Chaos Corona Forum

Chaos Corona for 3ds Max => [Max] Bug Reporting => Topic started by: Duron on 2018-10-14, 21:08:21

Title: Shadowcatcher not working properly
Post by: Duron on 2018-10-14, 21:08:21

I run into this issues very often. The shadowcatcher is producing wrong shadows at certain angles or light situations. Contact shadows look inverted and there is also ghosting visible in dark aeras. See front angle samples. On the rear wheel (left hand side) you can see through the car slightly.

This issue is common by many users.

Note: changing the "Shadow amount" makes no difference.

Title: Re: Shadowcatcher not working properly
Post by: romullus on 2018-10-14, 22:52:24

Duplicate: https://forum.corona-renderer.com/index.php?topic=16993.0

Title: Re: Shadowcatcher not working properly
Post by: Duron on 2018-10-15, 10:44:09

I thought the other topic is specified for the ghosting and reflections issue in dome mode. This one is mainly related to strange looking contact shadows.

Title: Re: Shadowcatcher not working properly
Post by: pokoy on 2018-10-15, 12:21:59

Maybe I'm wrong but the contact shadow artifacts are probably due to GI from the Matte material, which bounce back onto the matte plane etc., maybe even producing the 'look-through' effect since it's screen mapped. I guess if you use a RaySwitchMtl on the matte plane and use a different Material for GI it could probably solve all problems.

I think it always worked like this. It's not wrong either if you think about it, MatteMtl needs to look 100% like the source image which needs self illumination, which then again sends out GI and needs the RaySwitchMtl to override GI.

Title: Re: Shadowcatcher not working properly
Post by: maru on 2018-10-15, 13:16:19

@Duron - it looks almost like some kind of light leaking. Is it the same if you use path tracing + path tracing? (in the Performance tab)
Other than that, can you try changing the "shadow amount" value in your Shadowcatcher material to 10 and 0,1 and let me know if that helps in any way?

Title: Re: Shadowcatcher not working properly
Post by: Duron on 2018-10-15, 21:10:11

I tried several things now and i noticed that it depends on the ground brightness of the environment. So if there is a reflected patch of the sun then it procudes wrong shadows.
The brighter the enviroment on the ground or the brighter the geometry diffuse colour, the contact shadows get inverted.

Increasing the shadow amount sometimes compress this effect but shadows remain off. I couldn't notice any difference with both GI solver.

Rayswitch override for gi channel fixes this issue in many times. But for me this is a workaround. It would be good if the catcher is more trusty.

Title: Re: Shadowcatcher not working properly
Post by: Njen on 2018-10-16, 01:45:23

To fix 'light leaking', instead of using planes, use boxes, or geometry with some air-tight thickness.