I would not say so. How did you create your proposed image? If it was a grade in conjunction with the v55 rendering then it is effectively an LMT.
I was certainly able to obtain a similar result with an LMT consisting only of a matrix. The matrix was specific to that shot, but for extreme images like that one, this may frequently be necessary.
Thanks for your answer !
This was not a grade in conjunction with the v55. This is a complete different image formation chain. A similar one than the one I used a year ago for the blue bar.
If you feel this image is an edge case that should be solved on its own with a matrix or such, then we´re good I guess. If you feel like there is more to this example than meets the eye, well maybe we should re-visit a couple of stuff. 
Regards,
Chris
Thanks for your to me sophisticated reply. What I attempted to illustrate is that a ramp between two colors in ACEScg renders pretty ‘wonky’ when starting from a pure blue ramping to pure blue and a bit of equal amount red and green. Shifting aways from that with hue shows that the bumpy road smoothens out in both directions indicating that this undesirable effect only happens somewhere in the blue corner.
What I expect/hope to see is some form of continous change in chrominance and luminance. In my mind it shouldn’t raise, lower, raise again etc. Is that expectation ill informed? It feels like most other DRTs have this reasonably locked down.
At roughly what point can we classify an image to be extreme? Circling back to my initial question:
I created a random CG scene with a pure blue and pure red light lighting a neutral object in Blender. Would this also classify as an extreme image? To me an extreme image in context of ACES’ DRT would be one containing data outside of AP1.
First: v055 (noRGC), rest = bunch of other renderings.
I would love to know/understand why it’s happening in the first place whilst other renderings are smooth(er)?
The “bumpy” is indeed hugely problematic, although it would probably be prudent to pinpoint what the “bumpy” means.
We know that the spatiotemporal articulation will impact the continuity of cognized forms, for example, we can see that the fields interact with each other in a manner similar to magnetic fields.
Given we can’t impact this from the vantage of a per pixel picture formation chain, what we have to be cautious of is making matters worse. That is, this effect is very much related to the energy levels in relationship to the neurophysiological signals.
I suspect the rather foolish idea of a “CAM” or any of the other “UCS” myths are unfortunately bending the energy levels in a way that is exacerbating the problems. This is evident from looking at the “double upped” mountainous region when projecting a balanced wattage / current sweep series away from R=G=B. We can expect all sorts of wild folds and contortions as the metric is bent out of whack with respect to signal energy.
This is a particularly bad thing if it is happening. Polarity is of hyper importance in visual cognition. We know conclusively that polarity modulations from positive to negative yield “lustrous” sensations1. While not exclusive to polarity flip flops, it’s a huge warning flag. Can you show any specific polarity flips in terms of luminance or something “odd” you may have noticed?
It is very likely caused by the many deforming bends and contortions of the Hunt inspired model. It at least seems to be what is fundamentally a quantisation issue, allocating the bits at the formed picture incredibly poorly.
In the end, it feels like the problem surface is effectively one of balancing quantisation against density, and I suspect the legacy of Hunt’s rather bogus ideas around a Colour Appearance Model, which is largely an extension of the “Stimulus-As-Colour” world view propagated by Kodak, is making this problem worse.
I’d be keen to see if this is not the case.
Do you have a demonstration?
It does seem that the demarcation line between “extreme” is somewhat ill defined. Perhaps colourimetry is the problem here?
I have been forwarded these demonstrations, one of which was version 55.
We can of course discuss the complexities of “aligning” two pieces of footage, but I’d hope that the idea of “extreme” is somewhat elusive given that of the above samples, one is a very complex model and the other is literally doing nothing colourimetric to the FPGA quantal energy catch counts, and rolling through a sigmoid from a log encoding.
I suspect that a blind choice would be a no contest, and one of the options is all of about a dozen lines of script?
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1 Many pieces on this subject. This is a reasonable newer summary that is useful from Faul of Ekroll and Faul fame. Wendt, Gunnar, and Franz Faul. “Binocular Luster – A Review.” Vision Research 194 (May 2022): 108008. Redirecting.
I must say I see this type of renderings quite often, meaning incredible saturated colours.
3D artists who worked in a linear sRGB working space for years and years and “suddenly” the software is now ACES, but they punch in the same RGB values in lights and shaders as always.
In your case I assume your red and blue lights in Blender act like a “laser light source” and this is maybe not what the “3D artist” actually intended to do.
I think RGB sliders in ACES-DCCs should have maybe added a “meaning” of the values you put in?
You select a full red and the colorpicker tells you, this color will be even outside of Rec.2020 or so?
In any case I think ACES 2.0 must be able to make sense of AP-1 values and render them without artefacts.
When I look at the blue highlight on the Blender monkey I see the same flip to cyan where should be “pure” blue like in the “star” example some posts above.
All the other renderings seemingly do not hit the blue display primary, right?
I hope there can be a fix for this issue.
That is a reasonable solution for SDR only when you don’t have the requirements we have for the ACES 2.0 transforms. It’s essentially what the K1S1 transform does. But it does not tick any of these boxes, which we need to tick:
It’s the image directly below my statement.
Interesting experiment. Thanks for investigating.
If you plot on a chromaticity diagram the results of that hue rotation (assuming you are just applying Nuke’s HueShift node) although the ramp is initially entirely within AP1, the hue rotation takes it entirely outside AP1 after a few degrees, where it remains until the last few degrees of the 360. Most of the time it is entirely outside the spectral locus.
So because our rendering does not claim (or attempt) to gracefully render input outside AP1, the distortions you see are unsurprising. We did initially hope to produce a rendering with reasonable output for the majority of possible camera input. However we found that was an impossible task, given the constraints I list in my previous post. Therefore the RGC, or some other form of gamut mapping is still needed for some images. As @daniele says in his excellent video a custom 3x3 matrix for a particular image may often be preferable to a generic non-linear solution like the RGC. That is what I attempted to do in my above demonstration, although it was a very “quick and dirty” test, and I don’t claim in any way to be a colourist.
I did the test in After Effects with a BorisFX Saphire HueSatBright effect (native AE didn’t have a keyframable hue). No idea what their underlying math is but I couldn’t spot any negative values meaning it stayed inside AP1 right?
More importantly, where the ‘bumpy road’ is most present is actually the unaltered state of 0, 0, 1.0 to 0.18, 0.18, 1.0. (The moment where I paused at 3sec.)
Here’s another test I did after doubting the Gamut Compress inside the DRT. I disabled it in the DCTL and applied parametric compression (to taste) right before the DRT rather than the input stage pretending it’s sort of part of the DRT.
I’m able to get a smooth rendering with just this quick test on this image. Perhaps it’s worth looking at the gamut compression currently in place and see if this is (part of) the issue. I’m totally not an expert at this but maybe the first question could be is the stage or space the compression is applied the right one? Should it happen earlier or later? And the second would be is the algorithm itself doing what we want it to do for all values in AP1?
Hope this helps.
Curious what this means?
This is not correct. The above “do nothing” will never shred the way colourimetric scalars do. It’s a different line of thinking to abandon Kodak’s scalar colourimetry altogether.
The sole point is though, that doing nothing and arriving at a vastly superior pictorial depiction should be cause for pause. The problem surface:
Does this make reasonable sense?
Imagine taking the pictures from Star Wars: A New Hope and suggesting that folks go back to the stimuli in front of the camera to remake the pictures. Imagine suggesting for a moment that Darth’s lightsaber should be the familiar attenuated purity one that is part of the “canon” in one picture, and in another somehow be less attenuated in another picture?
If that is the premise, doesn’t it make sense to outline a protocol such that authorial intention can control that prior to engaging in forming the pictorial depictions?
If the goal is to outline a protocol whereby authors are creating their authored pictures, this protocol should have been fleshed out to facilitate the authorship. I suspect the vast majority of authors author a singular picture. If a cinematographer puts a white ultra bounce outside of a window, they are purposefully making the picture such that the ultra bounce is not seen.
If there are going to be decisions made in forming the picture, doesn’t it make sense to empower the authorship by providing them with a mechanism to choose whether they want their picture to be re-authored? I am trying to imagine Deakins with a one click “SDR” picture, and then a fundamentally different “HDR” picture? Surely he should have an authorial choice in this matter? What is the parameter space that can exert control over the “type” of HDR facets?
Given the visual system appears to do a dynamic normalization of sorts, which leads to the aforementioned Gamut Expansion and Gamut Contraction, what is the meaning of this? What’s the goal? We don’t cognize the stimuli, but the relational field, and the computed colour that emerges from the computed field is very different to what we think we are looking at.
For example…
Most reasonable folks think that the colour of the lightsaber is in the picture. What folks discover however, is that no such singular stimuli leads to a satisfactory match of the cognized and computed colour.
Given that cognitive computation of colour is happening, what do display medium gamuts mean in this?
The photographic Apex Predator - chemical film - is not invertible from the pictorial depiction. Nor is the entire genre of black and white photographic films.
For the case of specific workarounds requiring fast hacks to energy, would it have not made more sense to engineer a specific approach to solve the energy back projection instead of placing the constraint on the All-In-One Kitchen Sink? Given that the energy fields will be very different based on creative choices made in any given picture, no back-projection “inverse” will be correct to begin without a selection of energy gradient options.
This looks like the “Blue Light Fix” and is cognitively beginning to shred in the upper region, no? The purity is creating a fission mechanism that is shifting the depiction of “illumination” to being “in front of” or “ripped through” the offset haze. It’s a mess, no?
Maybe it’s just my myopic view, but the picture formation mechanism seems problematic?
sphere with colored lights in v55, all values within AP1 (no negative and 0 values).
at some point on the exposure ramp, the yellow shadow part went above and beyond and appeared “lustrous”.
I wish it would be possible to have two ACES 2.0 “looks”, one that comes without these problem areas and creates a mostly pleasing image that is then not invertible.
And a second look that is called “invertible” for everyone who wants to bypass the RRT&ODT at some point anyways.
Perhaps. I haven’t given it much thought but implementation wise that would mean one would live as LMT inside the other? There is always the global rendering + ODT that needs to be enabled. If that has some form of compression there are two compressors limiting the possibilities of the first? So the default, no look applied rendering would have to use no compression and look really bad? How would it work when you have to blend the two? Say a logo on top of footage.
I always have trouble fully understanding the inversion requirements. Maybe in some ways this management principle is based on suboptimal approaches and/or software limitations? If you color manage manually you can decide when an output transform is applied and layer stuff on top of it. With that approach you don’t even need an inverse for sake of logos/graphics.
On archival side I also struggle to understand this. Wouldn’t it be practical to archive a master without any overlayed graphics? And full titled master archive as is in the deliverable spaces, rather than an ACES2065-1 version?
Regarding compositing would we really need to have an exact inverse because we need to adapt the source image to the scene we are trying to place that in with compositing tools.
But tbh, I’m too distant from full ACES workflows to understand the benefits/downsides since I haven’t had the need to for any of my projects. For us it’s only grading camera images to Rec.709 and then it leaves the ACES world already.
Can’t help but like Daniel’s concept, but I would not call them “looks”… rather two color management schemes.
Also a critical aspect for me is to get consistent management of the various HDR and SDR. Obviously they will differ (as the tone scales do,) but I really appreciate a simple and minimal trim pass between them.
Another possibility with dealing with “extreme” colors can be to treat them as a secondary correction… isolate and fix. Perhaps this is like Shebbe’s “layer stuff on top”.
(not a professional grader myself, but wishing to get the best print (display) from my work)
Also Satrio’s video will not load/run for me - just spinning circle.
(Sorry if I totally misunderstood what you mean)
I used to color grade mostly commercials during the last few years. And if there is a screen replacement of a filmed smartphone / TV - half of the time the added footage comes not as camera source files, but already graded display referred video provided by a phone / TV brand. And it not always should behave like it was really there on set and to receive the same amounts of lens flare, atmosphere fog and other artifacts. On the last project, I keyframed color grading of the composed screen according to a night club stroboscope lighting. But not in a very realistic way, otherwise it would look too dark and flat (realism rarely looks good in a commercial). So I tried to find a balance between the realism and a good looking black level of a smartphone in the frame. Or sometimes it has not to have the look of the surrounding shot scene. Or any other weird case.
And sometimes VFX guys do the chromakey after color grading, right on top of the display referred graded image. While it is completely wrong from a pipeline point of view, sometimes it’s more cost-effective for the client.
So there are all kinds of strange and “wrong” ways of using the tools. And while I agree that using DRT inverse is strange and kind of a bad thing, it still seems to be required. Too much different and weird things happening when it’s not a movie, but a quick commercial with remote post production with workers from different cities or sometimes countries. So it’s better to have a lot of various tools, including the inverse.
I presume then that you are using OCIO and therefore the LUT baked version. The distortions you are seeing may due to the LUTs. I cannot replicate anything like that in Nuke using the Blink.
Again the Blink in Nuke does not produce the same level of bumpiness.
Surely that’s the point. You are free to use whatever adjustments you want prior to the DRT. As well as creative grades you can apply technical corrections such as gamut compression. And you can control it as needed, rather than it being a fixed part of the DRT.
The gamut compression in the DRT is at the output, and is intended to compress to the different target gamuts, so is not the same as a global gamut compression you might apply on the input.
I’m aware that these ‘wrong’ approaches like keying/compositing on graded footage happens. We’ve had these situations too for some of our projects. But I’m not fully confident that it makes it a reason for ACES to amend to such practices when at the same time it wants to be a pleasing DRT to use for grading? But that’s my view based on what I see. Could be proven totally wrong here.
I must admit that some human error has slipped in. While double checking against the exported .exr in resolve I must’ve copied the ACESTransform node rather than the DCTL version of v055 which showed the same. Apologies for this confusion, I checked again and this is indeed smooth!
The green curve is still trending down first before going up however. Not sure if that makes sense in the rendering because blue becomes more pure the less pure it becomes in ACEScg values, before further desaturating through remainder of the gradient.
I would also still hope there could be improvements in the DRT where compression creates hard transitions between compressed (out of gamut) and non compressed values when they transition in that blue area.
I was on the fence about sharing these tests I have been doing, but I was told it could help.
These sweeps are inspired but not equal to MacAdams Moments, this sweep has the same “moment” all around, the x axis is chromaticity angle/“hue”, and the Y axis are log2 steps.
I would say this mainly tests attenuation/path-to-white.
My test was on the assumption that a smooth gradient should be kept as smooth as possible when formed into an image. The sweep is outside the spectral locus but I believe that it shouldn’t matter, and it should be possible to map smoothly enough inside any display space.
I tested Reveal , the latest ACES 2.0 DCTL and my own picture formation.
As you can see, Arri’s can smoothly map everything well enough, even when many values are well outside LOGC4 , even if I it’s a LUT so its not the most accurate
ACES 2 seems to struggle, it creates very pointy flower shape. The largest discontinuity seems to be around the blue and red chromaticities ,which interesting enough are well inside rec709 before picture formation, and the AP1 clamp seems to be necessary for the “magenta” values , but it also breaks the things in other ways. I believe this behavior is mainly from the “Chroma Compression” step when it tries to bring everything inside rec709.
I have no idea how useful this is, I can only say that it’s possible to smoothly enough “map” the camara data, even if they are “non-sense” in terms of human vision.
Hope it helps in some way.
XYZd65ramp.nk (48.9 KB)
XYZd65 Ramp nk group
Thanks! I think comparisons to other DRTs are important. People for sure will compare it, so it’s better to do it before the release.
For me the 2 most important things are smoothness and reaching the corners, in this order.
It’s way more important than not collapsing to notorious 6 or HDR SDR visual match or even perfect invertibility.
Also, just tried JP-2499_DRT and I like how it’s handling the saturated colors in the shadows, thanks for sharing!
When seeing the last replies, I had a similar albeit simpler idea of using concentric circles around the whitepoint, (derived from the radial grid without the spokes), I used to show how the CAM model is distorting the space a few months ago. I found that visualisation quite useful but did not have the time, so thanks for doing that, especially the comparison with the other DRT, this is awesome.
I think it is beyond useful and a design requirement: a non smooth mapping producing a kink in one space will likely exhibit a kink in another one, unless being extremely lucky and that the space transformation happens to undo the kink.
Often, working in a space, doing processing and transforming out to another one will produce significant gradient changes and it is fine provided those changes are smooth. However, this should not introduce harsh discontinuities along the way or there will likely be visual artefacts.
I believe the shape happens due to the hue dependent nature of the chroma compression, that different hues are compressed different amount and that the compression reduces further out the values are from the achromatic (and also the fact the compression space is normalized with the AP1 cusp M). If it was just a constant compression for all hues (around that circle) it would be smoother. Here’s a quick test with a constant compression in v055:
(Note that this example is interpreting the input as AP1, not AP0, so the AP1 clamp is not affecting anything. The AP1 clamp will introduce sharp transitions (and create the “pointy flower” shape) always regardless of the compression being hue-dependent or not, when the input is outside AP1.)
That won’t invert to AP1. But here’s another test that still has hue-dependent compression limit but the compression space normalization is constant and should in theory invert to back to AP1:
This was the above input to the chroma compression (interpreted as AP1), after the tonescale and chroma compression rescaling steps:
And this is what it would have been if it was interpreted as AP0, due to the clamp:
(edit: ignore the “gap” in the circles above, it’s an issue with this particular chromaticity diagram output, it’s not in the actual input.)
