python opencv 画矩形框 外接矩形

画矩形

import cv2
image = cv2.imread('1.jpg')
cv2.rectangle(image, (xmin, ymin), (xmax, ymax), (0, 0, 255), 2)  
cv2.imwrite('2.jpg', image)

画圆点: 

  point_size = 1
        point_color = (0, 0, 255)  # BGR
        thickness = 4  # 可以为 0 、4、8

        for point in points:
            x1,y1=point
            cv2.circle(img, (int(x1),int(y1)), point_size, point_color, thickness)

外接矩形，最小外接矩形，cnt其实就是轮廓坐标：

import os

import cv2
import joblib
import numpy as np

image=cv2.imread("first.jpg")


roi=np.array([[10,10],[100,20],[100,150],[20,80]])

x, y, w, h = cv2.boundingRect(roi)
cv2.rectangle(image, (x, y), (x + w, y + h), (0, 255, 0), 2)

# 最小外接矩形框，有方向角
rect = cv2.minAreaRect(roi)
box = cv2.boxPoints(rect)
box = np.int0(box)
cv2.drawContours(image, [box], 0, (0, 0, 255), 2)

以下内容转自：

OpenCv-Python 最小外接圆、最小外接矩形、椭圆拟合、直线拟合_牧野的博客-CSDN博客

最小外接圆、最小外接矩形、椭圆拟合、直线拟合

#coding: utf-8
import cv2
import numpy as np
import imutils
 
 
im = cv2.imread('./5121.png')
imgray = cv2.cvtColor(im,cv2.COLOR_BGR2GRAY)
 
ret,thresh = cv2.threshold(imgray,0,255,cv2.THRESH_BINARY+cv2.THRESH_OTSU)  # 大津阈值
contours = cv2.findContours(thresh,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_NONE)  #cv2.RETR_EXTERNAL 定义只检测外围轮廓
 
cnts = contours[0] if imutils.is_cv2() else contours[1]  #用imutils来判断是opencv是2还是2+
 
for cnt in cnts:
    # 外接矩形框，没有方向角
    x, y, w, h = cv2.boundingRect(cnt)
    cv2.rectangle(im, (x, y), (x + w, y + h), (0, 255, 0), 2)
 
    # 最小外接矩形框，有方向角
    rect = cv2.minAreaRect(cnt)
    box = cv2.cv.Boxpoints() if imutils.is_cv2()else cv2.boxPoints(rect)
    box = np.int0(box)
    cv2.drawContours(im, [box], 0, (0, 0, 255), 2)
 
    # 最小外接圆
    (x, y), radius = cv2.minEnclosingCircle(cnt)
    center = (int(x), int(y))
    radius = int(radius)
    cv2.circle(im, center, radius, (255, 0, 0), 2)
 
    # 椭圆拟合
    ellipse = cv2.fitEllipse(cnt)
    cv2.ellipse(im, ellipse, (255, 255, 0), 2)
 
    # 直线拟合
    rows, cols = im.shape[:2]
    [vx, vy, x, y] = cv2.fitLine(cnt, cv2.DIST_L2, 0, 0.01, 0.01)
    lefty = int((-x * vy / vx) + y)
    righty = int(((cols - x) * vy / vx) + y)
    im = cv2.line(im, (cols - 1, righty), (0, lefty), (0, 255, 255), 2)
 
cv2.imshow('a',im)
cv2.imwrite('./result.jpg',im)
cv2.waitKey(0)