[GH-ISSUE #559] Software dimming function resets to full brightness a few seconds after adjusting. #420

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opened 2026-05-05 05:58:10 -06:00 by gitea-mirror · 2 comments

gitea-mirror commented

2026-05-05 05:58:10 -06:00

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Originally created by @giulianofichera on GitHub (Sep 3, 2021).
Original GitHub issue: https://github.com/MonitorControl/MonitorControl/issues/559

Originally assigned to: @waydabber on GitHub.

Before opening the issue, have you...?

Searched for existing issues
Looked through the wiki
Updated MonitorControl to the latest version (if applicable)

Describe the bug

When enabling software dimming for an HDMI TV (connected through a USB C hub) the TV dims accordingly but suddenly returns to full brightness.
This bug occurs sooner when my mouse changes display, I click something or I move the mouse rapidly.
Even without performing any action, the TV returns to full brightness inevitably.
I have tried all possible settings combinations: changing the brightness using the keyboard, the software slider, changing the brightness for all screens and also independently.
Also tried a reboot, reinstall, reinstall + reboot, unplugging and plugging the usb hub.

Steps to reproduce

Enable software dimming if required option.
Change brightness (using the keyboard shortcuts or the menu bar slider).
Move the mouse between screens to speed up the bug reproduction, or simply wait for it to happen some seconds after without any intervention.

Expected behavior

The software brightness adjusts itself accordingly and remains in the desired brightness level until changed.

Anything else?

https://user-images.githubusercontent.com/80286668/132044342-9ae1b5ff-ba66-4d05-b194-b4f1aa9a0bf2.mp4

Environment Information (please complete the following information)

- macOS version: 11.5.2 Big Sur
- Mac model: MacBook Air (M1, 2020)
- MonitorControl version: 3.0.0 Build 3095
- Monitor(s): Philco Pld50us9a1 4k
- Apple Silicon/M1 (yes or no): yes

- USB C Hub used: Anker (https://www.amazon.com/Anker-PowerExpand-Adapter-Delivery-Ethernet/dp/B087QZVQJX/ref=sr_1_5?dchild=1&keywords=anker+usb+c+hub&qid=1630689207&sr=8-5)

Originally created by @giulianofichera on GitHub (Sep 3, 2021). Original GitHub issue: https://github.com/MonitorControl/MonitorControl/issues/559 Originally assigned to: @waydabber on GitHub. ### Before opening the issue, have you...? - [X] Searched for existing issues - [X] Looked through [the wiki](https://github.com/MonitorControl/MonitorControl/wiki) - [X] Updated MonitorControl to the latest version (if applicable) ### Describe the bug When enabling **software** dimming for an HDMI TV (connected through a USB C hub) the TV dims accordingly but suddenly returns to full brightness. This bug occurs sooner when my mouse changes display, I click something or I move the mouse rapidly. Even without performing any action, the TV returns to full brightness inevitably. I have tried all possible settings combinations: changing the brightness using the keyboard, the software slider, changing the brightness for all screens and also independently. Also tried a reboot, reinstall, reinstall + reboot, unplugging and plugging the usb hub. ### Steps to reproduce 1. Enable software dimming if required option. 2. Change brightness (using the keyboard shortcuts or the menu bar slider). 3. Move the mouse between screens to speed up the bug reproduction, or simply wait for it to happen some seconds after without any intervention. ### Expected behavior The software brightness adjusts itself accordingly and remains in the desired brightness level until changed. ### Anything else? https://user-images.githubusercontent.com/80286668/132044342-9ae1b5ff-ba66-4d05-b194-b4f1aa9a0bf2.mp4 ### Environment Information (please complete the following information) ```markdown - macOS version: 11.5.2 Big Sur - Mac model: MacBook Air (M1, 2020) - MonitorControl version: 3.0.0 Build 3095 - Monitor(s): Philco Pld50us9a1 4k - Apple Silicon/M1 (yes or no): yes - USB C Hub used: Anker (https://www.amazon.com/Anker-PowerExpand-Adapter-Delivery-Ethernet/dp/B087QZVQJX/ref=sr_1_5?dchild=1&keywords=anker+usb+c+hub&qid=1630689207&sr=8-5) ```

gitea-mirror closed this issue

2026-05-05 05:58:11 -06:00

gitea-mirror commented

2026-05-05 05:58:15 -06:00

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@waydabber commented on GitHub (Sep 3, 2021):

It seems like the gamma table is being reset for some reason immediately after changing it. The fact that it happens upon some activity is because on most macs gamma table changes are not reflected on the screen unless there is an event that causes some part of the screen to redraw. This is why you need to move the mouse or do something else that changes something on the screen and then the brightness is changed back to full.

Don't you use any other software that does gamma table manipulation? Maybe some screen management app or anything else that changes the displays, gamma, tint, etc of the display (like f.lux)?

@waydabber commented on GitHub (Sep 3, 2021): It seems like the gamma table is being reset for some reason immediately after changing it. The fact that it happens upon some activity is because on most macs gamma table changes are not reflected on the screen unless there is an event that causes some part of the screen to redraw. This is why you need to move the mouse or do something else that changes something on the screen and then the brightness is changed back to full. Don't you use any other software that does gamma table manipulation? Maybe some screen management app or anything else that changes the displays, gamma, tint, etc of the display (like [f.lux](https://justgetflux.com))?

gitea-mirror commented

2026-05-05 05:58:18 -06:00

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@waydabber commented on GitHub (Sep 4, 2021):

Hi, I looked at the Anker device in more detail. It seems like the HUB is using some kind of compressed video streaming technology (marketed as 'Anker Media Display') to achieve 4K@60Hz via the HDMI port alongside USB3 speeds and gigabit ethernet. Or maybe uses chrome subsampled HDMI (?). Otherwise the standard 10GB bandwidth of USB-C would only allow USB2 speeds alongside full uncompressed 4K video at 60Hz. An other option is that maybe it uses the new DisplayPort 1.4 HBR3 internally and then converts the signal to HDMI, which theoretically could allow for the use of only two displayport lanes and still have room form USB 3+ speeds for the other ports. Since some kind of wizardry going on here, it might be possible that this interferes with the way how macOS handles gamma tables.

You might want to try changing the color calibration using the expert mode of the built in calibration tool and see how that works and if the issue persists with a custom calibration applied.

I also recommend trying a simple native USB-C to HDMI adapter to see if you have the same problem with that.

I'll convert this issue to a discussion as it might result to conclusions beneficial to others as well. Hopefully more info will come to light.

@waydabber commented on GitHub (Sep 4, 2021): Hi, I looked at the Anker device in more detail. It seems like the HUB is using some kind of compressed video streaming technology (marketed as 'Anker Media Display') to achieve 4K@60Hz via the HDMI port alongside USB3 speeds and gigabit ethernet. Or maybe uses chrome subsampled HDMI (?). Otherwise the standard 10GB bandwidth of USB-C would only allow USB2 speeds alongside full uncompressed 4K video at 60Hz. An other option is that maybe it uses the new DisplayPort 1.4 HBR3 internally and then converts the signal to HDMI, which theoretically could allow for the use of only two displayport lanes and still have room form USB 3+ speeds for the other ports. Since some kind of wizardry going on here, it might be possible that this interferes with the way how macOS handles gamma tables. You might want to try changing the color calibration using the [expert mode of the built in calibration tool](https://osxdaily.com/2015/10/14/access-expert-mode-screen-color-calibrator-mac-os-x/) and see how that works and if the issue persists with a custom calibration applied. I also recommend trying a simple native USB-C to HDMI adapter to see if you have the same problem with that. I'll convert this issue to a discussion as it might result to conclusions beneficial to others as well. Hopefully more info will come to light.