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Grading Eterna 400T for HD, SD and Web

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Francesco Krattiger
Grading Eterna 400T for HD, SD and Web
on Feb 12, 2013 at 6:44:00 pm

Hello All

Some time ago, I shot some footage on Eterna 400T, which was then scanned to DPX (2k).

I now want to grade on Resolve Lite with the intent to deliver to HD, SD and the web.

While I've some experience grading digital originated footage (After Effects), this is the first time that
I'm attempting to grade film originated footage and it's the first time I'm taking Resolve out for a spin as
well.

It'd be great to get some questions answered before I waste a lot of time on the grade due to the wrong
setup/assumptions. I realize these questions must seem very basic, but I'd really appreciate it if someone
out there could take a few minutes to answer them.


So here they are:


1. How am I supposed to go about linearizing the footage?

I assume this is supposed to happen via an appropriate LUT; if so, where do I obtain one for Eterna 400T?
Searching for an answer to this led me to a blog post by Mike Most (http://mikemost.com/?p=251), which
explains that applying an S-curve will do the trick.

I did apply an S-curve and it looks pretty good. So what am I to take from this? Mike's article mentions
that it's not exactly an ideal path unless you really know what you're doing. But then again, it looks good
to the eye, so isn't that what ultimately matters?


2. I'm grading off a calibrated, quality LCD monitor; will that get me home, or do I really need to grade off
an external reference monitor?


3. AE allows me to color manage my project, a feature that needs to be explicitly activated in the project
settings. In Resolve, I've yet to find a setting pertaining to color management. Is color management somehow
implicit in a Resolve project, or am I missing something here?


4. How do I grade to a given colorspace/gamma, say Rec 709?

Again, I get the impression this happens via a LUT as there are LUTs in Resolve that will take footage
straight from Log (Alexa LogC) to Rec 709. If that is correct, how do I get to Rec 709, departing from what
that hand-stitched S-curve spits out?


There, that's about all I can think of right now, thanks in advance!


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Joseph Owens
Re: Grading Eterna 400T for HD, SD and Web
on Feb 12, 2013 at 8:02:07 pm

Wouldn't it be loverly if WYSIWYG?

Resolve pretty much operates in Rec709 by default, unless you deliberately go away from it by slipping a LUT in the mattebox. Internal computer graphics previews are operating in sRGB, which is similar, but not exactly the same as 709. That is where external SDI Video I/O interfaces like Decklink come in -- and there are emulation modes included in many grade monitors that allow you to see your values as mapped to various colorspaces. That is the one big real advantage over graphics displays, plus of course accuracy and reliability.

Linearizing your dpx files in Resolve really is asking for the value scaling -- 0-1023 or 64-940?

As far as gamma characteristic goes, depending on whether the dpx files were digitized log or not, I would be surprised if anyone went to the extent of customizing an antilog for a specific stock -- that would have to be tweaked for every batch. Its a bit like the so-called film log curves that some digital cameras provide -- they're not log at all, but simply flattened out to try to avoid clip/crushing the high-and low-lights, and its "up to you" to eye-ball it out, and usually, with a scope, its not a challenge, and a hand-built S-curve is the most efficient path for that. Ultimately, make it look good - that's what we do.

And as the manual and various tutorials point out, the "log" controls in DaVinci primaries aren't specifically for reverse log operations -- they're just a remapping of the overall controls that are pinned at different control points, which you can slide around (pivot).

jPo

"I always pass on free advice -- its never of any use to me" Oscar Wilde.


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Francesco Krattiger
Re: Grading Eterna 400T for HD, SD and Web
on Feb 12, 2013 at 8:57:10 pm

Hey Joseph

Thanks for the information! It certainly helps and makes me think I'm more or less on the right track.

Would you mind elaborating a bit on your remark regarding the value scaling?

I looked up rec 709 black and white levels and from what I can tell the 64-940 range corresponds to
the black and white points in rec 709.

Am I correct in assuming that I need to watch my scopes and keep shadows above 64, if they are to retain
detail, while doing the same with the highlights with respect to 940?

Thanks again.

Francesco


PS: The footage was in fact digitized 10-bit log.


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Toby Tomkins
Re: Grading Eterna 400T for HD, SD and Web
on Feb 13, 2013 at 1:13:04 am

Try using an Alexa log c (important: film matrix ON) to rec709 LUT and grade before it (either load the LUT as the final node in a chain or load it as a node in track mode). This should get you nice results. LogC is the same as cineon log which is probably what your scans are.

I'm shooting my own tests on 10 35mm film stocks and 4 digital cinema cameras (Alexa, red, f65, c500). Off the back of that I'm creating various LUTs, some of which you might find useful. Let me know if you're interested and I'll keep you posted.

Toby


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Mike Most
Re: Grading Eterna 400T for HD, SD and Web
on Feb 13, 2013 at 5:00:56 pm

If you're going to use an Arri website generated LUT with a film original, you want the matrix OFF. The matrices that Arri offers for those LUTS is based on the Alexa camera's particular characteristics and is designed to restore proper saturation and specific color values when using that camera, and with the assumption that the in camera matrix was off while shooting. What you want is a LUT that does not incorporate a matrix because a film scan already has proper values (it's not the result of a Bayer pattern capture system, at least not at the camera end).

Second, LogC is NOT identical to Cineon log. It is slightly different in overall gamma and in specific areas of the curve. It is very similar to Cineon log, and can usually be used interchangeably with it if color grading is being done, but it is NOT the same (as opposed to, say, RedlogFilm, which IS identical to Cineon nog...).


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Francesco Krattiger
Re: Grading Eterna 400T for HD, SD and Web
on Feb 13, 2013 at 5:23:02 pm

Thanks for the clarification Mike - and thanks for writing that article in the first place.

Francesco



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Toby Tomkins
Re: Grading Eterna 400T for HD, SD and Web
on Feb 14, 2013 at 1:18:22 am

I think you want film matrix on (or configure the lut in the arri lut builder as if film matrix was on during recording of an Alexa log image)...Think of it like this, if you want to have an Alexa log image similar to a film scan, you would record with film matrix on, as specified on the arri website;

"Log C (film matrix on) applies a color matrix that makes the resulting image resemble a film negative scanned on an ARRISCAN. While this option somewhat reduces the color gamut in contrast to Log C (film matrix off), it provides an easy and fast way for colorists who are used to scanned negative, thus speeding up color grading. It is also a great option when combining ALEXA images with film originated images. The same caveats as for Log C (film matrix off) also apply."

Also from what I understand LogC is the same as cineon, here's a brief history I found;

"LogC stands for Cineon Log and is not an ARRI invention it is a Kodak invention created to be able to capture film scans across a wide dynamic range.

http://en.wikipedia.org/wiki/Cineon (http://en.wikipedia.org/wiki/Cineon)

And

"Arri adopted the use of the Cineon specification as a means of encoding image data in a log format for the ARRISCAN film scanner. This was implemented to properly allow the digital representation of the dynamic range that film delivers in a 10 bit logarithmic file format where each stop of exposure is mapped in equal intervals of digital code values, thereby creating a digital negative. The Cineon Format was developed by Kodak in the mid 90's for use in the Cineon Fim Scanner. ARRI adopted it for use in the ARRILaser ARRIScanner, D20/D21, and the Alexa.

Therefore the name LogC is essentially an abbreviation of Logarithm and Cineon referring to the way ARRI has chosen to implement it's log encoding of image data in the Cineon Format Specification and the corresponding characteristic curve. Just like SLog is Log encoding based on Sony's implementation of log in order to optimize their camera's output; and LogF is Log encoding based on the Filmstream format for the same reason. They are all characteristic curves developed to take advantage of the technology inherent in the camera systems that they come from. You can think of it in the same way that different film stocks offer different characteristic curves and therefore offer more or less dynamic range and tonality then other film stocks.

Truth is there's no perfect way to 'linearise' your files (FYI that term can mean many things), technically you could go to a scene referred colour spaces and then use an ODT for a given colourspace, but you'd still need an RRT which is subjective in itself. Experiment with curves (make them smooth!) and different LUTs and find what works best for this project. There is no one size fits all. You were 'limited' with film print LUTs before, where you had to grade in front of that LUT (so you could stay in log to deliver log files for the film print), but now if you're delivering in rec709, you're not finishing in log, so do what you want as long as it looks good.

From the sounds of it you're in need of a colourist with their own suite. There's plenty out there. Make a friend. Collaborate.

Toby


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Mike Most
Re: Grading Eterna 400T for HD, SD and Web
on Feb 14, 2013 at 4:21:20 am

>>Think of it like this, if you want to have an Alexa log image similar to a film scan, you would record with film matrix on...

That would be the case if you were starting with an Alexa generated image. The original poster specified that he is starting with a film image. You don't use a matrix designed for a specific Bayer pattern camera if your original material is not generated by that camera.

It is also absolutely true that LogC, while similar to Cineon, is NOT identical to it. Not everything you read on the Internet is true, including Wikipedia.

I stand by my original post.


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Toby Tomkins
Re: Grading Eterna 400T for HD, SD and Web
on Feb 14, 2013 at 9:35:23 am

The matrix is applied during recording, to emulate film, so the alexa logc rushes are comparable to film scans. It lets you use traditional film print LUTs and mix the alexa material with arrilaser film scans. As such, if using an alexa LUT for actual film scans, you would be better off using a LUT based around the matrix setting being on.


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Mike Most
Re: Grading Eterna 400T for HD, SD and Web
on Feb 14, 2013 at 4:11:30 pm

The matrix ***can*** be applied during recording, but that is optional and most often not done. In fact, many of us wish Arri did not offer that option because it causes a lot of confusion, just like it's doing right now.

The reason for the film matrix' existence is to provide better compatibility with traditional film DI pipelines and better results if you're working with a film print emulation LUT. It is not intended for "general purpose" pipelines, and it is not intended for any color pipeline that does not include film print emulation as a specific target. The original poster specifically said he was intending this material for 709 type targets - HD, SD, and Web. I don't see anything in there about a 3D film print emulation LUT, or film DI target. Color science doesn't exist in pieces, it exists as a color pipeline. If you're not using the back half of that pipeline, there's no reason to use the front half except to confuse things and cause incorrect color combinations.

I'm not going to post any more on this, though. You seem convinced of things that I know not to be the case, but you're entitled to your opinion.


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Toby Tomkins
Re: Grading Eterna 400T for HD, SD and Web
on Feb 14, 2013 at 4:26:52 pm

We're both saying some of the same things Mike, and I totally agree about the film matrix option.

Francesco, experiment until you find something you like. Like I said before, there's no right or wrong way to process your log files when going to Rec709, if it looks good to you, it works (-;

Mike, I'm sorry if I offended you, I'm only sharing what I've read.

Sadly you can't 'correctly' use the arri lut builder with 'film matrix on' material, so this whole discussion is a bit of a moot point actually. Arri expects you to have your own pipeline for film material and your own LogC to Rec709 LUT. So you will need to find a generic Cineon to Rec709 LUT after all.


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Mike Most
Re: Grading Eterna 400T for HD, SD and Web
on Feb 14, 2013 at 4:41:23 pm

Well, yes, because Arri is not in the business of providing film targeted LUT's, which really require specific negative and print stock emulations as well as assumptions about a lab process. A generic approach is not something Arri would support except as a general "look creation" tool, which is not the intent of the LUT builder. There are a number of print emulation LUTs floating around in various places for Cineon original if that's what one wants. But nowhere in the original post do I recall anything being said about print emulation. All he wanted was a way to create 709 type material from film scans. That can be done any number of ways depending on the expected result, but I would point out that we have done telecine transfers from film to various video formats for many, many years and never had "print emulation LUTs." Those only came into play when digital intermediate work began, and solely because the ultimate product of that process was a film print, thereby dictating that it be properly previewed. Film and electronic displays are different mediums, and you don't need to emulate film to achieve pleasing electronic pictures. Just look at any television series shot on film either now (very few now, actually, but there are some: Breaking Bad, True Blood, Castle, Glee, Grey's Anatomy, Boardwalk Empire - all of those are still on film) or in the past. That's the product of original negative transferred to a video format, with no print emulation.


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Toby Tomkins
Re: Grading Eterna 400T for HD, SD and Web
on Feb 14, 2013 at 4:46:27 pm

Try this Francesco: http://www.motionfx.gr/generic-lut.html


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Mike Most
Re: Grading Eterna 400T for HD, SD and Web
on Feb 14, 2013 at 4:54:47 pm

Here are some pretty nice emulation luts (actually from a RedUser post...):

http://juanmelara.com.au/downloads/log2hd_cube_luts.zip

.......**IF** that's what you want.... ;-D


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Toby Tomkins
Re: Grading Eterna 400T for HD, SD and Web
on Feb 14, 2013 at 4:58:28 pm

That's a fair point, you could use redlogfilm LUTs, look at AntlerPost LUTs.


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Francesco Krattiger
Re: Grading Eterna 400T for HD, SD and Web
on Feb 13, 2013 at 5:21:05 pm

Hey Toby, thanks for your input. I'll try that, modified by what Mike said.

I'd certainly be interested in what you come up with over the course of your test,
so please do keep me posted.

Francesco



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Francesco Krattiger
Re: Grading Eterna 400T for HD, SD and Web
on Feb 13, 2013 at 6:18:35 pm

I've a follow-up question: Where do I control the "film matrix" setting?
I can't seem to locate it.

Edit: Never mind, I figured it out.



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Joseph Owens
Re: Grading Eterna 400T for HD, SD and Web
on Feb 14, 2013 at 12:09:19 am

[Francesco Krattiger] "I looked up rec 709 black and white levels and from what I can tell the 64-940 range corresponds to
the black and white points in rec 709.

Am I correct in assuming that I need to watch my scopes and keep shadows above 64, if they are to retain
detail, while doing the same with the highlights with respect to 940?"


No, not really. Your dpx scans, if scanned full scale, will correspond to 0-1024 RGB and you should check that Resolve is mapping the same scalar overall 0-100 IRE range -- if your output preview is 709, then Resolve should be doing the work for you, but only if it is correctly interpreting the source files. You should be aiming for 0-100 709 if that is your ultimate output, even though in Y'CbCr those values are 64-940. That is the nature of so-called "linear video". This will be very obvious in an outboard SDI scope, where you will see either "floating" or "very crushed" blacks, and a stunted white level. If there is a scalar mapping error, it is not a linear fix as gammas will be proportionally incorrect across the grey scale.

jPo

"I always pass on free advice -- its never of any use to me" Oscar Wilde.


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Francesco Krattiger
Re: Grading Eterna 400T for HD, SD and Web
on Feb 15, 2013 at 8:34:43 am

One more time thanks to all for your input.
I think I got somewhat of an idea as to how to proceed now, so that's great!

Francesco



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