Lossless -
Direct substitution encoding of original data
Based on information theory (e.g., Shannon's entropy)
Dictionary based encodings - shorter encodings for more frequent patterns
Ziv and Lempel
LZW (Lempel-Ziv-Welch)
Run-length Encodings - single encodings for repeating patterns
Lossy -
Mathematically altered in some approximately reversible way
Tradeoff between distortion and compression
Aspects of data - space, time, and frequency
Transformation efficiency
Reversibility
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