Overlayable and Rotation-free Transmissive Circular Color Marker for Augmented Reality

This paper proposes a new design of overlayable transmissive color marker. Each marker is transparent and the marker has different colors, and outside of the marker is a region for estimating order of the overlay. ID patterns are detected from overlaid markers by splitting an input image in red, green and blue channel image. The overlaid order is estimated with the use of average color in the estimation area of overlaid order. Moreover this marker can estimate the relative degree of rotation angle between markers. To evaluate the performance of the proposed marker, we measured the misalignment which can be permitted when detecting each marker and the accuracy of estimated relative angle of the rotation. Moreover the maximum angle which can detect each marker between camera and marker is measured. INTRODUCTION A marker is a basic device to estimate three-dimensional position of the camera in augmented reality (AR). ARToolKit is very famous as tool of marker based AR [1, 2, 3]. Markers for specific application have proposed by modifying design and materials of the marker to apply markers to special environment [4, 5, 6]. Bluteau et al. proposed thermal markers consisted of thermal barrier material and thermal camera for supporting medical communication[4]. Park et al. proposed an invisible marker with the use of IR fluorescent pen and IR camera [5], and Nakazato et al. also proposed an invisible marker using translucent retro-reflectors, IR light source and IR camera [6] for tracking. Moreover Yasumuro et al. proposed 3D marker consisted of four 2D markers and spherical mirror for keeping optical consistency in an interactive virtual interior design [7]. However these proposed marker cannot use while overlaying multiple markers. An overlayable marker supports intuitive operation in case of stacking virtual objects. Imamura et al. proposed an overlayable transmissive color marker [8]. Figure 1 shows their proposed marker. Each marker is transparent and the marker has different colors: cyan, magenta and yellow. Several markers are detected from overlaid markers by splitting an input image in red, green and blue element image. And regions for estimating order of the overlay are added outside of the marker. In their research, interior simulator and video editing application were implemented and these applications have demonstrated an effectiveness of the proposed marker. However their designed marker is square, so the marker can be rotated only each 90 degrees. This paper proposes an improved design of marker in order to realize rotation-free marker. Moreover a performance of the proposed marker is evaluated through an experiment. PROPOSED MARKER DESIGN Figure 2 shows our proposed marker. The markers are printed to transparent OHP sheet in order to detect behind Figure 1. Existing overlayable transmissive color marker (Left) and its result (Right) marker. Color of each marker is cyan, magenta and yellow which are primary colors of subtractive mixture. And figure 3 shows the proposed marker design. The circle of outside of marker is area for judging order of the overlaid marker. This area is consisted of colored translucent part and white opaque part, and the order of overlaid markers is estimated by appearing color of this area. Table 1 shows appearing color by the order of overlaid marker. We can see that different color appears in the estimation area of overlaid order by the different order. Using this features, we can obtain the order of overlaid marker. Moreover the center of the marker has ID pattern region for identifying the marker. This ID pattern is associated with a virtual object, and the system can superimpose the virtual object on the marker. ! Figure 2. Examples of Proposed Marker CGIV 2012 Final Program and Proceedings 115