Increasing Resolution and Reducing Size of an Image in Java

Question

When I first asked this, I included as much information as I could, since I never know what will help someone if they can give m a solution, but from the answers, it seems I

Answer 1

This is tricky because, like so much in Java, you can't just access something in a simple way. Java does not keep track of DPI, but it does use dots per millimeter. Also, another part that is confusing is that you cannot change this kind of information in an image, or in a BufferedImage. You can only change this information when you are writing a BufferedImage out through an ImageWriter.

I was able to do this. As I said, I could specify the zoom on the image that was returned to me. No matter what zoom level, the output was 72 DPI. My goal was 300DPI. I specified a zoom level of 400%. So, on an 8" wide image of 72 DPI, that returned to me a 32" image of 72 DPI. All I had to do was specify a DPI of 288 (72 x 4) to override the default 72 DPI I was dealing with and then when it was written out, the image had the same number of pixels, but was considered to be done at 288 DPI rather than 72 DPI.

Here's a code snippet:

//Assumed there's already an ImageWriter iw

ImageWriteParam writeParam = writer.getDefaultWriteParam();
ImageTypeSpecifier typeSpecifier =
       ImageTypeSpecifier.createFromBufferedImageType(BufferedImage.TYPE_INT_RGB);
IIOMetadata metadata = writer.getDefaultImageMetadata(typeSpecifier, writeParam);
if (metadata.isReadOnly() || !metadata.isStandardMetadataFormatSupported()) {
    continue;
}

// Set Parameters and info

int DPI = 72 * scaling/100;
double dotsPerMilli = 1.0 * DPI / 10 / 2.54;
double checkDots = 1.0 * 144 / 10 / 2.54;
System.out.println("Dots per inch: " + DPI + ", DotsPerMilli: " + dotsPerMilli + ",
    CheckDots = " + checkDots);
IIOMetadataNode root = new IIOMetadataNode("javax_imageio_1.0");
IIOMetadataNode horiz = new IIOMetadataNode("HorizontalPixelSize");
horiz.setAttribute("value", Double.toString(dotsPerMilli));
IIOMetadataNode vert = new IIOMetadataNode("VerticalPixelSize");
vert.setAttribute("value", Double.toString(dotsPerMilli));
IIOMetadataNode dim = new IIOMetadataNode("Dimension");
dim.appendChild(horiz);
dim.appendChild(vert);
root.appendChild(dim);
metadata.mergeTree("javax_imageio_1.0", root);

// From here, just write out file using an ImageOutputStream

final ImageOutputStream stream = ImageIO.createImageOutputStream(outFile);
System.out.println("Output file: " + outFile);
try {
    writer.setOutput(ImageIO.createImageOutputStream(outFile));
    writer.write(metadata, new IIOImage(image_to_save, null, metadata),
    writeParam);
} catch (Exception e) {
    System.out.println("Caught exception " + e + " when trying to write out
        file.");
    System.exit(0);
} finally {
    stream.close();
}