@daniele thanks for the details and for the further parameterization
Here is Daniele’s function with the default values at 100 nits, and on a PQ y-axis (to better see the shadows).
Now, let’s add @KevinJW’s “Avg Data” & “Median Data”, as well as “ACESv1 - 100nits”, and “MMDC” (aka the Jed curve used in 3 current test candidates).
With the other curves also plotted, it is clear the default is quite a bit less contrasty than the other 4 curves, both in shadows and highlight rolloff. Therefore, I adjusted some of the values until I got something closer to what I think we’re aiming for:
This is using g = 1.2
to boost overall contrast and t_1 = 0.025
to pull the toe down a bit. I haven’t looked at any pictures with this yet, but from the plots at least, this should look pretty darn close to MMDC.
We can also compare them on log luminance y-axis.
HDR
As we know, ACES v1 is a bit weird because it uses the two part tone scale for SDR and the single-stage tone scale (SSTS) for >100 nit peak luminance. Furthermore, the preset for 108 nits puts mid-gray at 7.2 nits, but the three presets for 1000, 2000, and 4000 nits all set mid-gray at 15 nits - creating a very unclear reasoning for where when and how mid-gray should increase in relation to the peak luminance target. For example, how should one use the SSTS to create an OT for 600 nits? What do I set mid-gray to? None of the curves have a clear relationship. Also the “RRT” (10000 nits) is defined through 4.8 nits, so this also is very confusing.
We know that we want the v2 tone scale to increase mid-gray slightly as peak luminance increases. Both MMDC and Daniele’s curve here have defined a relationship for that and behave well with increased peak luminance. (I adjusted w_g = 0.12
)
Questions
One of the items in the RAE was to be able to describe the origin of all “magic” numbers and parameters.
So can we justify where we put everything for these curves?
- Was it ok to set the gamma higher in order to get it to closer match the other candidates?
- What should be value of flare? Should it correlate to something real or ok to change value in order to bring toe of curve down closer to the other shapes?
- What should be value of w_g?
- Do the
n_r
values of [128, 256, 384] for [100, 1000, 10000] make sense? - Is 18% at 9.901 close enough to our aim of 10 nits? Or do we desire that it hit 10.0 on the dot?
Here are the values for 0.18 and 1.0 compared for various output peak luminance:
100 nits
ACES | Daniele -Tuned | MMDC | ACES v1 |
---|---|---|---|
0.18 | 9.90 | 10.01 | 9.97 |
1.00 | 45.16 | 46.48 | 61.87 |
1000 nits
ACES | Daniele - Tuned | MMDC | ACES v1 |
---|---|---|---|
0.18 | 13.36 | 14.08 | 15.00 |
1.00 | 101.26 | 103.39 | 107.44 |
2000 nits
ACES | Daniele - Tuned | MMDC | ACES v1 |
---|---|---|---|
0.18 | 14.04 | 15.17 | 15.00 |
1.00 | 113.05 | 116.88 | 117.98 |
4000 nits
ACES | Daniele - Tuned | MMDC | ACES v1 |
---|---|---|---|
0.18 | 14.33 | 16.32 | 15.00 |
1.00 | 119.93 | 129.18 | 126.85 |
10000 nits
ACES | Daniele - Tuned | MMDC | ACES v1 |
---|---|---|---|
0.18 | 13.71 | 18.06 | 4.80 |
1.00 | 118.83 | 145.30 | 54.01 |
The big question for the group is “When can we “lock” the tonescale?” (and move on to focusing solely on the blues/reds and highlight rendering, etc.)