jordan I wonder if it's your cable that is triggering it due to lack of bandwidth maybe ?
This is quite possible, although I'm not sure that the math backs up this theory. The BlackMagic capture device itself is HDMI 2.0, and my DisplayPort to HDMI active cable is supposedly DisplayPort 1.4 (but the supported resolutions on the product page suggest that HDMI 2.0 is the bottleneck). For what it's worth, I did repeat most of the tests with an "Ultra High Speed HDMI" (48Gbps) cable, with identical results. The GTX 1080 also has HDMI 2.0, so with both ends supporting HDMI 2.0 as well as the cable, that should not be a bottleneck. I'd like to determine what the actual negotiated bandwidth is in macOS, but in any case this seems like plenty of margin for 1080p 60Hz (even with 10-bit color). The fact that we have to (actively) convert DisplayPort to HDMI or DVI (which appear to be very different signals) introduces a complexity that I wish we could avoid.
jordan I know someone for example did test dp off the quadro rtx 4000 (turing)gpu with the epiphan and he confirmed no dithering(I have the vid).
I am still trying to figure out how to identify dithering in an Epiphan capture. However, DVI and HDMI seem to be similar signals, and I only detected dithering over HDMI (with the Blackmagic device) on one machine to begin with, the MacBook Pro 15-inch Retina with AMD dGPU.
jordan Do you plan to try more gpus?
I am open to it. My primary goal was to find a Mac-compatible GPU with a DisplayPort output that doesn't dither, but so far I have not found one. I do have some interest in finding a safe GPU on the Windows side to use at work, however.