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Rendering on homogeneous background with shadows
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Rendering on homogeneous background with shadows // Archive: Tech Forum
Post by ToxicFrog // Aug 29, 2006, 12:51pm
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ToxicFrog
Total Posts: 17
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This question is very similar in nature to the other thread about rendering shadows against a transparent background.
I often render little widgets to use in Powerpoint presentations. I want it to look like the object is sitting on the page, so I need a convincing drop shadow.
(a quick example attached)
If the powerpoint slide has a uniform background, say a (208, 211, 218) grey, I need to render the object sitting on a "tabletop" of that color. The problem is: due to light attenuation, I get all sorts of shades of grey across the picture. If I raise the tabletop's luminance to get homogeneous lighting, the shadow gets washed out too.
The ideal solution would be a working shadow catcher, and a presentation software that can handle alpha channels... but at the moment I have to resort to photoshopping my trueSpace render before inserting it into Powerpoint.
Does anyone have an idea for a more graceful solution? |
Post by Zeipher // Aug 29, 2006, 1:21pm
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Zeipher
Total Posts: 224
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I have been trying this for you for ages, and can't even come close!!! Crazy... never thought of it before. It would be useful if constant did shadows, wouldn't it.. but then I guess it wouldn't be constant :confused:
I found it best to use a white floor, and white lights, and white background... this makes it easier to modify in a 2D app, but I'm afraid I can't help you do it in trueSpace. Sorry :o
I tried!!! :( |
Post by TomG // Aug 29, 2006, 3:19pm
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TomG
Total Posts: 3397
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I've been able to do this with my Catcher shader (though I never did get good results from the in-built one).
use a Constant color on a cube, then place a plane above it with the shadow catcher on it, and adjust the settings to match the lighting and shadow intensities to get the result you want.
Since the cube is Constant and doesn't receive shadows, the unshadowed areas will be your pure background color as required.
You do need ShaderLab of course. I'm working on contacting Scott to see if something can be done about ShaderLab distribution now that Primitive Itch is closed down.
http://www.tmgcgart.com/ShaderLab/html/shader_listing_1.htm#Catcher
The Catcher shader is free btw, except for the need to own ShaderLab of course. It's even in the ShaderLab install, and gives control over how bright the light has to be to count as max transparency, just how transparent max transparency is, how dark it has to be to count as min transparency, and just how transparent (how opaque, if you like) min transparency happens to be.
May take some adjusting to account for how much light is falling on the catcher plane, but it will do the job! Without all those parameters for what counts as light, what counts as shadow, and how transparent each should be, I don't find the inbuilt catcher as useful.
Oh it can catch reflections too if you want it to, as well as shadows :)
HTH!
Tom |
Post by ToxicFrog // Aug 30, 2006, 12:27pm
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ToxicFrog
Total Posts: 17
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Thanks for trying Zeipher, and thanks TomG -- I'll give your shadow catcher a try. It never occurred to me to put a constant-shaded tabletop underneath it.
I haven't tried yet but I'm guessing Shaderlab doesn't work with VRay... I've come to like VRay, but I suppose Lightworks is just as suitable for this trivial Powerpoint eye candy. |
Post by TomG // Aug 31, 2006, 3:32am
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TomG
Total Posts: 3397
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Yes, they won't work with V-Ray. Shaders are closely tied to the render engine they are written for (since they call upon its code and functions to do their work). Color shaders can work on multiple engines by getting sampled into textures for rendering, but such a thing is not possible for a reflectance shader - "how much light is on this point on the object" is a reflectance shader type question for its calculations, and only the render engine can answer that :)
I'd love to develop these shaders for V-Ray, but at present no system to do that exists (or rather no easy system like ShaderLab ;) )
HTH!
Tom |
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