FULL PRODUCT VERSION :
java version "1.5.0_13"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_13-b05)
Java HotSpot(TM) Client VM (build 1.5.0_13-b05, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
JPEG files include a JFIF header which indicates the density and density mode of the image. For example, we could specify a 300 DPI image via the metadata by setting the Xdensity attribute to 300, the Ydensity attribute to 300, and the resMode to 1 (density is in dots per inch). However, JPEGImageWriter is apparently ignoring these settings when the metadata is specified.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the program included with this report, using any JPG file as the first argument, and a file to write to as the second argument.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
When viewing the output file, the viewer should tell you what the DPI of the image is, and it should be 300 dpi.
ACTUAL -
The actual DPI of the output image is always the default when no density is specified: 72 dpi.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.awt.image.BufferedImage;
import java.io.File;
import java.util.Iterator;

import javax.imageio.*;
import javax.imageio.metadata.*;
import javax.imageio.stream.*;

import org.w3c.dom.Element;

public class SetDPI
{
    public static void main(String[] args) throws Exception
    {
        File infile = new File(args[0]);
        File outfile = new File(args[1]);
        
        FileImageInputStream in = new FileImageInputStream(infile);
        Iterator<ImageReader> iterator = ImageIO.getImageReaders(in);
        ImageReader reader = iterator.next();
        reader.setInput(in);
        
        IIOMetadata data = reader.getImageMetadata(0);
        
        // metadata format names are: javax_imageio_jpeg_image_1.0 or javax_imageio_1.0
        
        Element tree = (Element)data.getAsTree("javax_imageio_jpeg_image_1.0");
        Element jfif = (Element)tree.getElementsByTagName("app0JFIF").item(0);
        String dpiX = jfif.getAttribute("Xdensity");
        String dpiY = jfif.getAttribute("Ydensity");
        
        System.out.println(" Density of source is " + dpiX + "x" + dpiY);
            
        BufferedImage image = ImageIO.read(infile);
        
        ImageWriter writer = ImageIO.getImageWriter(reader);
        System.out.println("Writer class is " + writer.getClass());
        FileImageOutputStream out = new FileImageOutputStream(outfile);
        writer.setOutput(out);
        
        ImageWriteParam writeParams = writer.getDefaultWriteParam();
        writeParams.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
        writeParams.setCompressionQuality(0.75f);
        
        data = writer.getDefaultImageMetadata(new ImageTypeSpecifier(image), writeParams);
        tree = (Element)data.getAsTree("javax_imageio_jpeg_image_1.0");
        jfif = (Element)tree.getElementsByTagName("app0JFIF").item(0);
        jfif.setAttribute("Xdensity", dpiX);
        jfif.setAttribute("Ydensity", dpiY);
        jfif.setAttribute("resUnits", "1"); // density is dots per inch

        writer.write(data, new IIOImage(image, null, null), writeParams);
        
        in.close();
        out.close();
    }
}

---------- END SOURCE ----------