Shadow.Importance of Shadow- Shadows help to understand relative objectposition and size in a scene.-Shadows can alsohelp us understanding thegeometry of a complex receiver.- Shadows provide useful visual cues that helpin understanding the geometry of a complexoccluder（遮挡物）
Shadow • Importance of Shadow – Sh d h l t d t d l ti bj t Shadows help to understand relative object position and size in a scene. – Shadows can also help us understanding the geometry of a complex receiver. – Shadows provide useful visual cues that help in understanding the geometry of a complex in understanding the geometry of a complex occluder（遮挡物）
ShadowImportanceofShadowShadow helps to determine the geometry of receiver
Shadow • Importance of Shadow Shadow helps to determine the geometry of receiver
ShadowImportanceof ShadowShadow helps to determine the geometry of occluder
Shadow • Importance of Shadow Shadow helps to determine the geometry of occluder
Hard Shadowvs Soft Shadow.Hard Shadow vs Soft Shadow- The common-sense notion of shadow is a binarystatus, i.e. a point is either “in shadow" or not. Thiscorresponds to hard shadows, as produced bypointlightsources.-However,point light sources do not exist in practiceand hard shadows give a rather unrealistic feeling toimages.Note that even the sun, the most commonlight source in our daily life, has a significant angularextent and does not create hard shadows
Hard Shadow vs Soft Shadow Shadow vs Soft Shadow • Hard Shadow vs Soft Shadow – The common-sense noti f h d i bi tion of shadow is a binary status, i.e. a point is either “in shadow” or not. This correspond h d h d d db i ds to hard shadows, as produced by point light sources. – However, point light sources do not exist in practice and hard shadows give a rather unrealistic feeling to images. Note that even the sun, the most common light source in our daily life, has a significant angular extent and does not create hard shadows
Hard Shadowvs Soft Shadow.Hard Shadow vs Soft Shadow (2)- Still, point light sources are easy to modelin computergraphics and we shall see that several algorithms letus compute hard shadows in real time.-However,for a light sourcewith finite extent (actuallyan area source),the determination of the umbra andpenumbra is a difficult task in general, as it amountsto solving visibility relationships in 3D, a notoriouslyhard problem
Hard Shadow vs Soft Shadow Shadow vs Soft Shadow • Hard Shadow vs Soft Shadow（2） – Still i t li ht t d l i t Still, point light sources are easy to model in computer graphics and we shall see that several algorithms let us compute h d hd i li hard shadows in real time. – However, for a light source with finite extent (actually an area source), the determination of the umbra and penumbra is a difficult task in general, as it amounts to solving visibility relationships in 3D, a notoriously hard problem