Data Compression Flashcards

Number of characters $\times$ 7, because ASCII uses 7 bits per character.

To reduce the file size, so less storage is needed, and to make files faster to transmit, using less bandwidth.

Streaming or downloading high-definition video, and emailing or uploading large audio or image files.

Changing how data is represented so that fewer bits are needed to store it.

Huffman coding and run length encoding (RLE).

A compression method that gives each character a binary code based on how often it appears: the most frequent characters get the shortest codes.

Start at the root and follow the branches down to the character, writing down the 0 or 1 on each branch you pass.

Closest to the root, so they have the shortest codes.

ASCII uses 7 bits for every character. Huffman coding gives common characters codes shorter than that, so the total number of bits is smaller.

For each character, multiply its frequency by the length of its code, then add these together.

Bits saved = bits needed in 7-bit ASCII − bits needed using the Huffman codes.

A compression method that replaces each run of consecutive repeated values with a frequency/data pair.

The number of times a value repeats in a row, followed by the value itself.
e.g. 5 0 means five 0s in a row.

Data with long runs of consecutive repeated values, such as an image with large areas of the same colour.

If the data has few repeated values in a row, each single value becomes a pair, so the encoded data is longer than the original (eg MISSISSIPPI).

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