public void LzwEncodingIsReversible(LzwGifToolsTestCase testCase) // and decoding
{
LzwCompressor compressor = new LzwCompressor(testCase.LzwMinimumCodeSize);
LzwDecompressor decompressor = new LzwDecompressor(testCase.LzwMinimumCodeSize);
List <int> lzwCompressedStream = compressor.Compress(testCase.CodeStream);
List <int> lzwDecompressedStream = decompressor.Decompress(lzwCompressedStream);
CollectionAssert.AreEqual(testCase.CodeStream, lzwDecompressedStream);
}
public void AllMethodsWork(LzwGifToolsTestCase testCase)
{
LzwCompressor compressor = new LzwCompressor(testCase.LzwMinimumCodeSize);
StreamPacker packer = new StreamPacker(testCase.LzwMinimumCodeSize);
StreamUnpacker unpacker = new StreamUnpacker(testCase.LzwMinimumCodeSize);
LzwDecompressor decompressor = new LzwDecompressor(testCase.LzwMinimumCodeSize);
List <int> lzwEncodedCodeStream = compressor.Compress(testCase.CodeStream);
List <byte> packedBytes = packer.Pack(lzwEncodedCodeStream);
List <int> lzwEncodedCodeStream2 = unpacker.Unpack(packedBytes);
List <int> codeStream = decompressor.Decompress(lzwEncodedCodeStream2);
CollectionAssert.AreEqual(testCase.CodeStream, codeStream);
}
/// <summary>
/// Reads one lead payload at a time from the XLI compressed stream.
/// </summary>
/// <returns>Uncompressed lead data.</returns>
public int[] ReadLeadPayload()
{
var chunkHeader = new byte[8];
if (chunkHeader.Length != this.stream.Read(chunkHeader, 0, chunkHeader.Length))
{
throw new InvalidOperationException("Not enough data to read header from the stream");
}
// Each chunk begins with an 8 byte header consisting of:
// - 32-bit integer describing the length of the chunk
// - 16-bit integer (unknown payload, seemingly always 1)
// - 16-bit integer describing the first delta code
//
// After this header exists LZW-compressed delta codes, using 10-bit code words:
// 0 2 4 6 8 ...
// +--------+--------+--------+--------+--------+--------+--------+--------+--------+
// | Size | Unk. | Delta | LZW compressed deltas (10-bit codes) |
// +--------+--------+--------+--------+ |
// | ... [Size bytes] |
// +--------+--------+--------+--------+--------+--------+--------+--------+--------+
var size = BitConverter.ToInt32(chunkHeader, 0);
// CAW: var unknown = BitConverter.ToInt16(chunkHeader, 4);
var start = BitConverter.ToInt16(chunkHeader, 6);
var chunk = new byte[size];
if (chunk.Length != this.stream.Read(chunk, 0, size))
{
throw new InvalidOperationException("Not enough data in the compressed chunk");
}
// LZW 10-bit codes
using (var decompressor = new LzwDecompressor(chunk, 10))
{
var output = decompressor.Decompress()
.ToArray();
// Once the data is decompressed it is packed [HIWORDS...LOWORDS]
// and needs to be reconstituted.
var deltas = Unpack(output);
return(DecodeDeltas(deltas, start));
}
}
public void LzwDecodingAndVariableWidthDecompressionSuccessful()
{
byte[] imageData = vcvj.DataStream.GetTableBasedImages().First().ImageData.Bytes;
int lzwSize = vcvj.DataStream.GetTableBasedImages().First().ImageData.LzwMinimumCodeSize;
LzwDecompressor decompressor = new LzwDecompressor((byte)lzwSize);
LzwTools.Decoder decoder = new LzwTools.Decoder((byte)lzwSize);
List <int> decompressedStream = decompressor.Decompress(imageData.Select((b) => (int)b).ToList <int>());
List <int> decodedStream = decoder.Decode(decompressedStream.Select(x => (byte)x).ToList <byte>());
// assuming no error is thrown, we're... probably good. yeah this is kind of
// an awkward test until we can derive a lzw code table from the global
// color index and re-encode everything to match the original bytestream
Assert.IsTrue(decodedStream.Count > imageData.Length);
}
