Decoding a JPEG Huffman block (table)

Question

The following block is nested by Huffman block markers

-HUFF---------------------------------------------------------------------0084-
  10    0    1    2    4    3    4    6    5    6    8    a    9    4    2    3
   0    1    2   11    0    3    4   21    5   12   31    6   41   51   61   13
  22   71   81   91   a1   14   32   b1   d1   f0   15   23   35   42   b2   c1
   7   16   24   33   52   72   73   e1   25   34   43   53   62   74   82   94
  a2   f1   26   44   54   63   64   92   93   c2   d2   55   56   84   b3   45
  83   46   a3   e2
-------------------------------------------------------------------------------

0084 is the length of the table as an integer and is not included in the block here

according to the JPEG standard, the first address aparently makes it an AC table at destination 0 (0x10)

and aparently from there onwards it's a huffman table.

So, how is it decoded?

Answer 1

The next 16 bytes after the 0x10 tell you how many codes of each length. In your example, there are 0 codes of length 1 bit, 1 code of length 2 bits, 2 codes of length 3 bits, 4 codes of length 4 bits, 3 codes of length 5 bits, and so on.

These are then followed by the values that are encoded by those codes, in order. Again from your example:

Code length | Number | Symbol(s)
------------+--------+----------
1 bit       | 0      |
2 bits      | 1      | 0x01
3 bits      | 2      | 0x02 0x11
4 bits      | 4      | 0x00 0x03 0x04 0x21
5 bits      | 3      | 0x05 0x12 0x31
... etc

You then build a binary tree from the top down, assigning the symbols in order. In this example, you get:

Symbol | Code 
-------+------
0x01   | 00
0x02   | 010
0x11   | 011
0x00   | 1000
0x03   | 1001
0x04   | 1010
0x21   | 1011
...etc