Resolved Apple Cinema HD Display (23") - strange color banding (low bit depth?)

[TechAndOSWorld]

Hello, I'm experiencing an issue with my 2005 23" Apple Cinema HD Display. I used it as a main display until last year, and it was completely fine. Then, I upgraded it, and started using the ACD with one of my older hackintoshes. And immediately, I noticed strange looking dock and window shadows, Instead of fading smoothly, like they should, they look like solid translucent rectangles, with hard edges. Then, I noticed that some macOS wallpapers also look downright awful, and have really strong color banding.

Today, I checked the display details in System Profiler, and noticed that macOS only reports a 24-Bit Color. For comparison, my LG 32UN500 reports a 30-Bit Color in macOS Catalina, and my 2004 20" Apple Cinema HD Display reports a 32-Bit Color in OS X Yosemite.

The computer I use with my 23" ACD only has one iGPU (Intel HD 4000), but it should be able to handle a higher color depth, right?
Could that be the issue? and if so, can I somehow change it manually?

Or is that a sign of a dying display? cause it also started behaving weirdly shortly after I upgraded it. Now, it doesn't turn off anymore when there's no signal (I have to unplug the PSU to turn it off), I can't directly adjust the brightness anymore, and sometimes, it flashes the power LED to tell me it can't read the video signal, even when there's an image on the screen.

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Here's a photo of the display exhibiting the issue mentioned above (it's not compressed, that's how it looks like in person):

And here's what System Profiler reports. I don't use any 3rd party color profiles, or software to adjust the image (like Gamma Control).

Any help will be appreciated!

 

[Amethyst1]

Here's a photo of the display exhibiting the issue mentioned above (it's not compressed, that's how it looks like in person):

It looks like the display is only running at, say, 6 bpc (18 bpp = 262,144 colours). Does the display exhibit the same behaviour on another system?

And here's what System Profiler reports.

That means the framebuffer is running at 8 bpc (24 bpp = 16.7 million colours), which is fine. This is not the same as the display’s colour depth though. AGDCDiagnose might not print colour depth information on the HD 4600 iGPU (Haswell). You can check if @joevt ‘s AllRez provides it.

 

[TechAndOSWorld]

It looks like the display is only running at, say, 6 bpc (18 bpp = 262,144 colours). Does the display exhibit the same behaviour on another system?


That means the framebuffer is running at 8 bpc (24 bpp = 16.7 million colours), which is fine. This is not the same as the display’s colour depth though. AGDCDiagnose might not print colour depth information on the HD 4600 iGPU (Haswell). You can check if @joevt ‘s AllRez provides it.

I ran AllRez, as you suggested. There's a lot of information I don't really understand, but one line caught my eye.
It's this one: "[3] = { kConnectionColorDepthsSupported ' bpc' = 0x00000001 : RGB 6, },".
A full printout is in the attachments.

Also, it seems to be a problem with this specific system, rather than the monitor itself.

 

[Amethyst1]

I ran AllRez, as you suggested. There's a lot of information I don't really understand, but one line caught my eye.
It's this one: "[3] = { kConnectionColorDepthsSupported ' bpc' = 0x00000001 : RGB 6, },".

This confirms macOS runs the display at 6bpc RGB.

Also, it seems to be a problem with this specific system, rather than the monitor itself.

How is the display connected to the Hackintosh? What machine is it? As the HD 4600 is a mobile iGPU, I presume it's a laptop or NUC or other small form factor system?

Edit: I was wrong. The 4600 is a desktop Haswell iGPU. Sorry!

 

[TechAndOSWorld]

This confirms macOS runs the display at 6bpc RGB.


How is the display connected to the Hackintosh? What machine is it? As the HD 4600 is a mobile iGPU, I presume it's a laptop or NUC or other small form factor system?

There's a DVI connector on the motherboard (Gigabyte Z97-HD3), and the display's plugged directly into that. It's a system my friend built circa 8 years ago. A regular desktop with an i5-4460, just without a dedicated GPU (I don't have a spare Metal GPU, or a PSU to power it).

 

[TechAndOSWorld]

There's a DVI connector on the motherboard (Gigabyte Z97-HD3), and the display's plugged directly into that. It's a system my friend built circa 8 years ago. A regular desktop with an i5-4460, just without a dedicated GPU (I don't have a spare Metal GPU, or a PSU to power it).

update: it seems to be a problem with the monitor after all. tried it with other systems today, and they all have the same banding artifacts