Add example of finding rectangles

notes/find_rectangles.py

@@ -0,0 +1,28 @@
+import cv2
+
+img =  cv2.imread('demo-hand-written.png')
+gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
+
+thresh_inv = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY_INV+cv2.THRESH_OTSU)[1]
+
+# Blur the image
+blur = cv2.GaussianBlur(thresh_inv,(1,1),0)
+
+thresh = cv2.threshold(blur, 0, 255, cv2.THRESH_BINARY+cv2.THRESH_OTSU)[1]
+
+# find contours
+contours = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)[0]
+
+mask = np.ones(img.shape[:2], dtype="uint8") * 255
+for c in contours:
+    # get the bounding rect
+    x, y, w, h = cv2.boundingRect(c)
+    if w*h>1000:
+        cv2.rectangle(mask, (x, y), (x+w, y+h), (0, 0, 255), -1)
+
+res_final = cv2.bitwise_and(img, img, mask=cv2.bitwise_not(mask))
+
+cv2.imshow("boxes", mask)
+cv2.imshow("final image", res_final)
+cv2.waitKey(0)
+cv2.destroyAllWindows()