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alikim
05-18-2009, 07:00 PM
I'm trying to understand why a shadow becomes more blurry with the increasing distance from the object which casts it. I found two reasons which are the light source having some tangible size and diffraction of light which makes some part of it to "turn" around the edge.

Can anyone please tell me which of these is more dominant and what approach is used in 3D programs to successfully emulate the effect?

almightie
05-20-2009, 09:33 AM
I'm trying to understand why a shadow becomes more blurry with the increasing distance from the object which casts it. I found two reasons which are the light source having some tangible size and diffraction of light which makes some part of it to "turn" around the edge.

Can anyone please tell me which of these is more dominant and what approach is used in 3D programs to successfully emulate the effect?

Well I believe...this effect is even seen in real world....Software lights are originally generated by keeping physical light properties in mind (if I am not wrong) and when you use Photometric light (which basically follow physical light equations) It looses its energy on distant place from its origin.....so when you look at the shadow on distant angle it is blurred...I will still try to give more technical and point specific reason if its required

(by the way its well explained in Max's default tutorials)

kanooshka
05-20-2009, 01:06 PM
Shadow blurring is a relationship between the light sources size, distance to an object and an objects distance from its shadow. Imagine taking one light bulb to a cylinder and looking at the shadow. You would see one sharp shadow.
http://www.dockay.com/Tutorials/blurred_shadows_01.jpg

Now Imagine you have another light bulb and you place it a distance away from the first.
http://www.dockay.com/Tutorials/blurred_shadows_02.jpg
First you will notice that this shadow is at a different angle than the first. Second, you will notice that the shadows converge in one area. This area where the shadows converge is your darkest part of the shadow.

Now for a third scenario imagine there was a light source that covered the area that both light bulbs previously held.
http://www.dockay.com/Tutorials/blurred_shadows_03.jpg
The same principal is applied but in a much smoother way than the first.

in conclusion, the further an objects distance from its shadow and the further an object is from a light source the less rays hit the object and the blurrier the shadows.

To create this effect use an area light or its equivalence.

alikim
05-20-2009, 02:08 PM
Thanks guys, I know that shadows becomes blurry because of the finite size of the light source.

My question is not about that.

As I wrote in my original post, I'm asking about edge diffraction of light which also blurs shadows - if it's effect is comparable and if it's calculated in 3D software.

almightie
05-21-2009, 05:16 AM
Nicely explained Kanooshka.....

:bowdown:

playmesumch00ns
05-21-2009, 11:26 AM
Thanks guys, I know that shadows becomes blurry because of the finite size of the light source.

My question is not about that.

As I wrote in my original post, I'm asking about edge diffraction of light which also blurs shadows - if it's effect is comparable and if it's calculated in 3D software.

No, diffraction effects aren't calculated 'out of the box' in most renderers. It's also a negligible effect for most scenes.

FrancoisvdW
05-28-2009, 03:25 PM
Maxwell render renders light as a electromagnetic wave with a certain spectral range, and also supports diffraction through prims as an option. I'm not sure if it also takes the geometry's edges into account...

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