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LUT applied in camera by mistake - can it be fixed?

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Rhys Bart
LUT applied in camera by mistake - can it be fixed?
on Jul 15, 2015 at 2:28:45 pm

Hello everyone. I've been given some rushes shot on a Sony FS7 (mxf files) that have had a LUT applied to them in camera (as in burnt into the image, not just in the viewfinder). The director did not know about this and obviously he's not happy. He wants me to use Resolve to remove the LUT from the images, but I have no idea if this is even possible, and Google is throwing up no help.

Thanks for any advice.

Rhys


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Blaise Douros
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 15, 2015 at 5:11:18 pm

You might be able to use http://cameramanben.github.io/LUTCalc/ to generate a LUT that you can use to reverse the effects of the one applied in-camera. Normally you'd go sLog3 > Rec709, for example, but you might be able to generate a Rec709 > sLog3 LUT with this LUT Calculator.

What LUT was baked in? One of the presets, or a custom LUT?


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Rhys Bart
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 15, 2015 at 5:24:25 pm

Thank you. The LUT was baked in. I am assuming that it was one of the presets as they didn't seem to know they were shooting with it...

Since my last post I've gone into Resolve and removed the metadata from the clip and the image does not change, which makes me think that it's part of the image and can't be fixed.

It would be impossible to adjust the dynamic range after this has happened, yeah? I guess that's the issue here. The director want's the full range of sLog3, but I think all is lost...


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Blaise Douros
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 15, 2015 at 6:23:32 pm

With the FS7, when you bake in the LUT, it's not just something that happens in metadata--it changes the footage that gets recorded. So yes, you are stuck, for now, with the baked-in look.

However, re-read my above. What I'm suggesting is that you create, via LUT Calc, a new LUT that does the reverse of the one baked into the footage. In theory, since the footage is recorded at 10-bit 4:2:2, the information is pretty much still there, but the baked-in LUT just changes the distribution of the luminance data.

So, what you MUST find out is the exact LUT that was baked into the footage. With that information, go to LUT Calc and see if you can create a new LUT that goes from the baked-in look to sLog3.

It will likely not be as good as if they recorded the footage in sLog3, but you may be able to get it looking pretty flat again. However, it is likely that you will not extract the full dynamic range from the footage, and the director's just going to have to accept that--that is, simply, not your fault, and you can't be held responsible for trying to reverse an irreversible mistake made on-set.

The other thing you need to let the director know is that, if the LUT that was baked in was just a basic Rec709 look or similar, then he hasn't lost much--at some point during the coloring process, through a series of levels and curves adjustments, or through the application of a LUT, the colorist would have to get the footage to fit within the Rec709 color space anyway, so that it looks correct on consumer monitors. So working from a baked-in look is NOT the end of the world.


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Michael Gissing
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 15, 2015 at 10:11:26 pm

I can't see a reverse LUT getting the dynamic range back. If it is baked in the recorded file then you can't undo it.


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Blaise Douros
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 15, 2015 at 10:43:14 pm

It depends on the LUT used to bake into the footage. If the LUT isn't actually throwing away data by dropping the highlights and black clipping levels, they might have a fighting chance. But since what a LUT does in the first place is re-interpret the video color and luma data to be spread across a different curve, it stands to reason that you should be able to apply an inverse curve to re-distribute the data back to its original level, so long as none has been lost in the process.


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Bill Ravens
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 16, 2015 at 1:48:10 am
Last Edited By Bill Ravens on Jul 16, 2015 at 1:49:44 am

It is possible to reverse the color correction by applying an inverse LUT. However, as noted, the DR is irreversible. That cannot be undone. Subsequent color correction will not perform as efficiently as it would have with an original, unmodified file.



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Rhys Bart
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 16, 2015 at 8:29:47 pm

Thanks for such a detailed reply! The LUT they used in camera was REC709. I tried a few LUTs using the generator you suggested (thanks again) but the director wasn't happy. We are going to cut with the REC709 rushes as they are and then he wants to try and see how far he can save it in the grade.

I spoke to the AC and apparently they thought the LUT was just for the viewfinder only. I guess this is something the FS7 does differently?


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Blaise Douros
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 16, 2015 at 9:13:43 pm
Last Edited By Blaise Douros on Jul 16, 2015 at 9:14:33 pm

My company owns the FS7, and I work with it several times a week, both shooting and editing. It can apply LUTs selectively to different monitor outputs; but if you apply the LUT to the SDI-1 output, it will also bake it to the footage. This is pretty clearly labelled in the menu, so it sounds like this AC was not really paying attention. Not that I'm blaming and shaming, since I have done the same thing. My guess is that they were trying to get the waveform to display in the monitor, which it won't unless you apply the LUT to all outputs.

Regardless, I think you'll find that the footage is still eminently gradeable. At Rec709, it is still retaining a lot of usable color data at 10-bit 4:2:2. Good luck!


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Robert Ober
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 19, 2015 at 4:46:42 pm

[Blaise Douros] "My company owns the FS7, and I work with it several times a week, both shooting and editing. It can apply LUTs selectively to different monitor outputs; but if you apply the LUT to the SDI-1 output, it will also bake it to the footage. This is pretty clearly labelled in the menu, so it sounds like this AC was not really paying attention. Not that I'm blaming and shaming, since I have done the same thing. My guess is that they were trying to get the waveform to display in the monitor, which it won't unless you apply the LUT to all outputs.

Regardless, I think you'll find that the footage is still eminently gradeable. At Rec709, it is still retaining a lot of usable color data at 10-bit 4:2:2. Good luck!
"


Well said.

I own and FS7 and an Odyssey 7Q+ . I would suggest buying or renting an Odyssey 7Q+ and using that for viewing thru SDI2 or HDMI when shooting in Slog with a FS7. Starting with the 2015.5 firmware, the Oddy can send different LUTS to the display, SDI A IO, and SDI B IO. One can feed a video village or DP monitor with a LUT and not the display. Or put LC709A on the display and a standard 709 on the feed to the Video Village large TV.

Not anyone's employee, just very impressed with the LUT capability of the 7Q/7Q+. Convergent Design has a LUT explanation video on Youtube.

Y'all be cool,
Robert


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Marc Wielage
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 16, 2015 at 4:55:48 am

If I can make a suggestion: always, always, always do a workflow test prior to starting a project, and take the shot through color-correction and sound to make sure a) it looks good, b) the levels are right, c) all the metadata is there, and d) it stays in sync with sound.

Once the levels are clipped and crushed, they're gone forever. You can make it better, but you can't get back the full Log range no matter what you do when the look is baked in.


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Rhys Bart
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 16, 2015 at 8:32:01 pm

Hey Marc. We'd done a workflow test - this is why the director was so shocked when he saw the rushes. Apparently the AC thought the LUT was being applied to the viewfinder only and nobody thought to question it. An unfortunate mistake.


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Marc Wielage
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 17, 2015 at 6:10:30 am

That totally sucks! Wish the AC much luck on his next job.

I hope you guys can find a way to salvage it somewhat.


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Bill Ravens
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 20, 2015 at 10:58:22 am

Here's a critical point to think about. Some LUTS are "extended" meaning they convert the entire color range, from 0 to 255. However, most LUTs are limited to REC709 16-235. If this is the case, any information below 16 and above 235 has been clipped. This would be non-recoverable and you will have lost detail in the super whites and super black. I would hope that however you deconvolve the footage in post, you are aware to use an extended LUT.



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Marc Wielage
Re: LUT applied in camera by mistake - can it be fixed?
on Jul 21, 2015 at 2:49:10 am

The other problem is that many LUTs are destructive, in that they clip the whites and blacks in a way that nothing can be recovered from them later on. For this and other reasons, I'd rather avoid LUTs in my workflows and instead come up with a more graceful kind of correction that doesn't slam the whites and blacks so hard, even for dailies.

I sympathize with the o.p., particularly if you're using a new camera for the first time and you're trusting the operator to know what he or she is doing. I've been on shoots where we were suddenly surprised with a new camera and things went into unexpected, unanticipated directions...


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