OpenCV Python: Draw minAreaRect ( RotatedRect not implemented)

Here's a concrete example to draw the rotated rectangle. The idea is to obtain a binary image with Otsu's threshold then find contours using cv2.findContours(). We can obtain the rotated rectangle using cv2.minAreaRect() and the four corner vertices using cv2.boxPoints(). To draw the rectangle we can use cv2.drawContours() or cv2.polylines().

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Input -> Output

Code

import cv2
import numpy as np

# Load image, convert to grayscale, Otsu's threshold for binary image
image = cv2.imread('1.jpg')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
thresh = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY_INV + cv2.THRESH_OTSU)[1]

# Find contours, find rotated rectangle, obtain four verticies, and draw 
cnts = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
cnts = cnts[0] if len(cnts) == 2 else cnts[1]
rect = cv2.minAreaRect(cnts[0])
box = np.int0(cv2.boxPoints(rect))
cv2.drawContours(image, [box], 0, (36,255,12), 3) # OR
# cv2.polylines(image, [box], True, (36,255,12), 3)

cv2.imshow('image', image)
cv2.waitKey()

rect = cv2.minAreaRect(cnt)
box = cv2.cv.BoxPoints(rect) # cv2.boxPoints(rect) for OpenCV 3.x
box = np.int0(box)
cv2.drawContours(im,[box],0,(0,0,255),2)

should do the trick.

sources:

1) http://opencvpython.blogspot.in/2012/06/contours-2-brotherhood.html

2) Python OpenCV Box2D