Screen changes brightness on boot up

[gbf]

I have 2 macs. One iMac and the other a MacBook Pro 14 inch.

Since I’ve gotten both I’ve noticed that when you boot them up after you login screen it seems to change the brightness of the screen. It’s weird it goes bright then “dimmer”. It’s weird.

Anyone else notice this and no why it does this?

 

[scottrichardson]

Yes! I notice this on my 2020 i9 iMac with file vault enabled.

What I believe is happening is that the display is not using the correct colour profile during initial startup. And because the screen is actually a very wide-gamut P3 display, it's just loading the desktop wallpaper and messing the colour balance up, displaying all the colours too far into the saturated ends of the gamut provided by the P3 spectrum.

Once the system fully boots, the correct profile loads for the display.

Hope that makes sense? I could be wrong but it seems the most logical.

In other words, when its super vivid at the initial startup, it's showing colours at the most extreme saturation before correctly showing the colours at the saturation they are meant to be.

 

[gbf]

You’re amazing! Thank you. What is that FileVault? Is it needed?

 

[Gudi]

You’re amazing! Thank you. What is that FileVault? Is it needed?

Yes it is. Forget it, it has nothing to do with your display.

Several things alter your screen brightness. True Tone, Auto-Brightness (via the ambient light sensor) and when you unplug your MacBook from power cable, it automatically goes a bit dimmer to save battery life. All these effects are purposefully intended.

 

[scottrichardson]

Yes it is. Forget it, it has nothing to do with your display.

Several things alter your screen brightness. True Tone, Auto-Brightness (via the ambient light sensor) and when you unplug your MacBook from power cable, it automatically goes a bit dimmer to save battery life. All these effects are purposefully intended.

In the case of an iMac/desktop, when FileVault is enabled, the system only boots so far before the login screen appears. This is actually different to when FileVault is off. More things load into system memory before the login screen appears, including colour profiles for the display. But with FileVault enabled, only the minimum system parts are loaded into memory before the login screen to ensure full data security. The user's login must be entered successfully to unlock FileVault, and after that is when it loads the correct display profiles for your Mac.

 

[Gudi]

In the case of an iMac/desktop, when FileVault is enabled, the system only boots so far before the login screen appears. This is actually different to when FileVault is off. More things load into system memory before the login screen appears, including colour profiles for the display. But with FileVault enabled, only the minimum system parts are loaded into memory before the login screen to ensure full data security. The user's login must be entered successfully to unlock FileVault, and after that is when it loads the correct display profiles for your Mac.

Okay.

But he still shouldn't try to get rid of FileVault.

 

[scottrichardson]

Okay.

But he still shouldn't try to get rid of FileVault.

He should definitely keep FileVault. It's a good feature.