在OpenCV Python中围绕所有轮廓绘制矩形

Question

我有一个在视频帧上应用过滤器后识别轮廓的代码。现在，在我的例子中，我得到了3个轮廓，我通过在它们周围画矩形来显示它们，我想做的是在这3个轮廓矩形周围画一个矩形。就像是一个更大的矩形，包含3个检测到的矩形。 这是我的简单代码检测和绘制矩形周围的轮廓。

im2, contours, hierarchy = cv2.findContours(canny_img,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)

try: hierarchy = hierarchy[0]
except: hierarchy = []

# computes the bounding box for the contour, and draws it on the frame,
for contour, hier in zip(contours, hierarchy):
    (x,y,w,h) = cv2.boundingRect(contour)
    if w > 80 and h > 80:
            cv2.rectangle(frame, (x,y), (x+w,y+h), (255, 0, 0), 2)

cv2.imshow('Motion Detector',frame)

Answer 1

也许可以试试这样的：

im2, contours, hierarchy = cv2.findContours(canny_img,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)

try: hierarchy = hierarchy[0]
except: hierarchy = []

height, width, _ = canny_img.shape
min_x, min_y = width, height
max_x = max_y = 0

# computes the bounding box for the contour, and draws it on the frame,
for contour, hier in zip(contours, hierarchy):
    (x,y,w,h) = cv2.boundingRect(contour)
    min_x, max_x = min(x, min_x), max(x+w, max_x)
    min_y, max_y = min(y, min_y), max(y+h, max_y)
    if w > 80 and h > 80:
        cv2.rectangle(frame, (x,y), (x+w,y+h), (255, 0, 0), 2)

if max_x - min_x > 0 and max_y - min_y > 0:
    cv2.rectangle(frame, (min_x, min_y), (max_x, max_y), (255, 0, 0), 2)

从本质上讲，您需要跟踪什么是最小的x和y坐标，什么是最大的x和y坐标（包括宽度和高度），然后用这些坐标绘制一个矩形。

Answer 2

使用numpy：

boxes = []
for c in cnts:
    (x, y, w, h) = cv2.boundingRect(c)
    boxes.append([x,y, x+w,y+h])

boxes = np.asarray(boxes)
# need an extra "min/max" for contours outside the frame
left = np.min(boxes[:,0])
top = np.min(boxes[:,1])
right = np.max(boxes[:,2])
bottom = np.max(boxes[:,3])

cv2.rectangle(frame, (left,top), (right,bottom), (255, 0, 0), 2)