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LUTs (5 replies and 17 comments)

James
4 years ago
James 4 years ago

Hi,

I'm starting this topic because the other one was headed in a different direction so I thought this would be clearer.

The way that Roger and I work with the LUT: We create the LUT at eFilm. It is a unique LUT that we were able to create by sitting in the DI suite and looking at an image and making small tweaks until it provided the look that we want.

This LUT is NOT put into the Arri camera. When the image from the camera is fed into the color stream setup on set, any color or density corrections are set and then the LUT is applied to the image. You want the LUT to be last so the color corrections can carry through the process. That way the dailies corrections can be used during the VFX and be there on the first pass of the DI. Saves a lot of time!

I'm going to ask Matt, the Image Science guru, to post here too. His knowledge is vast!

James

Jacob Sacks-Jones
4 years ago
Jacob Sacks-Jones 4 years ago

Hearing about your workflow is really really fascinating...

How do you apply the LUT, if it isn't on the camera? Is there a device between camera and monitor or is it a special monitor? 

I've made a couple of LUTs for the Alexa, never quite to my satisfaction because they've never been done in a full professional suite! 

Thank you!

Jacob Sacks-Jones
4 years ago

I'm not sure if the fascinating comment sounded sarcastic by the way, but it definitely wasn't meant to! I love these kind of details 🙂

matthewtomlinson
4 years ago

Hi Jacob, This in Matt, the Image Science Guru that James mentioned. To answer your question of where is the Lut applied if is not in the camera, the answer is that it is applied in a separate device that goes between the camera and the monitor. The camera feed is NOT in the Rec709 state. It is set so that the LogC imagery comes out of the video tap. (Note, for this conversation I am using the Alexa camera as the camera we are speaking of, if you are not using the Alexa, of course, the term LogC does not apply). That feed is sent into the separate device. In the case of how Roger works, traditionally he will use the Colorstream device, which is an EFILM/EC3 proprietary device. If you are working on a show that is using a Deluxe facility I recommend inquiring about the Colorstream. Some D.I.T.'s may want to use their own device. That is often times (at the moment) the Livegrade Pomfort device. The Colorstream (and other devices) allow for color correction in for the for of ASC CDL. The Lut is applied POST Color Correction. That order of operations is extremely important. That allows the CDL color correction to carry beyond on set dailies. Those CDL values can be used as the starting point for the DI. It is a different workflow than putting the Lut in the camera (which the only Arri camera that I am aware of that you can actually put a custom 3D Lut into is the Amira and the mini but those cameras only output Prores. Roger and James specifically work in Raw.) (But wait, I thought I could put a "look" file in the Arri? You can but that is limited and does not apply to the Lut that Roger and James use). Back to the camera in the Lut in the camera question. The concept of putting the Lut in the camera means that the color correction occurs after the Lut. Which means that the color correction is occurring in the display space that the Lut is mapped to. Which means that CDL's cannot travel downstream because the display colorspace on set may or may not be the same colorspace as what occurs post dailies. Also if you color correct before the Lut you are doing so in Log space, if you color correct post Lut, you are doing so in gamma space. The two are not the same. Hope this helps. Let me know if I missed the intent of the question. - Matt

Jacob Sacks-Jones
4 years ago

Ah that's very helpful, thank you! Makes a fair bit of sense (although still trying to get to grips with this very technical side of high end digital shooting). I've shot on the Alexa before, and used custom look files, but never had the ability to access the kind of quite advanced workflow you're talking about (sadly...). I'm interested then to know a little bit about those limitations on the look file, and what the difference would be between the Arri's custom looks files and a full 3D LUT?

Assuming I don't have access to Deluxe facilities/the Colourstream (or similar) on a relatively low budget camera, what do you think might be the best way of working with the Alexa? Is using an in-camera 'look' good practice? Or best to just avoid that altogether, and accept that you've got an element of 'blindness' at monitor regarding the final image (i.e. a little like film, but less so, your on set monitor isn't going to give you 100% the final look of the image)?

Thanks,
Jacob

matthewtomlinson
4 years ago

Hi Jacob,
The exposure that I have had with the Look files that can be loaded into the Alexa camera allow you to put in a 1D Lut as a Tone map as well as a 3x3 matrix and CDL values. In respect to the Lut that Roger uses, it is not built in a way that trying to break it into those components would give an accurate representation of the full 3D Lut that Daiiles and DI would be using.

To build your own Look file I would recommend going on the Arri website and seeing what they have to offer. There are options on that site that are widely used in the industry.

If you would like to try to build your own I would recommend taking a Look file from the Arri Website and opening it in a word document and manipulating the formatting. This is way easier said than done. You really need to have a firm grasp of how to built a 1D Lut to at least get started. I have known DP's that will use a 1D version of the 3D Lut that is being used for the DI in the camera knowing that Color through the view finder is not accurate but the overall contrast is seen.

In the sense of "good practice", that is a difficult question to answer. I prefer to take the approach of doing what is best for the show. I completely understand the concept of the "run and gun" shoot with a no budget. From what I have seen there are a couple different routes you could take. Route one would be to set the camera to Rec709 mode and go with that. This is certainly valid if the core audience is the web. The second, would be to keep the video out of the Arri in Rec709 but you record LogC (AWG). Download the K1S1 Lut from the Arri Website and view your LogC imagery in something like Resolve with the K1S1 Lut active Post Color Correction node. Another way is simply go for a good exposure on set. Light your images onset as best you can and basically pretend you are shooting film and you do not have the ability to previz. From there your LogC captured imagery should allow you the maximum flexibility to get you where you need to go. At this point you can apply an Arri downloaded Lut or a Lut of your own.

If you are planning on customizing any Luts I would recommend that you do so gently. Try not to paint yourself into any corners with extreme looks. Allow the extreme looks to be created in the color correction.

Please let me know if there are any questions of if I my explanation is confusing or not on target of you intent.
Thanks
Matt

Jacob Sacks-Jones
4 years ago

Again, really really helpful - thanks Matt.

I'm reassured by your second option - I feel I'm not yet fully confident or experienced enough in the complexities of digital workflow to commit to a custom LUT, so am likely to continue shooting as you say 'like film', making heavy use of the light meter and waveforms. It feels like getting a good image on set is pretty fail safe. And then there's a lot of flexibility in the grade. I guess the question then is really how much contrast you put onto the image as read on the waveform, and how much you leave to be done in the grade.... but that's part of the job of course!

Of course, on productions where we have the luxury of working with companies and people like yourself who are on board for the full process, it might be a little different!

kuba
4 years ago

Hi Matthew!

Sorry to piggyback on responses from a few months ago but I have a question.

In the system you described in your first response to Jacob's comment, are the key monitors on set (video village, director's monitor, and of course whatever on board monitor/viewfinder is being used,etc.) able to see your work down the pipeline (CDL+LUT, etc.) in real time given the proper monitoring setups? Sorry if this is a stupid question, but much like Jacob I don't have the pleasure of using such sophisticated technology in my work quite yet. If that is indeed the case then could you possibly explain the monitor equipment that is used to achieve this and how "the look" everyone sees on their monitors gets there. If this isn't the case, then what does someone like Roger monitor in camera and is that different than what the director and producers are seeing at video village.

Thanks again for blessing us with your time and knowledge!

matthewtomlinson
4 years ago

Hi Kuba,
Can you give me a specific example of your workflow situation? I can probably help from there. For instance, can you tell me what camera you are planning on using? Or if you are planning on having a video preview device on set? If you are looking for more general workflow questions, I should be able to help, but want to make sure you do not have a specific situation in mind.
Please let me know if there are any questions,
Thanks
Matt

kuba
4 years ago

Hi Matt,
I don't have any specifics in mind just yet, so I guess I'm interested in a general overview of the workflow. Using Roger's system as example would be fine since that is already been discussed or maybe a different example you have in mind?
thanks
K

matthewtomlinson
4 years ago

Hi Kuba,
The short answer is that all monitors that need to see imagery on set can see imagery on set but there is a discussion that should occur between the Creatives to understand what monitors are the "hero" monitors so that extra care can be taken on these displays. Video Village is often a conglomeration of different monitors that all should be set to a spec colorspace. The feed to video village can be Lutted for that.

johandijkstra
4 years ago
johandijkstra 4 years ago

Dear James,
Thanks a lot for opening this topic, explaining your workflow and inviting Matt 'the Guru' 😉
Rogers always uses an optical viewfinder right? So he does not need any in camera LUT at all.
I use EFV's and for me its very important to have a in camera LUT that add some contrast for my own monitoring besides the on set monitors.

Matt,
Welcome and thanks for the clear explanation of your on-set workflow!
First of all sorry for my faltering English 😉
I think my way of working is quite the same as that of Jacobs.
Due budget reasons I mostly work with the Amira and the Sony PMW F55. Those camera's deliver great images and are extremely good purposed for 'one man operating'. I do always shoot in LOG, and I used to apply a in camera LUT for my EFV and the on set
monitors. I have some questions I hope you can help me with.

I recently used some Film Stock emulation LUTS. I apply a Cineon LOG LUT over the Amira's LOG, apply the corrections and finally add an positive film print emulation LUT that also pushes the footage to a Rec709 space. Are you familiar with this workflow, and I'm happy to hear what your opinion is.

Second thing is, I want to know more about color use and I love to create my own master LUT like Roger has. All Rogers digital movies do have their own 'look'. But he mentioned on this forum that he uses practically the same LUT since he shot Skyfall. Is the look totally created by lighting? Or do adjust a 'look' in the DI?

All Rogers movies look great, feel organic in a way, and do have a real cinematic film feeling. Did you try to emulate some film stock in Rogers LUT or does it only shapes the Alexa material in a way its even better?

And how far can I go in creating a master LUT for myself? Do you maybe have some tips?

First I want to thank you for putting your knowledge, effort and time in this forum! It helps and means a lot to me! Its great to take a look your kitchen and learn from the best! Thanks!

matthewtomlinson
4 years ago

Hi johandijkstra,

For your first question, if the workflow you are referencing has the order of operations of Source -->Input Lut from LogC AWG to Cineon Log --> Color Correction --> Film Emulation Lut mapped to Rec709, Yes, I am familiar with that work flow and I am in general a fan of it. (Please let me know if I misinterpreted the workflow you suggested)

For the next question, Roger has traditionally used one for each show, meaning he does not change the Lut based on if it's interior, exterior, day or night. It is the same Lut throughout the entire movie. Which means that customization of the look within different environments is based on lighting and DI color correction. The Lut that Roger and James use on each show is tested, vetted and approved by Roger before shooting begins. I would be irresponsible of me to break down the tone map and color map of any Lut that Roger and James have used without their consent.

To create your own Master Lut, My tip would be to understand the look that you want to achieve and use that as the reason to find out how to get there. If you want to learn more about Log curves, gamma, colorspace, white point, formatting, there is a lot that is available to you on the web. Wikipedia is surprisingly not bad. There is a fair bit of math involved and I would suggest a working knowledge of Excel (Numbers in Mac). I know that is a cryptic response but the question you are asking is massive and has been a back bone motivation for for over twenty years in this field. It's very difficult to sum up quickly. If you have a real world experience that left you with question, perhaps I can help with that?

I hope this helps,
Thanks
Matt

johandijkstra
4 years ago

Matt,
Again, thank you so much for sharing your knowledge with us!

First, the film stock emulation workflow you mentioned is exactly the one I'm using often! I Love the out of the box beautiful film like color's. Besides the color correction in the Cineon LOG its of course possible to ad a 'look'. Is that something you do when using this workflow? Or do you mostly stick to the film print colors with a decent correction in between?

And I do (off course) totally understand that you're not gonna breakdown James and Roger's LUT over here. All respect to that!
Besides it's very nice to know the workflow they are using. I like the simplicity and mindset of using one LUT and adjusting the 'look' on set. Thanks a lot again, and if there popup and questions about creating my Master LUT I will come back to you if thats okay? Thanks!

Johan

matthewtomlinson
4 years ago

Johan, if you have more questions, i will due my best to help.
Matt

sashamoric
4 years ago
sashamoric 4 years ago

This is a fascinating thread.  But can someone clarify for me what CDL stands for?

James
4 years ago
James 4 years ago

Hi Sashamoric,

It stands for "Color Decision List" and it carries any dailies color correction information as metadata. It is not baked into the original but travels with it so when you view it, you see the timing that was applied.

Hope that's helpful.

James

Almax
4 years ago
Almax 4 years ago

Here's an image from the Sicario B-roll. It shows a Sound Devices PIX2401 unit downstream of Rogers Alexa.

http://www.videodevices.com/products/portable-video-recorders/pix240i»

I am presuming Rogers Film LUT might reside here? Matthew?

I sure hope Roger & Denis do an audio track BTS for the Bluray!

https://www.rogerdeakins.com/wp-content/uploads/2015/12/sounddevices-pix2401.png
simon m
4 years ago

Matt, thanks so much for bringing your knowledge to Roger's forum. Just to get the terminology correct - is a CDL a LUT which is used to color correct the LogC output of the Alexa? Also, as Almax mentions above, would the monitor like the Pix 240i shown above accept such a CDL? Thanks.

sashamoric
4 years ago

I am guessing the CDL is the settings of the LUT that can be transferred to any colour suite. Its like an EDL edit decision list. So it is a LUT but its just the numerical values in a file. Thats what I think it is but I could be wrong

matthewtomlinson
4 years ago

Hello Simon,
A CDL is not really a Lut. Think of them more as color correction settings than a Lut. Here is a link to the ASC website that gives a quick definition of a CDL https://www.theasc.com/ac_magazine/September2009/CASPart2/page4.php»

And yes, generally my experience is to use it to color time the LogC material from the Alexa camera, but if you are using a camera that does not capture in a Log space, it is valid to use CDL's if you like. (Example if you are using a camera that only saves in a Rec709 mode, you can still apply a CDL) I have often used a CDL as the color correction for the shot. If you choose to use a Lut after the CDL or not is really your choice. There can be reasons for either one.

I do not have experience with putting a CDL in the monitor you referenced. I am more familiar with using the CDL's in Color Correction systems or on set Color Correctors.

Hope that helps, Let me know if there are any questions.
Matt

matthewtomlinson
4 years ago

Hi sashamoric,
A CDL is not structured as a Lut is (meaning the formatting is different). One could turn a CDL into a Lut but in general a CDL has specific settings that many color correctors will accept. Please see the website address I listed in my response to Simon to see the ASC definition of a CDL. Your comparison to an EDL is on target and I have experienced CDL information imbedded within an EDL.
Hope that helps.
Matt

apelike22
3 years ago

Hi there,
I'm a Nuke compositor and all of this information is incredibly helpful. Thanks to everyone for contributing. Color in the VFX pipeline is by far one of the most consistently onerous clogs in the pipeline and in my experience everyone from junior artists to senior supervisors is a little squirrelly when it comes to the hows and whys of applying CDLs and LUTs and getting everything to play nicely from ingest through delivery. This thread has helped enormously in my personal education on the topic.

On the question of CDLs, one extremely important difference between them and a LUT, as far as my work is concerned, is that a CDL is reversible. I can import a CDL into my vfx work and invert it to get back to the same image without any loss of data. 1D LUTs are the same as CDLs in this regard. The math in 3D LUTs prevents them from being reversible. I'ver never understood why that is, but if I'm understanding things correctly (Matt, please correct me if I'm wrong, I'm neither a color scientist nor a mathematician), 3D LUTs start in Log space and deliver an image that operates in Gamma space such as sRGB or rec709, thereby clipping values in the color channels. This would prevent the 3D LUT from being reversible.

One question I have, and I believe there's some discussion on this site about this already, is how ACES plays into this. The latest version of Nuke has a bunch of tools designed to work with ACES but in my ignorance I'm utterly bewildered by the enormous quantity of settings involved and figuring out which one to use and when.

Thanks again and I look forward to a deep dive on this site.

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