OpenCV image size limit

Question

I\'m trying to pass a huge Mat image (98304x51968) between openCV and itk using the ITK to openCV Bridge. I have an error :

Insufficient memory (OverFlow for imageS

Answer 1

Good news, since this pull request: handle huge matrices correctly #11505, you should be able to do something like this (code taken from the test):

Mat m(65000, 40000, CV_8U);
ASSERT_FALSE(m.isContinuous());

uint64 i, n = (uint64)m.rows*m.cols;
for( i = 0; i < n; i++ )
    m.data[i] = (uchar)(i & 255);

cv::threshold(m, m, 127, 255, cv::THRESH_BINARY);
int nz = cv::countNonZero(m);  // FIXIT 'int' is not enough here (overflow is possible with other inputs)
ASSERT_EQ((uint64)nz, n / 2);

Since countNonZero() returns an int, overflow is possible. This means that you should be able to create huge matrix but not all OpenCV function can handle correctly huge matrix.

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Regarding your issue, this is the code for ITKImageToCVMat in v5.0a02:

template
cv::Mat
OpenCVImageBridge::ITKImageToCVMat(const TInputImageType* in, bool force3Channels)
{
  // Extra copy, but necessary to prevent memory leaks
  IplImage* temp = ITKImageToIplImage(in, force3Channels);
  cv::Mat out = cv::cvarrToMat( temp, true );
  cvReleaseImage(&temp);
  return out;
}

As you can see, IplImage image is still used and should be the source of your error. Your best option currently should be to do the conversion yourself. Maybe something like (I don't know ITK, same input and output type, one channel):

typename ImageType::RegionType  region = in->GetLargestPossibleRegion();
typename ImageType::SizeType    size = region.GetSize();
unsigned int w = static_cast< unsigned int >( size[0] );
unsigned int h = static_cast< unsigned int >( size[1] );
Mat m(h, w, CV_8UC1, in->GetBufferPointer());

No copy is involved here. If you want to copy, you can do:

Mat m_copy = m.clone();