gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
gray = 255 - gray
gray = cv2.threshold(gray, 4, 255, cv2.THRESH_BINARY)[1]
gray = cv2.blur(gray, (15, 1))
contours, hierarchy = cv2.findContours(gray, cv2.RETR_LIST, cv2.
    CHAIN_APPROX_NONE)
for cnt in contours:
    area = cv2.contourArea(cnt)
if area > 150000 and area < 500000:
    cv2.drawContours(img, [cnt], 0, (255, 0, 0), 2)
cv2.imshow('img', img)
cv2.waitKey()
Floor Plan Edge Detection - Image Processing?