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Continue to ChatQuery : Color number is just half the game. The other is to compress the picture after color reduction. This lossless compression, searches for repeated patterns in scanline order. Long story, in short: https://vmapp.org/query/44292/Color-Number-Is-Just-Half-The-Game-The-Other-Is-To-Compress-The-Picture-After-Color-Reduction-This-Lossless-Compression-Searches-For-Repeated-Patterns-In-Scanline-Order-Long-Story-In-Short/