V-Log to linear and BM Film Log to linear

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Wizor
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V-Log to linear and BM Film Log to linear

#1

Post by Wizor » Thu Jul 11, 2019 2:20 pm

Hi, i have a problem. I wanna match my 3D renders with life footage. I got footage in V-Log (Panasonic GH5), Blackmagic Film Log(Blackmagic Pocket Cinema Camera 1st gen) and renders from Blender in 16-bit EXR. How do I convert these footage to linear colo spaces?

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Re: V-Log to linear and BM Film Log to linear

#2

Post by RBemendo » Thu Jul 11, 2019 2:40 pm

inside the gamut tool there's a "panasonic v-gamut" I'm guessing this is the right "log" conversion to use, add this as your Source space in the gamut tool and check "remove" gamma. I'm not seeing a BMD Film source space in the gamut tool, but i'm pretty sure there's a LUT in resolve that will go from BMDfilm to linear, but not sure if that work directly in Fusion.

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Re: V-Log to linear and BM Film Log to linear

#3

Post by SecondMan » Thu Jul 11, 2019 2:47 pm

That would be Gamut conversion. For Log conversions use the Cineon Log tool (gamut and log are entirely different things)...

To add to the confusion, gamma is a different thing again ;)

All three are important.

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Re: V-Log to linear and BM Film Log to linear

#4

Post by Wizor » Thu Jul 11, 2019 2:49 pm

Hmm is that possible I do not have that one "panasonic v-gamut" in gamut node? I dont see it.

Added in 2 minutes 43 seconds:
Oh so a little confusion here, should i use Cineon Log Tool(i see only conversion from BMD Film, no option for V-log) or Gamut?

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Re: V-Log to linear and BM Film Log to linear

#5

Post by SecondMan » Thu Jul 11, 2019 3:02 pm

V-Gamut and V-Log are supported in Fusion version 16. If you're in Fu9 you're out of luck I'm afraid.

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Re: V-Log to linear and BM Film Log to linear

#6

Post by Midgardsormr » Thu Jul 11, 2019 3:05 pm

From what I read elsewhere a while back, V-Log is similar enough to the standard Cineon curve that, lacking a published LUT, you can just use that and get close enough. At that time, Panasonic had published a V-Log -> 709 LUT but not V-Log -> linear.

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Re: V-Log to linear and BM Film Log to linear

#7

Post by asifbhushan » Thu Jul 11, 2019 9:51 pm

Firstly, The color space globally used for view purpose in Linear is REC 709 - For Video - Mostly this is what we see on screen.

The footage you received is a Log Footage shot in Panasonic and Blackmagic which means it is a raw footage.

Now you need to check what color space the renders have been taken from Blender because 3d renders are always linear and mostly in ACEScg.

lets assume your 3d renders are in ACEScg Color space and Input footage is Panasonic Log....

Import Footage in Fusion, add a OCIO Colorspace tool, Choose source space as Panasonic V-Log and Output space as ACESCG ( because our 3d renders are in ACESCG).

Do not do any changes for your 3d renders, just import the exrs. Now merger the 3D EXR with the OCIO Colorspace tool. Do anything like color changes or grade match or adding elements or whatever and then convert back the whole comp from ACESCG to Panasonic V-Log using another OCIO Colorspace tool.

Now your composition is completely back to Raw. For view purpose in actual Linear Colorspace, Convert the footage to REC 709 using OCIO Colorspace tool.

This is how a basic comp should be when converting from log to linear and dealing with 3d renders.

Hope this is clear, if not please let me know, I will try to provide a rough comp.

Thank You

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Re: V-Log to linear and BM Film Log to linear

#8

Post by Wizor » Fri Jul 12, 2019 3:37 am

Thanks for fast responding and help guys, i see Fusion have very friendly community although there is not too much tutorials for learning and sometimes its hard to find any info. Unfortunately I still do not understand how what is the correct workflow. Should i just use Cineon Tool after loading these footages and it will be fine?
Both from LOG to LIN, one for BMD Film nd one for Panasonic V-LOG, then merge it with 3D render and at the very end add gamut tool with output sRGB add gamma?

About color space of 3D render i think its just linear 16 bit exr, its render from Blender so its uses Filmic and i I heard its not ACES compatible.

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Re: V-Log to linear and BM Film Log to linear

#9

Post by RBemendo » Fri Jul 12, 2019 7:40 am

thanks for the detailed correction guys.... i've been doing it wrong

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Re: V-Log to linear and BM Film Log to linear

#10

Post by hendrik » Fri Jul 12, 2019 1:12 pm

V-log could be similar to cineon curve, don't know about that.
BMD film curve is a custom log curve, afaik it is not specified publicly but from Fu16 you could apply it to a grayscale ramp and reproduce it with some curve tool. Gamut conversions are irrelevant unless you can articulate what do you need it for (it is technically correct to do it but practically makes much less difference that using correct transfer curve).

Blender exr renders are by default (99% of cases) linear with rec709/sRGB gamut unless one has specifically used different viewer gamut and textures during whole look dev and creation phase. Filmic view transform is bypassed when rendering exr-s. ACEScg renders are highly unlikely, unless very explicitly stated as being such by whoever created the renders.

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Re: V-Log to linear and BM Film Log to linear

#11

Post by gez » Fri Jul 12, 2019 5:27 pm

@asifbhushan as hendrik said above, Blender is linear rec.709. Right now and until they remove completely some hardcoded rec.709 coefficients used internally, it's not only safe but sensible to stick with linear rec.709 and avoid any other colorspace, unless you know exactly what you're doing. Anything that says ACES in Blender is wrong, and anybody saying that Blender renders ACES is wrong (there's a quite famous youtuber spreading that, and it's completely wrong). Even when you use Filmic, the primaries are rec.709*

Now, regarding the OP question, when you have materials coming from different devices and sources, the first thing you have to do is to define a "working" colorspace for your project.
That means that you have to unify your colorspaces, so everything is consistent. If you use the ACES workflow it will be ACEScg for compositing, and you'll transform the colorspace of your souce material using IDTs from the device colorspace to the reference colorspace, then to the output.
If you're not using the ACES workflow (highly recommended in my opinion if you're targetting to HD and producing wide gamut outputs is out of question), then your reference working space will be linear rec.709.
It's important to keep in mind that "linear" is not a colourspace, but a characteristic of a colourspace: its transfer function.
Another important aspect of a colorspace is its primaries (i.e. the three lights, R,G,B used to encode chromaticity).
So if you have, say sRGB assets (sRGB is a colorspace with rec.709 primaries and a piecewise trasfer curve) then you have the primaries ok, but you need to linearize that transfer curve into a linear transfer.
If you have renders from Blender that are linear rec.709, then your assets are already in reference (provided that you're bringing them as EXRs)
And your camera footage will be in a colourspace where the primaries AND the transfer curve is not in your reference, so they have to be transformed.
As it was detailed above: you need to "remove" the log transfer in order to make the input linear AND convert the primaries with a gamut node, from your camera primaries to rec.709.
The former can be done directly from the loader, and the latter needs a gamut node.
The important thing to keep in mind is that everything you'll composite together must be in the same colorspace. Fusion gives you a lot of freedom in that regard, but it's also easy to make mistakes, so just pay close attention to what happens right after your loaders and before compositing work.


*) There's a special version of filmic designed for a P3 display in Troy Sobotka's Github.

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Re: V-Log to linear and BM Film Log to linear

#12

Post by Wizor » Sat Jul 13, 2019 12:03 pm

Ok i think i understand this process in theory, now I would like to see how it should look in practice. I think it should look like this(screens).
Linear_Workflow.png
ACES_Workflow.png
Please correct me if I'm wrong. In the aces method i also have some blanks. Can someone tell me what should i put there? I marked them with question marks.
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Re: V-Log to linear and BM Film Log to linear

#13

Post by hendrik » Sun Jul 14, 2019 5:26 am

First graph seems ok. You apply srgb gamma in the end, what is your output format?

ACES graph is messy. For BMD film choose appropriate IDT from list, it should have BMD Film listed. Output space is currently ACEScc, but should match others, VLog output is ACEScg, so use that. Exr input IDT should be linear sRGB, output again ACEScg. And again, what is your output format? You set ODT to rec709, not srgb as in first graph, any reason for difference?

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Re: V-Log to linear and BM Film Log to linear

#14

Post by Wizor » Sun Jul 14, 2019 8:23 am

Hmm What's the difference between srgb and rec709?
My output format will be .mov (or maybe you suggest other formats?)
And what is diffrence between ACEScg and ACEScc?
I cant see BMD film IDT on the list, i downloaded ocio cofig aces 1.0.3.
EXR Render IDT could look like this?(screen)
EXR_IDT.png
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Re: V-Log to linear and BM Film Log to linear

#15

Post by gez » Sun Jul 14, 2019 8:43 am

Wizor wrote:
Sun Jul 14, 2019 8:23 am
Hmm What's the difference between srgb and rec709?
The transfer curve. White Point and Primaries are the same, the transfer is different. Different gammas*.

*) Keep in mind that gamma is a lousy term for transfer curves in general. The term should be used only when you refer to gamma-correction, the process of compensating a device's non-linearity in order to produce radiometrically linear ratios. As an example: a linear transfer is not "linear gamma" and a contrast curve is not an S-shaped gamma.
Wizor wrote:
Sun Jul 14, 2019 8:23 am
My output format will be .mov (or maybe you suggest other formats?)
If your .mov is intended for HD (rec.709) delivery, your colourpsace has to be rec.709
But it really depends on the output. You need to define what's your output, check the format is suitable for that output, and use the proper colorspace.
So the first question to ask yourself is the intended output. Is it delivery? Is it editing/grading?
Wizor wrote:
Sun Jul 14, 2019 8:23 am
And what is diffrence between ACEScg and ACEScc?
ACEScg is linear and designed for compositing, while ACESScc is log and intended for grading.
Wizor wrote:
Sun Jul 14, 2019 8:23 am
I cant see BMD film IDT on the list, i downloaded ocio cofig aces 1.0.3.
If the IDT isn't on the list you have to craft one yourself and add it to your OCIO config, but it's probably better to use Fusion's gamut transform from BMD to ACES (I think it's ACES AP0 in Fusion 9) then go from ACES to ACEScg with ACES OCIO colorspace.