This paper introduces our implemented systems, which display shadows not only in their natural form, but also with colorful and illuminous effects on them.
Graphic Shadow: Augmenting Your Shadow on the Floor Hiroshi Kato, Takeshi Naemura and Hiroshi Harashima School of Information Science and Technology, The University of Tokyo {kato, naemura, hiro}@hc.t.u-tokyo.ac.jp 2 Pictorial Shadow
Abstract This paper proposes real-time interactive systems illuminating your shadows cast on the floor, which we name “Graphic Shadow.” They will make you experience an exciting space of interaction performing an illusion on your own shadow.
1 Introduction This paper introduces our implemented systems, which display shadows not only in their natural form, but also with colorful and illuminous effects on them. We call this “Graphic Shadow.” We introduce two independent systems, “Textured Shadow” and “Pictorial Shadow” as follows: Textured Shadow This system uses effects made by lights with complementary colors. Users will experience interactive shadows with colorful textures emerging from a plain white floor. Details are given in [1]. Pictorial Shadow This system creates shadows with images that cannot be handled by the effects of complementary colors. For example, Pictorial Shadows can be brighter than the surroundings.
Projector P1
Camera C1
Video Camera (Virtual Light)
User
Shadow S2
Textured Shadow [1] runs on the same basis of shadows cast in the real world that “blocking the physical light creates the shadows.” For further augmenting the shadow, Pictorial Shadow synthesizes shadows of real objects blocking the virtual light [2] and casts it onto the real world using projectors. It consists of two major processes. Synthesizing the shadow of the virtual light and eliminating the shadow created by the real object blocking the projector light. Fig.1 is a diagram of the system. a. Reference image Alpha-map of c. Shadow region shadow region from image difference b. Current image
Perspective Transform
Perspective Transform
d. Projection image for P1 d. Projection image for P2
Projector P2
Camera C2
Projector P1
Projector P2
Shadow S1
Synthesized Shadow
Figure 1. Diagram of Pictorial Shadow.
e. Synthesized shadow from virtual light source
Figure 2. Synthesizing Pictorial Shadow.
Proceedings of the Second IEEE and ACM International Symposium on Mixed and Augmented Reality (ISMAR ’03) 0-7695-2006-5/03 $17.00 © 2003 IEEE
a. Camera C1
a. Camera C2
Generate alpha-map of human region
Luminance is increased on human region
Perspective Transform
b. Alpha map to compensate for S1
Generate alpha-map of human region Perspective Transform
c. Synthesized shadow
d. Projection image for P1 Projector P1
b. Alpha map to compensate for S2
d. Projection image for P2 Projector P2
e. Shadows of the user occluding the projector lights are eliminated
Figure 3. Eliminating physical shadows. A video camera is used as a virtual light source, which controls the region where the synthetic shadow should be projected. Fig.2 summarizes the shadow synthesizing process. An alpha-map is created according to the subtraction distance of each pixel between the image acquired in advance (reference image Fig.2a) and the current image (Fig.2b). The reference image is a background image where no users are in the system. The alpha-map (Fig.2c) represents the object region of the system. It also represents the region where the synthesized shadows of the virtual light are to be cast. Any picture can be pasted on it. Finally, a perspective transform would be applied so that the alpha map image are converted to the projection image (Fig.2d) with the correct geometry when cast to the real world (Fig.2e). Each projector makes shadows of users on their other side. Projector P1 makes shadow S1 which can be eliminated by casting additional light from projector P2. Shadow S2 can be eliminated likewise using projector P1. Installing the camera just besides the projector, the shadowed re-
Figure 4. Scenes of users interacting with the Pictorial Shadow. gion S1/S2 can be estimated from the camera image C1/C2 (Fig.3a). Shadows S1/S2 can be eliminated by increasing the luminance of the human region in the alpha-map. The shadow projection images (Fig.3d) are created by blending the alpha-map (Fig.3b) with the image of the synthesized shadow (Fig.3c, Fig.2d). The shadows are eliminated when the two projector lights converge onto the floor (Fig.3e). Fig.4 shows some scenes of interaction with Pictorial Shadow. By applying bright textures, shadows may turn out brighter than the areas where virtual lights are cast.
3 Conclusions Users can interactively operate the images cast onto the floor just like their own shadows. Textured Shadow [1] showed better response and resolution of the shadow, but the flexibility of the shadows has increased significantly in Pictorial Shadow. Special thanks goes to Kazutaka Yasuda for editing the video. The projector and camera system was constructed with the support of Audio Visual Communications LTD.
References [1] H. Kato, T. Naemura, and H. Harashima, “Textured Shadow,” ISMAR2003, 2003. to appear. [2] T. Naemura, et al., “Virtual Shadows ...,” Trans. Virtual Reality Society of Japan, vol. 7, no. 2, pp. 227–238, 2002.
Proceedings of the Second IEEE and ACM International Symposium on Mixed and Augmented Reality (ISMAR ’03) 0-7695-2006-5/03 $17.00 © 2003 IEEE
