How to display CV_32FC2 images in ROS

edit

I'm trying to use OpenCV to calculate real-rime optical flow and display it in ROS. The task, using provided OpenCV's functionality, seems fairly easy. I've used uvc_camera and cv_bridge to capture images with ROS and convert them to cv::Mat. Then, I'm using calcOpticalFlowFarneback to calculate optical flow, which returns a cv::Mat optical flow image of type CV_32FC2.

The code I'm using to publish the image looks like this:

cv_bridge::CvImage flowImage;
sensor_msgs::ImagePtr flowImagePtr;

if (!_flow.empty()) {
  flowImage.header = cvImagePtr_->header; //copy header from input image
  flowImage.encoding = sensor_msgs::image_encodings::TYPE_32FC2;
  flowImage.image = _flow; //_flow is calculated elsewhere

  flowImagePtr = flowImage.toImageMsg();
  publishCvImage(flowImagePtr); //uses a publisher to publish image
}

The code works fine, but ROS is unable to display floating point images (I tried either image_view and rviz). What is the right way to convert those images to a displayable form?

Cheers, Tom.

Edit: Eventually I'm using these two methods to visualize the results (the below code bases on this):

cvImagePtr = cv_bridge::toCvCopy(image, sensor_msgs::image_encodings::RGB8);
    flowImage = cvImagePtr->image; //original RGB captured image, needs to be converted to MONO8 for cv::calcOpticalFlowFarneback
cv::Mat velx = cv::Mat(flowImage.size(), CV_32FC1);
cv::Mat vely = cv::Mat(flowImage.size(), CV_32FC1);
cv::Mat flowMatrix; //outcome of cv::calcOpticalFlowFarneback

void OpticalFlow::extractFlowFieldFarneback() {

    for (int row = 0; row < flowMatrix.rows; row++) {
        float *vx = (float*)(velx.data + velx.step * row);
        float *vy = (float*)(vely.data + vely.step * row);

        const float* f = (const float*)(flowMatrix.data + flowMatrix.step * row);
        for (int col = 0; col < flowMatrix.cols; col++) {
            vx[col] = f[2*col];
            vy[col] = f[2*col+1];
        }
    }
}

void OpticalFlow::overlayFlowFieldFarneback() {

    if (!velx.empty() && !vely.empty()) {

        for (int row = 0; row < flowImage.rows; row++) {
            float *vx = (float*)(velx.data + velx.step * row);
            float *vy = (float*)(vely.data + vely.step * row);

            for (int col = 0; col < flowImage.cols; col++) {
                double length = sqrt(vx[col]*vx[col] + vy[col]*vy[col]);

                if (length > 1) {
                    cv::Point2i p1(col, row);
                    cv::Point2i p2(col + (int)vx[col], row + (int)vy[col]);

                    cv::line(flowImage, p1, p2, cvScalar(255, 0, 0, 0));
                }
            }
        }
    }
}