python-opencv 的minAreaRect的详解

minAreaRect函数返回矩形的中心点坐标，长宽，旋转角度[-90,0)，当矩形水平或竖直时均返回-90

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# -*- coding:UTF_8 -*-
import cv2

img = cv2.imread('1.jpg')
cv2.imshow("src", img)
# 灰度处理,二值化
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
ret, img2 = cv2.threshold(gray, 50, 255, cv2.THRESH_BINARY)

# 寻找连通矩形
contours, hierarchy = cv2.findContours(img2, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

for contour in contours:
    # 获取最小包围矩形
    rect = cv2.minAreaRect(contours[0])

    # 中心坐标
    x, y = rect[0]
    cv2.circle(img, (int(x), int(y)), 3, (0, 255, 0), 5)

    # 长宽,总有 width>=height
    width, height = rect[1]

    # 角度:[-90,0)
    angle = rect[2]

    cv2.drawContours(img, contour, -1, (255, 255, 0), 3)
    print 'width=', width, 'height=', height, 'x=', x, 'y=', y, 'angle=', angle

cv2.imshow("contour", img)
rows, cols = img2.shape
# 逆时针旋转30度
M = cv2.getRotationMatrix2D((cols / 2, rows / 2), 30, 1)
img = cv2.warpAffine(img, M, (cols, rows))

cv2.imshow("rotation", img)
cv2.waitKey()
cv2.destroyAllWindows()