Writing JPEG with ImageIO

Question

Hi,
I wanted to do this little tool that:
1. read any type of image format supported by ImageIO
2. scaled it down to arbitrary size
3. wrote the image to the same format it was originally
I got the pieces together, used ImageIO to read the image, then java.awt.image.AffineTransformOp to scale it down and finally ImageIO again to write it back (I get the ImageWriter with ImageIO.getImageWriter(ImageReader)).
The problem I got was that AffineTransformOp on Linux (it uses native code) does not want to output anything else then ARGB images. If I read a YCbCr JPEG (the most common JPEG format) and do the AffineTransformOp, I get this ARGB image, which ImageIO will happily write back as an JPEG, but as CMYK JPEG file (which is really rare and not understood by most browsers)... which is not fine because the original was YCbCr.
The question now is, how do I get AffineTransformOp and ImageIO to play nicely together. Either I have to get AffineTransformOp to output to an BufferedImage that has the same colormodel as that read from the file, or I have to get ImageIO to write any BufferedImage to the exact same format as the original image file.
For the special case I stated above, I got the program to work by converting the BufferedImage I got from AffineTransformOp to a BufferedImage with RGB colormodel. This, however is not the solution because it assumes that we do not want to output ARGB... Anyway I did it whith the following code (yes, it is horrible).
// do scaling
BufferedImage scaled = op.filter(original, null);
// create a new RGB color model... no alpha
ColorModel rgbcm = new DirectColorModel(24, 0x00ff0000, 0x0000ff00, 0x000000ff);
// get the DataBuffer from the scaled version
DataBuffer db = scaled.getRaster().getDataBuffer();
// and its dimensions
int w = scaled.getRaster().getWidth();
int h = scaled.getRaster().getHeight();
// band masks for rgb (no alpha)
int[] bandMasks = new int[] {0x00ff0000,0x0000ff00, 0x000000ff}
// create new WritableRaster that has the same data, but different sample model
WritableRaster r = Raster.createPackedRaster(db, w, h, h, bandMasks, null);
// create a new BufferedImage with the no-alpha ColorModel and the raster
// with no-alpha SampleModel
BufferedImage rgbimg = new BufferedImage(rgbcm,r, scaled.isAlphaPremultiplied(), null);
My second question is, if I have to do this, is there any simpler way?

Answer 1

I just did a project similar to this actually, so you're in luck! My project was doing image compression rather than resizing, but the IO is the same. I used PixelGrabber to get the pixels, then created my new image in a BufferedImage just like you did (so you can keep all your reading and image creation the same since you seemed to use a BufferedImage also).
Once you have your BufferedImage, it's blazingly simple. There is a JPEGCodec package that is included in the JDK. It's not compiled though. but, if you open up the ZIP file that has the sources in it (it's copied to your java home directory, called "src.zip"), you can get all the sources you needed. In that package there are 2 classes that I used: JPEGCodec and JPEGImageEncoder. It works like follows:BufferedImage bi;
OutputStream os;
// create and fill your buffered image and instantiate your output stream (I used a FileOutputStream for obvious reasons).
JPEGImageEncoder jie = JPEGCodec.createJPEGEncoder(os);
jie.encode(bi); And that's it! The package does the rest! Let me know if you have any troubles with it.