High saturation primaries

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(Charles Boileau) #1

Hi to all,

We love the way ACES maps colors for our desired output. But sometimes it gets a bit funky looking!

I’m sure that we’re not the only one who noticed that certain primary colors tend to go a bit “electric” looking in ACEScc. I’m thinking red lipstick, Blue sweaters etc… (not the weird LED color clipping we already have an LMT for that).

Our approach to this is to add qualifiers and keys to tone these down. But, I was wondering if there’s anyone out there who has a CTL (or DCTL) to tone these down in a more “mathematical” manner.

Would this be even possible to do?


(Charles Boileau) #2

No one has any thing to contribute to this?

(Francois Lord) #3

Salut Charles,

Do you have any visual example of what you’re talking about?


(Charles Boileau) #4

I was under the impression that everyone noticed this. But Yes I could send some examples…

(Jim Houston) #5

Holiday weekend in the U.S.!

Yes, a matrix could be used on a problem shot. In essence, using a mapping from the AP1 primaries to a lesser
set of primaries. Red was already de-saturated to a modest degree in the RRT. A correction can be awkward in some shots because they might desaturate colors in shadows or faces a bit too much. So then you can start considering blending in a correction for a certain range of color or luminance. Sorry that this is a bit vague, but all I could describe at the moment for a potential image problem I haven’t seen.

(Charles Boileau) #6

How could such a matrix be built?

I’m still working on some examples.


(Oskar Larsson) #7

I really really wish there will be a permanent fix to this issue soon, but in the meantime, maybe the .ctl provided by Scott Dyer in this thread can help us:

I´d like to point out that it´s not only super saturated blues that have this issue, but also reds.

(Charles Boileau) #8

The issue that you’re referring to is totally different from what I’m mentioning here. I just feel that certain colors sometime feel a little bit “video” in ACES.

(Oskar Larsson) #9

Sorry, when reading your original post again I saw that you mentioned the LMT fix for the issue I thought you meant.

Examples of what you´re reffering too would be great, as others already pointed out.


(Charles Boileau) #10

I’m waiting after my colleague who’s busy working on a very colored movie (for which I hope he’ll give me some great examples).

(Jim Houston) #11

Hi Charles,

This is similar to what Scott did for the purple artifacts. (see his Nov 16 note in the color artifacts thread) You can create a matrix that ‘shrinks’ the color space available --oddly enough consider using a virtual set of primaries that are wider than AP1 and using the same white point. So just construct a standard transform matrix from AP1 to PX, then apply it in AP1 and treat the result as AP1. [works for modest displacements]. Note that you can play with the off-diagonal axis terms of a matrix to adjust RedxBlue for example, but the results have to be normalized and tweaked by eye. This is a bit risky.

The problem is a bit different than the artifacts referenced in Oscars note, partly caused by any set of primaries (ACES, Rec2020) that are perceptually out of balance
and then have a contrast building tone curve applied. The tone curve boosts the color contrasts as well as the luminance, and when red is perceptually twice as far out as before, you can get ‘electric’ reds. (or blues)
This was only partly addressed by some fixes in the RRT. (selective red desat and the ‘glow’ operation targeting a P3 look)

The group has thought about other ways to fix this, but don’t have a recommendation right now.


(Charles Boileau) #12

Yes that was what I was thinking (have a tool likes scott’s). But I have no idea how I would go about doing this… I guess I’ll have to wait for more people to get involved with ACES.