Copying two images pixel by pixel - c++

Question

I am trying to work with each pixel from depth map. (I am implementing image segmentation.) I don't know how to work with pixels from image with depth higher than 1.
This sample code copies depth map to another cv::Mat pixel by pixel. It works fine, if I normalize it (depth of normalized image = 1). But it doesn't work with depth = 3, because .at<uchar> is wrong operation for this depth.
cv::Mat res;
cv::StereoBM bm(CV_STEREO_BM_NORMALIZED_RESPONSE);
bm(left, right, res);
std::cout<<"type "<<res.type()<<" depth "<<res.depth()<<" channels "<<res.channels()<<"\n";// type 3 depth 3 channels 1
cv::Mat tmp = cv::Mat::zeros(res.rows, res.cols, res.type());
for(int i = 0; i < res.rows; i++)
{
for(int j = 0; j < res.cols; j++)
{
tmp.at<uchar>(i, j) = res.at<uchar>(i, j);
//std::cout << (int)res.at<uchar>(i, j) << " ";
}
//std::cout << std::endl;
}
cv::imshow("tmp", normalize(tmp));
cv::imshow("res", normalize(res));
normilize function
cv::Mat normalize(cv::Mat const &depth_map)
{
double min;
double max;
cv::minMaxIdx(depth_map, &min, &max);
cv::Mat adjMap;
cv::convertScaleAbs(depth_map, adjMap, 255 / max);
return adjMap;
}
left image - tmp, right image - res
How can I get the pixel from image with depth equal to 3?

Answer 1

Mat::depth() returns value equal to a constant symbolising bit depth of the image. If You get depth equal to for example CV_32F, to get to the pixels You would need to use float instead of uchar.
CV_8S -> char
CV_8U -> uchar
CV_16U -> unsigned int
CV_16S -> int
CV_32F -> float
CV_64F -> double
Mat::channels() tells You how many values of that type are assigned to a coordinate. These multiple values can be extracted as cv::Vec. So if You have a two channel Mat with depth CV_8U, instead using Mat.at<uchar> You would need to go with Mat.at<Vec2b>, or Mat.at<Vec2f> for CV_32F one.

Answer 2

When your images are of depth 3, do this for copying pixel by pixel:
tmp.at<Vec3b>(i,j) = res.at<Vec3b>(i,j);
However, if you are copying the whole image , I do not understand the point of copying each pixel individually, unless you want to do different processing with different pixels.
You can just copy the whole image res to tmp by this:
res.copyTo(tmp);