opencv中cv2.minAreaRect函数输出角度问题详解

cnts, _ = cv2.findContours(mask, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
rect = cv2.minAreaRect(cnts[0])
box = np.int0(cv2.boxPoints(rect))
print(rect)

import cv2
import numpy as np
 
def rotate(img, angle, center=None, scale=1.0, fill=0, interpolation=cv2.INTER_LINEAR, expand=True):
    if center is not None and expand:
        raise ValueError('`auto_bound` conflicts with `center`')
 
    h, w = img.shape[:2]
    if center is None:
        center = ((w - 1) * 0.5, (h - 1) * 0.5)
    assert isinstance(center, tuple)
 
    matrix = cv2.getRotationMatrix2D(center, angle, scale)
    if expand:
        cos = np.abs(matrix[0, 0])
        sin = np.abs(matrix[0, 1])
        new_w = h * sin + w * cos
        new_h = h * cos + w * sin
        matrix[0, 2] += (new_w - w) * 0.5
        matrix[1, 2] += (new_h - h) * 0.5
        w = int(np.round(new_w))
        h = int(np.round(new_h))
    rotated = cv2.warpAffine(
        img,
        matrix, (w, h),
        flags=interpolation,
        borderValue=fill)
    return rotated

rotate(img, -23, center=(201, 92), expand=False)

if rect[1][0] > rect[1][1]: # w > h 
    angle = int(rect[2]) 
else: 
    angle = -(90 - int(rect[2]))

rect = cv2.minAreaRect(cnts[0])

#include <iostream>
#include <string>
#include <math.h>
#include <vector>
#include <io.h>
#include <fstream>
#include <opencv2/opencv.hpp>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
 
using namespace cv;
using namespace std;
 
int main()
{  
	Mat image = imread("a11.jpg");  
	Mat gaussianimage,grayimage, cannyimage, thresholdimage;
 
//---------------------旋转-----------------
	//计算偏转角度
	GaussianBlur(image, gaussianimage, Size(5, 5), 3, 3);//尽可能多的去除杂质
	Canny(gaussianimage, cannyimage, 50, 150, 3);
	cvtColor(cannyimage, grayimage, CV_GRAY2BGR);
	vector<vector<Point>>vec_point;
	vector<Vec4i>hireachy;
	findContours(cannyimage, vec_point, hireachy, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);
 
	double degree = 0;
	for (size_t i = 0; i < vec_point.size(); i++)
	{
		RotatedRect minrect = minAreaRect(vec_point[i]);//minAreaRect():以X轴正方形为起点，顺时针为正，逆时针为负
		degree = minrect.angle;
		
        //此处目的是为了让目标图像旋转到水平位置
		if (degree > -90 && degree <= -45)
		{
			degree += 90;
		}
		else if (degree >-45 && degree < 0)
		{
			degree;
		}
		else
		{
			degree = 0;
		}		
		cout <<"degree:" << degree << endl;
	}	
 
	//旋转纠正
	Point center = Point(image.cols / 2, image.rows / 2);
	double angle = degree;
	double scale = 1;
	Mat rot(2, 3, CV_32FC1);
	rot = getRotationMatrix2D(center, angle, scale);//getRotationMatrix2D():以X轴正方形为起点，顺时针为负，逆时针为正
	Mat rotimage;
	warpAffine(image, rotimage, rot, image.size());
	namedWindow("rotation", 0);
	resizeWindow("rotation", 800, 600);
	imshow("rotation", rotimage);
}