drop shadow algorithm

[finecur]

Suppose I have a image and inside it there is a object. How can I draw
a drop shadow of the object in the image? I am looking for
computational algorithm.

Thanks,

ff

[Hans-Bernhard Bröker]

finecur wrote:
> Suppose I have a image and inside it there is a object. How can I draw
> a drop shadow of the object in the image?

You can't. There is nowhere near enough information in a 2D image to
compute the shadow a 3D object would cast in a 3D environment.

[Gernot Hoffmann]

Hans-Bernhard Bröker schrieb:

In Adobe graphic programs the technical term 'drop shadow'
means a fake shadow, merely a graphical effect (which is
certainly not welcome for the friends of Bauhaus):
http://en.wikipedia.org/wiki/Drop_shadow

Best regards --Gernot Hoffmann

[Kenneth Sloan]

Impossible - and yet easy.

Once you realize that you will have to be satisfied with a wrong answer,
do that 2.5D people have done for a half-century, or more: find the
outline of the object, shift it slightly down and to the right, darken
anything within the bounds of this shifted polygon that is NOT within
the outline of the original object.

Modify as needed, depending on any information you may have extracted
from the image, such as the distance between the object and the
background, the location of the light source, etc.

--
Kenneth Sloan Kennet...@gmail.com
Computer and Information Sciences +1-205-932-2213
University of Alabama at Birmingham FAX +1-205-934-5473
Birmingham, AL 35294-1170 http://KennethRSloan.com/