Create a Rec 709 conversion lut for Rec 2020 footage

[SimrunTech]

After finishing Grading my Rec 2020 footage, I would like to create a LUT so that it can also be viewed in rec 709, SDR. Right now when I export the footage, I only get my graded HDR footage.

it looks bad on SDR monitors, I would like to have a 709 conversion lut created so that it can viewed on SDR monitors.

I'm trying to do this so when I upload footage to youtube, I can attach the 709 lut so that it can grade the conversion properly.

Here is what is happening with regular HDR footage:

Composite Arf Hawk RC Turbine Jet - 4K HDR - YouTube  looks good on HDR monitors but bad on SDR

So I have to re-encode it using rec 709 color profile and reupload as a 2nd file:

Composite Arf Bae Hawk Carf RC Jet - 4K SDR - YouTube

obviously not very practical, so what can be done here. Youtube says it offers a way to have more control over SDR conversion but needs a lut to do this with. the instructions are for divinchi resolve.

[francis-crossman · Accepted solution]

We have an effect called SDR Conform which is available in Premiere Pro and Media Encoder which is designed for tonemapping HDR footage to a Rec709 color space.  You could apply it at the time of export by drilling into the export settings and finding SDR Conform in the Effects.  You can also use it in Media encoder in the same way.  Another way to approach it would be to duplicate your sequence and add an Adjustment layer.  I like this method, because you can more easily spot check through your program and make sure things are looking good in a Rec709 world.  There are some setting that you can adjust in the SDR Conform effect (Brightness, Contrast, Soft Knee).  Soft knee is how much you roll off the highlights.  This effects is better than a LUT because you can tweak it to best suite your specific content.  I hope this helps.

[Kevin-Monahan]

Thanks for the reply, Francis.

Kevin

[SimrunTech]

Yes I saw the SDR conform however, what happens to the output? My understanding that if I enable this I will get SDR output and loose HDR? Or are you saying it will output 2 graded files 1 for SDR and 1 for HDR?

OR.. will I get an HDR output along with a LUT that converts the HDR to SDR? This would be the ideal, I could then package both of these for youtube.

Sorry if I seem repetative, but I haven't found anyway to upload HDR footage to youtube that allows me to control the SDR conversion youtube does.

[excited_Genie16B8]

You need two exports.

[victorwuff]

Thanks for the information.

But beside adapting dynamic range BT2020 to Rec 709 also needs a colorshift. colorspace of BT2020 is not only wider but has also shifted colors. are there any plugins or adobe effects to shift Colors between this colorspaces?

[Birgit-Michelle5CB8]

There is a lut that corrects the color shift: cc-lut.hotglue.me 

[bernhard5CB8]

https://cc-lut.hotglue.me/

[victorwuff]

right: this lut helps a lot.

[chrisw44157881]

.

[bernhard5CB8]

@chrisw44157881 Hi, I did a quick comparison of your LUT with the one from pointecc and it is not similar, not even close! pointecc does an accurate translation of colors from BT.2020 to Rec.709, producing results comparable to color space transform in Davinci. The LUT you posted obviously shoots past the reds and is definiteley not a conversion from BT.2020 to Rec.709.

[chrisw44157881]

@bernhard5CB8 

yes, I made a mistake that the gamut wasn't also converted.

also, I don't personally agree with paying for a technical lut. a creative lut sure, but technical luts should belong to all the smart engineering people at ACEs who give away their knowledge for free.

here's a free online lut creator that you can create entirely in your web browser. I found that setting HLG  .2100 input and Rec 709 output is close with a higher gamma i think 2.2 instead of 2.4

http://cameramanben.github.io/LUTCalc/LUTCalc/index.html

[R Neil Haugen]

One thing to be aware of is a LUT is "the dumbest math out there" according to colorists. Yes, you can make one for this purpose, but as Francis notes above it's better applied on the timeline where you can 'trim' the clip to fit the LUT. Or you can have clipped/crushed or over/under saturated values.

A tonemapping is a far more complex operation and in many ways preferable for transform uses. Such as their SDR Conform, which both transforms color space and dynamic range from one standard space to the other. Not perfect but quite usable.

Neil

[chrisw44157881]

@R Neil Haugen ill have to double check if sdr conform changes the color gamut as well? if it does not, maybe a combination of gamut conversion lut and luma conversion.(brightness, softness, knee tonemapping.

I do all my funky stuff in resolve, so haven't played around with sdr conform like I should.

[R Neil Haugen]

SDR Conform by design must handle both gamut/space and dynamic range conversion. That's the reason it exists.

Neil