[JAVA2D] how can I automatically create good quality JPEG thumbnails?

[David Brown]

Hi everyone,
I am trying to automatically create small JPEG thumbnails from existing JPEG
images.  The basic code I am using is as shown below, which works but gives
the most horrendous, unusable results.  I don't know how to control the
quality of the thumbnail because I haven't seen any examples of how to do
it.  I have displayed the intermediate scaled buffered image on the screen
and it looks great, so it must be possible to get similar results in a file.
How do you do it?
Cheers
David

p.s. to run the code example below use the following syntax (which creates a
thumbnail file called "thumbnail.jpg" of height 150 from the image in the
file "original.jpg"):

   java Example original.jpg 150


import java.io.FileOutputStream;
import java.io.IOException;
import java.awt.image.BufferedImage;
import java.io.FileInputStream;
import com.sun.image.codec.jpeg.JPEGImageDecoder;
import com.sun.image.codec.jpeg.JPEGCodec;
import java.awt.image.AffineTransformOp;
import java.awt.geom.AffineTransform;
import java.awt.RenderingHints;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

public class Example

    public static void main(String[] arguments){
        String fileName = arguments[0];
        int thumbnailHeight = Integer.valueOf(arguments[1]).intValue();

        Example example = new Example();

        try {
            example.execute(fileName, thumbnailHeight);
        } catch(Exception e){
            System.err.println("oops");
            e.printStackTrace();
        }
    }


    public void execute(String fileName, int thumbnailHeight) throws
Exception

        // load the original JPEG image as a buffered image
        FileInputStream fis = new FileInputStream(fileName);
        JPEGImageDecoder decoder = JPEGCodec.createJPEGDecoder(fis);
        BufferedImage image = decoder.decodeAsBufferedImage();
        fis.close();

        // work out what the scaling factor is, assuming it the thumnail has
the given height
        double scalingFactor = thumbnailHeight / (double)image.getHeight();

        // prepare to rescale the image
        AffineTransform affineTransform =
AffineTransform.getScaleInstance(scalingFactor, scalingFactor);

        // sort out some rendering hints for the graphics engine
        RenderingHints hints = new RenderingHints(null);
        hints.put(RenderingHints.KEY_RENDERING,
RenderingHints.VALUE_RENDER_QUALITY);
        hints.put(RenderingHints.KEY_COLOR_RENDERING,
RenderingHints.VALUE_COLOR_RENDER_QUALITY);
        hints.put(RenderingHints.KEY_INTERPOLATION,
RenderingHints.VALUE_INTERPOLATION_BILINEAR);

        // rescale
        AffineTransformOp op = new AffineTransformOp(affineTransform,
hints);
        BufferedImage scaledImage = op.filter(image, null);

        // create the output file
        FileOutputStream fos = new FileOutputStream("thumbnail.jpg");

        //JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(fos, encp);
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(fos);
        encoder.encode(scaledImage);
        fos.close();
    }
}

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