OpenCV Matrix memory release after imread command

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I have a for loop in which I create a local cv::Mat object to store an image. The code looks like this:

for (int iter = 0; iter < totalNumberOfIterations; iter++)
{
    cv::Mat I = cv::imread(argv[1], 0);
    std::cout << "Reference count I: " << *I.refcount << std::endl;
    I.release();
}

During the first iteration of the loop, I found that memory is allocated for the variable "I" and it is deallocated when I call I.release(). During subsequent iterations, memory is not deallocated, the RAM consumption for my program remains constant. It seems as if OpenCV reserves memory for variable "I" for optimization purposes. Is this true?

The reference count for the variable "I" (*I.refcount) remains as 1 through all iterations of the for loop.

I am using OpenCV 2.4.4 and I am compiling my code using gcc 4.6.4. To check memory consumption, I was using the command "top" in my Ubuntu 13.04 machine.

EDIT: When I do not force OpenCV to read grayscale image, I notice that memory is being deallocated for variable "I". (Note second parameter is set to "1" in the imread command).

cv::Mat I = cv::imread(argv[1], 1);