how to undistort a jpeg image file using distortion coefficients?

Question

I have a distorted snapshot of my webcam. as jpeg file, intrinsic matrix and distortion coefficients:-

matrix intrisic matrix
      (1137.0919189453125,0.0,383.99273681640625)
      (0.0,264.17974853515625,312.74951171875)
      (0.0,0.0,1.0)

matrix distortion :-
    (-0.26913660764694214)
    (0.22259517014026642)
    (-0.0928017795085907)
    (0.26249778270721436)

I don't know how to load these distortion coefficients in CvMat in order to obtain undistorted image using these distortion coefficients. also, I want to do this using javacv only.

edit:- also, i know the function

IplImage mapx=cvCreateImage(cvSize(src_img),IPL_DEPTH_32F,1);
IplImage mapy=cvCreateImage(cvSize(src_img),IPL_DEPTH_32F,1);

cvInitUndistortMap(CvMat intrinsic,CvMat distortion, IplImage mapx, IplImage mapy); 
cvRemap(IplImage tm,IplImage src,IplImage mapx,IplImage mapy,CV_INTER_LINEAR|CV_WARP_FILL_OUTLIERS,cvScalarAll(0));

but i don't know how to initialize respective cvMats for intrinsic matrix and distortion coefficient.?

Answer 1

Why not use cv::undistort?

It takes your matrices as its parameters.

void undistort(const Mat& src, Mat& dst, const Mat& cameraMatrix, const Mat& distCoeffs, const Mat& newCameraMatrix=Mat())

The src matrix is your image.

The dst matrix is the undistorted image.

The cameraMatrix is your intrinsic matrix.

The distCoeffs matrix is your distortion matrix.

To quote from the documentation:

The particular subset of the source image that will be visible in the corrected image can be regulated by newCameraMatrix . You can use GetOptimalNewCameraMatrix to compute the appropriate newCameraMatrix , depending on your requirements.

---

OK. I just found the answer to your comment.... I think.

public static native void cvUndistortPoints(CvMat src, CvMat dst, CvMat camera_matrix, CvMat dist_coeffs, CvMat R/*=null*/, CvMat P/*=null*/); You can find this in http://www.java2s.com/Open-Source/Android/UnTagged/educationalrobots/name/audet/samuel/javacv/jna/cv.java.htm.

This is actually in imgproc.

Just make the last two parameters null.

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The second part - initializing a CvMat - is tougher than it looks, because you have to mess around with pointers if you want to do it elegantly, and I forget how to use JNA Pointers :)

So here's an alternate solution: Use this constructor public static CvMat create(int rows, int cols, int type);

So, for your matrix, you would have three rows and three columns.

Your type would be one of the types in cxcore.java, probably CV_64FC1, which is the single-channel double type. Otherwise, if you're using floats, it would be CV_32FC1.

Then you would set the values, one by one, by using: opencv_core.cvSet2D(matrix, i, j, value); Where i is row and j is column!

Any more questions?

Cheerio!