PackBitsDecoder.java
/*
* Copyright (c) 2008, Harald Kuhr
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* * Neither the name of the copyright holder nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package com.twelvemonkeys.io.enc;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
/**
* Decoder implementation for Apple PackBits run-length encoding.
* <p>
* <small>From Wikipedia, the free encyclopedia</small>
* <br>
* PackBits is a fast, simple compression scheme for run-length encoding of
* data.
* </p>
* <p>
* Apple introduced the PackBits format with the release of MacPaint on the
* Macintosh computer. This compression scheme is one of the types of
* compression that can be used in TIFF-files.
* </p>
* <p>
* A PackBits data stream consists of packets of one byte of header followed by
* data. The header is a signed byte; the data can be signed, unsigned, or
* packed (such as MacPaint pixels).
* </p>
* <table>
* <caption>PackBits</caption>
* <tr><th>Header byte</th><th>Data</th></tr>
* <tr><td>0 to 127</td> <td>1 + <i>n</i> literal bytes of data</td></tr>
* <tr><td>0 to -127</td> <td>One byte of data, repeated 1 - <i>n</i> times in the decompressed output</td></tr>
* <tr><td>-128</td> <td>No operation</td></tr>
* </table>
* <p>
* Note that interpreting 0 as positive or negative makes no difference in the
* output. Runs of two bytes adjacent to non-runs are typically written as
* literal data.
* </p>
*
* @see <a href="http://developer.apple.com/technotes/tn/tn1023.html">Understanding PackBits</a>
*
* @author <a href="mailto:harald.kuhr@gmail.com">Harald Kuhr</a>
* @version $Id: //depot/branches/personal/haraldk/twelvemonkeys/release-2/twelvemonkeys-core/src/main/java/com/twelvemonkeys/io/enc/PackBitsDecoder.java#1 $
*/
public final class PackBitsDecoder implements Decoder {
// TODO: Look at ICNSImageReader#unpackbits... What is this weirdness?
private final boolean disableNoOp;
private final byte[] sample;
private boolean reachedEOF;
/** Creates a {@code PackBitsDecoder}. */
public PackBitsDecoder() {
this(1, false);
}
/**
* Creates a {@code PackBitsDecoder}, with optional compatibility mode.
* <p>
* As some implementations of PackBits-like encoders treat {@code -128} as length of
* a compressed run, instead of a no-op, it's possible to disable no-ops for compatibility.
* Should be used with caution, even though, most known encoders never write no-ops in the compressed streams.
* </p>
*
* @param disableNoOp {@code true} if {@code -128} should be treated as a compressed run, and not a no-op
*/
public PackBitsDecoder(final boolean disableNoOp) {
this(1, disableNoOp);
}
/**
* Creates a {@code PackBitsDecoder}, with optional compatibility mode.
* <p>
* As some implementations of PackBits-like encoders treat {@code -128} as length of
* a compressed run, instead of a no-op, it's possible to disable no-ops for compatibility.
* Should be used with caution, even though, most known encoders never write no-ops in the compressed streams.
* </p>
*
* @param disableNoOp {@code true} if {@code -128} should be treated as a compressed run, and not a no-op
*/
public PackBitsDecoder(int sampleSize, final boolean disableNoOp) {
this.sample = new byte[sampleSize];
this.disableNoOp = disableNoOp;
}
/**
* Decodes bytes from the given input stream, to the given buffer.
*
* @param stream the stream to decode from
* @param buffer a byte array, minimum 128 (or 129 if no-op is disabled) bytes long
* @return The number of bytes decoded
*
* @throws java.io.IOException if a problem occurs during decoding.
*/
public int decode(final InputStream stream, final ByteBuffer buffer) throws IOException {
if (reachedEOF) {
return -1;
}
// NOTE: We don't decode more than single runs, because some writers add pad bytes inside the stream...
// Start new run
int b = stream.read();
if (b < 0) {
reachedEOF = true;
return 0;
}
int n = (byte) b;
try {
if (n >= 0) {
// Copy next n + 1 bytes literally
readFully(stream, buffer, sample.length * (n + 1));
}
// Allow -128 for compatibility, see above
else if (disableNoOp || n != -128) {
// Replicate the next byte -n + 1 times
for (int s = 0; s < sample.length; s++) {
sample[s] = readByte(stream);
}
for (int i = -n + 1; i > 0; i--) {
buffer.put(sample);
}
}
// else NOOP (-128)
}
catch (IndexOutOfBoundsException e) {
throw new DecodeException("Error in PackBits decompression, data seems corrupt", e);
}
return buffer.position();
}
static byte readByte(final InputStream pStream) throws IOException {
int read = pStream.read();
if (read < 0) {
throw new EOFException("Unexpected end of PackBits stream");
}
return (byte) read;
}
static void readFully(final InputStream pStream, final ByteBuffer pBuffer, final int pLength) throws IOException {
if (pLength < 0) {
throw new IndexOutOfBoundsException(String.format("Negative length: %d", pLength));
}
int total = 0;
while (total < pLength) {
int count = pStream.read(pBuffer.array(), pBuffer.arrayOffset() + pBuffer.position() + total, pLength - total);
if (count < 0) {
throw new EOFException("Unexpected end of PackBits stream");
}
total += count;
}
pBuffer.position(pBuffer.position() + total);
}
}