CoronaShadowCatcherMTL + Backplate Help

[jjduncs]

I'm after some help with fitting an object into a photo backplate.

Ive got the backplate setup in my viewport and in the environment map etc. It is showing up fine in the render.

I then set up the ground plane with a shadow catch mtl with the backplate plugged in, this seemed to work too.

The issue I am having is the exposure of the objects. I can't seem to change the exposure of the scene without affecting the exposure of the backplate. Also, is there a way to use photographic exposure without  affecting the exposure of the backplate?

I don't know why but my corona sun and coronasky intensity values have to be at 0.1 to get okay looking results.

If some one could talk me through the proper method for setting this type of thing up, with a backplate and a corona sun + sky for lighting, it would be hugely helpful! thanks.

[jjduncs]

Here is how i have it looking.

[juang3d]

Have you seen the videos here?:

https://forum.corona-renderer.com/index.php/topic,3995.0.html

I think your problem is commented there.

Cheers.

[jjduncs]

Thanks for that! I tried searching 'shadow catcher' and 'backplate' etc etc but couldnt find a relevant thread.

[jjduncs]

Part 3 covered it well. Just needed to use a CoronaMapOutput.

Thanks again.

[jjduncs]

got it sorted.

[juang3d]

Great! Glad you solved it :D

Cheers.

[jjduncs]

On doing some more renders with this scene, I've come across another problem.

Im getting more fireflies on my 3d elements when I use the "For compositing" mode in the shadowcatch material.
 
I'm using the direct visibility over ride as black so it should all be the same.

When I re-enable the backplate map in visibility over ride and turn shadow catch mtl back to always solid the fireflies are drastically reduced.

Anyone else experienced this?

[jjduncs]

both after 7 passes

[juang3d]

In your already comp pic you don't have reflectivity in the floor, but you have it in the black render, maybe this has something to do with this, but I haven't experienced the problem before.

Cheers.

Edit: sorry it's not reflectivity, it was a mistake, but why can I see part of your backplate in the black render?

[jjduncs]

Yeah those two images are renderered with exact same setttings for everything except with the shadow catch mtl turned to for 'forcompositing' mode and the direct visibility turned to black (bitmap unchecked) for the left one.

I think the backplate is showing up a little because of GI from the facade and surroundings.. with the alpha map mask this mostly goes away.

Still having issues with more fireflies in compositing mode though!

[Ludvik Koutny]

Quite strange. Do you use HDcache by any chance?

[jjduncs]

Yeah this is PT + HD Cache.

[Ludvik Koutny]

Could you try if same artifact appears with PT+PT? Just to be sure...

[jjduncs]

Yep PT + PT seems to fix this.

Is this normal for the Alpha Mode to effect the noise etc with HD cache?