I have a problem about how to find the biggest rectangle among these small rectangles in contours opencv please help me

Here is the small rectangles from cv2.findContours() I got a list of contours. I plot it and I got this

I want the yellow rectangle box

This is the codes

img_grey = cv2.cvtColor(bg_img,cv2.COLOR_BGR2GRAY)

ret,thresh_img = cv2.threshold(img_grey, 100, 255, cv2.THRESH_BINARY)

contours, _ = cv2.findContours(thresh_img, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

Does it have a way to find the big rectangle(yellow) Thank you

CodePudding user response：

You need to proceed from where you left after finding contours.

Approach:

• Initialize an array
• Iterate through each contour and store its points in the array
• Find the maximum and minimum values in both axis ( numpy is your friend!)
• Draw a rectangle using them.

Code:

# create copy of original color image
img2 = bg_img.copy()

# Initialize array with value (0,0)
cc = np.array([[0, 0]], dtype=int)

# Iterate through each contour
for i, c in enumerate(contours):
    # reshape from (L, 1, 2) to (L, 2), where L is a tuple of (x, y)
    c_modified = c.reshape(len(contours[i]), 2)
    # concatenate to initial array
    cc = np.concatenate((cc, c_modified), axis = 0)

# remove the first element of initialized array
new_cc = cc[1:]

# obtain max and min value along Y-axis
y2 = np.max(new_cc[:,1])
y1 = np.min(new_cc[:,1])

# obtain max and min value along X-axis
x2 = np.max(new_cc[:,0])
x1 = np.min(new_cc[:,0])

# Draw rectangle using those points on copy of the image
img2 = cv2.rectangle(img2, (x1, y1), (x2, y2), (255,255, 0, 3)

Result: