casting shadows on hdri image

[toniboni]

Hi there,

I would like my object to cast a shadow on the ground of the hdri image. I've searched the web a lot but could not find any solutions other than for 3d max. There it seems to work with the vray infinte plane which you can set invisbible although it receives the shadows of the objects in the scene.

Thanks for the help!

Best Toni

[fpedrogo]

Unfortunately we don't have the Matte Shadow option in V-Ray for Rhino. That is the option that allows you to cast shadow in an invisible plane. I usually make a shadow channel and an alpha channel. I use the alpha channel as a mask in Photoshop to remove the ground and just let the object. Then I invert the shadow channel and use the multiplier blending mode to control the shadows.


Best

[toniboni]

Hm. what a pitty. Would have been nice. But your way seems really good, too

[fooprobe]

You can also make a material using your HDR and apply it to the infinite plane, where it will receive shadows but otherwise appear to be invisible. Just make sure the material UVW is sen to GenEnvironment instead of GenChannel, and you'll have to adjust the brightness of the background to match the ground plane.

[Micha_cg]

But at 1.5 is a bug, that HDRI textures are not working. At 1.05 it works fine. If I remember me right, the bug isn't fixed yet.

[fooprobe]

Maybe I'm not sure what you mean by HDRI textures. It's working fine for me, using Desert Highway from sIBL:


but the only HDRI is in the skylight. i did try it again with the low res hdr in the sIBL pack, works fine (but low res)

[Micha_cg]

If your HDRI has more dynamic, you will see, that it is clamped always. Tested it today, the bug isn't fixed. Here it was discussed last:

http://www.chaosgroup.com/forums/vbu...503#post563503

[fooprobe]

ahh, got it.

[Micha_cg]

Problem solved - matte material is available.

http://www.chaosgroup.com/forums/vbu...extures-at-1-5

[fpedrogo]

Yes, the wrapper material will be available in the next release.
Here are two sample of wrapper material

Best

[Dana Arts]

Thanks for sharing. I was looking for a way to do this. Can't wait for the next release then.

Can we extract just the shadow of the object from the ground plane too? I've heard of matte objects, but don't know how that works.

[Micha_cg]

Yes, if you like you can get separate object and shadow, you would additional need to render a mask for the object only. Here a screenshot from my image browser where you can see a rendering with and without alpha - the shadow is part of the alpha.

[Dana Arts]

Thanks, That is good to know. I can easily render out the mask for just the object, but I don't get how to get the shadow only or even with the shadow as part of the alpha. How did you achieve that?

How do you make everything around the shadow be transparent? I've managed to exclude objects from the render by selecting "only in secondary" in the material. I can get just the shadow, but still no alpha info. for the shadow. Any help please?


_____________________________________

Wait, I just discovered something. I have been using the gi environments. Even thought there are shadows they would not show up in the shadows channel. I added 1 light and I have some shadows.

Is there a way to capture the gi shadows that are cast onto the ground plane?

[Dana Arts]

How did you get the shadow part of the alpha?

[Micha_cg]

Please look at the screenshot (alpha channel is chossed at the frame buffer). The important options are:

* matte enabled
* shadows
* affect alpha
* alpha contribution -1 !!!

also enable alpha channel at the global VFB channels option and save your rendering as PNG.

Sidenote: the free image browser XnView allow to enable/disable (later extract alpha too) the alpha of PNG per shortcut Ctrl+H. So, if I open a PNG at Photoshop, the alpha channel is enabled always, but if I don't need the alpha at the image than I can open the image at XnView, disable alpha and Ctrl+A (select the image) and Ctrl+C (Copy the image) and I can insert the image without alpha in Photoshop too. So I have the freedom to get my image with or without alpha from one PNG rendering. It's my daily workflow.