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Old 22-01-2007, 04:11 PM   #1
Razzie
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Default Cast shadows but no lumination

Hi there,

Im making a simple seen with a desk lamp just to fidle with Maya.
Is there a way to make a point light ( or any other light) cast shadows without luminating?
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Old 22-01-2007, 04:49 PM   #2
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Hey there Razzie,

why would you want to do that? If there are shadows cast but no source for the shadows then the scene will look pretty peculiar.

later,

Mat.
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Old 22-01-2007, 05:09 PM   #3
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Actually Jeremy Birn talks about creating shadow only lights in 'Digital Lighting and Rendering' - 'shadow only lights can be tremendously useful if you want to control the exact, size, angle and perspective of your shadow without changing the lighting of the scene'.

I haven't done this, but he says in maya, 'you can create a shadows-only light by sliding the light color down to pure black and setting the shadow color to a negative value'

Though, I agree with happymat, your scene will look perculiar with no obvious source of light.

Hope this helps.
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Old 22-01-2007, 06:04 PM   #4
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at the same time when you think about it, if a light doesn't illuminate then how can it cast shadows?

a shadow by definition is an area lacking in illumination from a light because another object is blocking the light rays.
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Old 22-01-2007, 06:17 PM   #5
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My sentiments exactly Neostrider,

but I suppose that's where artistic license comes into play.

Arran, the method you suggested works but as I suspected it does look a litle odd (I guess I've kind of gone to extremes though!!).

Cheers,

Mat.
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Old 22-01-2007, 06:37 PM   #6
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Originally posted by NeoStrider
at the same time when you think about it, if a light doesn't illuminate then how can it cast shadows?

a shadow by definition is an area lacking in illumination from a light because another object is blocking the light rays.
yes, but creating lights in maya doesn't necessarilly create the shadow that you want - using lights seems to be a process of cheating to create the effect that you want. So while a shadow might be theoretically correct, you might want to cheat and make the shadow longer, to make the shot more aesthetically pleasing. In that case you would need another light to create the shadow, but you would not want that light to create more illumination.

Another example might be deforming your character's arm to increase the effect of foreshortening to the camera. However, his shadow would look wierd, so you would need to create another non illuminating light and possibly an invisible object to create a 'correct' shadow.

Obviously you are using these methods with other lights in your scene, so it's not as if you would be creating a shadow without a source of light - you are just cheating to create an illusion.

Although I probably haven't done a good job of explaining, these are both examples taken from 'Digital Lighting and Rendering which I definately recommend if you haven't looked at it.
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Old 24-01-2007, 03:24 AM   #7
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Thanks guys, ill defo look into it. The reason for my question was my scene setup. I had a spotlight shining onto an object whitch is not transparant. But i do want the light to go trough it and cast shaddows. Its a bit tricky to explain but ill go on and fiddle with it some more. :attn:
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