LUT's forcing into video levels

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MattSteeves

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LUT's forcing into video levels

PostThu May 13, 2021 7:28 pm

Is there an easy explanation of why some LUT's crunch your data levels into video when they were previously at full? Also, when creating LUT's, how do you specify you want it with full data instead of video? Is it possible to edit a LUT to make it work in full?
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Peter Cave

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Re: LUT's forcing into video levels

PostFri May 14, 2021 1:53 am

LUTs can be created to work with Full Range or Legal Range. Resolve works in a full range 32bit RGB colourspace, so generally the Legal Range LUTs will show clipping in Resolve.

Some other editing apps work in a legal range colourspace which is why legal range LUTs exist.
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Marc Wielage

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Re: LUT's forcing into video levels

PostFri May 14, 2021 3:51 am

MattSteeves wrote:Is there an easy explanation of why some LUT's crunch your data levels into video when they were previously at full? Also, when creating LUT's, how do you specify you want it with full data instead of video? Is it possible to edit a LUT to make it work in full?

For a lot of reasons -- particularly the destructive nature of a lot of LUTs -- I try to avoid LUTs entirely and just duplicate the look of the LUT with a PowerGrade. It can often be done in Resolve, and once you've done it, you can reuse it for many projects.

Another technique you can try is put a node in front of the LUT and then another after the LUT. Sometimes if you adjust the first one, you can compensate for losses or clipping/crushing in the LUT, particularly in video levels.

My issue is that the person who created the LUT often doesn't know how well/badly-shot the material is, so it could well not work as expected. I don't have a problem with a technical LUT or a custom-made LUT (like a Show LUT) designed for a specific purpose.
marc wielage, csi • VP/color & workflow • chroma | hollywood
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Frank Glencairn

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Re: LUT's forcing into video levels

PostFri May 14, 2021 9:18 am

What Marc said - and yeah, just put a node after the LUT and pull it down.
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MattSteeves

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Re: LUT's forcing into video levels

PostSat May 15, 2021 10:00 pm

Is there a way to automatically deconstruct a LUT into native adjustments? (curves, primaries, etc)
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Peter Cave

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Re: LUT's forcing into video levels

PostMon May 17, 2021 1:17 am

Not that I'm aware of.
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Mark Foster

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Re: LUT's forcing into video levels

PostMon May 17, 2021 10:32 am

forget LUTs - learn grading ; -)




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MattSteeves

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Re: LUT's forcing into video levels

PostMon May 17, 2021 1:43 pm

I agree with that sentiment completely! So I use LUT's a little differently than most I'm guessing. I manually grade my shot, and then at the very end of the tree I might add a LUT (or a couple) at low opacity to sort of formulate a different look. I'm talking maybe 20-30%. It's just how I tend to do things lately, but discovering it may be more of a hassle than it's worth.
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Peter Cave

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Re: LUT's forcing into video levels

PostTue May 18, 2021 1:36 am

MattSteeves wrote:I agree with that sentiment completely! So I use LUT's a little differently than most I'm guessing. I manually grade my shot, and then at the very end of the tree I might add a LUT (or a couple) at low opacity to sort of formulate a different look. I'm talking maybe 20-30%. It's just how I tend to do things lately, but discovering it may be more of a hassle than it's worth.


I do the exact same workflow. Don't use video level LUTs in Resolve.
I do a check of all my LUTs on colour bars and sort them into full range and video range folders.
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Marc Wielage

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Re: LUT's forcing into video levels

PostTue May 18, 2021 7:28 am

MattSteeves wrote:Is there a way to automatically deconstruct a LUT into native adjustments? (curves, primaries, etc)

If you know what to look for, you could apply a LUT to an image, then grab that as a Gallery still, then start a new version, delete the LUT, and try to use the color-correction controls in Resolve to match the grade. In cases where there's unusual saturation curves and hue changes, it might be difficult to replicate, but you can at least get in the ballpark. It helps to actually use a color chart and see how the LUT is changing the chart on scopes, since the chart has absolute values you can quantify.

I'm known for slamming LUTs online, but I concede that technical LUTs have a real value, and there are cases where it's faster to just use the LUT, even if you have to place a Node before and after the LUT in order to prevent it from being too destructive. I just did an SLog3 project last week where I did use the stock SLog709A LUT to tame Sony's color science to something normal. There's also value in using a Color Space Transform Node in order to pull the camera into something close to Rec709 for final color.

Of course, if the post supervisors are using a Show LUT and demand that it be used at every step of the post process, then I think the best course is to use it. We always offer them the option of letting us match it, and I think we can generally get within about 5%, given enough prep time (and assuming there's only a half-dozen or so LUTs).
marc wielage, csi • VP/color & workflow • chroma | hollywood

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