# shadow matte object alpha + displacement **URL:** \ **Category:** General\ **Created:** [March 1, 2022, 10:14am UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104 "2022-03-01T10:14:52Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![s0real](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/s0real/32/47064_2.png) [@s0real](https://forums.chaos.com/u/s0real)\ **Post date:** [March 1, 2022, 10:14am UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/1 "2022-03-01T10:14:52Z")
hopefully this will be an easy one for someone. tried a few searches but i couldn’t find anything. maybe it’s just a setting i’ve not applied on the vray properties for the object? i have some objects i’m comping into a photo background. my shadow catcher planes have displacement to replicate the rough surface of the wall and floor, but the shadow from the displacement doesn’t seem to cast shadow onto itself if that makes sense? ![shadow1.JPG](https://europe1.discourse-cdn.com/chaosprd/original/3X/3/c/3c207e3f17b34d12416f09b17b3a0ab6fc371cc1.jpeg) ![shadow_alpha.JPG](https://europe1.discourse-cdn.com/chaosprd/original/3X/3/1/316b9d7dae41dd6d84897c0fcddd03039c53ce89.jpeg) ![shadow catcher properties.JPG](https://europe1.discourse-cdn.com/chaosprd/original/3X/d/7/d7db15f5911cb8cb01579e99bd3af077b2676123.jpeg) ---
**Author:** ![fixeighted](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/fixeighted/32/45854_2.png) [@fixeighted](https://forums.chaos.com/u/fixeighted)\ **Post date:** [March 1, 2022, 10:55am UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/2 "2022-03-01T10:55:52Z")
It appears that it works if you use a wrapper material instead of the Vray properties method. ---
**Author:** ![anon88455546](https://avatars.discourse-cdn.com/v4/letter/a/5fc32e/32.png) [@anon88455546](https://forums.chaos.com/u/anon88455546)\ **Post date:** [March 1, 2022, 11:08am UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/3 "2022-03-01T11:08:36Z")
**@[s0real](https://forums.chaos.com/member/67721-s0real)** Could it be a shadow bias issue? What is your current value? ---
**Author:** ![fixeighted](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/fixeighted/32/45854_2.png) [@fixeighted](https://forums.chaos.com/u/fixeighted)\ **Post date:** [March 1, 2022, 11:23am UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/4 "2022-03-01T11:23:27Z")
Not a bias thing…these examples look at each method… ![VRAY PROPS METHOD.jpg](https://europe1.discourse-cdn.com/chaosprd/original/3X/d/4/d4f96730b9304bfafc3dc1a3e4865a0d1bca740b.jpeg) ![WRAPPER METHOD.jpg](https://europe1.discourse-cdn.com/chaosprd/original/3X/5/8/5813164c42db5419f12d62a55c94500d4d7cef64.jpeg) ---
**Author:** ![hermit.crab](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/hermit.crab/32/46825_2.png) [@hermit.crab](https://forums.chaos.com/u/hermit.crab)\ **Post date:** [March 1, 2022, 12:11pm UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/5 "2022-03-01T12:11:20Z")
> [@s0real](#): > > …the shadow from the displacement doesn’t seem to cast shadow onto itself if that makes sense? I think disabling the “No GI on other Mattes” should do exactly that. > [@fixeighted](#): > > It appears that it works if you use a wrapper material instead of the Vray properties method. I’m getting identical results. Maybe you forgot to apply the base material to the object when you were rendering the object properties matte? ---
**Author:** ![fixeighted](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/fixeighted/32/45854_2.png) [@fixeighted](https://forums.chaos.com/u/fixeighted)\ **Post date:** [March 1, 2022, 12:35pm UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/6 "2022-03-01T12:35:25Z")
I notice that with the wrapper, ‘no GI on other mattes’ is unticked as default, so it just worked, whereas it is ticked as default via properties, so I overlooked that 🙂 ---
**Author:** ![s0real](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/s0real/32/47064_2.png) [@s0real](https://forums.chaos.com/u/s0real)\ **Post date:** [March 1, 2022, 12:56pm UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/7 "2022-03-01T12:56:55Z")
thanks for the replies - just working through things now. i have remade the shadow catcher object, and remade the catcher material + applied a wrapper, even merged into a fresh scene in case i’d done something wrong early on. it seems to work maybe a bit better using the wrapper (at least i can make changes now and preview in interactive mode!) as soon as i increase the displacement value, the issue re-occurs. it’s as if the shadow is self-occluding or something? ![shadow_wrapper.JPG](https://europe1.discourse-cdn.com/chaosprd/original/3X/d/a/da6f7a2b20c8b5e77e7cabaf6073316fbdf0e938.jpeg) ![shadow_wrapper_displace.JPG](https://europe1.discourse-cdn.com/chaosprd/original/3X/d/e/de2c1cea6ed084d18774f3412fe34ade242e3075.jpeg) ![wrapper.JPG](https://europe1.discourse-cdn.com/chaosprd/original/3X/8/2/825e419510023ef99e30608f329e6887c705a592.jpeg) ---
**Author:** ![s0real](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/s0real/32/47064_2.png) [@s0real](https://forums.chaos.com/u/s0real)\ **Post date:** [March 1, 2022, 1:01pm UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/8 "2022-03-01T13:01:24Z")
this is the displaced shadow catcher without the wrapper ![no_wrapper.JPG](https://europe1.discourse-cdn.com/chaosprd/original/3X/3/3/33c85d95828d6f6b9e5afd402c5213f4a5e82410.jpeg) ---
**Author:** ![fixeighted](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/fixeighted/32/45854_2.png) [@fixeighted](https://forums.chaos.com/u/fixeighted)\ **Post date:** [March 1, 2022, 1:08pm UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/9 "2022-03-01T13:08:26Z")
You need to un-tick the box that says ‘No GI on other mattes’ ---
**Author:** ![s0real](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/s0real/32/47064_2.png) [@s0real](https://forums.chaos.com/u/s0real)\ **Post date:** [March 1, 2022, 1:29pm UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/10 "2022-03-01T13:29:11Z")
this is with no GI unticked. ![no_gi.JPG](https://europe1.discourse-cdn.com/chaosprd/original/3X/a/b/aba71b84bcdd18eb4341102a406bff670504b568.jpeg) ---
**Author:** ![fixeighted](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/fixeighted/32/45854_2.png) [@fixeighted](https://forums.chaos.com/u/fixeighted)\ **Post date:** [March 1, 2022, 1:42pm UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/11 "2022-03-01T13:42:32Z")
Maybe something else is going on…posting a stripped scene may help solve it. ---
**Author:** ![s0real](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/s0real/32/47064_2.png) [@s0real](https://forums.chaos.com/u/s0real)\ **Post date:** [March 2, 2022, 4:49pm UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/12 "2022-03-02T16:49:52Z")
OK - simple test scene that replicates the issue attached It might be that it’s behaving as expected? I’ve fixed in post for now, but it would be good to know if i’m doing something wrong. Thanks! [shadow catcher test.zip](https://forums.chaos.com/uploads/short-url/nymPdtKBpi1zZZXbr0hRgJ2TvXU.zip) (1.32 MB) ![sample_alpha.JPG](https://europe1.discourse-cdn.com/chaosprd/original/3X/5/1/516d11001221b174db27b3ecddcee32a0d24cda1.jpeg) ![sample_output.JPG](https://europe1.discourse-cdn.com/chaosprd/original/3X/c/0/c048e9d3038f2452bd8d5ac2c867b336a946d14a.jpeg) ---
**Author:** ![fixeighted](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/fixeighted/32/45854_2.png) [@fixeighted](https://forums.chaos.com/u/fixeighted)\ **Post date:** [March 3, 2022, 8:06pm UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/13 "2022-03-03T20:06:13Z")
I agree; the result is not what you’d expect, after testing this. It seems like the matte cannot account for self-shadowing, so the result is just wrong and so maybe it’s not achievable right now. I do seem to remember a post a few years ago that noted the same, or a very similar issue. I’ll try to find it in the morning but for now maybe @hermit.crab has an explanation or fix if ithere is one 🙂 ---
**Author:** ![vlado](https://avatars.discourse-cdn.com/v4/letter/v/779978/32.png) [@vlado](https://forums.chaos.com/u/vlado)\ **Post date:** [March 4, 2022, 10:14am UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/14 "2022-03-04T10:14:25Z")
While somewhat unexpected, this seems to work as intended - the shadows of a matte object on itself are not matte shadows - the background plate is supposed to incorporate them already. I verified that similar results are obtained in Corona and Arnold. Best regards, Vlado ---
**Author:** ![s0real](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/s0real/32/47064_2.png) [@s0real](https://forums.chaos.com/u/s0real)\ **Post date:** [March 4, 2022, 10:30am UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/15 "2022-03-04T10:30:30Z")
ok, thanks for testing and confirming my results. ---
**Author:** ![fixeighted](https://dub1.discourse-cdn.com/chaosprd/user_avatar/forums.chaos.com/fixeighted/32/45854_2.png) [@fixeighted](https://forums.chaos.com/u/fixeighted)\ **Post date:** [March 4, 2022, 4:02pm UTC](https://forums.chaos.com/t/shadow-matte-object-alpha-displacement/109104/16 "2022-03-04T16:02:08Z")
Honestly that doesn’t really make sense to me. My test used a wall map and its displacement map, giving the results below. It’s obvious that the result is wrong when comparing the non-matte displaced output. So all the renderers giving the incorrect result is weird, or am I approaching this in the completely incorrect way? I don’t actually need this to work right now, but it would interesting to be able to understand what is the correct approach 🙂 ![MATTED LAYER.jpg](https://europe1.discourse-cdn.com/chaosprd/original/3X/d/e/de6e6a1cc1dac9abcd8a8b4ba18e646481e9c7e7.jpeg) ![IMAGINED BACKPLATE.jpg](https://europe1.discourse-cdn.com/chaosprd/original/3X/d/d/dd0d8d8c52db7c38235ed91d2eeb283761fa70f7.jpeg) ![DISPLACED WALL SHADOW RESULT.jpg](https://europe1.discourse-cdn.com/chaosprd/original/2X/3/327ab14a880b30cd66725d19e615eaadfacdcab6.jpeg) ![A MATTE COMP.jpg](https://europe1.discourse-cdn.com/chaosprd/original/3X/1/3/13633c7f4b2dd4675d698f49348b33d0e53745b2.jpeg)