FWIW, and mostly just because correcting the Japanese Hard-Boiled Blu-ray video has seemingly become some sort of cottage industry, I just took a stab at it. I started with the hypothesis that instead of adjusting brightness, we should mostly be adjusting gamma. Gamma correction affects chroma as well as luma, so in addition to bringing down the brightness, it would increase the color saturation.

I'm pretty impressed with the results and will probably use this for myself in the long term (paired with Matt's excellent audio and subtitles, of course).

It doesn't fix every problem, of course--particularly some of the hospital shots which look washed out no matter what we do to them (and maybe they just look like that...), but for a global fix without any scene-specific tweaks, it's pretty good.

I'm still rendering ATM, so no screenshots for a few days if anyone's interested. Also, I know the Blu-ray is already cropped on the right, but I couldn't handle how the frame edges occasionally wobbled (particularly along the bottom edge), so I cropped mine further to 1.85:1 just to get a stable frame.

AviSynth code below:

Levels(0,0.55,255,0,255)

Tweak(0,1,0.8,1)

Crop(0,20,0,-22)

AddBorders(0,21,0,21)