async It will definitely NOT send the same to the capture card as to the monitor unless you spoof the EDID. You can use BetterDisplay to download the monitor EDID. I don't have a capture card myself, but it should be possible to spoof the EDID.
This suggestion guided me in the right direction. I was able to spoof the EDID of one of my real monitors (with a macOS display EDID override file) to the BMD capture device, and it was still able to work and capture video. What I ultimately discovered was that regardless of EDID spoofing or not, my AMD Radeon Pro WX 5100 will only output a signal with temporal dithering if the capture device is connected at boot time. Disconnecting and reconnecting the capture device causes the output to no longer have temporal dithering until the next reboot… strange! Regardless, this resolves the main discrepancy I encountered regarding the WX 5100 GPU not seeming to have temporal dithering while the visual experience suggested otherwise. The fact that temporal dithering was only detected via DisplayPort and not via HDMI on all GPUs I tried (with the exception of my 2015 MacBook Pro 15" with an AMD dGPU, which exhibited it on both) was another interesting discrepancy which may yield helpful insights.
JTL I might have more to add later, but one reason I went for the DVI2PCIe is you can program an arbitrary EDID binary to the card, and it remains persistent.
If you mean the $1,400 DVI2PCIe Duo… ouch. 🙁 The Blackmagic device was $70 (used) on eBay, plus the cost of the Thunderbolt cable.
Seagull I would be careful about making assessments about dithering by eye though.
A valid point, and I completely agree. Correct me if I'm wrong, but my impression was that empirically measuring temporal dithering from a physical LCD panel requires sophisticated cameras/tools which are out of reach for most people. As far as visual assessment, I try to limit my reliance on it to getting a general sensation of image stability, and have that form the basis for further empirical investigation.
photon78s Do you still see dithering from your video analysis when you disable dithering inside color control?
I never got that far, as it looked like I needed to reboot my workstation to make ColorControl work fully, and I was unable to do so at the time. However, I expect I would have reached the same results that you did. My main concern for that workstation was that dithering is off on the normal display (which was what ColorControl seemed to indicate), and then I had secondary concerns that the BMD capture device may not be getting the same output that a standard monitor would (which now seem mostly resolved, at least on macOS).
@DisplaysShouldNotBeTVs, are you willing to share your method for disabling temporal dithering on the AMD GPU on the MacBookPro11,5, as you've mentioned elsewhere? Now that I have a means of reliably measuring temporal dithering, I want to start trying to disable it, leveraging all possible methods.