HDRI lighting in Carrara

williebouwer.mail_fed69a20c4

Hi, I searched the forum but didn't see any relating to this. Sorry if this was answered before, but I'm on a tight deadline and need an answer asap. Is it possible to render in Carrara using ONLY the lighting information from an HDRI and NOT see the HDRI in the background. I want to render an object and then composite that in AFX over a filmed background plate using an HDRI to make the object more realistic. In other words, the alpha channel must not be destroyed by an HDRI in the background.

Any help and suggestions will be appreciated.

stu sutcliffe

In the render room go to the output tab and tick the alpha channel box.

evilproducer

Many video packages don't handle pre-multiplied alpha by default, so try straight alpha first. Your mileage may vary. ;-)

Also, just so that you're aware, you can use an alpha just fine, but if there are reflective surfaces, the HDRI will reflect.

One other thing you may or may not know is that Carrara has a shadow catcher lighting model in the Texture room. You can apply it to any object just like a shader. It will be invisible in the final render, and it not only receives shadows, but it can also act as a mask, so that anything behind the shadow catcher is hidden in the final render.

A simple example would be this video. I applied a shadow catcher to a simple vertex plane and also to some animated grass. Where the grass is in front of the dinosaur, it reveals the background plate. High Def would make this trick pretty obvious, but standard res, it worked nicely as I didn't have to try and match the texture and shading on my grass blades.
https://www.youtube.com/watch?v=_8puXTRXt7Y