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Obtaining image metadata

Using the Java Image I/O API | 2 comments

The Java program given below reads the metadata from one or more image files given as arguments to the program. The metadata is read into an XML Document Object Model (DOM) tree, and a simple method is used to print each element and attributes (if present). The code for printing the tree is roughly based on the example given in Handling Metadata (Java Image I/O API Guide).

import org.w3c.dom.*;

import java.io.*;
import java.util.*;
import javax.imageio.*;
import javax.imageio.stream.*;
import javax.imageio.metadata.*;

public class Metadata {

    public static void main(String[] args) {
        Metadata meta = new Metadata();
        int length = args.length;
        for ( int i = 0; i < length; i++ )
            meta.readAndDisplayMetadata( args[i] );
    }

    void readAndDisplayMetadata( String fileName ) {
        try {

            File file = new File( fileName );
            ImageInputStream iis = ImageIO.createImageInputStream(file);
            Iterator<ImageReader> readers = ImageIO.getImageReaders(iis);

            if (readers.hasNext()) {

                // pick the first available ImageReader
                ImageReader reader = readers.next();

                // attach source to the reader
                reader.setInput(iis, true);

                // read metadata of first image
                IIOMetadata metadata = reader.getImageMetadata(0);

                String[] names = metadata.getMetadataFormatNames();
                int length = names.length;
                for (int i = 0; i < length; i++) {
                    System.out.println( "Format name: " + names[ i ] );
                    displayMetadata(metadata.getAsTree(names[i]));
                }
            }
        }
        catch (Exception e) {

            e.printStackTrace();
        }
    }

    void displayMetadata(Node root) {
        displayMetadata(root, 0);
    }

    void indent(int level) {
        for (int i = 0; i < level; i++)
            System.out.print("    ");
    }

    void displayMetadata(Node node, int level) {
        // print open tag of element
        indent(level);
        System.out.print("<" + node.getNodeName());
        NamedNodeMap map = node.getAttributes();
        if (map != null) {

            // print attribute values
            int length = map.getLength();
            for (int i = 0; i < length; i++) {
                Node attr = map.item(i);
                System.out.print(" " + attr.getNodeName() +
                                 "=\"" + attr.getNodeValue() + "\"");
            }
        }

        Node child = node.getFirstChild();
        if (child == null) {
            // no children, so close element and return
            System.out.println("/>");
            return;
        }

        // children, so close current tag
        System.out.println(">");
        while (child != null) {
            // print children recursively
            displayMetadata(child, level + 1);
            child = child.getNextSibling();
        }

        // print close tag of element
        indent(level);
        System.out.println("</" + node.getNodeName() + ">");
    }
}

Example output

Below the metadata output of the Java program is given for an image in png format.

java Metadata frog-2.png
Format name: javax_imageio_png_1.0
<javax_imageio_png_1.0>
    <IHDR width="96" height="96" bitDepth="8" colorType="RGB"
compressionMethod="deflate" filterMethod="adaptive" interlaceMethod="none"/>
</javax_imageio_png_1.0>
Format name: javax_imageio_1.0
<javax_imageio_1.0>
    <Chroma>
        <ColorSpaceType name="RGB"/>
        <NumChannels value="3"/>
        <BlackIsZero value="true"/>
    </Chroma>
    <Compression>
        <CompressionTypeName value="deflate"/>
        <Lossless value="true"/>
        <NumProgressiveScans value="1"/>
    </Compression>
    <Data>
        <PlanarConfiguration value="PixelInterleaved"/>
        <SampleFormat value="UnsignedIntegral"/>
        <BitsPerSample value="8 8 8"/>
    </Data>
    <Dimension>
        <PixelAspectRatio value="1.0"/>
        <ImageOrientation value="Normal"/>
    </Dimension>
    <Transparency>
        <Alpha value="none"/>
    </Transparency>
</javax_imageio_1.0>
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