Mat::data empty after image operation (threshold())

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Dear all,

In my code I want to

1. read in an image from file
2. use threshold-operation on that image

3. access the data from thresholded image, in order to read the pixel values

   `// read image source
   Mat src = imread("image.png", CV_LOAD_IMAGE_COLOR); if(src.empty()) {
   return -1; }

   cvtColor(src,src,CV_RGB2GRAY);

   threshold(src, src, 220, 255, CV_THRESH_BINARY );

   int line[1200];
   

   int lineCount = 0;

   for(int i=src.rows; i>src.rows/2; i-=10)
   { uchar* rowi = src.ptr(i-1);

   int columnCount = 0;
   // begin on the left of the image
   for(int j=0; j<src.cols; j++)
   {
       uchar grayscale = src.at<uchar>(rowi[j]);   
   
   // write data to array
   line[columnCount] = grayscale;
   
   columnCount++;
   
   
   }`
   

My Problem: After using the threshold-operation on the image the src::date is " ". What can I do to fix that?

Thanks, Cima