HDR 10 with "old" iMac2017 and Benq PD2700U 4k 60hz HDR10 monitor

[Mmazzilli73]

I own the folowing:

- iMac2017, 27", 5K Retina
- BenQ PD2700U 4K HDR monitor
- UsbC-DP 1.4 cable

I am trying to understand more about HDR on Mac as I am not sure I am getting it all right.
I selected the HDR checkbox in the Display Settings for the second monitor. I have no Saturation or Refresh setting but just Resolution. Monitor is set to HDR mode and can't change it from OSD (I think because he knows he is on an HDR source). If I use monitor's software called "Display Pilot" I can force the monitor to go on sRGB or Rec709 although (I think) Apple will continue to send out HDR signal. If I want I can change Display Settings un-checking HDR, then set monitor to sRGB and get it saturated exactly like the iMac screen.
Now.. my questions are...

1) Apple says iMac2017 is NOT HDR compatible but I believe they say so just because the internal 5K screen is not HDR, not because HDR can't be achieved through external monitors

2) Apple sells a 70$ dongle that is said to be compatible with iMac 2017. I contacted Apple and they told me that using that I will NOT get HDR so they say (but might be wrong) that I will get 4k and 60hz but not HDR. I think they are wrong as, I believe, since Catalina any Mac can have on external devices through proper cabling, HDR

3) HDR has (almost) nothing to do with graphic card. Sure, it needs to be powerful enough, but 10bit, Rec2020 color space etc... has nothin to do with the graphic card. It is more about available bandwidth on the output ports and correct cabling. Am I right here? So Thunderbolt 3 can do HDR10 as this requires "DP Alt Mode" achievable on TB3 with the right cable.

4) HDR receiving Rec709 signal will probably display washed out colours with little contrast. Am I right?

So what happens to me is this.
When I am just on my desktop (no particular apps) the HDR is washed out but the monitor says "HDR" (non "HDR emulated mode".. just "HDR"). What is going on here? I believe Apple is sending HDR signal (so the monitor correctly displays HDR) but the signal Apple (Big Sur) is creating is wrong. Is really sRGB and looks washed out.

If I open VLC and play some HDR file downloaded from the web.. it is playing ok. Colours are great and full of contrast. SO what is going on here? The app is overriding system settings? Other apps have similar problems. Da Vinci Resolve shows me a washed up image on the second monitor (used in full screen direct mode). This is somehow expected although I should be able in Rec2020 color space mode to reach full saturation on the second monitor (with, in that case, totally off-scale saturation in the iMac main monitor). Adobe applications (again.. full screen mode) will NOT open if the second monitor is on. I need to open the apps first and only then switch on the monitor.

So... is it Apple Big Sure really supporting HDR?
Or is it just passing out an HDR formatted signal but is really a sRGB or Rec709 ?
Am I missing something here?

Will something change when my new Mac mini M1 gets here?

Thanks

 

[Ritsuka]

VLC can't output HDR on macOS. It will convert it to SDR. Try a HDR video in QuickTime Player.
If macOS lets you enable HDR in the Display settings, it means HDR is supported. But an app needs to know how to display HDR on an HDR monitor, and VLC doesn't know how to do so.

 

[Mmazzilli73]

and VLC d

Can you tell me a list of tested apps on Mac that output HDR ?
Is OSx itself HDR? because to see seems it is not.
If an app is HDR what should happen? I would see vivid colors inside the app and not outside? Or only if I put it full screen?
Do you know if Adobe Premiere and Da Vinci Resolve output HDR on Mac?

 

[Ritsuka]

macOS UI is SDR. An app needs to tell macOS which of its surfaces are HDR.
You should see HDR when playing a HDR video, as in the luminosity of the video can go up to the max nits of your monitor.
I know QuickTime Player and Final Cut Pro handles HDR correctly. I don't have a HDR monitor, I can't test other apps.

 

[joevt]

macOS UI is SDR. An app needs to tell macOS which of its surfaces are HDR.
You should see HDR when playing a HDR video, as in the luminosity of the video can go up to the max nits of your monitor.
I know QuickTime Player and Final Cut Pro handles HDR correctly. I don't have a HDR monitor, I can't test other apps.

Would be nice if surfaces that are SDR would use the correct colors while HDR is activated in the Displays preferences panel.

 

[Mmazzilli73]

I don't think this is possibile. HDR is not only software. The panel needs to be HDR. If it isn't will try to show the same frame but will have bands or will clip luma or some colors

 

[joevt]

I don't think this is possibile. HDR is not only software. The panel needs to be HDR. If it isn't will try to show the same frame but will have bands or will clip luma or some colors

Who are you replying to? If me then, what I meant was:

If I have an HDR display, and I enable HDR, then windows that are not HDR should use the proper colors so they don't appear washed out.

Maybe it's not an easy thing to do. Maybe you need apps to identify themselves as HDR compatible or not. If they are HDR compatible, then they'll choose their colors properly. If they are not HDR compatible, then some macOS service or graphics driver will transform the colors for the app using a more expensive method (maybe it could be as simple as a copy from the window frame buffer to the display framebuffer with some pixel transformations).

 

[Mmazzilli73]

Still doing some tests.
As far as I understand VLC could playback HDR but ONLY if the 1st monitor connected to the Mac (or the internal monitor in case of iMac) is HDR . So on my old iMac2017 what VLC will do is to configure itself NOT for my second HDR monitor but only for iMac color space. This will look good (but not HDR) on the iMac screen but very washed out when I drag it on the second screen. And as far as I understand VLC so will not play videos in HDR in hybrid situations.

Quicktime (and Final Cut... based on Quicktime) will understand on what monitor it is and will try to adapt.

Who are you replying to? If me then, what I meant was:

If I have an HDR display, and I enable HDR, then windows that are not HDR should use the proper colors so they don't appear washed out.

Maybe it's not an easy thing to do. Maybe you need apps to identify themselves as HDR compatible or not. If they are HDR compatible, then they'll choose their colors properly. If they are not HDR compatible, then some macOS service or graphics driver will transform the colors for the app using a more expensive method (maybe it could be as simple as a copy from the window frame buffer to the display framebuffer with some pixel transformations).

I am seeing strange things so I am confused. In an ideal world once I connect correct hardware, configure the right display colourspace, they should match 100% (OS X should compensate colors etc). then (just to be tricky) I could adapt colors to my room (daylight, yellow light etc) but they should match already. Wich they don't. Then all softwares should just play in the right (HDR) colourspace. Which they don't. They all react differently.

 

[Ritsuka]

No, VLC can't playback HDR. All it can do is convert HDR to SDR, so it will more or less display it correctly on a SDR monitor (but it's not HDR anymore).

 

[Mmazzilli73]

But on their website they say they do it... strange

 

[Ritsuka]

It does HDR to SDR tonemap. Maybe on Windows it can display HDR on an HDR display. But on macOS it surely can't.