opencv 角点检测+相机标定+去畸变+重投影误差计算

https://blog.csdn.net/u010128736/article/details/52875137

https://blog.csdn.net/h532600610/article/details/51800488

python 角点检测+相机标定+去畸变+重投影误差计算：

#coding:utf-8
import cv2
import numpy as np
import glob

# 找棋盘格角点
# 阈值
criteria = (cv2.TERM_CRITERIA_EPS + cv2.TERM_CRITERIA_MAX_ITER, 30, 0.001)
#棋盘格模板规格
w = 9
h = 6
# 世界坐标系中的棋盘格点,例如(0,0,0), (1,0,0), (2,0,0) ....,(8,5,0)，去掉Z坐标，记为二维矩阵
objp = np.zeros((w*h,3), np.float32)
objp[:,:2] = np.mgrid[0:w,0:h].T.reshape(-1,2)
# 储存棋盘格角点的世界坐标和图像坐标对
objpoints = [] # 在世界坐标系中的三维点
imgpoints = [] # 在图像平面的二维点

images = glob.glob('calib/*.png')
for fname in images:
    img = cv2.imread(fname)
    gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
    # 找到棋盘格角点
    ret, corners = cv2.findChessboardCorners(gray, (w,h),None)
    # 如果找到足够点对，将其存储起来
    if ret == True:
        cv2.cornerSubPix(gray,corners,(11,11),(-1,-1),criteria)
        objpoints.append(objp)
        imgpoints.append(corners)
        # 将角点在图像上显示
        cv2.drawChessboardCorners(img, (w,h), corners, ret)
        cv2.imshow('findCorners',img)
        cv2.waitKey(1)
cv2.destroyAllWindows()

# 标定
ret, mtx, dist, rvecs, tvecs = cv2.calibrateCamera(objpoints, imgpoints, gray.shape[::-1], None, None)

# 去畸变
img2 = cv2.imread('calib/00169.png')
h,  w = img2.shape[:2]
newcameramtx, roi=cv2.getOptimalNewCameraMatrix(mtx,dist,(w,h),0,(w,h)) # 自由比例参数
dst = cv2.undistort(img2, mtx, dist, None, newcameramtx)
# 根据前面ROI区域裁剪图片
#x,y,w,h = roi
#dst = dst[y:y+h, x:x+w]
cv2.imwrite('calibresult.png',dst)

# 反投影误差
total_error = 0
for i in xrange(len(objpoints)):
    imgpoints2, _ = cv2.projectPoints(objpoints[i], rvecs[i], tvecs[i], mtx, dist)
    error = cv2.norm(imgpoints[i],imgpoints2, cv2.NORM_L2)/len(imgpoints2)
    total_error += error
print "total error: ", total_error/len(objpoints)

标定 cv2.calibrateCamera函数文档：https://docs.opencv.org/2.4.1/modules/calib3d/doc/camera_calibration_and_3d_reconstruction.html

c++ 角点检测+角点绘制：

#include <iostream>
#include <cv.h>
#include <cxcore.h>
#include <highgui.h>
using namespace std;

int main( )
{
    cout<<"Draw Chess OpenCV!"<<endl;
    char* filename="..//image5.jpg";
    char* filename2="..//5.jpg";
    IplImage* imgRGB = cvLoadImage(filename);
    IplImage* imgGrey = cvLoadImage(filename,CV_LOAD_IMAGE_GRAYSCALE); 

    if (imgGrey==NULL){//image validation
        cout<< "No valid image input."<<endl;
        char c=getchar();
        return ;
    } 

    //-------find chessboard corners--------------
    int corner_row=;//interior number of row corners.(this can be countered by fingers.)
    int corner_col=;//interior number of column corners.
    int corner_n=corner_row*corner_col;
    CvSize pattern_size=cvSize(corner_row,corner_col);
   // CvPoint2D32f* corners=new CvPoint2D32f[corner_n];
    CvPoint2D32f corners[];
    int corner_count;

    int found=cvFindChessboardCorners(//returning non-zero means sucess.
        imgGrey,// 8-bit single channel greyscale image.
        pattern_size,//how many INTERIOR corners in each row and column of the chessboard.
        corners,//an array where the corner locations can be recorded.
        &corner_count,// optional, if non-NULL, its a point to an integer where the nuber of corners found can be recorded.
       // CV_CALIB_CB_ADAPTIVE_THRESH|CV_CALIB_CB_FILTER_QUADS// check page 382-383.

        );
     cout<<"corner_count = "<<corner_count;
    //-------Draw the corner pattern-------
    cvDrawChessboardCorners(
        imgRGB,
        pattern_size,
        corners,
        corner_count,
        found
        );
    cvSaveImage(filename2,imgRGB);
    //to summary a bit of findings.
    cout<<"found="<<found<<endl;
    cout<<"x="<<corners[].x;
    cout<<",y="<<corners[].y<<endl;

    cvNamedWindow("Find and Draw ChessBoard",  );
    cvShowImage( "Find and Draw ChessBoard", imgRGB );

    cvWaitKey(); 

    cvReleaseImage(&imgGrey);
    cvReleaseImage(&imgRGB);
    cvDestroyWindow("Find and Draw ChessBoard"); 

    return ;
}

注意事项：

• pattern_size参数传递内点数，8*8的棋盘只有7*7内点。
• 图像选取应注意减少干扰，例如光照与背景等。
• Corners中的角点坐标顺序排列规律不一定是以行从左上到右下。使用坐标计算映射关系时应提高警惕，对坐标进行重新排列。

关键函数参数说明：

int cvFindChessboardCorners( const void* image, CvSize pattern_size, CvPoint2D32f* corners, int* corner_count=NULL, int flags=CV_CALIB_CB_ADAPTIVE_THRESH );

Image:

输入的棋盘图，必须是8位的灰度或者彩色图像。

pattern_size:

棋盘图中每行和每列角点的个数。

Corners:

检测到的角点

corner_count:

输出，角点的个数。如果不是NULL，函数将检测到的角点的个数存储于此变量。

Flags:

各种操作标志，可以是0或者下面值的组合：

CV_CALIB_CB_ADAPTIVE_THRESH -使用自适应阈值（通过平均图像亮度计算得到）将图像转换为黑白图，而不是一个固定的阈值。

CV_CALIB_CB_NORMALIZE_IMAGE -在利用固定阈值或者自适应的阈值进行二值化之前，先使用cvNormalizeHist来均衡化图像亮度。

CV_CALIB_CB_FILTER_QUADS -使用其他的准则（如轮廓面积，周长，方形形状）来去除在轮廓检测阶段检测到的错误方块。