Craig Marshall wrote:....
Jason Myres, professional Colorist and Moderator on the Lift/Gamma/Gain Forum expresses succinctly why so I will quote his recent comment to a similar question:
[i]"GPU output (DP/HDMI) and a Decklink/mini monitor card output) ..are two very different things and it goes way beyond whether they are 8 or 10-bit. The first one is a standard graphics card output, the second (Mini Monitor) is a Baseband SDI/ HDMI video output.
....
Well- this is bit of myth and legacy approach.
Here is another view which is adjusted to current technology possibilities.
Resolve and other grading tools work in RGB and use GPU to do its magic. GPU is connected
directly (in typical case) to a monitor. This is all what we need.
This link is actually more accurate and better than using video card because:
- data goes directly from GPU to monitor without any additional delay
- it's rather always 4:4:4, where probably 80% of typical studio setups still uses 4:2:2 YUV path (to save bandwidth)
- it avoids RGB->YUV->RGB conversion (which is never 100% lossless)- this happens on every YUV video chain
- it uses less resources- no need to copy data from GPU to card
- saves money and slot (no need for any additional card)
- it can be even 16bit pipe, where most video cards can do max 12bit
- it can use V-sync to guarantee proper sync, like video chain does
- it actually avoids problems on wrong conversion between RGB<->YUV (it's 1:1 RGB pipe from GPU to monitor)
- it's not restricted to specific refresh rates (just by connection bandwidth limits, e.g. HDMI 2.0 ect)- it can do about everything what your monitor will accept, e.g. 120Hz
- it's the only easy solution which allows atm. to monitor 8K (or 4K 50/60p 4:4:4)
Accuracy- it's just a matter of software. It's fairly easy to separate preview from any OS influence. There are software which already do it- just not Resolve.
When we talk about grading software which works in RGB and then about video pipe (which in most cases is YUV) then whole point of video pipe almost looses sense. RGB pipe to monitor is what you ideally want. YUV pipe is juts a compromise to save bandwidth.
If we were talking about some broadcast chain which operates in YUV then yes- you don't want to go to RGB anymore (we already left RGB world when YUV master was made). In case of Resolve, compositing, finishing tools you want RGB preview to your device and GPU is ideal for providing it.
Issues with GPU monitoring:
-because it uses HDMI/DP technology cable length is limited (use converter to SDI to gain distance if needed)
-maybe interlacing issue, although it can be sorted and it's soon will be gone anyway
Issue with refresh rate is very easy to sort out and some tools (e.g. Flame) already do it, even for PC monitors which has to be "forced" to different refresh rates. When you start Flame project it checks what fps you chosen and it tries to force monitor to correct refresh (you can even use e.g. 48Hz or 72Hz for 24p projects). All what you need is proper "video" monitor.
For small studios where monitors/TVs are next to machines GPU monitoring is ideal.
Video pipes are good for broadcast and places where signal has to go long way. This soon also going to be replaced by IP based workflows, which allow to send video (as data) at way longer distances. Times of old fashion SDI video chains are counted.