CODEWITHSUNDEEP
c#algorithmgif
skkap
skkap

Reputation: 348

Reading variable-length code from byte array [c#]

I have some numbers, encoded in byte array using variable-length code. Actually it's GIF89a image data, whith I have to decode.

Because the LZW compression used for GIF creates a series of variable length codes, of between 3 and 12 bits each, these codes must be reformed into a series of 8-bit bytes that will be the characters actually stored or transmitted. The codes are formed into a stream of bits as if they were packed right to left and then picked off 8 bits at a time to be output. Assuming a character array of 8 bits per character and using 5 bit codes to be packed, an example layout would be similar to:

     +---------------+
  0  |               |    bbbaaaaa
     +---------------+
  1  |               |    dcccccbb
     +---------------+
  2  |               |    eeeedddd
     +---------------+
  3  |               |    ggfffffe
     +---------------+
  4  |               |    hhhhhggg
     +---------------+
           . . .
     +---------------+
  N  |               |
     +---------------+

How I can convert it to common [ex. integer] format using c#. Some features?

Also, I can't understand how to recognize - when size(in bits) of this numbers is increasing (+1 to size)? I just know size of the first number?

Upvotes: 2

Views: 726

Answers (1)

Richard Schneider
Richard Schneider

Reputation: 35477

You want to use a BitStream. See http://www.codeproject.com/KB/cs/bitstream.aspx for a good example.

Upvotes: 2

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