In data compression, what is the compression scheme?
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The scheme is the set of methods used to make the file smaller.
For example, there’s “lossless” compression where the scheme looks for patterns or redundancies in the data such that it can represent them in a smaller form that, when uncompressed again, is bit-for-bit identical to the original file.
Examples of lossless compression are PNG images, ZIP archives and FLAC audio. What you put into them, you get exactly the same thing back out.
Then there are “lossy” compression schemes. Lossy schemes look for ways to throw away or generate an approximation of input data which will produce a different output that is hopefully just *not easily distinguishable* from the original.
For example, MP3 and AAC audio work by throwing away or smudging sounds that their “psychoacoustic model” thinks that you won’t be able to hear.
Video compression schemes like H.264 and VP9 work by looking for similarities and patterns within *and even* ***between*** frames of a video and fudging them in such a way that it isn’t very noticeable. They also tend to handle brightness/darkness (“luma”) and colors (“chroma”) in a biased way so that they can more heavily fudge certain differences in colors and shading that they think you can’t see.
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