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bug

macrumors regular
Original poster
Feb 2, 2004
188
21
Vancouver, BC
Hi All -

So I recently got an LG 38WK95C-W. This is part of a multi-minotor setup with a Dell U3219Q and a Dell U3417W.

The U3417W is fairly comparable on paper - similar DPI, aspect ratio, and max brightness anyway. Just smaller. ...but it doesn't have this problem....

The problem I have is that any brightness value above about 250 is 'maximum' - so, for example, the RGB colour '250/250/250' is just as white as '255/255/255'. On every other monitor in the house (of which there are many), I can see the '250' value as grey. On this screen if you have a block of white at 250 next to a block of white at 255 it looks like a continuous block (any other screen in the house shows it as very light grey next to white). So it seems like the LG is hitting its max white point too soon. This is not changed at all by any brightness/contrast/gamma/white balance/colour settings. So if you lower the brightness (for example), all white are darker but there's still no variation from 250-255.

As others have noticed, the LG 38WK95C-W is detected by macOS as a TV (in that if you go to 'System Report->Graphics/Displays' it lists with the spec "Television: Yes"). For some people this seems to have the colour space be sent to the screen as YCbCr, although I'm not so sure that is happening here. My reasoning is that I have used the script linked to here (Force RGB Mode) and it correctly created a new EDID for the monitor that is correctly being used (as the monitor now shows up as 'LG HDR WQHD - forced RGB mode (EDID override)'). This didn't actually change the colours at all (although it removed the 'HDR' checkbox, which is fine as that looks like crap on this screen). Also note that the EDID change didn't impact the spec listing of "Television: Yes" in my System Report. I could not find anyone say if I should expect that to change or not.

Also note that the colours seem fine. Other than reaching maximum brightness early, the colours match my other monitors closely. I have no calibration hardware, and I'd be happy to get one if I thought it would solve this problem, but given that the shades look identical regardless of screen settings I'm not sure that will help.

Generally this monitor is driven by a 2018 Mac Mini (Catalina 10.15.4) with a 5700XT in an eGPU, but I have tested it directly connected to the Mini, to a MacBook, and to a MacBook Pro. It is identical in all cases. I've used a USB-C cable, an HDMI cable, and a Displayport cable (multiple of each in fact). No change.

To be clear, the resolution is fine (I mean the DPI isn't amazing but it is what it is and I knew what I was getting into there - that's why I have the U3219Q if I need to see it in 4K).

So -

Any feedback? Are LGs just kinda like that? Is there somewhere I can look to definitively see what colour space is being used?

...ironically I would have just gotten Dell's 38" but I read about macOS problems with that screen and got the LG instead. All else being equal I'd rather have the Dell so it hasn't turned out to be a great decision so far!
 
AB4406A9-D6B1-4B0D-BEA8-5E7507D3F3CE.jpeg


...in case this helps. (service menu)
 
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