Subscriber callback function not called when trying to capture data using Kinect [Solved]

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This is my current code. It's a node, and I use rosrun to execute/run it.

#include <iostream>
#include <ros/ros.h>
#include <sensor_msgs/Image.h>
#include <sensor_msgs/image_encodings.h>
#include <cv_bridge/cv_bridge.h>
#include <opencv2/highgui/highgui.hpp>
#include <string.h>
#include <ros/callback_queue.h>

using namespace std;

char filename[50];
int imgtype;

bool done=false;

static const int MY_ROS_QUEUE_SIZE = 100;

void depth_node_callback(const sensor_msgs::Image::ConstPtr& msg)
 {


 cout << "Entering Callback" << endl;

 cv_bridge::CvImageConstPtr cv_ptr;
 cv_ptr = cv_bridge::toCvShare(msg);

 double max = 0,min=0;

 cv::minMaxLoc(cv_ptr->image, &min, &max, 0, 0);
 cv::Mat normalized,op;
 cv_ptr->image.convertTo(normalized, CV_32F, 255/(max-min), -min) ;

 cv::imwrite(filename,normalized);

 done=true;
 }

int main(int argc, char **argv)
 {
 string type;
 strcpy(filename,argv[1]);
 imgtype=atoi(argv[2]);

 ros::init(argc, argv, "depth_node");

 cout << "Ready to save image" << endl;
 ros::NodeHandle nh;

 if(imgtype==1)
 type="camera/rgb/image_color";

 else if(imgtype==0)
 type="camera/depth_registered/image_raw";

 ros::Subscriber sub = nh.subscribe(type,MY_ROS_QUEUE_SIZE, depth_node_callback);


 while(!done && ros::ok()) ros::spinOnce();
 cout <<filename<<" Saved" << endl;
 return 0;
 }

The callback function doesn't get called at all. It just kind of gets stuck and doesn't do anything.

I am attempting to execute this node above that I have created at specific intervals and every interval it should take the necessary images and move forward to the next command (without having to ctrl+c myself), but it gets stuck without entering the callback function.

Update I didn't mention properly that I use rosrun to call this node. But I also use rosrun right before this to call another node. Does that make any difference? I don't have an issue with the one before this (but that's not my own code/node).

I noticed similar posts here which all mentioned spinOnce() which I included based on their suggestion right at the beginning.

Update 2 Based on the given answer I added the rate.sleep(). However that leads to two issues. One I enter the callback initially and exit, without it doing anything, then it repeats that and writes the image as it's supposed to. So I don't know what that "blank call" the first time. And it either does that multiple times or not at all, so is that an issue with the Kinect trying to get the image? or with the code?

Done!
Kinect
Ready to save image
Entering Callback
Entering Callback
Entering Callback
c_jac00.png Saved
Ready to save image

The second issue is that I am running two rosrun commands back to back for this node. The first one is to get image_color (rgb), the second to get image_raw gets "stuck" again. What's the reason behind that?

I also get the following warning

[ WARN] [1438986321.518503590]: TF exception:
Lookup would require extrapolation into the past.  Requested time 1438986013.498032942 but the earliest data is at time 1438986311.630285300, when looking up transform from frame [camera_depth_optical_frame] to frame [camera_rgb_optical_frame]

Solution @allenh1 's answer worked ... (more)