houdini shadow catching?

[aeroba]

  How to make a mia like arnold shadow catcher to render shadow on background pic?

 

 

 

https://support.solidangle.com/display/AFMUG/Shadow+Catcher

Edited July 31, 2014 by aeroba

[Matt_K]

Hey,

See if this scene file helps.

 

The grid has a shadowmatte shader applied and the light has the grid excluded from casting shadows.

 

Matt.

shadow_matte_example.hip

[mirHadi]

hello

 

I see the black grid in the render. I want the shadow catcher to be in visible in the render and see only the shadow that It catches ( like the middle image). what do I need to do please?

 

thank you 

[mestela]

This might help:

 

http://forums.odforce.net/topic/23548-render-cg-with-live-action/?p=138732

[mirHadi]

mestela 

thank you very much. It was very good setup and It helped me a lot.

 

I have a question:

 

the thing I want is a clean ( just shadow ) in the alpha and a good shadow composite in the beauty render , like the images. but  I get a black plate in the render (however the alpha is fine)

( using shadow matt material assigned to the plate)

 

in maya It is simple as that to use a background shader( with arnold , shadow catcher),

but in houdini I'm stuck!! , I can't get rid of the black plate in the render.

 

hope It makes sense.

Edited February 2, 2016 by haaranoos

[mestela]

Unless I'm misunderstanding your question, isn't that in the example hip I linked? I had to look at that hip again and do a render, the beauty channel is a reasonable composite, the alpha contains a matte for the shadow. 

 

 

 

As an aside, the guy who wrote our in-house pathtracer at work would get pretty worked up about shadow mattes. Pointed out that once you start doing multi-bounce everything, colour bleeding this into that, then the concept of a shadow matte becomes vague and murky. Took a while for us to adjust, but we're now about 99% shadow matte free. Compers aren't so convinced....

 

-matt

 

[mirHadi]

matt!

yes I did render again and makes perfect sense now. thank you

 

 

- by any chance do you know how to create arnold shadow catcher in houdini ?  ( with arnold shaders)

 

- I've attached the image of the shadowmatt material. this setup should work also ( I mean we should see the color ) but I get black plane. why is it happening?

[mestela]

Sorry, don't use arnold. :/

[mirHadi]

O.k..

 

I figured it out.  now It works perfectly.

thank you again.

 

I wonder why shadowMatt shader doesn't provide this kind of setup by default. 

Edited February 2, 2016 by haaranoos

[miccetro]

@haaranoos how did u solve this problem. Would love to know. Thanks.

[HGBarca]

@haaranoos, i'm also curious how used the shadow matte in htoa?

[6ril]

I'm using shadowmatte with arnold, what is your concern?

[HGBarca]

I know how to use it in Maya but i can't get it going in Houdini. I'v made a shader with a shadow matte and put this on the plane but i don't get the shadow seperate. Look at the hip. 

 

generic_studio_outdoor_v0100.hip

Edited February 7, 2017 by HGBarca

[violalyu]

On 2/7/2017 at 11:22 AM, 6ril said:

I'm using shadowmatte with arnold, what is your concern?

@6ril Hi, I'm trying to use the shadow matte in arnold for Houdini, however it is only usable in ArnoldVopnet, and I'm not sure what I should connect as the input of the shadow_matte vop node. Currently it is rendering RGB and alpha totally opposite. Where I get shadow in alpha doesn't have anything in RGB, vice versa. If you don't mind to explain some of the details or share a simple example file will be great! I tried to find example on the documentation site, but didn't find one. Thank you so much!!!

[6ril]

oups! sorry, I haven't checked ODForce lately.

@violalyu@HGBarca

For the simple case ( ie sphere on a plane) 2 ways to use shadow matte :

-render without BG and include BG in post (most flexible option for me) : just apply a shadowmatte material to the plane. It will be black in RGB which is fine as the Alpha channel will be white only in the shadow.
best way tho is to use AOVs to fully separate that shadow, or just another ROP with a take where the sphere is not visible to cam.

-make it all at render time : a bit more difficult as Arnold weirdly doesn't allow camera bg image, and the OUT_environment will allow only Sky or flat color (as far as I know). So you'd have to do a little trick (mapping you bg on a plane facing your cam, with "visible to cam" as the only option checked in the Arnold Visibility tab of that plane). And in the matteshadow shader, you need to connect the bg image into the background color input of the shadowmatte node.
But, if you BG is an hdr (spherical map) then you can avoid the "plane facing cam" hack, just make an env shader with image into sky into out_env (in a arnold vop in shop) (don't forget to uncheck diffuse glossy otherwise it will light up your scene).

 

not time to make a hip now, but it's I'm unclear, let me know : /

Edited March 4, 2017 by 6ril

[violalyu]

Thanks @6ril! I was able to have it working the other day, but there's only a shadowmatte vop, so I just connected the output to rgba, not sure if I was doing the right thing but the result seems to be correct.

[6ril]

I used the wrong terminology, I said shadowmatte "material", which is wrong. It is indeed a vop, and I use it just like you (into color diffuse).