Hi Everyone,
I bought this week a new LG40WP95C , to replace my old mate iMac5K 2014, and wanted to connect on my light MacBook Air M1 (2020). Like everyone around, I was struggling with 5k2k support on such Macbook, and after a couple of time reading the posts, and did myself a bit a research and it turns out that things are more simple to understand that we think... there is no magic / obscure resolution choices ... it is just math.
First of all, let's start with obvious information :
- the LG40WP95C has a native resolution of 5120x2160 , which is named 5k2k , with a ratio of 21,4:9 ( = 2,37 ratio )
- compared to resolutions that Apple prefers like the Studio Display 5k ( 5120x2880 , ratio 16:9 = 1,77 ) and XDR 6k ( 6016 x 3384 , ratio 16:9 = 1,77 )
- things would be better if the LG was also 2880 vertical resolution ... anyway, it is not the case today.
That means:
- this LG will never support native resolution of the Studio Display , due to the ratio / vertical amount of pixels
- it is not a good idea to try to send more pixel to the panel, thinking it will "increase the quality" ... this panel is physically 5120x2160, panel board is designed for the correct amount of pixels , period.
About the Macbook M1 ... looks like people are confused with others result/posts, because of the M1 model tested (or not mentioned):
- Standard M1 ( like MacBook Air M1 2020 ) supports 2560 x 1600 native pixels on internal display and
one 6k 60Hz
over Thunderbolt 3 ( native USB-C DisplayPort ) -- well , in reality it can provide 72Hz too ( my LG receives correctly 72Hz, which is cool for smoother moves )
- M1 Pro ( like MacBook Pro 14 ) support 3024 x 1964 native pixels on internal display and
two 6k 60Hz over
Thunderbolt 4
- M1 Max ( like MacBook Pro 14 ) support 3024 x 1964 native pixels on internal display and
three 6k 60Hz over +
one 4K 60Hz over
Thunderbolt 4
- I let you check the MacBook Pro 16 , Studio ...
What does it means ?
- First , M1 has a thunderbolt interface with less bandwidth ( TB3 ) than M1 Pro/Max ( TB4 ) , so you can expect less pixels potential been sent to the external display (I do not argue on pixel compressions send over TB if there is any btw) , that's why you can only connect one 6k display btw ... but well, does it matter for the LG which is a 5k2k ? ... no.
- Second, M1 vs M1 Pro/Max don't have the same internal display buffer size to compute the screens. There is a simple rule hidden into the specs ... the buffer won't exceed what the MacBook can output to its internal display and the external display ... so it is obvious that M1 Pro/Max have bigger buffer to handle higher internal resolutions and external displays ...
Last, the HIDPI ( or scaling ) , it is Apple choice to increase the display (retina) readability by doubling the artifacts / fonts , so you benefits of high resolution screen ... by default, they use half the size of the real resolution...
So the graphical interface (UI) mention a resolution half of your screen size ( if you check the system report , while screen resolution represents the total size of the display buffer ... ) , then the display is scaled to the screen resolution. And you can scale a bit, but this requires additional compute power ( see small warning when you play with scale, beside the normal "half" resolution choice ).
In the case of the Apple Air M1 , which is native to 2560x1600 , it is by default set to 1680x1050 (scaled), so it won't hurt your eyes
The Low resolution choices just means : straight pixels display without HIDPI User interface artifacts / fonts , resulting mostly on blurry texts if you do not run the native resolution of your screen ...
So, in the case of the LG40WP95C , we have the choices :
- Connect over TB3 ( Macbook M1 ) or TB4 ( Macbook M1 Max / Pro ), with native resolution ( non HIDPI ) resulting of a very small UI and Texts ...
- Connect over HDMI , there you are always blocked to HDMI max bandwidth ( 4k 60 Hz if I'm right )
- Use scaling options ... and by default, due to the 5120x2160 , the default choice is 2560x1080 , which is the "half" scaling resolution.
Not so nice, this resolution makes the screen UI too big, but there is something to notice already :
- native resolution is 5120x2160 ( Ultra Wide 5k) and 72 Hz ... which is confirmed by the LG OSD
Then comes the confusions , depending of your Macbook, you will see additional scaling resolutions ( I won't talk about "low resolution" choices , just the HIDPI ):
The list is based on the following limitations:
- The native resolution ( or physical amount of horizontal pixels ) send to an external display WON'T exceed 6k ( = 6144 pixels ). If you try to send more, you'll get your screen trying to scale down to its own native resolution for nothing, or even flicker / complains ... so never exceed 6k , until apple tells the thunderbolt interface allows more than 6k per screen ...
- The display buffer, which compute the display image ( = it is an internal buffer which pre-draw your screen ) , has a resolution based on the following : twice the size of the normal resolution
- The screen must receive an image which respecte the scale of the native resolution, otherwise it will just show black horizontal or vertical bars, or tries to stretch the image ( if you enable it via OSD ) and you get blurry texts too
I did then a couple of tests with two tools ( SwitchResX and BetterDisplay ) , both has the ability to modify the list of available resolutions ( = custom resolutions ). And I came to the following results, so I recall I have a MacBook Air M1 , so my internal display buffer is certainly smaller that M1 Pro and Max.
- it is important to stay close to the native screen ratio when it comes to send pixels to the TB port, which is 2,37 ( 5120/2160 ) if you want to avoid black vertical or horizontal bars or even more stretch.
- it is important to not unnecessary increase the virtual display buffer by trying exotic high resolution like 10kx4k thinking it will increase the "quality" ... first it is not true, because things are scaled down to the native resolution, second it may consume more memory to pre-compute the images before scaling down
- it is also good to stick close to the screen horizontal resolution ( 5120 ) or the Thunderbolt maximum resolution ( 6144 ) , so less scaling is done ether by the MacBook or the screen board ...
With the LG screen configured like this :
- Input : Thunderbolt
- Image Format : Original Signal ( no stretch )
- Display Port version : 1.4
I end up with this table :
It looks like each time you get out of the 2,27 - 2,37 ratio, the display isn't full screen ( you get black borders ).
So when sticking to resolution ration between those two , you can try tuning the horizontal and vertical pixel counts , so my strategy was to stick on standard horizontal value ( 5120 or 6144 ) then calculate the vertical , based on the ratio value between 2,27 to 2,37 ... to validate this choice, I tried some unusual resolution, trying to increase ether horizontal or vertical, but it turns out that macOS somehow is converging always to the same values ...
So far , for today, I end-up with the following optional choice:
- native resolution : 5120 x 2250 , which gives a HDPI resolution of 3072x1350
which is the maxed choice in horizontal x vertical HDPI I could achieve with the M1 AIR over thunderbolt 3.
Btw it gives exactly the same result has the 6144x2700 which is in fact what the macOS is taking when you ask HDPI 3072x1350 ... and it cap the 6K horizontal limitation, and good news, it remains 72Hz too, while the UI looks adequate for a ultra-wide screen. It's comparable to the HDPI UI size of my old 5k iMac.
my guess is : oversampling won't increase the UI quality or decrease the UI artifacts size , if you go out of the screen ratio, and maximum horizontal resolution sent to the thunderbolt port / max buffer size supported by your Macbook M1.
I think people who get higher HDPI resolution display are only those with M1 Pro/Max because their buffer is bigger to support more screens by default and internal screen has also bigger pixels ... so the UI can computed on bigger internal buffer before been scaled down to 6k before it is sent out over thunderbolt with 6k signal to the LG screen, which certainly does also a 6k to 5k scale down.
I did some try also with the "mirror" dummy display ( if you look more in details into the tool ) , and was able to get smaller UI ... but I didn't investigate too much into this, while I prefer to have only a "simple" resolution tuning than having a complex internal workaround which certainly consume more memory / cpu power to achieve a little bit smaller UI , which is to be honest far good now in 3072x1350.