Dictionary Coding
Computer Science: OCR A Level, topic 3.1.3
Dictionary Coding
Dictionary coding is used to store text in a lossless format.
Dictionary coding
- The coder scans through a body of text.
- Each word is replaced by the binary number of the word in a dictionary.
- Each time it finds a new word which is not in its dictionary, it will add it to the dictionary and give it a binary number.
- The word in the actual text is replaced with the binary number.
Benefits of dictionary coding
- Dictionary coding is a type of compression. It takes less bits to store a 2 digit binary number than we can a 10 letter word.
- No data is lost, so the coding is lossless.
- The encoder may not always build its own dictionary. A pre-existing dictionary may be used to encode the text.
Test yourself on Dictionary Coding
Which type of data is compressed using dictionary coding?
What happens when the dictionary coder finds a word that is not in the dictionary?