Chaos Corona Forum

Chaos Corona for 3ds Max => [Max] I need help! => Topic started by: JCdeBlok on 2015-11-18, 10:11:06

Title: Matte/shadow catcher issue
Post by: JCdeBlok on 2015-11-18, 10:11:06
I'm adding some 3d to a 360 panoramic photograph and I'm having trouble with the matte objects.

These object are there to generate the shadow that falls onto the CGI and maybe to bounce some light back onto the pavement and only that.  But I'm having a hard time making the matte objects themselves invisible, they seem to catch some light and I need them out of the equation with alpha=0. I could generate a mask render element but I'm hoping for a more elegant solution..

See attached images for problem and some relevant settings, any clues?
Title: Re: Matte/shadow catcher issue
Post by: maru on 2015-11-18, 11:23:24
Hi, basically you need an invisible object, which casts shadows? Optionally generates some GI?
I think you should use RaySwitch mtl with everything set to invisible (empty) except for GI, which should be set to CoronaMtl with pure black diffuse color - then you won't get any GI, but it will cast shadows.
Or you can plug the ShadowCatcher into the GI slot - then it should generate GI based on the backplate.
Title: Re: Matte/shadow catcher issue
Post by: JCdeBlok on 2015-11-18, 11:49:01
Hi, basically you need an invisible object, which casts shadows? Optionally generates some GI?

As silly as it sounds it quite a common requirement when mixing reality with cg! :)  It can get even worse if I add a 3d light source to the scene,  the matte object should catch that. If I add a 3d car with headlights in the street I want it to add light and illuminate the matte objects.

I'll give the suggestion a try, thx!
Title: Re: Matte/shadow catcher issue
Post by: PROH on 2015-11-18, 12:36:10
AFAIK the problem is, the Corona Shadow Catcher isn't a full blown matte/shadow material, but "only" a Shadow Catcher.

It would be extremely nice, if it was made into a full blown matte/shadow material, so we wasn't forced to use other render engines for this kind of everyday work :)
Title: Re: Matte/shadow catcher issue
Post by: JCdeBlok on 2015-11-18, 13:47:54
AFAIK the problem is, the Corona Shadow Catcher isn't a full blown matte/shadow material, but "only" a Shadow Catcher.

It would be extremely nice, if it was made into a full blown matte/shadow material, so we wasn't forced to use other render engines for this kind of everyday work :)

Indeed! I've put up a feature request here https://forum.corona-renderer.com/index.php/topic,10327.0.html
Title: Re: Matte/shadow catcher issue
Post by: selant on 2015-12-05, 10:31:57
In car renders, which contains an HDRI background, i need to put a simple plane on the ground to catch the shadows. It must be transparent. But i couldnt catch the result.
I tried to make with  RaySwitch mtl also, but i cant make it to be transparent. Any tutorials or ideas on this ? Thank you

(http://i.hizliresim.com/LgDOAj.png)

(http://i.hizliresim.com/kL6XGD.png) - (http://i.hizliresim.com/v8PJJA.png)
Title: Re: Matte/shadow catcher issue
Post by: selant on 2015-12-05, 12:44:11
I guess this video tutorial would help anybody interested :


Title: Re: Matte/shadow catcher issue
Post by: Nekrobul on 2015-12-05, 14:04:19
Just make you're plane bigger.
Title: Re: Matte/shadow catcher issue
Post by: Ludvik Koutny on 2015-12-05, 15:28:18
Yep, environment around the car casts quite long shadows, you just need to make your ground plane bigger so there's more space for shadow to be caught on.
Title: Re: Matte/shadow catcher issue
Post by: selant on 2015-12-05, 18:43:42
Yep the answer is sometimes too close or simple, but trying to figure out lots of parameters then i'm lost.. Bigger plane solves the issue. Thanks all.