获取Java中的图像宽度和高度

Question

I just want to ask how to get the width and height of an image, because this returns -1 for width and height:

private void resizeImage(Image image){
    JLabel imageLabel = new JLabel();

    int imageWidth = image.getWidth(null);
    int imageHeight = image.getHeight(null);
    System.out.println("Width:" + imageWidth);
    System.out.println("Height:" + imageHeight);
}

Answer 1

You should do something like this :

BufferedImage bimg = ImageIO.read(new File(filename));
int width          = bimg.getWidth();
int height         = bimg.getHeight(); 

as this post says

Answer 2

Exactly why this happens in your case is unclear, you don't specify exactly what image actually is.

Anyway, the answer can be found in the JavaDoc :

public abstract int getWidth(ImageObserver observer)

Determines the width of the image. If the width is not yet known, this method returns -1 and the specified ImageObserver object is notified later.

The width and height obiously cannot be immediately determined for the image in question. You need to pass an ImageObserver instance which will have this method called when height and width can be resolved.

Answer 3

    public static BufferedImage resize(final Image image, final int width, final int height){
    assert image != null;
    final BufferedImage bi = new BufferedImage(width, height, image instanceof BufferedImage ? ((BufferedImage)image).getType() : BufferedImage.TYPE_INT_ARGB);
    final Graphics2D g = bi.createGraphics();
    g.drawImage(image, 0, 0, width, height, null);
    g.dispose();
    return bi;
}

The code posted above is one way of resizing an image. Generally to get the width and height of an image, you may do:

image.getWidth(null);
image.getHeight(null);

This is all under the assumption that the image is not null.

Answer 4

With Apache Commons Imaging , you can get image width and height with better performance, without reading entire image to memory.

Sample code below is using Sanselan 0.97-incubator (Commons Imaging is still SNAPSHOT as I write this):

final ImageInfo imageInfo = Sanselan.getImageInfo(imageData);
int imgWidth = imageInfo.getWidth();
int imgHeight = imageInfo.getHeight();