[JAVA2D] Saving ARGB BufferedImages as JPEG with ImageIO

[Jürg Lehni]

I have problems with saving ARGB BufferedImages as JPEG with ImageIO:

It seems that ImageIO thinks to have a CMYK image due to the 4 channels 
and does it all wrong. I tried to find a way of telling imageio to take 
only the 3 RGB channels and I also found something like that, but it 
still generates very strange files that are too big (about 3 times as 
big as they should be) and don't display correctly on some viewers.

Here's my code:

-----
File file = new File(filename);
ios = ImageIO.createImageOutputStream(file);
writer.setOutput(ios);
// Set some parameters
ImageWriteParam param = writer.getDefaultWriteParam();
if (param.canWriteCompressed() && quality >= 0.0 && quality <= 1.0) {
       param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
       param.setCompressionQuality(quality);
}
// if bi has type ARGB and alpha is false, we have to tell the writer 
to not use the alpha channel:
// this is especially needed for jpeg files where imageio seems to 
produce wrong jpeg files right now...
if (bi.getType() == BufferedImage.TYPE_INT_ARGB) {
       // create a new ColorModel with OPAQUE transparency and no alpha 
channel.
       ColorModel cm = new 
ComponentColorModel(bi.getColorModel().getColorSpace(), false, false, 
Transparency.OPAQUE, DataBuffer.TYPE_BYTE);
       // tell the writer to only use the first 3 bands (skip alpha)
       param.setSourceBands(new int[] {0, 1, 2});
       // although the java documentation says that SampleModel can be null, 
an exception is thrown in that case
       // therefore a 1*1 SampleModel that is compatible to cm is created:
       param.setDestinationType(new ImageTypeSpecifier(cm, 
cm.createCompatibleSampleModel(1, 1)));
}
// Write the image
writer.write(null, new IIOImage(bi, null, null), param);
ios.flush();
-----

The interesting part happens in here:
-----
       // create a new ColorModel with OPAQUE transparency and no alpha 
channel.
       ColorModel cm = new 
ComponentColorModel(bi.getColorModel().getColorSpace(), false, false, 
Transparency.OPAQUE, DataBuffer.TYPE_BYTE);
       // tell the writer to only use the first 3 bands (skip alpha)
       param.setSourceBands(new int[] {0, 1, 2});
       // although the java documentation says that SampleModel can be null, 
an exception is thrown in that case
       // therefore a 1*1 SampleModel that is compatible to cm is created:
       param.setDestinationType(new ImageTypeSpecifier(cm, 
cm.createCompatibleSampleModel(1, 1)));
-----

If I replace this with the following it all works well, but this uses 
far too much memory due to the allocation of another BufferedImage:

-----
       BufferedImage buffered = new BufferedImage(bi.getWidth(null), 
bi.getHeight(null), BufferedImage.TYPE_INT_RGB);
       buffered.createGraphics().drawImage(bi, 0, 0, null);
       bi = buffered;
-----

Does anyone have experiences with this? What exactly am I doing wrong?

Best

Jürg Lehni

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