Look at these new logs:

https://hackaday.io/project/24834-3rgb-image-lossless-compression-format/log/60063-colorspace
https://hackaday.io/project/7385-recursive-range-reduction-3r-hwsw-codec/log/60068-breakthrough

The have some similarities with µδ but they differ in critical ways:

• µδ works with median and difference while the new transform creates a sum (σ) and one of the operands (let's call it α). The new transform shall then called σα.
• µδ works inside a ring (a closed set with wrap-around) but σα "escapes" this (the output is not constrained inside the original boundaries), which allows actual compression for some combinations of values.
• actually σα has an initial value range that is a ring, however each operand can have its own original ring, they both are combined and the boundaries remain as auxiliary data in the background.
• σα is used with VLC (variable length codes) while µδ uses fixed-length words.

σα already has a fantastic application in the color decomposition of RGB pictures and will make 3R a truly entropy coder... Follow the developments there !