I'm trying to isolate letters in a captcha, I managed to filter a captcha and that result in this black and white image:
![enter image description here](https://i.stack.imgur.com/qmldb.png)
But when I tried to separate the letters with findContours method of OpenCV it just found a external contour that wraps my entire image, resulting in this image (black contour outside image).
![enter image description here](https://i.stack.imgur.com/f0fo3.png)
I'm using this code with Python 3 and OpenCV 3.4.2.17:
img = threshold_image(img)
cv2.imwrite("images/threshold.png", img)image, contours, _ = cv2.findContours(img, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)for i, contour in enumerate(contours):area = cv2.contourArea(contour)cv2.drawContours(img, contours, i, (0, 0, 0), 3)cv2.imwrite('images/output3.png', img)
I just want my final result is 5 contours outside each character.
The contour to be extracted should be in white, background being black. I have modified your code a bit, eliminated the lines which were not adding any value.
import cv2
img = cv2.imread('image_to_be_read',0)
backup = img.copy() #taking backup of the input image
backup = 255-backup #colour inversion
I am using RETR_TREE as the contour retrieval mode, which retrieves all the contours and creates full family hierarchy list. Please find the documentation for the same here
_, contours, _ = cv2.findContours(backup, cv2.RETR_TREE, cv2.CHAIN_APPROX_NONE)
In opencv4, the finContours method has been changed. Please use:
contours, _ = cv2.findContours(backup, cv2.RETR_TREE, cv2.CHAIN_APPROX_NONE)
Then iterate through contours and draw the rectangle around the contours
for i, contour in enumerate(contours):x, y, w, h = cv2.boundingRect(contour)cv2.rectangle(img, (x, y), (x + w, y + h), (0, 255, 0), 1)
Save the image
cv2.imwrite('output3.png', img)
I got result which looks like this -
![enter image description here](https://i.stack.imgur.com/s4Lay.png)