Okay. I followed your advice and I'm now able to return the array. Thank you!
However, the pixelData array in my getData function is filled with zeroes. If I print out the array to the console from my mouseRelease function I get the pixel values that is in pixelData. How come I can access pixelData from my mouseRelease function and not my getData function??

Code:
public class MouseMotionEventDemo extends JPanel implements MouseMotionListener, MouseListener {
	private int mX,mY;
	private static int size = 201;
	private int prevX = 0;
	private int prevY = size/2;
	private Boolean mousePressed = false;

	private double pixelData[] = new double[size]; 
  
	public MouseMotionEventDemo() {
	    addMouseMotionListener(this);
	    addMouseListener(this);
	    setVisible(true);
	}

	public void mouseMoved(MouseEvent me) {
	  
	}

	public void mouseDragged(MouseEvent me) {
		mX = (int) me.getPoint().getX();
		mY = (int) me.getPoint().getY();
		repaint();
		if(mX<size){
			pixelData[mX] = mY;
	 }
	  prevX=mX;
	  prevY=mY;
	 }
	  
	 public void mousePressed(MouseEvent e) {
		  mousePressed = true;
	 }
	  
	 public void paint(Graphics g) {
		 if(mousePressed==true){
			 g.setColor(Color.white);
			 g.fillRect(0, 0, getWidth(), getHeight());
			 g.setColor(Color.black);
			 g.drawLine(0, getHeight()/2, getWidth(),getHeight()/2);
			 mousePressed = false;
		 }
		 //g.fillRect(mX, mY, 5, 5);
		 g.drawLine(prevX,prevY,mX,mY);
	  }

  @SuppressWarnings("deprecation")
	public static void run(int x, int y, String name) {
	    JFrame f = new JFrame();
	    f.getContentPane().add(new MouseMotionEventDemo());
	    f.setSize(size, size);
	    f.setTitle(name);
	    f.setLocation(x,y);
	    f.show();
	}
  
  	public void mouseEntered(MouseEvent e) {
		// TODO Auto-generated method stub
		
	}


	public void mouseExited(MouseEvent e) {
		// TODO Auto-generated method stub
	}


	public void mouseReleased(MouseEvent e) {
		for(int x=0;x<size;x++){
			System.out.println((pixelData[x]/(size/2)-1)*-1);	//Prints the correct values      from pixelData
		}
	}

	public void mouseClicked(MouseEvent e) {
		// TODO Auto-generated method stub
	}
	
	public double[] getData() {
	    double[] outData = new double[size];
	    for(int x=0;x<size;x++){
			System.out.println(pixelData[x]/(size/2)-1)*-1);              //prints zeroes...?
		}
		return outData;
	}
}