Hi there,
I’m recently diving into the wondrous world of ACES head on and possibly drowning soon. I roughly understand the ACES colour space but I mostly see the space being set at the start of the pipeline (during grading). What I’m unsure is if the graded footage are all done in Rec709, is there still a way to work them in the ACES space? I’ve tried inputting the color mgt node (from rec709 to acesCG) on the footage but doesn’t seem to be correct.
Thanks in advance!
As I understand it, this is the best method for moving from REC709 to ACES. It’s an inverted view transform. Using the same, without the invert selected, will take you back to REC709. I was using a slightly different setup, but I had some problems with extreme highlights, I think this view transform fixes it.
this is the way, I go over all the possible things you can do with display reffered media in my logik live episode : Logik Live Episode #46: ACES & Subtractive CG Comping with Finn Jäger - YouTube
That said, working with graded footage in a aces world is not going to give you much benefits vs staying in legacy. nobody should have to do CG compositing on graded material 
awesome! that works!
thanks so much guys 
Hey @JustAnotherBoy
It is good to take a deep swim in ACES. The whole colour management topic is an important one and at first glance can easily throw you off balance.
Will you indulge me in a brief splurge about colourspace?
It is worth considering what makes up a colourspace. There are basically three things that dictate a colourspace.
The white point. I generally ignore this but I will mention it so that you can ignore it. There are only really two that need to be considered so this bit is easy. It is probably very badly summed up by saying warm or cool. But that is how I like to think of it. You get most colourspoce hitting the D65. Your sRGB, rec.709 and rec2020. Some hit D60 like ACES2065-1. D60 is a bit warmer than D65 but generally I don’t worry about the white point.
The next one is important. Gamma. For now lets consider a log curve and a gamma curve to be the same sort of thing. Or lets think of it the other way. Is it linear or none linear. Log-C. S-log, sRGB all have a log cure (or gamma) that are part of the colourspace. Linear, like ACEScg, does not have a log or gamma curve.
Finally what most people think of is colour gamut. This is often referred to as the primaries. It refers to the amount of colour available to display. Or where the Red, Green and Blue primaries sit of the Spectrum Locus.
Everyone’s favorite, the Spectrum Locus
Jumping around from one colour space to another is made easier by ACES. That is the best take away from my long splurge.
ACES isn’t just a linear colourspace with a wide colour gamut and a white point of D60. It is also a collection of interchanges. It has the profile of cameras, display devices like monitors and projectors. It provides you with a destination to head to from one type of camera so that another type of camera can be used together and a way of transforming out so that you can hit a certain display like a television or a cinema projector and have it look the way you intended.
Phew! I am not on a salary with ACES in case you were wondering.
So that was a long intro. Sorry 'bout that. I’m sure you know all this.
Lets get to your question. Graded rec.709. This has been my world for most of my career and unfortunately the bad news is that once graded, the chain has been broken. Even if you knew what camera it was shot on you have no way of accurately figuring out what the grade has done to the image. Warm or cold. Gamma up or down. It has been worked beyond all hope.
But there is hope.
You might not have the High Dynamic range available or the wide Colour Gamut but you can make use of the linear aspect of ACES. It has excellent tone mapping that will make ugly clipping much harder.
I will not bore you any more with the advantages of compositing in a linear colour space but even with your low dynamic range, graded rec.709, you can take advantage of it.
What you are looking for when you use the colour mgt node is the viewing monitor to look like nothing has changed. You want your F1 input to look exactly the same as the F4 result. If it doesn’t you are either doing the conversion wrong or your viewing LUT is wrong. Simple as that.
If you are going to use ACEScg as your working colour space then the first thing to do is have your viewing LUTs correct.
Next you need to use the ViewTransform. Originally conceived for going from high dynamic range to small dynamic range. Make use of the Invert button and go backwards from rec.709 to ACEScg.
This is a bit of a hack. You haven’t really given your footage any more information. There aren’t any more colours being displayed but you are now in a linear colourspace.
The way this transform makes your footage linear is special because it not only removed the 2.4 gamma curve from the Rec.709 footage, it also did an inverted tone mapping of the footage to extend the highlight and shadow values.
You should find that your linear footage has values that go beyond the range 0 - 1. This has a huge effect on how your linear footage behaves when you composite.
It is still a hack. Highlights will not get any of the clipped information back. In fact those bright colours will be mapped to some very bright values. But you can comp your CG and take advantage of realistic blurs and then invert the ViewTransform getting you back to your graded rec.709 footage.
dude, you’re awesome! thanks so much!
i’ve posted this elsewhere here but here’s a great ACES / colorspace over view if you want to learn more why we jump through all these hoops
Thanks for that detailed reply!
Hi Rufus…why not an Input transform from Rec709 to ACEScg???
Because it changes the image, which, may be a dealbreaker in this particular case. A Rec to ACEScg Input Transform via ACES does map values as you’d expect them to be, but, at the expense of changing the look of the image. The Inverted View Transform hack maps values “not as you’d expect” but the image looks unchanged. So, pick your poison.
Hats off to you @randy
You covered a lot in that video. Lots of really helpful tips, tricks and gotchas.
You even talk about the Input Rules (very useful) without mentioning glob. Hey do you think that Autodesk would expand rules to look at file location?
Glad its helpful. Theres so much content out there, but, its super intimidating. Hopefully this gets someone using it and not having to invest a ton of time.
You’d want the rules to include searching filename paths?
Yeah covering it in a non intimidating way is the key. Good length as well. Conveniently the same length as my render.
I just got really excited and had a play but I find glob has its limits based off the file name. Would be good to have an extra option. All of our graded footage (Rec.709) gets exported as EXR. If I had an additional rule to look at the folder name.
Not a biggie but if it is sitting in a folder called graded_selects or rec709.
