JPEGImageEncoder: Reducing the size of the JPEG without resizing the Image

I am using JPEGImageEncoder in order to encode a BufferedImage into a JPEG file.
The problem is that I would like to restrict the files size to a maximum of 200KB, without affecting the height/widht of the image. So I guess that the only option that is left is quality.

The code I am using is something like:

BufferedImage thumbImage = new BufferedImage(
image.getWidth(),
image.getHeight(),
BufferedImage.TYPE_INT_RGB);

Graphics2D graphics2D = thumbImage.createGraphics();
graphics2D.setRenderingHint(
                 RenderingHints.KEY_INTERPOLATION,
                 RenderingHints.VALUE_INTERPOLATION_BILINEAR);
      graphics2D.drawImage(image, 0, 0, image.getWidth(), image.getHeight(), null);

      imageOut = new FileOutputStream(yetAnOtherFile);
      out = new BufferedOutputStream(imageOut);
      encoder = JPEGCodec.createJPEGEncoder(imageOut);
      enparam = encoder.getDefaultJPEGEncodeParam(thumbImage);
      int quality = 100;
      enparam.setXDensity(100);
      enparam.setYDensity(100);

        enparam.setQuality( (float) quality / 100.0f, false);
        encoder.setJPEGEncodeParam(enparam);
        encoder.encode(thumbImage);


I also tried a do/while loop till the out file gets an accepted size, decreasing the quality in each step. It didn't work as expected. Is there an other solution to the problem ?
LVL 10
NelliosAsked:
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objectsConnect With a Mentor Commented:
can't think of one, the size of the file will depend on the actual contents of the image and how much it can be compressed.

the loop would be something like:

byte[] bytes = null;
int quality = 80;
while (bytes==null && quality>0)
{
   bytes = encode(image, quality);
   if (bytes.length>maxsize)
   {
       bytes = null;
   }
   else
   {
       quality -= 10;
   }
}
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objectsCommented:
that approach should work, what problem were u having?
btw, u probably should start quality at 80 max, theres no real value going any higher.
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objectsCommented:
be better off wrting it to a ByteArrayOutputStream rather than a file.
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NelliosAuthor Commented:
The problem was that I ended up in an infinite loop. I didn't like the approach anyway so I stoped working on it. If there isn't a better one, then I guess I will work on this one.
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NelliosAuthor Commented:
I am accepting objects proposal as a solution to this, since its the only feasible way to solve the problem that I am aware of.

I am not very fond of that solution, neither I applied it to my problem yet. I will provide further feedback in this thread as soon as I do so.
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NelliosAuthor Commented:
I promised you feedback didn't I?

So here's exactly what worked for me:

 int size = 1024000;
     for (int quality = 80; size > 921600; quality -= 2) {

        imageOut = new FileOutputStream(new File(tmpdir + "tmpImageName.jpg"));
        out = new BufferedOutputStream(imageOut);
        encoder = JPEGCodec.createJPEGEncoder(imageOut);
        enparam = encoder.getDefaultJPEGEncodeParam(thumbImage);

          enparam.setXDensity(100);
          enparam.setYDensity(100);
          enparam.setQuality( (float) quality / 100.0f, false);
          encoder.setJPEGEncodeParam(enparam);
          encoder.encode(thumbImage);
          out.close();
          imageIn = new FileInputStream(new File(tmpdir + "tmpImageName.jpg"));
          this.in = new BufferedInputStream(imageIn);
          size = in.available();
       }

with this for loop the image quality will gradually decrease till the output file is less than the maximum allowed size.

This is the implementation of my original idea influenced by Objects. Currently I am using temporary files to do so. It would also work with Piped Streams, though it would involve threads and would make things a bit more complicated :-D
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objectsCommented:
you can avoid using a file by writing the image to a ByteArrayOutputStream.
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