Package org.jpedal.io.filter

Class LZWOutputStream

java.lang.Object
java.io.OutputStream
java.io.FilterOutputStream
org.jpedal.io.filter.LZWOutputStream
All Implemented Interfaces:
Closeable, Flushable, AutoCloseable
public class LZWOutputStream extends FilterOutputStream
An output stream that lazily encodes LZW encoded data to a wrapped stream

Data encoded using the LZW compression method shall consist of a sequence of codes that are 9 to 12 bits long. Each code shall represent a single character of input data (0–255), a clear-table marker (256), an EOD marker (257), or a table entry representing a multiple-character sequence that has been encountered previously in the input (258 or greater).

Initially, the code length shall be 9 bits and the LZW table shall contain only entries for the 258 fixed codes. As encoding proceeds, entries shall be appended to the table, associating new codes with longer and longer sequences of input characters. The encoder and the decoder shall maintain identical copies of this table.

Whenever both the encoder and the decoder independently (but synchronously) realise that the current code length is no longer sufficient to represent the number of entries in the table, they shall increase the number of bits per code by 1. The first output code that is 10 bits long shall be the one following the creation of table entry 511, and similarly for 11 (1023) and 12 (2047) bits. Codes shall never be longer than 12 bits; therefore, entry 4095 is the last entry of the LZW table.

For more details on encoding, check the Adobe TIFF Revision 6.0 spec, which defines the full algorithm. This algorithm takes a slightly different approach,