ojluni/src/main/java/javax/imageio/ImageTranscoder.java

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package javax.imageio;

import javax.imageio.metadata.IIOMetadata;

/**
 * An interface providing metadata transcoding capability.
 *
 * <p> Any image may be transcoded (written to a different format
 * than the one it was originally stored in) simply by performing
 * a read operation followed by a write operation.  However, loss
 * of data may occur in this process due to format differences.
 *
 * <p> In general, the best results will be achieved when
 * format-specific metadata objects can be created to encapsulate as
 * much information about the image and its associated metadata as
 * possible, in terms that are understood by the specific
 * <code>ImageWriter</code> used to perform the encoding.
 *
 * <p> An <code>ImageTranscoder</code> may be used to convert the
 * <code>IIOMetadata</code> objects supplied by the
 * <code>ImageReader</code> (representing per-stream and per-image
 * metadata) into corresponding objects suitable for encoding by a
 * particular <code>ImageWriter</code>.  In the case where the methods
 * of this interface are being called directly on an
 * <code>ImageWriter</code>, the output will be suitable for that
 * writer.
 *
 * <p> The internal details of converting an <code>IIOMetadata</code>
 * object into a writer-specific format will vary according to the
 * context of the operation.  Typically, an <code>ImageWriter</code>
 * will inspect the incoming object to see if it implements additional
 * interfaces with which the writer is familiar.  This might be the
 * case, for example, if the object was obtained by means of a read
 * operation on a reader plug-in written by the same vendor as the
 * writer.  In this case, the writer may access the incoming object by
 * means of its plug-in specific interfaces.  In this case, the
 * re-encoding may be close to lossless if the image file format is
 * kept constant.  If the format is changing, the writer may still
 * attempt to preserve as much information as possible.
 *
 * <p> If the incoming object does not implement any additional
 * interfaces known to the writer, the writer has no choice but to
 * access it via the standard <code>IIOMetadata</code> interfaces such
 * as the tree view provided by <code>IIOMetadata.getAsTree</code>.
 * In this case, there is likely to be significant loss of
 * information.
 *
 * <p> An independent <code>ImageTranscoder</code> essentially takes
 * on the same role as the writer plug-in in the above examples.  It
 * must be familiar with the private interfaces used by both the
 * reader and writer plug-ins, and manually instantiate an object that
 * will be usable by the writer.  The resulting metadata objects may
 * be used by the writer directly.
 *
 * <p> No independent implementations of <code>ImageTranscoder</code>
 * are provided as part of the standard API.  Instead, the intention
 * of this interface is to provide a way for implementations to be
 * created and discovered by applications as the need arises.
 *
 */
public interface ImageTranscoder {

    /**
     * Returns an <code>IIOMetadata</code> object that may be used for
     * encoding and optionally modified using its document interfaces
     * or other interfaces specific to the writer plug-in that will be
     * used for encoding.
     *
     * <p> An optional <code>ImageWriteParam</code> may be supplied
     * for cases where it may affect the structure of the stream
     * metadata.
     *
     * <p> If the supplied <code>ImageWriteParam</code> contains
     * optional setting values not understood by this writer or
     * transcoder, they will be ignored.
     *
     * @param inData an <code>IIOMetadata</code> object representing
     * stream metadata, used to initialize the state of the returned
     * object.
     * @param param an <code>ImageWriteParam</code> that will be used to
     * encode the image, or <code>null</code>.
     *
     * @return an <code>IIOMetadata</code> object, or
     * <code>null</code> if the plug-in does not provide metadata
     * encoding capabilities.
     *
     * @exception IllegalArgumentException if <code>inData</code> is
     * <code>null</code>.
     */
    IIOMetadata convertStreamMetadata(IIOMetadata inData,
                                      ImageWriteParam param);

    /**
     * Returns an <code>IIOMetadata</code> object that may be used for
     * encoding and optionally modified using its document interfaces
     * or other interfaces specific to the writer plug-in that will be
     * used for encoding.
     *
     * <p> An optional <code>ImageWriteParam</code> may be supplied
     * for cases where it may affect the structure of the image
     * metadata.
     *
     * <p> If the supplied <code>ImageWriteParam</code> contains
     * optional setting values not understood by this writer or
     * transcoder, they will be ignored.
     *
     * @param inData an <code>IIOMetadata</code> object representing
     * image metadata, used to initialize the state of the returned
     * object.
     * @param imageType an <code>ImageTypeSpecifier</code> indicating
     * the layout and color information of the image with which the
     * metadata will be associated.
     * @param param an <code>ImageWriteParam</code> that will be used to
     * encode the image, or <code>null</code>.
     *
     * @return an <code>IIOMetadata</code> object,
     * or <code>null</code> if the plug-in does not provide
     * metadata encoding capabilities.
     *
     * @exception IllegalArgumentException if either of
     * <code>inData</code> or <code>imageType</code> is
     * <code>null</code>.
     */
    IIOMetadata convertImageMetadata(IIOMetadata inData,
                                     ImageTypeSpecifier imageType,
                                     ImageWriteParam param);
}