String due to the community flagging the post as hateful conduct.
[quote=“Thomas Mansencal, post:19, topic:5161, username:Thomas_Mansencal”]
What I did is showing that a basis change, a simple 3x3 matrix, causes that. Again, the ACES 1.x DRT does the same and it is RGB rendering. No need to go down the rabbit hole or 4-dimensional chess game to find an explanation.
[/quote]
1. ACES is a terrific demonstration if one seeks to show that poor design doesn’t work. Nothing more.
2. Did one actually test the claim about per channel?
Here is the basic idea, again. Apologies, perhaps it’s a language barrier?
- Because of On/Off and Off/On neurophysiological signals, polarity matters, specifically at the “null”.
- The combined force of chrominance-luminance is a threshold, where luminance can be broadly correlated to the Protan+Deutan absorptive combination, and the remaining two signals are effectively (Protan+Deutan)-Tritan, and Protan-Deutan, in both On/Off and Off/On variations. (At risk of grotesque oversimplifications.)
- Per channel, devoid of colourimetric transforms, does not induce a polarity flip.
It is perfectly fine to reject the first point, which dismisses all subsequent points.
However, if anyone detects the same cognitive “oddness”, then the premise might hold veracity. Note this is the same general premise that Briggs covers in a video if one wants to see a live demonstration.
Note I am not 100% confident the max(RGB)
is “the” threshold, but I’m leaning toward it being the combined neurophysiological force that correlates with the combined force of chrominance and luminance. I believe this can be shown mathematically as well.
Now, again, if the premise of polarity playing a foundational role in visual cognition, then it can be shown that:
- Per channel mechanics devoid of colourimetric transforms will not exhibit this. This can be tested.
- Colourimetric transforms, by way of a 3x3 matrix can and will exhibit polarity flips.
- All of these glorified luminance-devoid-of-chrominance-contribution mappers will induce a polarity exchange.
Again, folks are free to reject the polarity issue outright. That’s fine. However, if there is a visual result that is indeed cognitively disruptive, then points 2 and 3 are valid concerns.
This isn’t “4 dimensional chess”. It’s actually very basic deductive reasoning by way of removing complexities.
A case in point, I would encourage anyone to distill and reduce the complexities by way of:
- Generate a PBR case where R=G=B at 100% albedo for an ideally reflective surface emulation.
- Set any chromatic textures to the discs that are biased in balance.
- Set the “diffuse source” close to the top of the surface, and render such that the upper most point is 1.0 units, to showcase a “gradation” of the model “light fall off”.
- Render using BT.709 or any working space such at BT.2020, without any colourimetric transforms.
- Apply a simple inverse EOTF to the values for display, or analyse the origin RGB tristimulus colourimetry.
It should reveal that no such polarity “flip” will result where the chromatic discs exceed the “illumination”. The same applies for any monotonic per channel curve.
In terms of visual cognition, zero of the swatch samples will “pop out”.
Again, and I stress, if folks want to reject the literature about polarity, they are free to do so. Move along. Carry on. Nothing to see here! No problem!
If folks have concerns about the polarity, it is worth understanding the various discrete signal processing positions that such polarity errors will manifest, and understand their causation.
The choice is up to the individual.