MP All Models SOLVED: 8k Displays Running on Mac Pro? Any? What Video cards would work that support 8k HDMI 2.1/Displayport 1.4/2.0 displays on Mac Pro? YES you can

[hardwickj]

I felt the need to chime in here because there appears to be some confusion around how/why the Dell UP3218K can work at 8k...

From Anandtech:

For interconnection with host PCs, as a single DisplayPort 1.3/1.4 cable does not provide enough bandwidth for the 7680×4320@60 Hz configuration Dell is targeting, the UltraSharp UP3218K uses two DisplayPort 1.3 inputs to provide the necessary bandwidth, stitching the two display streams together internally using tiling. This is similar to early 5K displays, which used a pair of DisplayPort cables to get around the bandwidth limitations of DisplayPort 1.2. Using two cables not a big problem given the target market, but it's interesting to note that because 7680×4320@60Hz alone consumes all of the bandwidth supplied by the two cables, there isn't any leftover bandwidth to support HDR or the Rec. 2020 color space.

On a side note, while the company could have used DisplayPort 1.4's Display Stream Compression 1.2 (DSC) feature to reduce the bandwidth requirements of the monitor, they opted not to. DSC is promoted as visually lossless, but given how demanding many professionals are and problems that potential artifacts introduced by DSC could bring, Dell decided to stick to two DisplayPort cables as a result.

Had Dell opted to support DSC, then it would have been possible to run this monitor at 8k@60hz via a single cable on MacOS. However, because they opted to forego DSC, then a single cable will at best get you 8k@30hz. Combine that with MacOS's lack of proper MST support (which is also why you can't daisy chain USB-C monitors in anything but "Mirrored" mode), means that running at 8k@30hz is the only possible option with that monitor for the time being.

I'm hoping that with CES just around the corner, we'll get a few more options in this regard. There were already a few announced last year, but I'm guessing due to COVID + supply chain issues, they just haven't materialized as planned. Dell is also overdue for an update to this monitor that includes DSC (and hopefully USB-C DP-Alt mode w/ power over a single cable!)

I'm also holding out hope that Apple finally comes forward and properly supports MST, given how they tout the M1 Pro/Max's ability to edit multiple 8k video streams, it's fairly ironic that they can't actually *display* an 8k video stream.

 

[hardwickj]

Is anyone aware of any Dual DisplayPort adapters that can actively apply DSC and reduce to a single DP 1.4 connection? That's what we'd need given the current options on the market. Something akin to this from OWC which I unfortunately assume is only a passive DSC support.

 

[ZombiePhysicist]

That's interesting. It would be a great solution to have a box that basically takes one signal, breaks it up so that it's outputting like 2 monitors, and then the monitor could somehow combine it into one display. I guess the dell display allows something like this with its dual DP1.4 port connection.

Sadly, I think the world is waiting for apple to provide some HDMI 2.1 support, because for right now, most of the real big 8k options use only HDMI 2.1.

I dont know of any 8k TVs that use USBc or display port, and that's part of the problem with compatibility right now.

In the mean time, I got my graphics card, now just waiting on the 8k TV to start testing some options. Fingers crossed.

 

[hardwickj]

This also might do the trick: https://github.com/waydabber/BetterDummy

It might be possible to use that to create a dummy display, which you then use as the basis for mirroring the 2nd tile of the UP3218K from.

 

[ZombiePhysicist]

Thanks, I posted that a while back along with SwitchResX. But appreciate the helping hand on the thought. Hoping that combo and some combo of cable/adapters get me to at least 8k@30hz to the Samsung TV using HDMI2.1.

SOLVED: 8k Displays Running on Mac Pro? Any? What Video cards would work that support 8k HDMI 2.1/Displayport 1.4/2.0 displays on Mac Pro? YES you can

I wonder if using this app might somehow be able to trick an 8k output. We do know of one 8k monitor that works on the Mac, I think. The 8k Dell monitor with 2 DisplayPort ports that I guess drive 2 halves of the screen. Perhaps using BetterDummy monitor in someway, perhaps in combination with...

forums.macrumors.com

 

[hardwickj]

I posted that a while back along with SwitchResX

That must have been in another thread then.

Just as a follow-up, the author of BetterDummy seems to think that it may be possible.

 

[Pressure]

I'm not sure 4K HiDPI or normal 4K is going to be that distinguishable from the distances you need to sit from a 65" screen to make sense.

The 4K HiDPI works on the Dell UP3218K because your face is around 24" (60 cm) away from the screen and it has a pixel density of 279 ppi.

30Hz is doable with specific workloads in 8K but after finally having gotten 60Hz to work it would be hard to go back.

 

[hardwickj]

@Pressure so you do actually have 60hz working? I saw your comment here originally about getting it working using one-key-hidpi, but then after seeing some of your other comments that you made after that one I was under the impression that you actually only had it working at 30hz.

And to confirm, you're still using Catalina? It sounds like the one-key-hidpi project is dead and doesn't work with Monterey

 

[ZombiePhysicist]

I'm not sure 4K HiDPI or normal 4K is going to be that distinguishable from the distances you need to sit from a 65" screen to make sense.

The 4K HiDPI works on the Dell UP3218K because your face is around 24" (60 cm) away from the screen and it has a pixel density of 279 ppi.

30Hz is doable with specific workloads in 8K but after finally having gotten 60Hz to work it would be hard to go back.

I'll have an 85" screen 24" from my face. Thats around 105ppi I think so I probably will keep it 1 for 1 pixel for a humungous desktop. I'll have to play with the HiDPI to see if it makes sense.

Agree re 60hz, but 30hz will 'get me by' until apple starts to actually support HDMI2.1 more fully. My old 30" cinema displays (now 15 years old, working 24/7) are finally starting to flicker and die, so I really am now motivated to get a replacement. If they hung on another year or so, I suspect this transition would be much easier. Fingers crossed.

 

[ZombiePhysicist]

@Pressure so you do actually have 60hz working? I saw your comment here originally about getting it working using one-key-hidpi, but then after seeing some of your other comments that you made after that one I was under the impression that you actually only had it working at 30hz.

And to confirm, you're still using Catalina? It sounds like the one-key-hidpi project is dead and doesn't work with Monterey

Am I misunderstanding it? I was under the impression that @Pressure one-key-hidpdi solution is now supplanted with the availability of BetterDummy? I was under the impression they are achieving the same thing (just more easily now with BetterDummy).

 

[hardwickj]

Am I misunderstanding it? I was under the impression that @Pressure one-key-hidpdi solution is now supplanted with the availability of BetterDummy? I was under the impression they are achieving the same thing (just more easily now with BetterDummy).

No, BetterDummy doesn't yet support certain features required to make 8k@60hz work, but the developer said that they could support them and may very well do so.

 

[ZombiePhysicist]

No, BetterDummy doesn't yet support certain features required to make 8k@60hz work, but the developer said that they could support them and may very well do so.

Thanks for the correction, much appreciated!

 

[mikas]

I'm certainly interested on this. And I'd like to hear your opinion about the usability of the set-up afterwards.
It is a big screen to look at from that said distance, and with that resolution. But I would believe it will be an experience at least.

It all depends on point of view, I'd say.

 

[ZombiePhysicist]

Ok so a big update. I got my screen, I got my card, and I tried a bunch of variations.

TLDR, no go.

8k does not work on a Mac to an HDMI2.1 device no matter the combination of cables used. Currently, the only way to get 8k on a Mac is to have a display with DisplayPort 1.4. Longer story below.

I have the following base equipment:
(1) 2019 Mac Pro (on macOS 12.1)
(2) AMD Radeon 6900XT (I think reference card) from Sonnet with ports: 1-USBc, 2-DisplayPort 1.4, 1-HDMI2.1:
(3) AMD Radeon™ Pro WX 9100 with 6-miniDisplayPort 1.4 ports:
(4) Samsung QN85QN900AFXZA 85" 8K TV with 4-HDMI2.1 ports

The results with the above setup and various cable combinations listed below are as follows:
FakeAlmost8k: 8K is rastered by macOS but what gets pumped out to the TV is a 4k signal, but the desktop is shown as if 8k was working, but at a much lower resolution. I got this result if I tried 8k at 60hz, 30hz or 24hz (although I was mostly concentrating on trying to get 30hz working). This is what I mean:

Here is a screen shot of the SwitchResX panel on the 8k display in 8k mode and it looks perfect in memory as a screenshot:

But, below, is how it appears on the TV. So you can see, while in memory it does hold a 7680x4320 image of the desktop; however, what it essentially does on the TV is map everything to the size as if it were that 8k desktop, but uses only 4k of resolution to render it, and you get this garbled mess. This essentially confirms/duplicates @Arvine 's experience.

The other thing that is weird with the TV, but perhaps this is a settings thing, that even in 4k HiDPI mode, the rasterization is not clean. Text has this kind of fuzziness to it. Here is a photo:

For example, look at the check box, you can see its doing weird overscan/anti-aliasing.

One other thing, that even in this 4k mode, it's images get dithered rather than have pure colors, you can kind of see the halftone dots in my avatar:

Perhaps this is some setting in the TV or some weird effect of 4k on an 8k TV set?




Anyway, onwards with the cable connection tests.

Card	Connection Source	Connection Target	Result	Cable Used
WX9100	MiniDP1.4 port 2	TV HDMI2.1 port 1	FakeAlmost8k	CableMatters MiniDP1.4 to HDMI2.1 Cable
WX9100	MiniDP1.4 port 2 via HDMI adapter (CableMatters)*	TV HDMI2.1 port 1	FakeAlmost8k	CableMatters HDMI2.1 to HDMI2.1 Cable
6900XT	HDMI2.1 port 1	TV HDMI2.1 port 1	FakeAlmost8k	CableMatters HDMI2.1 to HDMI2.1 Cable
6900XT	DisplayPort1.4 port 2	TV HDMI2.1 port 1	FakeAlmost8k	CableDeconn DisplayPort1.4 to HDMI2.1 Cable
6900XT	USB-c port 4	TV HDMI2.1 port 1	No signal	CableMatters USB-c to HDMI2.1 Cable
6900XT	USB-c port 4 via HDMI adapter (Sabrent)	TV HDMI2.1 port 1	FakeAlmost8k	CableMatters HDMI2.1 to HDMI2.1 Cable
6900XT	USB-c port 4 via DP adapter (CableMatters)	TV HDMI2.1 port 1	FakeAlmost8k	CableDeconn DisplayPort1.4 to HDMI2.1 Cable

So not sure why the straight USB-c to HDMI connection didnt work, yet did work via the USBc adapters. Perhaps I got a bad USBc to HDMI cable. Also, the MiniDP1.4 to HDMI adapter* was somewhat erratic. It would kind of disconnect and reconnect, seemingly at random.

Soooo. This was disappointing as the display is crazy bright! The colors are crazy vibrant! Also, from a desktop stand point, a single 8k display is bigger than my 6 30" Cinema displays. It's literally the same horizontal resolution and ~2.7x the vertical resolution.

It's amazing! Also, I can tell at 24" distance, this will be great. The worst part is the display is not curved, so on an 85" display, about 65" worth is pretty easy to see just tilting your head. The rest is so far, you will have to lean to see it. I see this as useful as I can move stuff I dont use too often to the edges as a work/prep area, and then stuff around the middle for active work. You'll probably need Menuwhere or an app like it for the menu bar . This might suggest people just get the 65" display, however I like how size scales. It basically has a similar size/resolution as the 30" cinema displays so moving an 8x11" document from one place to the other works out to about the same size on the 85" screen. With the 65" screen it will be a bit more scrunched, but I suspect some people will like that.


But I digress...

Anyway, I was hoping one of the adapters would have stifled a signal in a way that the 8k resolution would work. There might be something to it as the adapters with USBc did work, wile a direct connect cable did not. But again, maybe it's just a bad cable.

I have yet to try BetterDummy or Resolutionator. Not sure if some combination of those would do anything.

Curious if anyone has any ideas or thoughts on what else to try; it would be much appreciated!

 

[ZombiePhysicist]

Just a quick followup. Messed around with BetterDummy and Resolutionator, and they really weren't obviously helpful.

So this looks like it's just an macOS driver being incomplete for HDMI2.1 issue. Basically we are at Apple's mercy for whenever they feel like making their drivers actually work with HDMI2.1 8k resolutions. Which is kind of crazy with them touting 8k work flows so much, and the damn Mac basically cannot actually (drive/output) an 8k DISPLAY. Nuts!

 

[joevt]

Ok so a big update. I got my screen, I got my card, and I tried a bunch of variations.

TLDR, no go.

8k does not work on a Mac to an HDMI2.1 device no matter the combination of cables used. Currently, the only way to get 8k on a Mac is to have a display with DisplayPort 1.4. Longer story below.

I have the following base equipment:
(1) 2019 Mac Pro (on macOS 12.1)
(2) AMD Radeon 6900XT (I think reference card) from Sonnet with ports: 1-USBc, 2-DisplayPort 1.4, 1-HDMI2.1:
(3) AMD Radeon™ Pro WX 9100 with 6-miniDisplayPort 1.4 ports:
(4) Samsung QN85QN900AFXZA 85" 8K TV with 4-HDMI2.1 ports

The results with the above setup and various cable combinations listed below are as follows:
FakeAlmost8k: 8K is rastered by macOS but what gets pumped out to the TV is a 4k signal, but the desktop is shown as if 8k was working, but at a much lower resolution. I got this result if I tried 8k at 60hz, 30hz or 24hz (although I was mostly concentrating on trying to get 30hz working). This is what I mean:

Here is a screen shot of the SwitchResX panel on the 8k display in 8k mode and it looks perfect in memory as a screenshot:
View attachment 1930658
But, below, is how it appears on the TV. So you can see, while in memory it does hold a 7680x4320 image of the desktop; however, what it essentially does on the TV is map everything to the size as if it were that 8k desktop, but uses only 4k of resolution to render it, and you get this garbled mess. This essentially confirms/duplicates @Arvine 's experience.
View attachment 1930655

You can see in SwitchResX that all the 8K modes have the Scaled checkbox. If you double click each of them, it will show the pixel clock is like ≈600MHz and the active pixels is 4K.
It would be interesting to see the resolutions sorted by Scaled so we can see what modes are not scaled.

The other thing that is weird with the TV, but perhaps this is a settings thing, that even in 4k HiDPI mode, the rasterization is not clean. Text has this kind of fuzziness to it. Here is a photo:
View attachment 1930665
For example, look at the check box, you can see its doing weird overscan/anti-aliasing.

One other thing, that even in this 4k mode, it's images get dithered rather than have pure colors, you can kind of see the halftone dots in my avatar:
View attachment 1930667

Perhaps this is some setting in the TV or some weird effect of 4k on an 8k TV set?

Don't TVs in general have this screen door effect? They're usually supposed to be viewed from the couch at least 6 feet away.

For each test, (all the cables, GPUs, GPU ports) create an AGDCDiagnose output file. That way we can see what the EDID is for each test (different ports of the TV will have different EDIDs).

The AGDCDiagnose output will tell us what the output pixel format is. Some artifacts might be caused by chroma sub sampling but I can't explain the dithering - I know a camera will see weird stuff if put too close to a display.

The AGDCDiagnose output will also show what DisplayPort to HDMI chip is being used in each adapter or cable and may indicate if the firmware is not the latest.

Give each file a descriptive name describing the connection. zip them altogether and attach to a post. Then I can compare.

Anyway, onwards with the cable connection tests.

Card	Connection Source	Connection Target	Result	Cable Used
WX9100	MiniDP1.4 port 2	TVHDMI2.1 port 1	FakeAlmost8k	MiniDP1.4 to HDMI2.1 Cable
WX9100	MiniDP1.4 port 2 via HDMI adapter	TVHDMI2.1 port 1	FakeAlmost8k	HDMI2.1 to HDMI2.1 Cable
6900XT	HDMI2.1 port 1	TVHDMI2.1 port 1	FakeAlmost8k	HDMI2.1 to HDMI2.1 Cable
6900XT	DisplayPort1.4 port 2	TVHDMI2.1 port 1	FakeAlmost8k	DisplayPort1.4 to HDMI2.1 Cable
6900XT	USB-c port 4	TVHDMI2.1 port 1	No signal	USB-c to HDMI2.1 Cable
6900XT	USB-c port 4 via HDMI adapter	TVHDMI2.1 port 1	FakeAlmost8k	HDMI2.1 to HDMI2.1 Cable
6900XT	USB-c port 4 via DP adapter	TVHDMI2.1 port 1	FakeAlmost8k	MiniDP1.4 to HDMI2.1 Cable

To make the table more readable, you should include the manufacturer name (e.g. Cable Matters) and abreviated product name (DP 1.4 to HDMI 8K).

So not sure why the straight USB-c to HDMI connection didnt work, yet did work via the USBc adapters. Perhaps I got a bad USBc to HDMI cable.

Maybe try a different display to see if the cable works with anything else? Maybe the AGDCDiagnose command will show something? chip type, firmware version, connection status...

 

[ZombiePhysicist]

You can see in SwitchResX that all the 8K modes have the Scaled checkbox. If you double click each of them, it will show the pixel clock is like ≈600MHz and the active pixels is 4K.
It would be interesting to see the resolutions sorted by Scaled so we can see what modes are not scaled.


Don't TVs in general have this screen door effect? They're usually supposed to be viewed from the couch at least 6 feet away.

For each test, (all the cables, GPUs, GPU ports) create an AGDCDiagnose output file. That way we can see what the EDID is for each test (different ports of the TV will have different EDIDs).

The AGDCDiagnose output will tell us what the output pixel format is. Some artifacts might be caused by chroma sub sampling but I can't explain the dithering - I know a camera will see weird stuff if put too close to a display.

The AGDCDiagnose output will also show what DisplayPort to HDMI chip is being used in each adapter or cable and may indicate if the firmware is not the latest.

Give each file a descriptive name describing the connection. zip them altogether and attach to a post. Then I can compare.


To make the table more readable, you should include the manufacturer name (e.g. Cable Matters) and abreviated product name (DP 1.4 to HDMI 8K).


Maybe try a different display to see if the cable works with anything else? Maybe the AGDCDiagnose command will show something? chip type, firmware version, connection status...

So here are the resolutions by scaled vs non scaled:

So all the 8k resolutions basically shown are scaled, and many of the 4k resolutions too:

When I double click the 8k resolution @30hz, I see this:

And @60hz, I see this:

As for AGDCDiagnose output files. I'd be happy to do it, but I dont know what it is, or how to make the files. Would appreciate a pointer on how to get it done.

As for if all TVs do this "screen door effect" not sure. I think it's a function of scaling modes. When I plugged in my OLED I don't remember this effect, although it was just a 4k screen. But you may be right, I'm not an expert on the TV side of things.

I put links to all the manufacturers in the table and updated it with manufacturer names.

Good idea on trying it with a different display. Will see if I can fit another TV in here to try! AYE!, it's getting screen crowded in here, like a house of mirrors but with screens!

 

[joevt]

As for AGDCDiagnose output files. I'd be happy to do it, but I dont know what it is, or how to make the files. Would appreciate a pointer on how to get it done.

/System/Library/Extensions/AppleGraphicsControl.kext/Contents/MacOS/AGDCDiagnose -a > AGDCDiagnose_descriptionofdisplayandportandadapter.txt 2>&1

Also, can you show a screenshot of the Display Information tab in SwitchResX? Check each connection tab to see if they all show the same info. I am wanting to see what it says for the frequency ranges in each case and we can compare that with the frequencies in the AGDCDiagnose outputs.

 

[ZombiePhysicist]

/System/Library/Extensions/AppleGraphicsControl.kext/Contents/MacOS/AGDCDiagnose -a > AGDCDiagnose_descriptionofdisplayandportandadapter.txt 2>&1

Also, can you show a screenshot of the Display Information tab in SwitchResX? Check each connection tab to see if they all show the same info. I am wanting to see what it says for the frequency ranges in each case and we can compare that with the frequencies in the AGDCDiagnose outputs.

So when do I run that? Before or after I plug things in for each type of connection? I'm guessing after, but want to make sure. Thanks!

This is the display tab with the resolution set to 8k@30:

 

[joevt]

So when do I run that? Before or after I plug things in for each type of connection? I'm guessing after, but want to make sure. Thanks!

After. We want to see the connection status, pixel format, and EDID of the display which can't happen until after the display is connected.

This is the display tab with the resolution set to 8k@30:
View attachment 1930766

Which GPU and port and adapter is that for?

It says Pixel clock max is 1217 MHz. For 8K60, we'll probably need a pixel clock of 2376MHz (the EDID will show what pixel clocks the display expects) so override the value in SwitchResX with something like 3000 MHz.
But that's probably not the problem - 8K30 only requires 1188MHz.
Also, do you have Catalina? I want to make sure the problem isn't with Apple's change in support for DSC. Well, that won't work with the 6900. And the 9100 doesn't support DSC since it's a VEGA card so never mind.

I am wondering how it calculates a value of 1217 MHz. HBR3 limit is 1080MHz for 8bpc but DSC @ 12bpp would allow 2160MHz. 8K60 isn't going to happen unless the TV allows a timing that is more like CVT-RB (2090 MHz) instead of HDMI (2376MHz) or if macOS allows DSC @ 8bpp (which allows up to 3240 MHz)

HDMI 2.0 limit is 1200MHz using 4:2:0 8bpc (effectively 12bpp).

Can the TV accept arbitrary 4K resolutions between 60Hz and 120Hz using CVT-RB? Create custom timings in SwitchResX in that range and see which are accepted. Of course, with a max pixel clock of 1217MHz it should have accepted the TV's 4K120 timing already...

 

[ZombiePhysicist]

After. We want to see the connection status, pixel format, and EDID of the display which can't happen until after the display is connected.


Which GPU and port and adapter is that for?

It says Pixel clock max is 1217 MHz. For 8K60, we'll probably need a pixel clock of 2376MHz (the EDID will show what pixel clocks the display expects) so override the value in SwitchResX with something like 3000 MHz.
But that's probably not the problem - 8K30 only requires 1188MHz.
Also, do you have Catalina? I want to make sure the problem isn't with Apple's change in support for DSC. Well, that won't work with the 6900. And the 9100 doesn't support DSC since it's a VEGA card so never mind.

I am wondering how it calculates a value of 1217 MHz. HBR3 limit is 1080MHz for 8bpc but DSC @ 12bpp would allow 2160MHz. 8K60 isn't going to happen unless the TV allows a timing that is more like CVT-RB (2090 MHz) instead of HDMI (2376MHz) or if macOS allows DSC @ 8bpp (which allows up to 3240 MHz)

HDMI 2.0 limit is 1200MHz using 4:2:0 8bpc (effectively 12bpp).

Can the TV accept arbitrary 4K resolutions between 60Hz and 120Hz using CVT-RB? Create custom timings in SwitchResX in that range and see which are accepted. Of course, with a max pixel clock of 1217MHz it should have accepted the TV's 4K120 timing already...

Sorry, I misread. It's on the 6900XT, in the HDMI2.1 port, 8k@60hz

As for custom resolution, if you tell me what to put in here, will happily test it:

Also, the 12bpp, that may explain the dithering/halftone I'm seeing!

 

[ZombiePhysicist]

Ok going to make a post with uploads of AGDCDiagnose files here.

 

[Arvine]

Ok so a big update. I got my screen, I got my card, and I tried a bunch of variations.

Thanks for confirming this. I had the same results..

The dithering may be the dots of the TV, each “pixel” is built up by three physical dots, RGB.

 

[joevt]

As for custom resolution, if you tell me what to put in here, will happily test it:
View attachment 1930784 View attachment 1930786

Also, the 12bpp, that may explain the dithering/halftone I'm seeing!

For the 4K refresh rate test, use CVT-RB, 3840x2160 60Hz, then duplicate it a dozen times and for each one increase the refresh rate by 5.

The 12bpp doesn't mean it's doing 4bpc. It's an average.

For 4:2:0, there are 8 pixels in a 4x2 arrangement, which has 8 luminance values but only 2 Cr and 2 Cb components - 12 components total where normally there would be 24. In the case of 8bpc, each component is still 8 bits so you still get millions of colors. There's just half as many components (it's just lower resolution except only for the color info - a grayscale image will have full resolution).

DSC also does not reduce bpc. It uses a compression method that is smarter about what information it throws away compared to chroma sub sampling.

Basically, if the image is of a single color, 4:2:0 and DSC will not use dithering.

Ok going to make a post with uploads of AGDCDiagnose files here.

Some interesting stuff. I don't see any problems.

You have 1 Cinema Display from 2006, one from 2007, and four from 2010. The one from 2006 doesn't support HDCP but your Apple Mini DisplayPort to Dual Link DVI adapters don't care, unlike third party or new USB-C to dual link adapters which must have an HDCP OFF firmware to work with the 2006 model. The EDIDs are otherwise identical (except for serial numbers, dates, and different product number and white color for the 2006).

The EDID of the TV is unchanged in the two tests (since you did not change the port used or the TV settings).
It appears to be connecting with HDMI 2.0 modes:
1) 3840x2160 60Hz 594 MHz, 4:2:0 10bpc HDR10
2) 3840x2160 30Hz 297 MHz, 4:4:4 10bpc HDR10

The modes from the EDID that we want to have working are these:

edid-decode --vic 118
edid-decode --vic 196
edid-decode --vic 199

VIC 118:  3840x2160  120.000000 Hz  16:9    270.000 kHz   1188.000000 MHz
               Hfront  176 Hsync  88 Hback  296 Hpol P
               Vfront    8 Vsync  10 Vback   72 Vpol P
VIC 196:  7680x4320   30.000000 Hz  16:9    132.000 kHz   1188.000000 MHz
               Hfront  552 Hsync 176 Hback  592 Hpol P
               Vfront   16 Vsync  20 Vback   44 Vpol P
VIC 199:  7680x4320   60.000000 Hz  16:9    264.000 kHz   2376.000000 MHz
               Hfront  552 Hsync 176 Hback  592 Hpol P
               Vfront   16 Vsync  20 Vback   44 Vpol P

so you should try adding them as custom resolutions (along with your 4K tests). Don't forget to override the max pixel clock in the Display Information tab.

The 6900's HDMI 2.1 port has no DisplayPort information which is to be expected since it is a real HDMI output and does not use a DisplayPort to HDMI adapter. We should probably assume that Apple didn't enable FRL so I don't think we should try getting HDMI 2.1 link rates from it.
But you could try disabling HDR (which requires 10 bpc) in the Display preferences panel to see if 8bpc will allow 8K30 or 4K120 to be used with 4:2:0 to get under the HDMI 2.0 limit.

 

[ZombiePhysicist]

For the 4K refresh rate test, use CVT-RB, 3840x2160 60Hz, then duplicate it a dozen times and for each one increase the refresh rate by 5.

The 12bpp doesn't mean it's doing 4bpc. It's an average.

For 4:2:0, there are 8 pixels in a 4x2 arrangement, which has 8 luminance values but only 2 Cr and 2 Cb components - 12 components total where normally there would be 24. In the case of 8bpc, each component is still 8 bits so you still get millions of colors. There's just half as many components (it's just lower resolution except only for the color info - a grayscale image will have full resolution).

DSC also does not reduce bpc. It uses a compression method that is smarter about what information it throws away compared to chroma sub sampling.

Basically, if the image is of a single color, 4:2:0 and DSC will not use dithering.


Some interesting stuff. I don't see any problems.

You have 1 Cinema Display from 2006, one from 2007, and four from 2010. The one from 2006 doesn't support HDCP but your Apple Mini DisplayPort to Dual Link DVI adapters don't care, unlike third party or new USB-C to dual link adapters which must have an HDCP OFF firmware to work with the 2006 model. The EDIDs are otherwise identical (except for serial numbers, dates, and different product number and white color for the 2006).

The EDID of the TV is unchanged in the two tests (since you did not change the port used or the TV settings).
It appears to be connecting with HDMI 2.0 modes:
1) 3840x2160 60Hz 594 MHz, 4:2:0 10bpc HDR10
2) 3840x2160 30Hz 297 MHz, 4:4:4 10bpc HDR10

The modes from the EDID that we want to have working are these:

edid-decode --vic 118
edid-decode --vic 196
edid-decode --vic 199

VIC 118:  3840x2160  120.000000 Hz  16:9    270.000 kHz   1188.000000 MHz
               Hfront  176 Hsync  88 Hback  296 Hpol P
               Vfront    8 Vsync  10 Vback   72 Vpol P
VIC 196:  7680x4320   30.000000 Hz  16:9    132.000 kHz   1188.000000 MHz
               Hfront  552 Hsync 176 Hback  592 Hpol P
               Vfront   16 Vsync  20 Vback   44 Vpol P
VIC 199:  7680x4320   60.000000 Hz  16:9    264.000 kHz   2376.000000 MHz
               Hfront  552 Hsync 176 Hback  592 Hpol P
               Vfront   16 Vsync  20 Vback   44 Vpol P

so you should try adding them as custom resolutions (along with your 4K tests). Don't forget to override the max pixel clock in the Display Information tab.

The 6900's HDMI 2.1 port has no DisplayPort information which is to be expected since it is a real HDMI output and does not use a DisplayPort to HDMI adapter. We should probably assume that Apple didn't enable FRL so I don't think we should try getting HDMI 2.1 link rates from it.
But you could try disabling HDR (which requires 10 bpc) in the Display preferences panel to see if 8bpc will allow 8K30 or 4K120 to be used with 4:2:0 to get under the HDMI 2.0 limit.

Sorry, this is going a little over my head. Apologies. I know it's frustrating trying to remote control from across the internet, particularly when I'm a dummy on this. I really appreciate all the help!

When you make a custom resolution the above is the starting point. Do you want me to start the highlighted vertical scan rate at 60hz, and then increment it to 65, 70...120hz and leave all other setting shown there the same?

Assuming that is correct, what do I do once I create the custom entry to try it with the TV? there seems to be noway to engage that mode in SwitchResX?

Lastly, someone suggested that there might be a way to use Picture by Picture mode or something like that on the Samsung TV where I use 2 cables. Basically make half the screen screen one powered by one input cable, and then the other half of the screen powered by another cable.

Not sure the Picture in Picture thing would work, but it was an interesting thought.