[noggin]

Aha - so the dithering is similar to the approach used by Quantel's patented "Dynamic Rounding", which they've used since the 80s to avoid banding on broadcast kit during colourspace conversion and bit depth truncation (as is common in broadcast video processing like mixing, keying etc.), and which people like Sony have licensed in the past (Digital Betacam used it)

Dynamic Rounding
Dynamic Rounding is a clever technique devised by Quantel for truncating the word length of pixels – a process you can't avoid when you are processing images. Rather than simply losing the lower bits, Dynamic Rounding uses their information to control, via a randomiser, the dither of the LSB of the truncated result. This effectively removes any artefacts that would otherwise be visible. Dynamic rounding is non-cumulative on any number of passes and produces statistically correct results. Dynamic rounding eliminates any truncation artefacts leaving you great looking pictures whatever the bit depth, whatever the processing. Dynamic Rounding is patented technology that you simply can't get anywhere else.

http://digitalfactbook.tv/d/dynamic-rounding/
Not sure if the Quantel patent still applies...