Converting camera frames to float on GPU?

edit

Hi All,

I've got a very basic example that grabs frames from a camera, uploads them to a GpuMat, and displays them in a namedWindow with CV_WINDOW_OPENGL as its type. The code below works as expected, but I don't understand why I have to perform the data type conversion using the host mat.

#include <opencv2/core/core.hpp>
#include <opencv2/core/cuda.hpp>
#include <opencv2/highgui/highgui.hpp>

#include <iostream>

int main() {
    using namespace cv;
    using cv::cuda::GpuMat;

    VideoCapture cap(0);
    if (!cap.isOpened())
        return -1;

    // create opengl window
    namedWindow("webcam", CV_WINDOW_OPENGL);

    // Gpu mat to display
    GpuMat g;

    // Host frame buf
    Mat frame;

    bool grabFrame = true;
    while (grabFrame) {
        // Grab frame
        cap >> frame;

        // Why is this line necessary?
        frame.convertTo(frame, CV_32F);

        // Upload to gpu
        g.upload(frame);

        // convert to normalized float
        g.convertTo(g, CV_32F, 1.f / 255);

        // show in opengl window
        imshow("webcam", g);

        // maybe quit
        if (cv::waitKey(30) >= 0)
            grabFrame = false;
    }

    return 0;
}

If I comment out that line and try to perform the conversion and division in one step, I get a black image. I thought it could be the order in which the conversion happens (i.e scale followed by conversion), so I tried this

g.convertTo(g, CV_32F);
g.convertTo(g, CV_32F, 1.f / 255);

but had no luck. Checking the type of image the camera yields returns 16, which is a 3 channel single byte image. I tried replacing CV_32F with CV_32FC3 but it didn't make a difference. For what it's worth, though, the final dataType of the gpumat is 21, which is CV_32FC3. The thing that breaks it seems to be the type conversion.

Are there limits on the data types we can convert?