Shadows and Alpha

[airion]

hello

im new to this forum but ive noticed alot of usefull information.
I have a small problem perhaps anybody could help

thank you in advance

the following image describes my problem.
What i have is a plane, with a projected texture on top.
I want this because i need the reflection in the object ( in this case a sphere )
I have a light that casts a soft shadow.
With a copy of that underlaying plane (the one i use for the reflection), i want to catch the shadows. ( with the help of a matteshadow material)
So my render in the end has my object (with reflection) + soft shadows... in the alpha.
NOT the entire underlaying plane in the alpha. Is there any way i can make the plane transparent so that its alpha is only the shadow that it catches? In vray there is an option AlphaContribution -1 ... that always saved the day for me.

I would like to find this in mentalray also.
Perhaps mentalray thinks differently than if im doing this totally the wrong way, do tell me

thank you for the help
air

http://www.qualitas-keukens.be/temp.jpg

[airion]

also what would be handy if that all is possible with one underlaying plane. instead of 2...

[strangerman]

Use a environment/ Background switcher instead a plain jpg image. This is happening because you are passing an image to the camera mapped background, which needs to be either a plain color with the alpha value set to 0 or a environment/background switcher with a plain color like said as the background value (i always use black), and the image you want to be reflected as environment in the value Environment/Reflections. This way you'll obtain a valid output to compose in post.

PS If you are camera mapping an image, you should use the environment/ background camera mapping map into the switcher

Search "production shaders" in google, there are several tutorials to do this, or go directly to the source ( of mental ray knowledge ;)) mentalraytips.blogspot.com, the production shaders's programmer blog

Hope this helps

[airion]

Use a environment/ Background switcher instead a plain jpg image. This is happening because you are passing an image to the camera mapped background, which needs to be either a plain color with the alpha value set to 0 or a environment/background switcher with a plain color like said as the background value (i always use black), and the image you want to be reflected as environment in the value Environment/Reflections. This way you'll obtain a valid output to compose in post.

PS If you are camera mapping an image, you should use the environment/ background camera mapping map into the switcher

Search "production shaders" in google, there are several tutorials to do this, or go directly to the source ( of mental ray knowledge ;)) mentalraytips.blogspot.com, the production shaders's programmer blog

Hope this helps

aha tnx for the help
I will check it out!

[Shimrod]

Use a environment/ Background switcher instead a plain jpg image. This is happening because you are passing an image to the camera mapped background, which needs to be either a plain color with the alpha value set to 0 or a environment/background switcher with a plain color like said as the background value (i always use black), and the image you want to be reflected as environment in the value Environment/Reflections. This way you'll obtain a valid output to compose in post.

PS If you are camera mapping an image, you should use the environment/ background camera mapping map into the switcher

I totally agree. Max help's files are very well filled on this subject. ;)