Digital Image Processing: Practical Approach by Borko Furht & Esad Akar & Whitney Angelica Andrews

Author:Borko Furht & Esad Akar & Whitney Angelica Andrews
Language: eng
Format: epub
ISBN: 9783319966342
Publisher: Springer International Publishing

With the table established, the next step is to iterate over every character, look up its Huffman code, and pack the bits of the code inside 8-bit bytes. Packing is necessary because the smallest unit of data is the 8-bit byte and if we were to write the Huffman code to our file vector as is without packing, a code that is potentially smaller than 8 bits would get converted in an 8-bit byte (uint8) before being written to the vector, which defeats the purpose of compression. As a result, we need to pack multiple codes into one byte before writing.

To pack a stream of bits, we start with the most significant bit of the byte being written to and record every bit of the code from left to right. Every 8 bits, we write the full byte to the vector and resume writing to a new byte. For the sequence ‘abbcccdddd’, packing is shown in Table 6.4.Table 6.4The bits of the Huffman code are packed together inside bytes

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