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True Tone problem on external display with 2018 MBP

J

jaredm1

macrumors regular
Original poster
Jun 27, 2009
121
54
Bucks, UK
I just upgraded from a 2012 to 2018 MBP. I have an external display (LG 34UC97) that uses ThunderBolt 2 and I bought an Apple TB2->USB-C adapter.

I'm experiencing some kind of colour anomaly that is making my eyes go funny. When browsing some websites I see bits of text in red and other bits in blue (when they should be black).

Attached is a screenshot taken on my phone of a recent HN thread (https://news.ycombinator.com/item?id=17634547) but it happens on other sites too.

I'm running the same version of MacOS on both laptops (latest High Sierra from AppStore) and the display continues to work on my 2012 MBP without these issues.

The issue is resolved by unchecking 'True Tone Display' for the built-in display in Display Settings. Is there any way to have True Tone enabled only for the built-in display and not the external one? Also, I've checked that Night Shift is disabled on the external display.
 

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Reported this to Apple - waiting to hear back from engineering (should take 3-5 days they say).
 
jaredm1 said:
I just upgraded from a 2012 to 2018 MBP. I have an external display (LG 34UC97) that uses ThunderBolt 2 and I bought an Apple TB2->USB-C adapter.

I'm experiencing some kind of colour anomaly that is making my eyes go funny. When browsing some websites I see bits of text in red and other bits in blue (when they should be black).

Attached is a screenshot taken on my phone of a recent HN thread (https://news.ycombinator.com/item?id=17634547) but it happens on other sites too.

I'm running the same version of MacOS on both laptops (latest High Sierra from AppStore) and the display continues to work on my 2012 MBP without these issues.

The issue is resolved by unchecking 'True Tone Display' for the built-in display in Display Settings. Is there any way to have True Tone enabled only for the built-in display and not the external one? Also, I've checked that Night Shift is disabled on the external display.
Click to expand...

I experienced this issue too..I thought it was my display cable. it would be good to hear an update from you when the engineers get back to you.
 
This is because of the nature of the display, and also because of a process called subpixel rendering. To render text entirely black would result in extremely blocky looking text, especially so on low pixel density monitors. Pixels are not 3 colors on top of each other, they are 3 separate areas of color. Due to chance of text, you could have an "i" show up on just a blue portion and a red portion of a "pixel" It's somewhat hard to explain, but if you're interested in getting very technical, then google subpixel rendering. By the way it becomes less of a problem on high pixel density displays, which is why text looks so clean on retina macbooks
 
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christarp said:
This is because of the nature of the display, and also because of a process called subpixel rendering. To render text entirely black would result in extremely blocky looking text, especially so on low pixel density monitors. Pixels are not 3 colors on top of each other, they are 3 separate areas of color. Due to chance of text, you could have an "i" show up on just a blue portion and a red portion of a "pixel" It's somewhat hard to explain, but if you're interested in getting very technical, then google subpixel rendering. By the way it becomes less of a problem on high pixel density displays, which is why text looks so clean on retina macbooks
Click to expand...

Do you have any idea why different cables might cause this issue though? When I used my USB-C to displayport cable, I noticed this happening, but when I use just an HDMI cable plugged into my USB-C hub, the problem goes away. Seems kind of strange to me that the subpixel rendering phenomena only appears with the use of a certain cable. I'm using the same display, same computer, but different cable with different results.
 
Last edited:
joshi3joshi said:
Do you have any idea why different cables might cause this issue though? When I used my USB-C to displayport cable, I noticed this happening, but when I use just an HDMI cable plugged into my USB-C hub, the problem goes away. Seems kind of strange to me that the subpixel rendering phenomena only appears with the use of a certain cable. I'm using the same display, same computer, but different cable with different results.
Click to expand...
That is odd, my best guess is some sort of hardware difference in how the signals are interpreted inside the monitors hardware, but that’s something that’s more above my head. Sorry!
 
HDMI inputs are often processed differently by displays, as the presumption is that hdmi output is 'video' output and displayport/dvi output is 'monitor' output, usually this is seen as a slightly softer picture on HDMI, which is probably what's hiding the artefacts.
 
jaredm1 said:
I just upgraded from a 2012 to 2018 MBP. I have an external display (LG 34UC97) that uses ThunderBolt 2 and I bought an Apple TB2->USB-C adapter.

I'm experiencing some kind of colour anomaly that is making my eyes go funny. When browsing some websites I see bits of text in red and other bits in blue (when they should be black).

Attached is a screenshot taken on my phone of a recent HN thread (https://news.ycombinator.com/item?id=17634547) but it happens on other sites too.

I'm running the same version of MacOS on both laptops (latest High Sierra from AppStore) and the display continues to work on my 2012 MBP without these issues.

The issue is resolved by unchecking 'True Tone Display' for the built-in display in Display Settings. Is there any way to have True Tone enabled only for the built-in display and not the external one? Also, I've checked that Night Shift is disabled on the external display.
Click to expand...

Just an update on this: I fixed my problem by following the instructions here: http://www.mathewinkson.com/2013/03...-quality-of-an-external-monitor#comment-15886

Don't know exactly the technical details behind why this works, but I followed the instructions, and my dell u2717d is pretty much fixed because of this now.
 
I had the same problem with my new MBP and my Dell U2515H external display but only when connected with a DP or mDP cable. With a cheap HDMI 1.4 cable everything looks fine and True Tone is working on both the built in display and the Dell monitor

My setup is: MBP -> TB3 to TB2 adapter -> OWC TB2 dock -> HDMI/DP/mDP to monitor
 
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