Contours/Shape Detection

Firstly, some useful function that we need

• cv2.findContours()

• cv2.contourArea()

• cv2.drawContours()

• cv2.arclength()

• cv2.approxPolyDP()

• cv2.rectangle()

• cv2.putText()

def getContours

def getContours(img):
    contours, hierarchy = cv2.findContours(img, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)
    for cnt in contours:
        area = cv2.contourArea(cnt)
        #print(area)
        if area > 500:
            cv2.drawContours(imgContour, cnt, -1, (255, 0, 0), 3)
            peri = cv2.arcLength(cnt, True)
            #print(peri)
            approx = cv2.approxPolyDP(cnt, 0.02*peri, True)
            print(len(approx))
            objCorners = len(approx)
            x, y, w, h = cv2.boundingRect(approx)
            if objCorners == 3:
                objectType = "Tri"
            elif objCorners == 4:
                aspectRatio = w/float(h)
                if aspectRatio > 0.95 and aspectRatio < 1.05:   objectType = "Square"
                else: objectType = "Rectangle"
            elif objCorners > 4: objectType = "Circle"
            else:
                objectType = "None"
            cv2.rectangle(imgContour, (x, y), (x+w, y+h), (255, 0, 0), 2)
            cv2.putText(imgContour, objectType, (x+(w//2)-10, y+(h//2)-10), cv2.FONT_ITALIC, 0.6, (0,0,0), 2)