Processing + Arduino face tracking webcam port issue

siia

I'm new to Processing and Arduino and trying to to work on face tracking pan and tilt system. Processing and Arduino to control pan and tilt system with OpenCV and a webcam. I have found this code online and it seems to work on with built-in Isight webcam, but when I plug in the external webcam, Processing can't seem to recognize the port and I get NullPointerException error. Any ideas on how this can be fixed?

**Processing: **

  import gab.opencv.*;
  import processing.video.*;
  import java.awt.*;
  import processing.serial.*; //The serial library is needed to communicate with the Arduino.

Capture video;
OpenCV opencv;

/////////////////////////////////////////////////////////////
//Screen Size Parameters
int width = 320;
int height = 240;

// contrast/brightness values
int contrast_value    = 0;
int brightness_value  = 0;

Serial port; // The serial port

//Variables for keeping track of the current servo positions.
char servoTiltPosition = 90;
char servoPanPosition = 90;
//The pan/tilt servo ids for the Arduino serial command interface.
char tiltChannel = 0;
char panChannel = 1;

//These variables hold the x and y location for the middle of the detected face.
int midFaceY=0;
int midFaceX=0;

//The variables correspond to the middle of the screen, and will be compared to the midFace values
int midScreenY = (height/2);
int midScreenX = (width/2);
int midScreenWindow = 10;  //This is the acceptable 'error' for the center of the screen. 

//The degree of change that will be applied to the servo each time we update the position.
int stepSize=1;
//////////////////////////////////////////////////

void setup() {
  String[] cameras = Capture.list();
  size(width, height);
  video = new Capture(this, width/2, height/2, cameras[0]);
  opencv = new OpenCV(this, width/2, height/2);
  opencv.loadCascade(OpenCV.CASCADE_FRONTALFACE);  
  video.start();
////////////////////////////////////////////////////  
  port = new Serial(this, "/dev/tty.usbmodem411", 57600);   //Baud rate is set to 57600 to match the Arduino baud rate.



  //Send the initial pan/tilt angles to the Arduino to set the device up to look straight forward.
  port.write(tiltChannel);    //Send the Tilt Servo ID
  port.write(servoTiltPosition);  //Send the Tilt Position (currently 90 degrees)
  port.write(panChannel);         //Send the Pan Servo ID
  port.write(servoPanPosition);   //Send the Pan Position (currently 90 degrees)
/////////////////////////////
}

void draw() {
  scale(2);
  opencv.loadImage(video);

  image(video, 0, 0 );

  noFill();
  stroke(0, 255, 0);
  strokeWeight(3);
  Rectangle[] faces = opencv.detect();
  println(faces.length);

  for (int i = 0; i < faces.length; i++) {
    println(faces[i].x + "," + faces[i].y);
    rect(faces[i].x, faces[i].y, faces[i].width, faces[i].height);
  }
///////////////////////////////////////////
  //Find out if any faces were detected.
  if(faces.length > 0){

    //If a face was found, find the midpoint of the first face in the frame.
    //NOTE: The .x and .y of the face rectangle corresponds to the upper left corner of the rectangle,
    //      so we manipulate these values to find the midpoint of the rectangle.
    midFaceY = faces[0].y + (faces[0].height/2);
    midFaceX = faces[0].x + (faces[0].width/2);

 //Find out if the Y component of the face is below the middle of the screen.
    if (midFaceY > (midScreenY + midScreenWindow)) {
      if (servoTiltPosition >= 5)servoTiltPosition -= stepSize; //If it is below the middle of the screen, update the tilt position variable to lower the tilt servo.
    }
    //Find out if the Y component of the face is above the middle of the screen.
    else if (midFaceY < (midScreenY - midScreenWindow)) {
      if (servoTiltPosition <= 175)servoTiltPosition +=stepSize; //Update the tilt position variable to raise the tilt servo.
    }
    //Find out if the X component of the face is to the left of the middle of the screen.
    if(midFaceX < (midScreenX - midScreenWindow)){
      if(servoPanPosition >= 5)servoPanPosition -= stepSize; //Update the pan position variable to move the servo to the left.
    }
    //Find out if the X component of the face is to the right of the middle of the screen.
    else if(midFaceX > (midScreenX + midScreenWindow)){
      if(servoPanPosition <= 175)servoPanPosition +=stepSize; //Update the pan position variable to move the servo to the right.
    }
  }
  //Update the servo positions by sending the serial command to the Arduino.
  port.write(tiltChannel);      //Send the tilt servo ID
  port.write(servoTiltPosition); //Send the updated tilt position.
  port.write(panChannel);        //Send the Pan servo ID
  port.write(servoPanPosition);  //Send the updated pan position.

    if(faces.length == 0){
    servoTiltPosition = 90;
    servoPanPosition = 90;

    }   
  //delay(1);
}





void captureEvent(Capture c) {
  c.read();
}

**Arduino: **

#include <Servo.h>  //Used to control the Pan/Tilt Servos

//These are variables that hold the servo IDs.
char tiltChannel=0, panChannel=1;

//These are the objects for each servo.
Servo servoTilt, servoPan;

//This is a character that will hold data from the Serial port.
char serialChar=0;

void setup(){
  servoTilt.attach(2);  //The Tilt servo is attached to pin 2.
  servoPan.attach(3);   //The Pan servo is attached to pin 3.
  servoTilt.write(90);  //Initially put the servos both
  servoPan.write(90);      //at 90 degress.

  Serial.begin(57600);  //Set up a serial connection for 57600 bps.
}

void loop(){
  while(Serial.available() <=0);  //Wait for a character on the serial port.
  serialChar = Serial.read();     //Copy the character from the serial port to the variable
  if(serialChar == tiltChannel){  //Check to see if the character is the servo ID for the tilt servo
    while(Serial.available() <=0);  //Wait for the second command byte from the serial port.
    servoTilt.write(Serial.read());  //Set the tilt servo position to the value of the second command byte received on the serial port
  }
  else if(serialChar == panChannel){ //Check to see if the initial serial character was the servo ID for the pan servo.
    while(Serial.available() <= 0);  //Wait for the second command byte from the serial port.
    servoPan.write(Serial.read());   //Set the pan servo position to the value of the second command byte received from the serial port.
  }
  //If the character is not the pan or tilt servo ID, it is ignored.
}