How to store the depth data from kinect(/camera/depth_registrered/image_raw) as gray scale image?

edit

I now is an old thread. But just for the others that need to store a depth image (from camera or from rosbag) to a png file. This is what you should do on the depth image subscription callback or in any place you want to perform this operation with python:

def callback(self, data):
    try:
        # The depth image is a single-channel float32 image
        # the values is the distance in mm in z axis
        depth_image = self.bridge.imgmsg_to_cv(data, '32FC1')
        # Convert the depth image to a Numpy array since most cv2 functions
        # require Numpy arrays.
        depth_array = np.array(depth_image, dtype=np.float32)
        # Normalize the depth image to fall between 0 (black) and 1 (white)
        cv2.normalize(depth_array, depth_array, 0, 1, cv2.NORM_MINMAX)
        # At this point you can display the result properly:
        # cv2.imshow('Depth Image', depth_display_image)
        # If you write it as it si, the result will be a image with only 0 to 1 values.
        # To actually store in a this a image like the one we are showing its needed
        # to reescale the otuput to 255 gray scale.
        cv2.imwrite('capture_depth.png',frame*255)
    except CvBridgeError, e:
        print e

I'm using at the moment ubuntu 12.04 and Ros Hydro

depth_image = self.bridge.imgmsg_to_cv(data, '32FC1')

you should change the code to

depth_image = self.bridge.imgmsg_to_cv(data, "passthrough")

then, you'll get depth_image as float32.

(no longer transform using np.array is not needed.)

Here you can find a short code to store depth data into CV image:

unsigned int depthSamples = msg->image().width() * msg->image().height();
float f;
// cppchecker recommends using sizeof(varname)
unsigned int depthBufferSize = depthSamples * sizeof(f);

float *depthBuffer = new float[depthSamples];
uint16_t *imageBufferHalf = new uint16_t[depthSamples];

memcpy(depthBuffer, msg->image().data().c_str(), depthBufferSize);

float maxDepth = 0;
for (unsigned int i = 0; i < msg->image().height() * msg->image().width(); ++i) {
    if (depthBuffer[i] > maxDepth && !std::isinf(depthBuffer[i])) {
        maxDepth = depthBuffer[i];
    }
}

cv::Mat image(msg->image().height(), msg->image().width(), CV_8UC3);
unsigned int idx = 0;
double factor = 255 / maxDepth;
for (unsigned int j = 0; j < msg->image().height(); ++j) {
  for (unsigned int i = 0; i < msg->image().width(); ++i) {
    float d = depthBuffer[idx++];
    if (d > maxDepth)
        d = maxDepth;
    d = 255 - (d * factor);
    cv::Vec3b color;
    color[0] = d;
    color[1] = d;
    color[2] = d;
    image.at<cv::Vec3b>(cv::Point(i, j)) = color;
  }
}