Question

Is there a way where I can converts a CvMat * to a CvMat? I am stuck in the code at a place where I have to clone a CvMat using cvCloneMat(). This gives me CvMat * where as I need it as a CvMat.

I have tried that dereferencing thing but somehow it doesnt work. I am writing a jitter/max external that has a matrix of image as an input and a matrix as output. here is the piece of code

    //Convert input and output matrices to OpenCV matrices
    cvJitter2CvMat(in_matrix, &source);
    cvJitter2CvMat(out_matrix, &edges);

    //Calculate threshold values
    thresh1 = x->threshold - x->range;
    thresh2 = x->threshold + x->range;
    CLIP(thresh1,0,255);
    CLIP(thresh2,0,255);



    //calculate
    //cvCanny( &source, &edges, thresh1, thresh2, 3 );
    tempo = cvCloneMat(&source);
    edges = (*tempo);   
} else {
    return JIT_ERR_INVALID_PTR;
}

out:
jit_object_method(out_matrix,gensym(“lock”),out_savelock);
jit_object_method(in_matrix,gensym(“lock”),in_savelock);
return err;
}

The problem is that when I use “cvCanny()” instead of cvCloneMat() it works. the output is displayed as edges of the video stream. but if I use cvCloneMat(), it displays a blank image.

Answer 1

This is true for any pointer-related stuff:

CvMat* pMat = cvCloneMat(...);
CvMat mat = (*pMat);
functionThatNeedsMat(*pMat);
otherFunctionThatNeedsMat(mat);

Check also this article about pointer dereferencing