTTON:
        xi, yi = x, y   #get the position where you want to type                  


img = cv2.imread('watch.jpg')
cv2.namedWindow('Watch')
cv2.setMouseCallback('Watch',take_posi)
font = cv2.FONT_HERSHEY_SIMPLEX

i = 10
while(1):
    cv2.imshow('Watch',img)
    k = cv2.waitKey(33)
    if k==27:    # Esc key to stop
        break
    elif k==-1:  # normally -1 returned,so don't print it
        continue
    else:
        print (k) # else print its value
        cv2.putText(img, chr(k), (xi, yi), font, 1, (0, 255, 0), 1, cv2.LINE_AA)
        xi+=15   #increment cursor 

cv2.waitKey(0)
cv2.destroyAllWindows()

Answer 1

Off the top of my head the approach I would take would be to use stack and save locations and values where the changes have occurred.

For example, the following modification to your code handles the case of the backspace button. Although, more testing is required.

Basic idea is:

1. save a copy of the old image before printing text
2. take the difference between new and old images
3. find out locations and values where the changes have occurred

When backspace is pressed:

1. Pop the values and locations from stack
2. Restore the image
3. Update cursor position.

Code

from collections import deque   # import double ended queue

xi, yi = -1, -1  # set default position
def take_posi(event, x, y, flags, param):
    global xi, yi
    if event == cv2.EVENT_FLAG_LBUTTON:
        xi, yi = x, y  # get the position where you want to type

stack = deque()  # create stack to keep track of overwritten values
img = cv2.imread('watch.jpg')
cv2.namedWindow('Watch')
cv2.setMouseCallback('Watch', take_posi)
font = cv2.FONT_HERSHEY_SIMPLEX

i = 10
while True:
    cv2.imshow('Watch', img)
    k = cv2.waitKey(33)
    if k == 27:  # Esc key to stop
        break
    elif k == -1:  # normally -1 returned,so don't print it
        continue
    elif k == 8:  # backspace
        if stack:
            coords, vals = stack.pop()
            img[coords] = vals
            xi -= 15
    else:
        old_img = img.copy()
        cv2.putText(img, chr(k), (xi, yi), font, 1, (255, 0, 0), 1, cv2.LINE_AA)
        coords = np.nonzero(old_img - img)
        stack.append((coords, old_img[coords]))
        xi += 15  # increment cursor

cv2.waitKey(0)
cv2.destroyAllWindows()