FS7: Custom LUT usefulness

JPNola

JPNola

Veteran
I shoot but have no role in post. I hand the footage off to a client and my role ends there. I never have any involvement with the grading or with the application of LUTs in post. I don't communicate with the person doing the post work, either pre-shoot or post-shoot. I never bake any LUT into the footage.

With my working that way, is there any reason for me to be interested in custom LUTs? Would a custom LUT serve any purpose for my type of shooting or are the Fs7's built-in LUTs all I need for in-field confidence checking of the exposure? Is it correct that custom LUTs are only useful if you know that the LUT will be applied in post?
 
I don't understand why viewing any MLUT would be useful for determining the proper exposure? What difference does a MLUT make? S-LOG is either correctly exposed or it is not. No matter which MLUT someone chooses to view (if any at all) the correct exposure for the underlying S-LOG video being reocorded is exactly the same. Modifying the exposure based on the image someone is seeing in their viewfinder or on a field monitor would be akin to adjusting the recording volume of a microphone based on how the sound was being EQ'd in their headphones.

But with that said, I'd leave it to the client to decide for themselves what LUT they want to apply in post. That is the beauty of S-LOG, all options are open to them.
 
I wrote about LUTs a while ago in a post here on DVX which you might find useful.

LUT primer quick quide & history: http://www.dvxuser.com/V6/showthread.php?329613-F5-F7-F55-CineEI-LUT-primer-quick-quide-amp-history

To answer your question, if you are use to working in log and producing images with good quality the way you are working then I don't think you need to worry about custom LUTs or the built-in ones.

The internal LUTs (namely LC709 and 709(800)) are good to get an idea of what it might look like after a general grading in post. If you were working more closely with the post side, they can build a LUT based on the "look" they have established for the project so you can load it and it could be monitored on set.

As pointed out in the post I linked to, you need to very careful about judging exposure with a LUT applied as values can be mapped anywhere depending on how the LUT was made. So if you expose using the LUT the underlaying values in slog can be somewhere you were not expecting. You're better off continuing to monitor in slog or do thorough testing of the mapped values so you know what that specific LUT is doing.
 
Thank you for the kind reply, star central. And also for the link where I can find further information.

So the short answer is that all these cool custom LUTs are of no use to a pure shooter like myself, unless I want to bake a LUT in and force a client to use my creative commitment.


fyi- A fellow shooter hooked me up with this article by Alister Chapman which addresses the issue of the LUT being blown out and details a camera function for dealing with just that:

http://www.xdcam-user.com/2015/02/using-the-highlow-key-function-on-the-pxw-fs7-pmw-f55-and-pmw-f5/
 
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JPNola
I shoot and edit, I mostly use slog, and only apply lut in Davinci. Only disadvantage is that I got used to the washed out images in the viewfinder.
Theoretically that could influence the coloring in Davinci I think.
For me it is a fool proof method because this workflow is so easy, with mostly always the same settings.
 
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JPNola,

I have to rather disagree about the usefulness and accuracy of MLUTs for viewfinder and exposure use. For sure, zebra and waveform levels will differ from the underlying log, but it is fairly easy to find out what the equivalent levels are for (at least) all the available options internal to the F55 / F5 / FS7. I wrote a bit of software to give a guide to it called LUTCalc. You can take run it in your browser from here (the code is pretty large, so might take a bit of time on a slow connection).

Two big advantages arise from operating with an MLUT. First, since the contrast is higher in the midtowns through to 100% reflectance, if you know correct levels then changes in exposure are more obvious on both zebras and waveform. And to repeat, it is eminently possible to get precisely the correct values to map to 'correct' values in the underlying log. For example, with the LC709 Type A look, mid gray is 40%, caucasian highlights (for conventional video shooters who are used to 70% zebras) is 58% and 90% reflectance (the conventional white reference card) is 71%. With Rec709(800%), the equivalent levels are 44%, 70% and 89% (very much like a 'conventional' video setup).

The second advantage is that we are supposed to be more than just pressing record and keeping things in focus. I light and setup shots with an eye to the end result; I also like to be able to notice if something unexpected or untoward is in the shot. Neither of these are particularly clear observing a flat, muted picture. I do tell post what LUT I have been using; in fact, since I use a custom LUT I tend to include a copy with rushes adjusted for whatever post software is to be used. That way, at least in theory the post process can see the footage as I intended it to be. They can choose to ignore that, but at least I know it's there. I would also never dream of leaving log footage up on the client monitor; they will have been seeing what I would like post to, at least initially, see. I also know precisely what zebra levels are appropriate for my custom LUT.

I mentioned LC709 Type A before. This is frequently mentioned as being a copy of the original Arri Rec709 look. If you ever shoot with an Amira, a point with Arri's workflow is that the camera is designed around hiding log from you. Arri includes LUT details in the metadata, so all being well, what post sees when they open footage on the timeline is what you saw on the shoot. Of course the LUT can be removed, but it should be there. Post can see the footage as the skills and tastes of the cameraperson intended, which is as it should be. I'm not sure I know anyone who chooses to spend their time viewing unLUTted log in an Amira viewfinder. There just isn't really any point.

My basic point is, provided you don't clip and you are consistent in your approach it is really difficult to b*gger up log footage, so why not work off nice pictures?

Ben
 
cameramanben said:
I also know precisely what zebra levels are appropriate for my custom LUT.
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Yes, that is exactly my point. Having an MLUT turned on or off is a matter of choice, but it ought to be used purely for aesthetics just to have a prettier picture to look at. It shouldn't have any bearing on the final exposure because the MLUT does not change the underlying S-LOG. As you have pointed out, if you know where zebra levels should land for a particular MLUT, then the use of the MLUT neither helps nor hinders arriving at the correct exposure. One thing has nothing to do with the other and the use of MLUTs is independent of exposure considerations. The best thing you can do for your client is to expose as consistently and as precisely as possible throughout the shoot. It has always been that way and it always will.
 
Fair enough Doug, but by that token viewing the underlying log rather than an MLUT also neither helps nor hinders arriving at correct exposure.

Take raw for example. I couldn't care less what 16-bit linear value 59% S-Log2 equates to, but when setting a shot 59% S-Log2 gets used as a datum, even though the camera is actually recording that 16-bit linear value. In shooting, you are using a more convenient analogy (S-Log2) to the actual data (16-bit linear).

Returning to log recording, I do know that 89% Rec709(800%) equates precisely to 59% S-Log2 (being the 90% white card levels for each), so provided I set my zebras to 89% when viewing with a Rec709(800%) MLUT I can set my exposure to precisely match with zebras set at 59% viewing S-Log2, but I have a richer, more contrasty picture closer to the final result.

In my case, I don't personally use Rec709(800%), but because I know the equivalent levels for the LUTs I do use, the same applies and I find I can easily get a handle on the end aesthetics of what I'm shooting (without needing a LUTted monitor to hand), which to my mind is pretty fundamental to being a lighting cameraperson (even if post just ends up completely ignoring me :-) ).

As I say though, each to their own. I only piped up because the suggestions on the thread seemed to be a bit dismissive of MLUTs. I really don't mean to knock or push either approach, just point out that MLUTs can be useful for exposure as well as look on a Sony, as they are on an Arri.

Ben
 
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cameramanben said:
Fair enough Doug, but by that token viewing the underlying log rather than an MLUT also neither helps nor hinders arriving at correct exposure.
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Yes, I absolutely agree with you.

And I hope you would agree with this statement: If the correct exposure for an un-MLUTed S-LOG or RAW image is f/2.8; then the correct exposure is still f/2.8 no matter what kind of MLUT someone chooses to view in their viewfinder or on a monitor. In other words, exposure should not be dictated by, or influenced by, whatever is being done to create a prettier picture during production. And whether someone chooses to use an MLUT or not is totally optional and independent of exposure. That's all I'm trying to say.
 
Doug, I couldn't put it better!

To me, the thing is that consistency in approach - whatever that approach - makes post's life easier and more likely to fit with your intentions.

Ben

PS and I haven't mentioned CineEI once ... D'oh :-)
 
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Well then I am going to mention Cine EI. I find the use of MLUT's very helpful both as a way of seeing a good looking image which helps me light and as a way of allowing me to have a consistent method of exposure if I am not exposing for the Native EI - which most people don't use. I usually use an MLUT based on the Varicam 709 gamma because I like the punchier look and set my exposure either by looking at a DSC one shot chart or using Zebras and it will always be consistent. Depending on the circumstances of the shot I may vary the CINE EI setting and I think it would drive me crazy to remember what the proper IRE settings were for EI 800 vs EI 1250 for example. Fortunately one MLUT will always work the same with different EI's in the camera. Alistair Chapman makes a good case for using the 709(800) MLUT in tandem with the hi-low settings in the FS7 as a way to quickly judge exposure.

By the way if I need to work in situation that is a lot different than Sony's "%$#*&" 3 color presets, I also have a variety of homemade LUT's made in LUTCalc that will correct for various fluorescent and other settings. Its hard to light under fluorescents or any mixed lighting if you can't see the green to make your own lights match . LUTCalc is especially handy for this because you can use a still frame from the mixed environment, enter it into LUTCalc as your preview image and then create an MLUT to correct it. Its a fabulous tool. Its hard to be exact but you can close enough so that its helpful.

In Post of course it can be tricky to correct if you are changing EI because depending on your program you may want LUT's that are already exposure corrected for the Cine EI setting. Again you can make these in LUTCalc and try to label your scenes to clue the grader on to what EI to use.

Lots of ways to work. Just choose the ones you find most useful.
 
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Not to derail the thread - but JP - don't you ever get requests for WYSIWYG footage? In other words, you will merely hand off the footage at end of day and that person has no knowledge of custom / cineEI or any interest in log or learning to grade log footage. What do you do then? Burn in one of Sony's LUTs ? Shoot custom and tweak your paint settings? Or do similar "tweaking" by using a custom MLut baked in?
 
JP..Like you I have zero participation on the grade, just shoot and handover.. I will sometimes send off a Custom LUT,just by email.. to the production co..or straight to the dir who was on the shoot.. that was used on as an MLUT on the dir monitor.. sometimes its used and they are thankful .. sometimes not I would guess.. probably depends on whoever is doing the grade ..

Also wonder like Lenny.. you only ever get requests for Slog footage.. ?
 
cameramanben said:
I really don't mean to knock or push either approach, just point out that MLUTs can be useful for exposure as well as look on a Sony, as they are on an Arri.
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I would argue that an MLUT is more useful for exposure on a Sony than an equivalent look LUT is on an ARRI. Since the ALEXA bakes in the selected EI, and S-Log(2/3) doesn't, an MLUT will show you the EI compensated image, where the S-Log won't. That is unless you use e.g. S-Log3 as the MLUT, and see exposure compensated S-Log3. But then you don't get to send a LUTted image to the client/agency people on set without using an external LUT box, as the LUT capability of the camera is already used up (if I remember correctly) applying the exposure compensation to the S-Log3.

A particular IRE in S-Log3 is only the correct level for 18%/90%/whatever if you are exposing for the native EI. With an MLUT enabled, the same IRE will represent the same exposure at whatever the shooting EI is.

In S-Log2, 59% is the correct exposure for 90% white at the native 2000 EI, but at 1000 EI it is 72% in S-Log2, and at 500 EI it's 84%. With the LC709A MLUT on, 71% IRE always represents correctly exposed 90% white, and that is the same if you are shooting S-Log2 or S-Log3. And 18% grey is always at 40% IRE in LC709A.

See this video I made for Convergent Design:
https://www.youtube.com/watch?v=QdOb7A0csyE
 
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What Lenny and Nick said.

I tend not to go crazy changing CineEI (oh well, it's already been mentioned now), generally holding to one or two ratings on a project, but I don't often work off the 'native' ISO (I tend to pull 2/3 stop as my base). MLUT means my zebra and waveform values stay consistent when I do change, and that I don't have to think about effective S-Log levels rating at my pulled 'preferred' ISO, as Nick points out.

Ben
 
LennyLevy said:
That reminds me of the other reason to use an MLUT - so if appropriate you can burn in the LUT .
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Yes, that's what I was getting at. Not to start another debate... but for me (not necessarily recommending this for others) if I'm going to be judged on my DP abilities on shooting WYSIWYG - by someone who doesn't want Slog footage - then on most jobs, I personally would prefer to shoot in CineEI baking in a lut (usually a custom one) on my FS7 then shoot in custom mode.
 
markfpv said:
Not to derail the thread - but JP - don't you ever get requests for WYSIWYG footage? In other words, you will merely hand off the footage at end of day and that person has no knowledge of custom / cineEI or any interest in log or learning to grade log footage. What do you do then? Burn in one of Sony's LUTs ? Shoot custom and tweak your paint settings? Or do similar "tweaking" by using a custom MLut baked in?
Click to expand...

I've baked in the LC709a for situations like this before - resulting in happy clients. It'd be nice to have some LUTS "ready to rock" for similar situations, I currently do not.
 
The biggest problem with burning in a MLUT is that you don't have adequate control over white balance. When you need a WYSIWYG workflow with basically a finished look right out of the camera, that's what Paint Menus and scene files are for. A lot of cameras don't give you that option anymore, but thankfully Sony cameras still do.
 
other problems with burning in luts especially the lc709a is that the skin tones lie dangerously close to the where the lut starts desaturating ca. 70 ire and besides the lut is a starting point for grading not the ending point you usually need to lower the blacks and raise the highlights and saturation otherwise you get these "artsy" low contrast low sat crap people delude themselves into liking these days. I offer clients that don't want to deal with grading a quick grade in Resolve as part of an extended Data management scheme. For really fast turnaround (news etc.) I usually go into custom mode with HG8/7 and lower the blacks to -5 to -8.
 
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