LUTs and CoronaOutput texmap

[romullus]

I constantly need to render some product shots on a flat specific colour background. My usual workflow is similar to the one shown in this topic: https://forum.corona-renderer.com/index.php/topic,11345.0.html where i plug CoronaColour through CoronaOutput to shadow catcher and it works really great, up to the moment when i decide to apply LUT. After that, i can't get exact colour background that i need. I tried to apply the same LUT to CoronaOutput texmap, but it doesn't help. I know, that CoronaOutput has warning message, that states that LUTs does not work with affect by tone mapping. Is there some workaround to my problem?

[ileste]

To apply LUT in Photoshop

[pokoy]

Or counter this in PS by applying inverse LUT on the backplate part of the image, before or after rendering... not sure how to achieve that, though.

[romullus]

To apply LUT in Photoshop

How that would solve my problem? Even in photoshop LUT still would affect background. Not to mention the fact that LUTs gives different result in photoshop than in Corona VFB.

Or counter this in PS by applying inverse LUT on the backplate part of the image, before or after rendering... not sure how to achieve that, though.

My hope was that CoronaOutput could do that, but...

I really would like to solve this issue, so if anyone has some ideas, please don't hestitate to throw them to me.

[JoeVallard]

Set your Shadow Catch material's alpha to "always transparent" And use the alpha to mask the LUT render.

[maru]

So basically you would like to apply LUT only to the rendered object, not to the background?
I don't see any way to do it now in a single render.
Just our of curiosity, is it so important to you to add LUT to the rendered object? Is this to make it look like it was photographed with some specific camera?

[romullus]

No, it isn't SO important to use a LUT, but it is sitting there, inviting to use it, and i like output with LUT more than without it. Anyway i ditched that idea, because for me it is more important to be able to output several renders out of VFB quickly and bypassing photoshop (which wouldnt help me anyway). I'll just wait when shadowcatcher's for compositing mode will be fixed and all my troubles should go away...

[Juraj]

Imho it's important for those who want to composite backplates directly in CGI, which is very common.

I don't do it either because backplates, are mostly already photography with some post-production applied. If I use LUT to grade the framebuffer content, I don't want to effectively double that for backplate.

But the whole idea of Output was to negate any framebuffer post-production. Currently it does so probably to extent of 30perc.  (only half of the features, and then it still registers changes requiring restart).

Post-production makes this easy workaround currently (except for ultra-slow compositing mode as Romullus stated) and I like the flexibility anyway, but the feature is there and is arguably broken so.

[romullus]

Imho it's important for those who want to composite backplates directly in CGI, which is very common.

Sorry for confusing, i should've wrote that it is not important for me in that particular case. I can't speak for others of course :]

[Juraj]

Important is always subjective... I would gladly use it if it worked correctly, but I am also fine to do it in Photoshop.