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OpenCV ref count: function returning cv::Mat?

asked 2014-11-23 02:39:38 -0600

wal-o-mat gravatar image

I am tracing a strange bug in my very simple code, and I suspect that I am using cv::Mat in a wrong way, although with reference counting, there is not much that should go wrong.

My code is this:

cv::Mat rowwise_maximum(const cv::Mat& src, int32_t width)
{        
    cv::Mat dest = src.clone();

    for(int row = 0; row < dest.rows; ++row)
    {
        for(int col = 0; col < dest.cols; ++col)
        {
            dest.at< double >(row, col) = 0.5 * src.at< double >(row, col);
        }
    }

    std::cout << "ok" << std::endl;

    return dest;
}

// call
cv::Mat max_foo = rowwise_maximum(thresholded, 7);

I am pretty sure that the depth of src is CV_64F and therefore the way I use at is correct. I observe a program crash after leaving the program block calling this code, and the debugger displays max_foo.refcount to be 0.

I would expect it to be 1 ...

Can someone provide me a hint?

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Stupid me ... see comment below the accepted answer. The code above is ok, it's my assumption about the depth which was wrong. I used 'cv::matchTemplate' before, and this gives me a 32 bit floating point image, not 64 bit ...

wal-o-mat gravatar imagewal-o-mat ( 2014-11-28 14:14:43 -0600 )edit

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answered 2014-11-23 12:32:25 -0600

Hi!

This should not be a problem... Please add:

 CV_ASSERT(src.depth()==CV_64F);

That way, you are sure the matrix type is OK... You should also use direct access to speedup a little the iterations:

 cv::Mat rowwise_maximum(const cv::Mat& src, int32_t width)
 {
    CV_ASSERT(src.depth()==CV_64F);
    cv::Mat dest = src.clone();
    double* singleRowSrc, singleRowDest;
    for(int row = 0; row < dest.rows; ++row)
    {
        singleRowSrc = src.ptr<double>(row);
        singleRowDest= dest.ptr<double>(row);
        for(int col = 0; col < dest.cols; ++col)
        {
            singleRowDest[col] = 0.5 * singleRowSrc[col];
        }
    }

    std::cout << "ok" << std::endl;

    return dest;
 }

max_foo.refcount is still 0 because code probably crash before assignment (I think it occurs while removing that data from the stack).

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You are totally right! Crashed before, and yes, I reated my image as 'CV_64F', but this is not what 'cv::matchTemplate' creates ... the documentation clearly states that 32 bit are the result.

wal-o-mat gravatar imagewal-o-mat ( 2014-11-28 14:13:01 -0600 )edit

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Asked: 2014-11-23 02:39:38 -0600

Seen: 918 times

Last updated: Nov 23 '14