I am still perplexed by the appearance of "recombination noise". In my assorted proof-of-concepts of the HSL-mix technique, I haven't come across this kind of anomaly. (Although it did prompt the further development of the process -- normalizing the Lightness spectrum between the sources. That alone was worth the work.)

Can you link to non-recompressed, full-sized caps in .PNG format of that exact frame from the Blu-ray (1920x1080) and the Criterion (letterbox) Laserdisc (720x480)? Even if you're not going to consider this approach, I'd like to look into the problem. (Thanks.)