MP 7,1 Color Banding Transparencies - DisplayPort vs HDMI?

[dspdoc]

I hope someone can help make sense of this. I called Apple and they didn't know. I've noticed that when using a DisplayPort cable vs HDMI that the transparencies are much smoother. I will post photos to demonstrate. I know that this is expected behavior probably and that nothing is “wrong”, but I want to know the technical reason for it. I have tried 4 different 2560x1440 monitors and they exhibit the same banding over HMDI.

2019 MP Vega II

HDMI: Horrible banding

DisplayPort: Smooth

 

[dspdoc]

Wow. Not one response...

 

[mattspace]

Give it a BIT of time. Might be that HDMI is outputting a limited RGB range to the display over HDMI. Does the display have an option for "HDMI RGB Range" or similar?

 

[dspdoc]

Give it a BIT of time. Might be that HDMI is outputting a limited RGB range to the display over HDMI. Does the display have an option for "HDMI RGB Range" or similar?

No options like that on any of the displays. I agree though; it looks like a limited bit thing. I don't understand why this isn't answered anywhere online though. I guess a lot of people just aren't detail oriented or paying attention.

 

[joevt]

Is the framebuffer pixel format set to 10bpc (ARGB2101010)? See Graphics/Displays in System Information.app. An app like SwitchResX can explicitly change the framebuffer pixel format from 8bpc (millions of colors) to 10bpc (billions of colors) but this does not necessarily change the output pixel format.

What does the AGDCDiagnose command say is being output for pixel format and pixel depth in each case?

The only method macOS gives the user for changing the pixel output format is the HDR setting since HDR requires 10bpc.

It used to be that HDMI 4K60 would output 10bpc 4:2:0 YPbPr but maybe now MacOS is outputting 8bpc 4:4:4? Still, an app can use dithering to remove banding. Take a screenshot. View it using Quick View in the Finder (select the screenshot and press space-bar). Then open the screenshot in Preview.app. I think Preview.app does dithering but Quick View usually does not.

 

[dspdoc]

Is the framebuffer pixel format set to 10bpc (ARGB2101010)? See Graphics/Displays in System Information.app. An app like SwitchResX can explicitly change the framebuffer pixel format from 8bpc (millions of colors) to 10bpc (billions of colors) but this does not necessarily change the output pixel format.

What does the AGDCDiagnose command say is being output for pixel format and pixel depth in each case?

The only method macOS gives the user for changing the pixel output format is the HDR setting since HDR requires 10bpc.

It used to be that HDMI 4K60 would output 10bpc 4:2:0 YPbPr but maybe now MacOS is outputting 8bpc 4:4:4? Still, an app can use dithering to remove banding. Take a screenshot. View it using Quick View in the Finder (select the screenshot and press space-bar). Then open the screenshot in Preview.app. I think Preview.app does dithering but Quick View usually does not.

 

[dspdoc]

You can clearly see the color banding of the desktop through the transparency of Safari even in a screenshot. This is using HDMI. When using DisplayPort this is a non-issue.

 

[dspdoc]

There you can clearly see where the drop shadow is not rendering smoothly. That occurs on an Asus ProArt display.

 

[mattspace]

No options like that on any of the displays. I agree though; it looks like a limited bit thing. I don't understand why this isn't answered anywhere online though. I guess a lot of people just aren't detail oriented or paying attention.

macOS outputting RGB-limited over HDMI is a WELL documented problem. I don't know if it's contributing, but, part of your problem might also be down to the display itself only being an 8-bit panel.

27" Asus PA278QV - Specifications

Specifications of Asus PA278QV. Display: 27 in, IPS, W-LED, 2560 x 1440 pixels, Viewing angles (H/V): 178 ° / 178 °, Brightness: 350 cd/m², Static contrast: 1000 : 1, Dynamic contrast: 100000000 : 1, Refresh rate: 49 Hz - 75 Hz, sRGB: 100 %, Dimensions: 615 x 372 x 51 mm, Weight: 4.96 kg.

www.displayspecifications.com

 

[dspdoc]

macOS outputting RGB-limited over HDMI is a WELL documented problem. I don't know if it's contributing, but, part of your problem might also be down to the display itself only being an 8-bit panel.

27" Asus PA278QV - Specifications

Specifications of Asus PA278QV. Display: 27 in, IPS, W-LED, 2560 x 1440 pixels, Viewing angles (H/V): 178 ° / 178 °, Brightness: 350 cd/m², Static contrast: 1000 : 1, Dynamic contrast: 100000000 : 1, Refresh rate: 49 Hz - 75 Hz, sRGB: 100 %, Dimensions: 615 x 372 x 51 mm, Weight: 4.96 kg.

www.displayspecifications.com

I didn't know about the HDMI limitation. I bet that's it!