Java中的无损JPEG旋转(90/180/270度)？

是否有用于以90度为增量旋转JPEG文件的Java库,而不会导致图像质量下降？

我发现了这个:http://mediachest.sourceforge.net/mediautil/

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

以Henry的答案为基础,这是一个如何使用MediaUtil根据EXIF数据执行无损JPEG旋转的示例:

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
    ...
}

关于EXIF数据的问题不一定正确处理,因为EXIF数据在许多情况下都无关紧要,这里的示例代码仅演示了LLJTran无损JPEG旋转功能(感谢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(); 
}

如果你让输入和输出File对象引用同一个文件,你可以一遍又一遍地运行它,并观察图像不会降低,无论它经过多少次迭代.