Vray Matte shadow

[Guest]

Hi,

In rhino how do I render a matte shadow material so I can later composite the render onto a background in Photoshop? I would like the floor to catch shadow information only. Cant seem to find an obvious way to do this in Rhino.

Thanks,

[Micha_cg]

You could enable the matte shadow output at the channels, but it works for raytraced lights without "store with IM" only. In the future you can use it with the dome light (HDRI env).

[Guest]

Hmm not sure I follow. I want to do this http://rhinotoday.com/2008/09/vray-m...adow-material/ but it seems a really long winded way of doing it. Is there an easier/quicker method like there is in 3ds max for example?

[Micha_cg]

Interesting, my old Vray experiment can be found still.

The easiest way is to create a soft studio ground, convert it to a mesh and use the frontal mapping tool from here:

http://www.chaosgroup.com/forums/vbu...l-render-tools

Maybe you find the old thread that is linked there. It could be here a the VfR forums.

[Guest]

Hi,

I did not realise at first that you wrote the tutorial Its not the camera projection I want to do its the rendering of the shadow on a ground plane. I wish to save out a PNG file with the shadow information only and then composite onto my own background in Photoshop. Your method of having to render the bottom view etc. seems a long winded process compared to doing it in 3ds Max for example. Is your method explained in that tutorial the only way?

Thanks,

[Micha_cg]

first method - render a bottom view ...

second method - direct rendering of the background per frontal mapping

third method - matte output channel and Photoshop

And your are missing a material where the transparency is controlled by the shadows, right? It's not available and the beta will not change it.

fourth method - my trick: set alpha contribution of the white ground 0, save rendering as PNG, open it at Photoshop, Ground is gone, now I use the image browser XnView and open the image there -> Ctrl+A -> Ctrl+C -> so you can copy the image with ground to PS per Ctrl+V, in PS I create an alpha mask at the complete image at the lowest layer and place the rendering there per Ctrl+V and invert it per Ctrl+I and adjust the level a little -> ready

If you have it done a few times than it's quick done. The trick is that XnView allow to extract two version from the rendering, with and without alpha. So you get the object and ground separated from one rendering.

[Guest]

Thanks for that. The scene is lit by HDRI. The first method although at first it seemed a long process, seems to be the quickest.

[Guest]

Hmm I tired the bottom view but when I render from the bottom the result is just black. Even with double sided material un-ticked. Do you have a scene file I could look at?

[Micha_cg]

Do you check that the normal dir (command _dir) of the ground surface show upward? From the front side the light will be catched and I suppose so your normal is flipped only.

[Guest]

No didn't check this, can I rotate the ground plane 180 degrees to do this?

[Micha_cg]

Yes, or use the _dir command and the normal arrows should show upwards to the light.

[Guest]

Hmm, OK got it working but I see the bottom of the object as well in the render. This is of course a coloured object.

[Gijs]

@ Micha: just save as TGA, then you already have the alpha channel included. I've made a shortcut in PS (use actions for this) that automatically extracts the foreground rendering from a TGA file (based on the alpha channel)

What I normally do is set alpha for the groundplane material to 0 same as Micha. With the right lighting you need just little adjustment to the background so the edges of the rendering are white (with level adjustment: use the white color picker and hold alt to see exactly what becomes 100% white)

[Guest]

Sounds like a pain to do something so simple:/ Any idea of matte shadow is included in the new Beta?