Print out the values of a Mat matrix in OpenCV C

Question

I want to dump the values of a matrix in OpenCV to the console using cout  I quickly learned that I do not understand OpenvCV s type system nor C   templates well enough to accomplish this simple task   Would a reader please post  or point me to  a little function or code snippet that prints a Mat   Regards  Aaron  PS  Code that uses the newer C   Mat interface as opposed to the older CvMat interface is preferential

User · Answer

include  lt opencv2 imgproc imgproc hpp gt   include  lt opencv2 highgui highgui hpp gt    include  lt iostream gt   include  lt iomanip gt   using namespace cv  using namespace std   int main int argc  char   argv        double data 4     -0 0000000077898273846583732  -0 03749374753019832  -0 0374787251930463  -0 000000000077893623846343843       Mat src   Mat 1  4  CV 64F   amp data       for int i 0  i lt 4  i            cout  lt  lt  setprecision 3   lt  lt  src at lt double gt  0 i   lt  lt  endl       return 0

User · Answer

If you are using opencv3  you can print Mat like python numpy style   Mat xTrainData    Mat  lt float gt  5 2   lt  lt  1  1  1  1  2  2  2  2  2  2    cout  lt  lt   xTrainData  python        lt  lt  endl  lt  lt  format xTrainData  Formatter  FMT PYTHON   lt  lt  endl  lt  lt  endl    Output as below  you can see it e more readable  see here  for more information     But in most case  there is no need to output all the data in Mat  you can output by row range like 0   2 row    include  lt opencv2 imgproc imgproc hpp gt   include  lt opencv2 highgui highgui hpp gt    include  lt iostream gt   include  lt iomanip gt   using namespace cv  using namespace std   int main int argc  char   argv          row  6  column  3 unsigned one channel     Mat image1 6  3  CV 8UC1  5           output row  0   2     cout  lt  lt   image1 row  0 2     lt  lt  endl  lt  lt        lt  lt  image1 rowRange 0  2   lt  lt  endl  lt  lt  endl         row  8  column  2 unsigned three channel     Mat image2 8  2  CV 8UC3  Scalar 1  2  3            output row  0   2     cout  lt  lt   image2 row  0 2     lt  lt  endl  lt  lt        lt  lt  image2 rowRange 0  2   lt  lt  endl  lt  lt  endl       return 0      Output as below

User · Answer

I think using the matrix at lt type gt  x y  is not the best way to iterate trough a Mat object  If I recall correctly matrix at lt type gt  x y  will iterate from the beginning of the matrix each time you call it I might be wrong though   I would suggest using cv  MatIterator   cv  Mat someMat 1  4  CV 64F   amp someData    cv  MatIterator  lt double gt   it   someMat begin lt double gt     for   it  someMat end lt double gt      it         std  cout  lt  lt    it  lt  lt  std  endl

User · Answer

See the first answer to Accessing a matrix element in the  quot Mat quot  object  not the CvMat object  in OpenCV C   Then just loop over all the elements in cout  lt  lt  M at lt double gt  0 0    rather than just 0 0  Or better still with the C   interface   cv  Mat M  cout  lt  lt   M      lt  lt  endl  lt  lt        lt  lt  M  lt  lt  endl  lt  lt  endl

[c++] Print out the values of a (Mat) matrix in OpenCV C++

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