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    <p>In LZW the dictionary is not stored with the compressed file. (Or the dictionary <em>is</em> the file, depeneding on your perspective.) Each value that is written to the file is of a predefined bit width according to its location. For example, it can start off as pairs of 9-bit dictionary indexes followed by 8-bit data, until the indexes are exhausted (which happenes at a precise location) when it switches to 10-bit indexes. </p> <p>The details depened on how you implement the compression. Some do a constant 12-bit indexes. But in no case are extra delimiters required.</p> <p>Also, since the data is not aligned on 8-bit boundaries, there isn't a way to detect delimiters if you are not already reading the data correctly!</p> <p>Edit:</p> <p>If you are hoping for the LZW compression algorithm to actually generate <em>smaller</em> data than the input, then there are several things that you should do.</p> <p>First, you must write the file as binary rather than text. Writing it as text will expand rather than contract the size of the file. The value 127 can be stored in a single byte in binary (01111111), but requires four bytes of UTF-8 with a delimiting space ("127 " = 00110001 00110010 00110111 00100000).</p> <p>Second, LZW is designed to work with code values that are larger than one byte but less than two bytes, so you must do some bit-twiddling to output the data correctly. A single byte is only enough to encode the first 256 implicitly defined table entries. Another bit will give you another 256 entries to work with, but the entries in a 9-bit indexed table are exhausted quickly. With 12 bits, you can get 4096 table entries, which is a reasonable table size. If you were to use two full bytes, then you would have a rather large table with 65 K entries. The trouble with this is that if you are not using the full capacity of your table space, then you are wasting bits. The output would have lots of bits in it that are always zero, and this will be really bad for your compression ratios.</p> <p>Third, a streaming coder/decoder cannot do single values at a time, because the encoded data overlaps byte boundaries. If a constant 12-bit code size is used, then some multiple of two coded values may be processed at one time. But in general the algorithm is designed to work with complete files.</p>
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    1. POLZW (Limpel-Ziv-Welch) Dictionary coding delimiter issue
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    1. USJeffrey L Whitledge
    1. USJeffrey L Whitledge
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    1. COCan you answer my question? Is this dictionary a suffix-tree? Would it be simplier to show a tree to discuss this problem?
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    2. CO@epitaph - No it isn't a suffix tree. That is something else.
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    3. COThank you very much!
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