On a summer evening seating in my apartment in Baltimore, I noticed this character popping up on the sheer curtain moving by the wind. The shape morphed constantly and were read as different characters. From Geisha to a demon..a lady with a large bag pack and anything you could imagine of. I started photographing them as it appeared so interesting!
And I wondered how does this actually occur?
Objects cast shadows and move along with the moving objects in the scene, due to which object shape distortion occurs in the foreground, they typically differ signiﬁcantly from the background.
Shadows are due to the occlusion of the light source by an object in the scene, which here is the figure of Geisha seating on the window frame. The part of an object that is not illuminated is called self-shadow (less lit areas of the figure), while the area projected on the curtain by the figure is called cast shadow and is further classiﬁed into umbra and penumbra. The umbra corresponds to the area where the direct light is totally blocked by the object, whereas in the penumbra area it is partially blocked.
Notice that the frontal silhouette of the Geisha in shadow remains constant except the change in overall scale while the rear silhouette gets stretched or pulled in.
Refer to the figure shown below to further understand umbra and penumbra.
Note that it is the angular size of the source that really matters. Here the source is the sun which is huge, but since it is so distant its angular diameter is only half a degree.
Hope this information was easy enough to grasp for you all!