P: Add Rec 709 to LUT color spaces in new enhanced profiles

The color space specified by Space refers to the color space on which the LUT is defined to operate.  So if you select Rec 2020, then the LUT will be assumed to take as input color numbers in Rec 2020 and produce as output color numbers in Rec 2020.

I believe that internally, ACR transforms that LUT to operate on color numbers in the internal working space of ACR (Melissa RGB, a variant of ProPhoto RGB). But I haven't verified that yet.

Thanks ; more and more, 3DLUT creator seems like the best option for me.

Also Lattice isn't a WYSIWYG freeform LUT editor like 3DLUTCreator. By that I mean it's not such that one can select a range of colors and modify them. It's more a GUI for LUT math. Similar to LUTcalc https://cameramanben.github.io/LUTCalc/LUTCalc/index.html but in my opinion far more intuitive and provides a bit more options. 

Andrew, if you're comfortable with command look into this. From the creator of Lattice.

https://github.com/gregcotten/pylut

https://www.jasonmyres.com/converting-3d-luts-for-resolve-lustre-and-nuke-using-pylut-in-osx

I agree. I commented on Julieanne Kost's blog post about it as well. http://blogs.adobe.com/jkost/2018/04/lightroom-cc.html

Copy/Pasting my comment from the post:

Question about the LUTs in the SDK. In regards to Space and Clip/Extend. What specifically is this referring to? The RGB data being input, output?

For instance if I have a LUT that converts Rec709 Gamut/sRGB Gamma -> Rec709/Cineon > Kodak 2383/Rec709 Emulation would I select space: srgb/clip?

Basically do I need to make my LUT loop back into whatever colorspace I define in ACR? For instance ProphotoRGB/Gamma 1.8 -> Rec709/Cineon -> Kodak2383/Rec709 Emulation -> ProphotoRGB/Gamma 1.8.

How does ACR/LR interpret the RGB data after it’s run through the LUT?

I assume it has to process the data from LR Internal working space > some RGB > LUT > Interpret RGB DATA > Convert for display icc.

I feel like it’d be useful to add a couple parameters that define how to encode the RGB data going into the LUT and another for how to interpret the output data from the LUT. A few standard ones can be:

LUT Input Space (This is the data fed into the LUT/Exported out of ACR):

Rec709/Cineon Log
Rec709/sRGB
Rec709/Gamma 2.4
Rec709/Rec709 Gamma
P3D65/Gamma 2.6
P3D60/Gamma 2.6
P3D65/sRGB (DisplayP3)
ACESCG/Gamma 1.0
ProphotoRGB/Gamma 1.0
ProphotoRGB/Gamma 1.8
ProphotoRGB/sRGB

LUT Output Space(This is the data fed out of the LUT/Interpreted by ACR):

AdobeRGB/Gamma 2.2
Rec709/sRGB
Rec709/Gamma 2.4
Rec709/Gamma 2.2
Rec2020/Gamma 2.4
P3D65/Gamma 2.6
P3DCI/Gamma 2.6
P3D60/Gamma 2.6
P3D65/sRGB (DisplayP3)
ProphotoRGB/Gamma 1.8
ProphotoRGB/sRGB

Thanks so much!

Thanks, interesting video's on Lattice. I have to see if the $99 version of 3D LUT creator is going to cut it for starting out or, their Standard version which is on par price wise with Lattice:
https://3dlutcreator.com

I don't have any experience with 3D LUT Creator.  I've used Lattice a little for technical transforms of LUTs. 

Very interesting, thanks!
Obviously I need to dig into LUT's and creation a lot more know that we have such features in ACR/LR. I'm toying with buying 3D LUT Creator; are you familiar with it and if so, is the entry level ($99) version sufficient? 
TIA.

As an indication of the need for Rec 709, this LR feature request for the ability to use LUTs in LR has 97 votes:
https://feedback.photoshop.com/photoshop_family/topics/id_love_to_get_the_ability_to_use_3d_luts_in_...

"So what happens if the color space isn't in sync? That is, you pick sRGB or ProPhoto but you want Rec 709? Like with ICC profiles, does that screw up the color appearance?"

Yup.  

sRGB is pretty close to Rec 709, with the same primaries but modestly differently gamma encoding.  A Rec 709 LUT applied to an sRGB image will often / usually result in an image acceptably close to that LUT applied to the Rec 709 version of the image, though I can often see differences in the shadows, as you'd expect.

"if you use such a LUT, does one have to use them only on images that are in the same color space (seems that wouldn’t be necessary with raws that have to be encoded into something at some point)."

No, the enhanced profile containing the LUT can be applied to any image that ACR / LR can read.  Looking at the profile's .xmp file, the color space isn't recorded anywhere, just an encoded LUT.  I'm guessing that encoded LUT represents the specified LUT, converted to the working space of ACR (MelissaRGB).