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They’re not dimming the SDR content. It is an optical illusion. The HDR white is actually a lot brighter than the SDR white (which means the LEDs behind those

by alin23 5y ago

They’re not dimming the SDR content. It is an optical illusion. The HDR white is actually a lot brighter than the SDR white (which means the LEDs behind those pixels are allowed to go to full brightness). You can see that effect if you watch this video in Safari on a 2021 MacBook Pro: https://files.alinpanaitiu.com/hdr-test-pattern.webm https://files.alinpanaitiu.com/hdr-test-pattern.webm Here's an article where the nits value is measured using a calibration device: https://www.notebookcheck.net/The-new-MacBook-Pro-14-only-manages-500-nits-with-SDR-contents.575327.0.html https://www.notebookcheck.net/The-new-MacBook-Pro-14-only-ma... The measurement shows that SDR content goes up to 500 nits (which was the peak value of previous MacBook displays as well) while HDR content goes up to 1607 nits.

fulafel 5y ago
If we have a monitor that has a brightness of 1600 nits, and whites of some content ("sdr") shows up much dimmer, the pixels the monitor is asked to display by the systmes are dimmed relative to max brightness - no?
- alin23 5y ago
  Yes, that’s another way of putting it. But people usually look at this, relative to previous displays, not relative to peak brightness (since the peak brightness is not achievable for prolonged periods of time because of overheating)
  - fulafel 5y ago
    Overheating sounds interesting! So what happens if you display a max brightness hdr image on the screen for a long time, does the monitor shut off? Edit: apparently at least on some laptops your screen may automatically adjust brightness downwards if you are in a hot climate and the cooling system fails to keep up: https://9to5mac.com/2022/02/04/macbook-pro-limited-brightness-pro-display-xdr/ https://9to5mac.com/2022/02/04/macbook-pro-limited-brightnes...
    - alin23 5y ago
      Yes, the system monitors the display temperature and caps the brightness accordingly. Here are some interesting functions I found related to this inside the system frameworks: SkyLight.framework: SLSDisplayIsThermallyLimited CoreBrightness.framework -[CBDisplayModuleSKL hasThermalMitigation] -[CBThermalBrightnessCap getCurrentCap] -[CBThermalBrightnessCap setJetMode:]

by alin23 5y ago

fulafel 5y ago

If we have a monitor that has a brightness of 1600 nits, and whites of some content ("sdr") shows up much dimmer, the pixels the monitor is asked to display by the systmes are dimmed relative to max brightness - no?

alin23 5y ago
Yes, that’s another way of putting it. But people usually look at this, relative to previous displays, not relative to peak brightness (since the peak brightness is not achievable for prolonged periods of time because of overheating)
- fulafel 5y ago
  Overheating sounds interesting! So what happens if you display a max brightness hdr image on the screen for a long time, does the monitor shut off? Edit: apparently at least on some laptops your screen may automatically adjust brightness downwards if you are in a hot climate and the cooling system fails to keep up: https://9to5mac.com/2022/02/04/macbook-pro-limited-brightness-pro-display-xdr/ https://9to5mac.com/2022/02/04/macbook-pro-limited-brightnes...
  - alin23 5y ago
    Yes, the system monitors the display temperature and caps the brightness accordingly. Here are some interesting functions I found related to this inside the system frameworks: SkyLight.framework: SLSDisplayIsThermallyLimited CoreBrightness.framework -[CBDisplayModuleSKL hasThermalMitigation] -[CBThermalBrightnessCap getCurrentCap] -[CBThermalBrightnessCap setJetMode:]