Image Dimensions

[Trey German]

I'm trying to get the width/height of an image.
The image is named 'image'. I'm using image.getWidth(this); (same for height) and it returns -1. Anyone got any tips?

[Brian McCallister]

You need to use java.awt.Image (or the equivalent, look up in the javadocs). Notably, if you are running under *nix wihout an X session open you will need to specify headless execution on the commandline or it will get crnaky.
-Brian

[Jim Yingst]

The java.awt.Image API explains why -1 is returned. This API is actually rather tricky - it's asynchronous. This means that you can (and often do) get an Image object that's not yet fully loaded. Methods like getHeight() may return -1 to indicate that the height() data is not yet available - try again later. The class was designed this way because frequently you might be downloading images from a slow source, and you have the option to use those parts of the image data that are available, as they become available, rather than waiting for the whole thing. (A typical example - if you're laying out a web page, you can set aside space for an image once you know it's height and width - even though you can't display the image yet.) Anyway, in order to use Image effectively you typically have to make use of the ImageObserver class to create an object that will notify you when the data you need is loaded. Here's a class I made some time ago to do this:

import java.awt.*;
import java.awt.image.*;
import java.io.*;
import java.net.*;
 
/**
 *  A class which determines the height and width of an image by
 *  inspecting the image file.
 */
public class ImageSizer
{
  private int height;
  private int width;
 
  private static Toolkit toolkit = Toolkit.getDefaultToolkit();
 
  /**
   *  Create an ImageSizer to find the size of a given image file.
   *  This constructor will block until enough of the image is loaded
   *  to determine both height and width.
   *  This constructor times out after 1 second.
   *  @param fileName Image file to load
   *  @exception IOException Indicates any problem in reading the image file,
   *      including timeout.
   */
  public ImageSizer(String fileName) throws IOException
  {
    this(fileName, 1000);
  }
 
  /**
   *  Create an ImageSizer to find the size of a given image file.
   *  This constructor will block until enough of the image is loaded
   *  to determine both height and width.
   *  @param fileName Name of image file to load
   *  @param timeout Number of milliseconds to wait before timing out
   *  @exception IOException Indicates any problem in reading the image file,
   *      including timeout.
   */
  public ImageSizer(String fileName, long timeout) throws IOException
  {
    File file = new File(fileName);
    if (!file.exists())
      throw new FileNotFoundException(file.getAbsolutePath());
    if (!file.canRead())
      throw new IOException("Can't read file " + file.getAbsolutePath());
    Image image = toolkit.createImage(fileName);
    load(image, timeout, file.getAbsolutePath());
  }
  /**
   *  Create an ImageSizer to find the size of a given image file.
   *  This constructor will block until enough of the image is loaded
   *  to determine both height and width.
   *  @param url URL of image file to load
   *  @param timeout Number of milliseconds to wait before timing out
   *  @exception IOException Indicates any problem in reading the image file,
   *      including timeout.
   */
  public ImageSizer(URL url, long timeout) throws IOException
  {
    Image image = toolkit.createImage(url);
    load(image, timeout, url.toString());
  }
 
  private void load(Image image, long timeout, String name) throws IOException
  {
    long endTime = System.currentTimeMillis() + timeout;
    Observer observer = new Observer();
    boolean keepWaiting = true;
    while (keepWaiting)
    {
      height = image.getHeight(observer);
      width = image.getWidth(observer);
      if (height >= 0 && width >= 0)
        keepWaiting = false;
      else
      {
        long waitTime = endTime - System.currentTimeMillis();
        if (waitTime < 0)
          throw new IOException("Image load timed out: " + name);
        synchronized (observer)
        {
          try { observer.wait(waitTime); }
          catch (InterruptedException e) {}
        }
        if (observer.isImageAborted())
          throw new IOException("Image aborted - reason unknown. " + name);
      }
    }
  }
 
  public int getHeight() { return height; }
 
  public int getWidth() { return width;  }
 
  /** Demo for testing */
  public static void main(String[] s) throws Exception
  {
    Object[] params =
        {
          new URL("file://D:/test/nofile.gif"),
          new URL("file://D:/test/sample.html"),
          new URL("file://D:/test/test.gif"),
          new URL("file://D:/test/test2.gif"),
          new URL("file://D:/test/test.jpg"),
          new URL("file://D:/test/test2.jpg"),
          "D:\\test\\nofile.gif",
          "D:\\test\\sample.html",
          "D:\\test\\test.gif",
          "D:\\test\\test2.gif",
          "D:\\test\\test.jpg",
          "D:\\test\\test2.jpg"
        };
    long startTime = System.currentTimeMillis();
    for (int i = 0; i < params.length; i++)
    {
      Object param = params[i];
      System.out.println(param);
      try
      {
        ImageSizer sizer;
        if (param instanceof String)
          sizer = new ImageSizer((String) param);
        else
          sizer = new ImageSizer((URL) param, 5000);
        int height = sizer.getHeight();
        int width = sizer.getWidth();
        System.out.println("\theight\t" + height);
        System.out.println("\twidth:\t" + width);
      }
      catch (Exception e)
      {
        System.out.println(e);
      }
    }
    long endTime = System.currentTimeMillis();
    System.out.println("Elapsed time " + (endTime - startTime) + " ms");
    System.exit(0);
  }
 
  private static class Observer implements ImageObserver
  {
    private boolean isImageAborted;
 
    /* Defined by ImageObserver */
    public synchronized boolean imageUpdate(Image img, int infoflags, int x, int y,
        int width, int height)
    {
      notifyAll();
      isImageAborted = (infoflags & ImageObserver.ABORT) > 0;
      boolean heightReady = (infoflags & ImageObserver.HEIGHT) > 0;
      boolean widthReady = (infoflags & ImageObserver.WIDTH) > 0;
      boolean keepLoading = !isImageAborted && (!heightReady || !widthReady);
      return keepLoading;
    }
 
    public synchronized boolean isImageAborted()
    {
      return isImageAborted;
    }
  }
}