cvGetCol(), cvGetRow(), cvGetDiag(), cvGetSubRect()

cvGetSubRect

asked 2013-02-19 23:59:53 -0600

Almaz
1

updated 2013-02-20 00:16:25 -0600

Alexander Smorkalov

5862 ●2 ●22 ●58 http://alex-alchemist....

My code:

float a[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
CvMat b = cvMat( 3, 3, CV_32FC1, a );
float c[] = { 6, 7, 8, 9 };
CvMat d = cvMat( 2, 2, CV_32FC1, c );
CvMat* e = cvGetSubRect( &b, &d, cvRect( 0, 0, 1, 1 ) );
cout << *( e->data.fl + 0 ) << "   " << *( e->data.fl + 1 ) << "   " << *( e->data.fl + 2 ) << "   " << *( e->data.fl + 3 ) << "\n";

The result: 1 2 3 4

But must be: 1 2 4 5

What am I doing wrong?

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answered 2013-02-20 02:03:37 -0600

rics

1093 ●1 ●14 ●21

When you create CvMat* e with cvGetSubRect you only create a matrix header which means matrix b is not copied and e points to the memory location of b. Your dereferences in cout point to the memory locations following the starting memory position of b.

Your expected result can be achieved like this (I assume older OpenCV version): CV_MAT_ELEM(e, float, 0, n) with n=0,1,2,3.