How to get the dpi of an image(Java)

Question

In c#, we can use Image.HorizontalResolution and Image.VerticalResolution.

But in java, how to get it?

I found ImageInfo.java, but it only supp

Answer 1

With the help of an ImageReader instance, you can get the image meta data in a neutral format, and then parse it for what you need. A DTD is here.

    ImageInputStream iis = ImageIO.createImageInputStream(new File(path));
    Iterator it = ImageIO.getImageReaders(iis);
    if (!it.hasNext())
    {
        System.err.println("No reader for this format");
        return;
    }
    ImageReader reader = (ImageReader) it.next();
    reader.setInput(iis);

    IIOMetadata meta = reader.getImageMetadata(0);
    IIOMetadataNode root = (IIOMetadataNode) meta.getAsTree("javax_imageio_1.0");
    NodeList nodes = root.getElementsByTagName("HorizontalPixelSize");
    if (nodes.getLength() > 0)
    {
        IIOMetadataNode dpcWidth = (IIOMetadataNode) nodes.item(0);
        NamedNodeMap nnm = dpcWidth.getAttributes();
        Node item = nnm.item(0);
        int xDPI = Math.round(25.4f / Float.parseFloat(item.getNodeValue()));
        System.out.println("xDPI: " + xDPI);
    }
    else
        System.out.println("xDPI: -");
    if (nodes.getLength() > 0)
    {
        nodes = root.getElementsByTagName("VerticalPixelSize");
        IIOMetadataNode dpcHeight = (IIOMetadataNode) nodes.item(0);
        NamedNodeMap nnm = dpcHeight.getAttributes();
        Node item = nnm.item(0);
        int yDPI = Math.round(25.4f / Float.parseFloat(item.getNodeValue()));
        System.out.println("yDPI: " + yDPI);
    }
    else
        System.out.println("yDPI: -");

(Source/Inspiration: David Thielen)

Note that you will get a dpi only if it is there.

If you wonder what's in the Metadata XML, use this code:

    StringWriter xmlStringWriter = new StringWriter();
    StreamResult streamResult = new StreamResult(xmlStringWriter);
    Transformer transformer = TransformerFactory.newInstance().newTransformer();
    transformer.setOutputProperty(OutputKeys.INDENT, "yes"); // http://stackoverflow.com/a/1264872/535646
    transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");
    DOMSource domSource = new DOMSource(root);
    transformer.transform(domSource, streamResult);
    System.out.println (xmlStringWriter);