Notice of Meeting - Output Transforms Architecture VWG - January 19, 2022

Output Transforms Architecture VWG Meeting

Wednesday, January 19, 2022
1pm Pacific time
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The recording and notes from meeting #38 are now available.


A little post about the flare compensation model used in OpenDRT:

The tonescale function has the following parameters

  • s0 - input domain scale
  • s1 - output domain scale
  • p - power function controlling contrast
  • t0 - toe compression for flare/glare compensation

Here is a graph with just the function. Play with the parameters to get a feel for what they do.

Here is a graph with the model I’ve built to describe a mapping between scene-referred images to display-referred output images. This model is based on my own testing and preferences and can absolutely be modified as deemed necessary.

The flare compensation is defined in the model as t_{0}=\frac{1}{L}, where L = display peak luminance. This simple relationship seemed to describe well the amount of flare compensation required as display peak luminance increased (at least on my single hdr display device). This puts flare compensation for SDR at 0.01, which is pretty strong. Feel free to modify as deemed necessary.

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Thanks for the details, thinking through the flare compensation in real display environments; we should consider the impact of the surround as well as what the effect of power budget in HDR devices resulting in limited capabilities for full screen brightness.

Perhaps we need to also figure out the displays’ own flare and how this interacts (very much a refinement in my book)


The power budget in current HDR devices in an annoying thing and it applies mostly to LCD screens as OLED screens are already rated to a lower peak brightness. You can either grade to 60% of the rated peak brightness or grade to the peak brightness and trust them to do the right thing. I prefer the later option considering that LCD devices rated for peak 1500 nits and sustained 1000 nits are already starting to appear :slight_smile: . Btw, LG OLEDs rated for 600 peak nits do a great job at downmapping content graded for 1200 nits.