javaopencvnullpointerexceptiontemplate-matching
Null Pointer Exception in MatchTemplate example using OpenCV and Java
This question is continued from this thread. I could download the com.larmor.opencv.MatchTemplate library from here (in case anyone needs the link in future.)
Now coming down to my question.
When I run the code I am getting null pointer exception. Attaching the error messages for reference. Also this is the exact same project downloaded from here So I am not mentioning the code in the question.
Can anyone help me with how do I get rid of these errors.
EDIT
I had provided a link to the code above. So I didn't paste the entire code here. Anyways, here's the code:
package templatematching;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Panel;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.geom.Rectangle2D;
import java.awt.image.BufferedImage;
import javax.media.Buffer;
import javax.media.CaptureDeviceInfo;
import javax.media.CaptureDeviceManager;
import javax.media.Manager;
import javax.media.MediaLocator;
import javax.media.Player;
import javax.media.control.FrameGrabbingControl;
import javax.media.format.VideoFormat;
import javax.media.util.BufferToImage;
import javax.swing.JButton;
import javax.swing.JComponent;
import com.larmor.opencv.MatchTemplate;
/**
* This example match WebCam Area.
* <br>
* The class uses <a href="http://java.sun.com/products/java-media/jmf/" target="_blank">Java Media Framework API (JMF)</a>,
* and <a href="http://java.sun.com/javase/6/docs/technotes/guides/imageio/index.html" target="_blank">JAI-Java Image I/O Technology</a>
* and <a href="http://java.sun.com/products/java-media/jmf/">Java Media Framework API (JMF)</a>
* (for dowload: <a href="https://jai.dev.java.net/" target="_blank">https://jai.dev.java.net/</a>,
* <a href="https://jai-imageio.dev.java.net/" target="_blank">https://jai-imageio.dev.java.net/</a> and
* <a href="http://java.sun.com/products/java-media/jmf/2.1.1/download.html" target="_blank">http://java.sun.com/products/java-media/jmf/2.1.1/download.html</a>).<br>
* <br>
*
* 1) press button "select area" for stop image
* 2) using mouse select area to matching (red rectangle)
* 3) press button "start matching" for play webcam and starting matching (green rectangle)
*
* @author Pier Paolo Ciarravano Larmor
* License: GNU General Public License
* @version Vers. 0.5 beta (April.2008)
*/
public class TestMatchWebCamArea extends Panel implements ActionListener,
MouseListener, MouseMotionListener {
static Player player = null;
CaptureDeviceInfo di = null;
MediaLocator ml = null;
JButton matchCam = null;
JButton selectArea = null;
Component sourceComp = null;
DoubleBufferPanel dbPanel = null;
int areaX = 0;
int areaY = 0;
int areaWidth = 0;
int areaHeight = 0;
int stateButton;
BufferedImage buffImgTemplate = null;
public TestMatchWebCamArea() {
stateButton = 0;
setLayout(new BorderLayout());
// setSize(320,240);
selectArea = new JButton("Select Area");
selectArea.addActionListener(this);
matchCam = new JButton("Start Matching");
matchCam.addActionListener(this);
matchCam.setEnabled(false);
// String str1 = "vfw:Logitech USB Video Camera:0";
String str2 = "vfw:Microsoft WDM Image Capture (Win32):0";
di = CaptureDeviceManager.getDevice(str2);
ml = di.getLocator();
try {
Manager.setHint(Manager.LIGHTWEIGHT_RENDERER, Boolean.TRUE);
player = Manager.createRealizedPlayer(ml);
player.start();
if ((sourceComp = player.getVisualComponent()) != null) {
sourceComp.addMouseMotionListener(this);
sourceComp.addMouseListener(this);
// sourceComp.setBounds (0, 0,
// sourceComp.getPreferredSize().width,
// sourceComp.getPreferredSize().height);
dbPanel = new DoubleBufferPanel();
dbPanel.setLayout(new BorderLayout());
dbPanel.add(sourceComp);
// dbPanel.setBackground(Color.BLUE);
// dbPanel.setBounds (0, 0, sourceComp.getPreferredSize().width,
// sourceComp.getPreferredSize().height);
add(dbPanel, BorderLayout.CENTER);
}
add(selectArea, BorderLayout.NORTH);
add(matchCam, BorderLayout.SOUTH);
} catch (Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
Frame f = new Frame("Test Match WebCam - By Larmor");
f.setResizable(false);
f.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
playerclose();
System.exit(0);
}
});
TestMatchWebCamArea cf = new TestMatchWebCamArea();
f.add("Center", cf);
f.pack();
// f.setSize(new Dimension(320,240));
f.setVisible(true);
}
public static void playerclose() {
player.close();
player.deallocate();
}
public BufferedImage getPlayerImage() {
// Grab a frame
FrameGrabbingControl fgc = (FrameGrabbingControl) player.getControl("javax.media.control.FrameGrabbingControl");
Buffer buf = fgc.grabFrame();
// Convert it to an image
BufferToImage btoi = new BufferToImage((VideoFormat) buf.getFormat());
Image img = btoi.createImage(buf);
// Convert to BufferedImage
BufferedImage bi = new BufferedImage(sourceComp.getPreferredSize().width, sourceComp.getPreferredSize().height, BufferedImage.TYPE_BYTE_GRAY);
Graphics2D g = bi.createGraphics();
g.drawImage(img, 0, 0, null);
g.dispose();
return bi;
}
public void actionPerformed(ActionEvent e) {
JComponent c = (JComponent) e.getSource();
if (c == selectArea) {
stateButton = 1;
player.stop();
selectArea.setEnabled(false);
} else if (c == matchCam) {
// Validate Area
if ((areaX >= 0)
&& (areaY > 0)
&& (areaWidth > 0)
&& (areaHeight > 0)) {
buffImgTemplate = getPlayerImage().getSubimage(areaX, areaY, areaWidth, areaHeight);
MatchTemplate.displayBufferedImage(buffImgTemplate, "template");
stateButton = 2;
player.start();
matchCam.setEnabled(false);
selectArea.setEnabled(true);
}
}
}
// @Override
public void mouseClicked(MouseEvent arg0) {
}
// @Override
public void mouseEntered(MouseEvent arg0) {
}
// @Override
public void mouseExited(MouseEvent arg0) {
}
// @Override
public void mouseMoved(MouseEvent arg0) {
}
// @Override
public void mousePressed(MouseEvent arg0) {
arg0.consume();
if (stateButton == 1) {
areaX = arg0.getX();
areaY = arg0.getY();
dbPanel.repaint();
}
}
// @Override
public void mouseReleased(MouseEvent arg0) {
arg0.consume();
if (stateButton == 1) {
areaWidth = arg0.getX() - areaX;
areaHeight = arg0.getY() - areaY;
dbPanel.repaint();
matchCam.setEnabled(true);
}
}
// @Override
public void mouseDragged(MouseEvent arg0) {
arg0.consume();
if (stateButton == 1) {
areaWidth = arg0.getX() - areaX;
areaHeight = arg0.getY() - areaY;
dbPanel.repaint();
}
}
class DoubleBufferPanel extends Panel {
Image offscreen;
/**
* null out the offscreen buffer as part of invalidation
*/
public void invalidate() {
super.invalidate();
offscreen = null;
}
/**
* override update to *not* erase the background before painting
*/
public void update(Graphics g) {
paint(g);
}
/**
* paint children into an offscreen buffer, then blast entire image at once.
*/
public void paint(Graphics g) {
if (offscreen == null) {
offscreen = createImage(getSize().width, getSize().height);
}
Graphics og = offscreen.getGraphics();
og.setClip(0, 0, getSize().width, getSize().height);
super.paint(og);
if (stateButton == 1) {
Graphics2D g2 = (Graphics2D) og;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2.setPaint(Color.red);
Rectangle2D e = new Rectangle2D.Float(areaX, areaY, areaWidth, areaHeight);
g2.draw(e);
} else if (stateButton == 2) {
// match template
BufferedImage buffImgSource = getPlayerImage();
long startTime = System.currentTimeMillis();
MatchTemplate matchObj = new MatchTemplate(buffImgSource, buffImgTemplate);
Point matchPoint = matchObj.matchTemplateBestPoint(MatchTemplate.CV_TM_CCOEFF_NORMED);
long totalTime = System.currentTimeMillis() - startTime;
System.out.println("totalTime for matching:" + totalTime);
Graphics2D g2 = (Graphics2D) og;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2.setPaint(Color.green);
Rectangle2D e = new Rectangle2D.Float(matchPoint.x, matchPoint.y, areaWidth, areaHeight);
g2.draw(e);
}
g.drawImage(offscreen, 0, 0, null);
og.dispose();
}
}
}
Solution
The null pointer is caused by the following lines in the constructor of TestMatchWebCamArea:
String str2 = "vfw:Microsoft WDM Image Capture (Win32):0";
di = CaptureDeviceManager.getDevice(str2);
ml = di.getLocator(); //NullPointerException
The only way you can get a NullPointerException on that line is if di == null, so we look at where di is set, and look at the relevant Javadoc:
Returns: A CaptureDeviceInfo object that corresponds to the specified device name. Returns null if the specified device could not be found.
It seems therefore that the method can't find a device with the name "vfw:Microsoft WDM Image Capture (Win32):0".
I've never used the Java Media Framework, but the example given for the method you're calling doesn't look anything like the device name you've provided:
Parameters: deviceName - A String that contains the name of the device for which you want to get a CaptureDeviceInfo object. For example: "SunVideo"
- Spring Boot Unable to Locate `javax.servlet.Filter` Class
- Which lib to create an Identity provider to connect to service provider
- Developing with docker and vscode, sometimes the intellisense works sometimes it doesn't
- Lombok is not generating getter and setter
- How to display GUI content to a txt file?
- Algorithm for parse formula excel from original cell to destination cell
- Spring JPA selecting specific columns
- How to Dockerize a tomcat app
- Java System.identityHashCode returning different value internally
- Java: ChaCha20 w/ Poly1305 as MAC for general purpose file encryption
- Test RabbitTemplate#convertAndSend as lambda with Mockito & JUnit
- Mark unit test as an expected failure in JUnit
- Java's new Scanner vs Scanner.create()?
- How to unit test spring's gateway?
- Java 8 Stream.skip() with Predicate
- Adding Spring Dependency Injection in JavaFX (JPA Repo, Service)
- Embeddable and ElementCollection nesting
- StringBuffer append() or String +?
- how to resolve Joda date/time type `org.joda.time.DateTime` not supported by default
- How do you set in Jetty 12 a max request size programmatically
- Kafka Connect running out of heap space
- Intellij generate javadoc for methods and classes
- Spring-AMQP client does not recover after broker restart with idle channels getting stuck
- Can I run a JAX-RS web service on com.sun.net.httpserver.HttpServer?
- Why is PostConstruct not called?
- Is there any way to check colour spaces in a pdf file
- Java production: java.lang.IndexOutOfBoundsException Unable to build SpringBoot project
- Best practice for parameter naming in Java constructors and simple setters
- Unable to import Maven Project in Eclipse as Next and Finish buttons are disabled
- 'Git is not installed' on intellij