Lossless JPEG Rotate (90/180/270 degrees) in Java?

问题:

Is there a Java library for rotating JPEG files in increments of 90 degrees, without incurring image degradation?

回答1:

I found this: http://mediachest.sourceforge.net/mediautil/

API: http://mediachest.sourceforge.net/mediautil/javadocs/mediautil/image/jpeg/LLJTran.html

回答2:

Building on Henry's answer, here's an example of how to use MediaUtil to perform lossless JPEG rotation based on the EXIF data:

try {
    // Read image EXIF data
    LLJTran llj = new LLJTran(imageFile);
    llj.read(LLJTran.READ_INFO, true);
    AbstractImageInfo<?> imageInfo = llj.getImageInfo();
    if (!(imageInfo instanceof Exif))
        throw new Exception("Image has no EXIF data");

    // Determine the orientation
    Exif exif = (Exif) imageInfo;
    int orientation = 1;
    Entry orientationTag = exif.getTagValue(Exif.ORIENTATION, true);
    if (orientationTag != null)
        orientation = (Integer) orientationTag.getValue(0);

    // Determine required transform operation
    int operation = 0;
    if (orientation > 0
            && orientation < Exif.opToCorrectOrientation.length)
        operation = Exif.opToCorrectOrientation[orientation];
    if (operation == 0)
        throw new Exception("Image orientation is already correct");

    OutputStream output = null;
    try {   
        // Transform image
        llj.read(LLJTran.READ_ALL, true);
        llj.transform(operation, LLJTran.OPT_DEFAULTS
                | LLJTran.OPT_XFORM_ORIENTATION);

        // Overwrite original file
        output = new BufferedOutputStream(new FileOutputStream(imageFile));
        llj.save(output, LLJTran.OPT_WRITE_ALL);

    } finally {
        IOUtils.closeQuietly(output);
        llj.freeMemory();
    }

} catch (Exception e) {
    // Unable to rotate image based on EXIF data
    ...
}

回答3:

Regarding the issue of EXIF data not necessarily being handled correctly, since EXIF data is irrelevant in many situations, here's example code demonstrating only the LLJTran lossless JPEG rotation feature (with thanks to user113215):

final File              SrcJPEG  = new File("my-input.jpg");
final File              DestJPEG = new File("my-output.jpg");
final FileInputStream   In       = new FileInputStream(SrcJPEG);

try {
    final LLJTran           LLJT = new LLJTran(In);

    LLJT.read(LLJTran.READ_ALL, true);
    LLJT.transform(LLJTran.ROT_90);

    final FileOutputStream  Out = new FileOutputStream(DestJPEG);

    try {
        LLJT.save(Out, LLJTran.OPT_WRITE_ALL);
    } finally {
        Out.close();
    }

} finally {
    In.close(); 
}

If you make the input and output File objects refer to the same file, you can run this over and over again, and observe that the image does not degrade, no matter how many iterations it is put through.

回答4:

You don't need an external library for this kind of thing, it's all built into SE. The easiest being the rotate() function of the Graphics2D object.

For example:

   Image rotatedImage = new BufferedImage(imageToRotate.getHeight(null), imageToRotate.getWidth(null), BufferedImage.TYPE_INT_ARGB);

    Graphics2D g2d = (Graphics2D) rotatedImage.getGraphics();
    g2d.rotate(Math.toRadians(90.0));
    g2d.drawImage(imageToRotate, 0, -rotatedImage.getWidth(null), null);
    g2d.dispose();

no loss!

Or, if you want to be extra careful, just use BufferedImage.getRGB(x,y), and translate it pixel by pixel on to the new image.