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Franz Borrematte shadow 3ds max
by on Aug 3, 2009 at 11:10:54 pm

Hi, I realy hope someone could help me out integrating a 3D object with a 2D image.

My setting is imitating a photo with a table on a floor, where I would like the sphere to cast shadow on the table and the floor, without the 3D box (imitating the table) to cast shadow on the floor?

I have used a matte shadow material on the box (tabel) and the plane (floor). The problem is that I can't get the box (table) to block the shadow from the sphere falling on to the floor.
How can I achieve this?

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Franz Borre_
by on Aug 4, 2009 at 12:20:58 am


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Franz BorreRe: matte shadow 3ds max
by on Aug 4, 2009 at 9:23:02 am

Posting images of my scene here

In this last image I would like the table (box) to block out some of the shadow from the sphere falling on to the floor, like in the real world.


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Tiago RibeiroRe: matte shadow 3ds max
by on Aug 6, 2009 at 4:13:05 am

what did you do for the table not to appear in the last image?
did you just hide it from render, or did you disable shadow casting from it?
if you don't find another way, maybe you coult try doing multiple render passes, and compositing them:
p1: one that shoudld basically be what you used on the last image
p2: one where you render only the shadows casted from the table, with black background
ap: object alpha pass, with no shadows (just a black and white image, white corresponding to the sphere and the table, black corresponding to everything else)

so what you would want to see is a final image composited from:

first, (1/ap) means inverting the alpha pass, because you need to flip black/white
second, multiply this inverted pass with the table shadow pass (p2), and the result will be the table shadow pass, except the areas where there should be objects visible (because ap was inverted, so objects will be black, so multiplying will result in black). we want this "except", because of the subtraction on the third step
so to finish, in third place, you subtract the result from step 2 from your p1 (your currend render)
the subtraction will eliminate the shadows that were casted over the table's shadow, so i think you will get the result you want. the first step was to keep these subtractions from damaging the rest of your scene, because if you move the camera in a way that the table's shadow underlaps the table, subtracting the table's shadow from the render would also subtract part of the table, and you don't want that. so first, multiply it by the objects inverse alpha, so you make sure you won't cut out wrong stuff
be sure you render p2 with black background, because this will be a subtracting image. so black will be neutral on that. if you don't, you will subtract white out of all your image, and that's not what you want =)

i can't guarantee you this will do the complete job, i just read your post and replied while seeing it happen in my head =)
but if you get those 3 passes, you can quickly try the composition using photoshop-like software, using layer blending to do the subtraction and the multiplication

anyway, i algo think it should be possible to get the shadow ok, right out of max, without having to go through all this, but for that, i'll have to do a test on my own before i give you an answer, and i can't do that right now, so i'll just leave you an alternative solution =)

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Franz BorreRe: matte shadow 3ds max
by on Aug 7, 2009 at 8:47:03 am

Thaks a lot for your reply!

In my last render for the table I used matte/shadow material and disable shadow casting.

I`ll try out your solution with multiple render passes, interesting stuff to learn!

Hope it`s also possible to make shadow ok, right out of max too...

thanks again


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Joe ViceRe: matte shadow 3ds max
by on Aug 23, 2009 at 7:54:51 pm

Depending on your Photoshop skills, you could also render out two separate passes - one with the floor and one without then merge them back in together.

Architectural Renderings

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Charles PerezRe: matte shadow 3ds max
by on May 19, 2012 at 9:34:04 pm

Why don't you try rotoscoping?

Architectural Renderings

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