Backlight and gamma problems with Lenovo Ideapad L340

vertesian · 2021-08-14 16:13:47

I got a Lenovo Ideapad L340 recently and installed Arch Linux on it, but the backlight controls weren't working, and the default gamma made the screen look reddish-yellow. Here's all the hopefully relevant information:

- X failed to start with the Nouveau drivers, so I'm using the Nvidia drivers. I'm using awesomewm, and starting it directly from .xinitrc without a display manager.

- After some experimentation, I can get decent colors with

xrandr --output DP-0 --gamma 0.85:0.90:1

...but it's clearly not perfect.

- Running nvidia-settings resets the colors to the reddish-yellow on exit, but I'm not sure why.

- I don't have access to a colorimeter or any calibration devices. I couldn't find an ICC profile on the Lenovo support website (unless it's hidden in an exe somewhere) but after following a recommendation from another thread, I found an ICC profile here. But, applying it with xcalib makes it reset to the reddish-yellow again. Which is very confusing, and makes me wonder if something else is wrong other than the monitor calibration.

- I don't have redshift or anything that should automatically change the gamma installed.

- On the brightness front, changing 'acpi_video0' manually or via brightnessctl doesn't seem to affect anything. Setting 'acpi_backlight=vendor' in the kernel parameters replaced acpi_video0 with a device called 'ideapad' of class 'backlight', which I thought was progress, but doesn't do anything either.

- Separately, though it's not super important for me, the keyboard backlight doesn't display in brightnessctl, and I can't find it anywhere else. The controls for the caps lock and scroll lock LEDs show up, so I'm assuming the keyboard backlight should to, but it doesn't.

I'm not sure what to do from here, it's all very confusing.

seth · 2021-08-14 18:21:10

Those tools all operate on the same gamma ramps, so their interference isn't unexpected.
I'm not sure what you mean by "reddish-yellow", but according to https://laptopmedia.com/de/review/lenov … carefully/ the panel has a slight blue/green bias (as most consumer displays because that makes them look brighter and more appealing to idiots in shopping malls) - your perception of what are the "correct" colors might be wildly biased by some even worse example that you're using as a reference?
sRGB is much "redder" than you (and most people) probably think it is and the ICC profile you found is likely correct. If you want a definitive answer, you'll need a colorimeter, it's impossible to judge this over the internet.

Anyway, you can set the gamma values through some xorg configlet in /etc/X11/xorg.conf.d/

Section "Monitor"
    Identifier "DP-0"
    Gamma 0.85 0.9 1.0
EndSection

but because this is a server property, all tools (xcalib, xrandr, nvidia-settings, redshift …) will operate on the same values and impact this accordingly (it's essentially the same as calling your xrandr command automagically w/ the server start)

About the backlight:
Can you control the backlight through /sys/class/backlight/acpi_video0/brightness ?
https://wiki.archlinux.org/title/Backlight#ACPI

The keyboard might require some vendor specific WMI, but this is very model specific. Have you asked google about this?
The caps/scroll and num LEDs are different from that, but you can try whether "xset -led <n>" resp. "xset led <n>" can toggle the keyboard backlight (<n> in [1-32])

vertesian · 2021-08-14 18:50:49

seth wrote:

Those tools all operate on the same gamma ramps, so their interference isn't unexpected.
I'm not sure what you mean by "reddish-yellow", but according to https://laptopmedia.com/de/review/lenov … carefully/ the panel has a slight blue/green bias (as most consumer displays because that makes them look brighter and more appealing to idiots in shopping malls) - your perception of what are the "correct" colors might be wildly biased by some even worse example that you're using as a reference?
sRGB is much "redder" than you (and most people) probably think it is and the ICC profile you found is likely correct. If you want a definitive answer, you'll need a colorimeter, it's impossible to judge this over the internet.

I wasn't surprised they interfered with each other, I was surprised that the default was so off. (That said, on reflection, it's probably just resetting the gamma to 1.)

But it's definitely off, it's not a subtle color difference, it's visibly yellow even without comparing it to another screen.

That said, I did some more testing, and you might be right. The ICC profile doesn't change the color as visibly as the factory settings, so maybe that really is how it's supposed to look? I'll try it out for a while, but it still feels too red at the moment.

seth wrote:

About the backlight:
Can you control the backlight through /sys/class/backlight/acpi_video0/brightness ?
https://wiki.archlinux.org/title/Backlight#ACPI

No, /sys/class/backlight/acpi_video0/brightness doesn't affect the brightness. But, if I set "acpi_backlight=vendor" in the kernel parameters, /sys/class/backlight/acpi_video0/ goes away and /sys/class/backlight/ideapad/ appears instead. I thought that might do something, but it doesn't affect the brightness either.

seth wrote:

The keyboard might require some vendor specific WMI, but this is very model specific. Have you asked google about this?
The caps/scroll and num LEDs are different from that, but you can try whether "xset -led <n>" resp. "xset led <n>" can toggle the keyboard backlight (<n> in [1-32])

Oh, sorry, I figured it out, you just need to press Fn + Space. I hadn't thought about looking it up before since I was distracted by everything else -- my bad.

seth · 2021-08-14 22:13:49

The change you apply would kinda move it from 6500K towards 9300K…
If you have white™ paper (higher density is typically better) you can move the notebook outside (you need daylight, ideally at noon and no clouds), make the output display white (#ffffff) and compare it directly to the paper.

The panel is TN (so the view angle matters a lot!) and probably has no rgb backlight but pseudo-white LED and a distribution foil.
If the LED is off (it's actually blue with yellow phosphor coating and the amount of phosphor will define its temperature - more phosphor makes it more yellow and "warmer") or the foil has a tint, you could end up w/ a bad instance below 6500K.

Try to add /usr/share/X11/xorg.conf.d/20-nvidia.conf

Section "Device"
    Identifier "Default nvidia Device"
    Driver "nvidia"
    Option "RegistryDwords" "EnableBrightnessControl=1"
EndSection

and see wether that allows you to control the backlight (though it's supposed to be enabled by default)

I assume Fn+F11 / F12 doesn't control the backlight bypassing the OS either?

vertesian · 2021-08-16 10:15:35

Yeah, I definitely think the backlight is part of the gamma problems. I already did the RegistryDwords thing, and no, unless there's some combination of keys or something that I'm missing, the Fn keys don't affect the backlight either.

seth · 2021-08-16 14:58:57

Those should be meaningful options:

acpi_backlight=video # you had this 
acpi_backlight=vendor # and apparently this to w/o success
acpi_backlight=native
acpi_backlight=none

The model comes up a lot when googled along "backlight", so this seems a systematic issue
Is the backlight on full steam and can you control it w/ the keys eg. in the UEFI?

Arch Linux

#1 2021-08-14 16:13:47

Backlight and gamma problems with Lenovo Ideapad L340

#2 2021-08-14 18:21:10

Re: Backlight and gamma problems with Lenovo Ideapad L340

#3 2021-08-14 18:50:49

Re: Backlight and gamma problems with Lenovo Ideapad L340

#4 2021-08-14 22:13:49

Re: Backlight and gamma problems with Lenovo Ideapad L340

#5 2021-08-16 10:15:35

Re: Backlight and gamma problems with Lenovo Ideapad L340

#6 2021-08-16 14:58:57

Re: Backlight and gamma problems with Lenovo Ideapad L340

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