opencv multi channel elemnt access

Question

Hi All,

I'm trying to learn how to use openCV's new c++ interface.

How do I access elements of a multi channel matrix. for example:

Mat myMat(size(3, 3), CV_32FC2);

for (int i = 0; i < 3; ++i)
{
    for (int j = 0; j < 3; ++j)
    {
        //myMat_at_(i,j) = (i,j);
    }
}

What is the easiest way to do this? Something like cvSet2D of the old interface
What is the most efficiant way? Similar to using direct pointers in the old interface.

Thank you

Answer 1

I'm trying to use the "new" 2.0 c++ version of OpenCV, but everything is else like in simple C version. I have some problem with changing the values in image.

The image is CV_8UC3.

for (int i=0; i<image.rows; i++)
{
    for (int j=0; j<image.cols; j++)
    {
        if (someArray[i][j] == 0)
        {
            image.at<Vec3i>(i,j)[0] = 0;
            image.at<Vec3i>(i,j)[1] = 0;
            image.at<Vec3i>(i,j)[2] = 0;
        }
    }
}

What i'm doing wrong???

Thank you!

Answer 2

Vic you must use Vec3b instead of Vec3i:

for (int i=0; i<image.rows; i++)
{
    for (int j=0; j<image.cols; j++)
    {
        if (someArray[i][j] == 0)
        {
            image.at<Vec3b>(i,j)[0] = 0;
            image.at<Vec3b>(i,j)[1] = 0;
            image.at<Vec3b>(i,j)[2] = 0;
        }
    }
}

Answer 3

how to represent this into Mat structure? considering r = row, c = column ch = channel

(float)imgp->imageData[r*imgp->widthStep+(c*imgp->nChannels+ch)*sizeof(float)];

i've tried imgp.at(r,c)[ch] my image result is bad