DXT compression - part 4 - Entropy

Welcome to part 4 of the DXT compression series. In this series I go over the techniques and results used to compress Firefall's texture data as they are uncovered and implemented. 

In this post I go over a lossy algorithm reducing the data size on disk - Or how I went from 2.5bpp to 1.5bpp with very little visible and measurable loss in quality. 

Previous posts on this topic:
Part 1 - Intro
Part 2 - The Basics
Part 3 - Transposes

In Part 2 we determined the baseline of optimized LZMA compression on DXT5 data, which is 2.28bpp on average for my test data set from Orbital Comm Tower in Firefall.

In Part 3, we went over various transposes of data and found that they only make a small impact to 2.25bpp.

Alright, here we go!

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