For someone who has been so adamant about cycle-accurate emulation I was surprised to see such ad hoc color transformations being used. Has anyone in the emulation community tried to accurately estimate the end-to-end response of these systems? Something along the lines of using a colorimeter with a reference monitor (like a Sony PVM CRT) and homebrew ROM that generates test patterns.
There's certainly limits to idealism. This is currently the best we have for the listed systems, I'm afraid. Hopefully someone reading about this will take interest in trying some things like you mentioned and helping to improve the situation.
As mentioned, the systems that need this most don't have even frontlit displays, so a colorimeter would not work on them. There's also the question of what the correct contrast setting should be on the analog adjustment wheels these systems had. Ideally you'd want to capture multiple contrast settings, and then try and devise an underlying adjustment algorithm from all the data sets to approximate the full analog range of positions for it.
I'm not into emulation at all, but I wonder how low level the passive LCD panels were software controlled in game or system ROM?
The wikipedia page on Walsh functions says:
>They are also used in passive LCD panels as X and Y binary driving waveforms where the autocorrelation between X and Y can be made minimal for pixels that are off.
Not sure how applicable that is on which of the systems you are considering. Sorry for the rabbit hole ;)