Abstract:
A depth image-based modeling method and apparatus. A depth information-based modeling method using a three-dimensional (3D) polygonal mesh includes: extracting a bounding volume (BV) for the 3D polygonal mesh; obtaining a 3D grid by dividing the BV using a plurality of sampling lines; selecting some of a plurality of vertices of the 3D grid that intersect the 3D polygonal mesh as valid vertices; obtaining depth information and color information of the valid vertices by using a plurality of vertices of the 3D polygonal mesh; and modeling an object using the depth information and the color information of the valid vertices.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2005-0001951, filed on Jan. 8, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a depth image-based modeling method and apparatus, and more particularly, to a depth image-based modeling method and apparatus which obtain depth and color information from a polygonal model. 
     2. Description of Related Art 
     Depth image-based representation (DIBR) is a technique of synthesizing a plurality of images obtained from respective virtual points of an object rendered in a still or moving image and pixel-wise depth information of the images. In general, DIBR is divided into the following two processes: re-projecting a plurality of points of an original image to a three-dimensional (3D) space using depth information of each pixel of the original image; and projecting the re-projection results onto an image plane of a virtual camera located at a given viewing location. In other words, DIBR includes the re-projection of a two-dimensional (2D) image to a 3D world and the projection of the re-projection result back to a 2D space. 
       FIGS. 1A through 1C  are diagrams illustrating a conventional DIBR modeling method. Referring to  FIG. 1A , in the conventional DIBR modeling method, a plurality of virtual cameras  11  are placed at a plurality of locations near the object  10 , thereby obtaining a plurality of images of an object  10 .  FIG. 1B  illustrates a plurality of color images  12  and a plurality of depth images  13  of the object  10  of  FIG. 1A  obtained by the virtual cameras  11 . The depth images  13  are gray scale images having depth information. The color images  12  and the depth images  13  of the object  10  are taken by the virtual cameras  11 , which are respectively located on the left, right, upper, and lower sides of the object  10 , as illustrated in  FIG. 1A .  FIG. 1C  illustrates a DIBR image obtained by synthesizing the color images  12  and the depth images  13  of  FIG. 1B . 
     The conventional DIBR modeling method, however, requires a plurality of virtual cameras to render an object, and thus results in a low rendering speed. This problem becomes more apparent when rendering of the object is complicated because the more complicated the rendering, the more virtual cameras are required. 
     In addition, in the conventional DIBR modeling method, a camera bounding volume (BV), which is a minimum volume that can surround an object as illustrated in  FIGS. 2A and 2B , must be manually adjusted. Thus, a user&#39;s capability to manually adjust the camera BV has a considerable effect on the quality of a DIBR image. For example,  FIG. 2A  illustrates an example of a well-optimized BV, and  FIG. 2B  illustrates an example of a poorly optimized BV. 
     Moreover, in the conventional DIBR modeling method, a virtual camera range needs to be set by a user according to the complexity of an object to be rendered. 
     BRIEF SUMMARY 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
     An aspect of the present invention provides a depth information-based representation (DIBR) modeling method and apparatus which obtain 3D depth information and color information using vertex coordinates in a 3D polygonal mesh structure representing an object to be rendered. 
     According to an aspect of the present invention, there is provided a DIBR modeling method using a three-dimensional (3D) polygonal mesh. The DIBR modeling method includes: extracting a bounding volume (BV) for the 3D polygonal mesh; obtaining a 3D grid by dividing the BV using a plurality of sampling lines; selecting some of a plurality of vertices of the 3D grid that intersect the 3D polygonal mesh as valid vertices; obtaining depth information and color information of the valid vertices by using a plurality of vertices of the 3D polygonal mesh; and modeling an object using the depth information and the color information of the valid vertices. 
     According to another aspect of the present invention, there is provided a DIBR modeling method. The DIBR modeling method includes: converting a 3D polygonal mesh into a 2D polygonal mesh by generating a texture map for the 3D polygonal mesh; generating a grid laid over the 2D polygonal mesh; obtaining depth information and color information of a plurality of vertices of the grid by using a plurality of vertices of the 2D polygonal mesh; and modeling an object by using the depth information and the color information of the vertices of the grid. 
     According to another aspect of the present invention, there is provided a DIBR modeling apparatus. The DIBR modeling apparatus includes: a division unit which extracts a BV for a 3D polygonal mesh and obtains a 3D grid by dividing the BV using a plurality of sampling lines; a vertex extraction unit which selects some of a plurality of vertices of the 3D grid that intersect the 3D polygonal mesh as valid vertices; a depth information extraction unit which obtains depth information of the valid vertices by using a plurality of vertices of the 3D polygonal mesh; a color information extraction unit which generates a texture map for the vertices of the 3D grid and obtains color information of the valid vertices by using texture coordinates on the texture map that correspond to the vertices of the 3D grid; and a modeling unit which models an object using the depth information and the color information of the valid vertices. 
     According to another aspect of the present invention, there is provided a depth information-based modeling apparatus comprising: a texture map generator which converts a three-dimensional (3D) polygonal mesh into a two-dimensional (2D) polygonal mesh by generating a texture map for the 3D polygonal mesh; a grid generator which generates a grid laid over the 2D polygonal mesh; a depth information extracting unit which obtains depth information and color information of a plurality of vertices of the grid by using a plurality of vertices of the 2D polygonal mesh; and a modeling unit which models an object by using the depth information and the color information of the vertices of the grid. 
     According to other aspects of the present invention, there are provided computer-readable storage media encoded with processing instructions for causing a processor to execute the aforementioned methods of the present invention. 
     Additional and/or other aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following detailed description, taken in conjunction with the accompanying drawings of which: 
         FIGS. 1A through 1C  are diagrams illustrating a conventional depth image-based representation (DIBR) modeling method; 
         FIGS. 2A and 2B  are diagrams illustrating camera bounding volumes (BVs); 
         FIG. 3  is a block diagram of a DIBR modeling apparatus according to an exemplary embodiment of the present invention; 
         FIG. 4  is a flowchart illustrating a DIBR modeling method according to an exemplary embodiment of the present invention; 
         FIG. 5  is a diagram illustrating a 3D grid obtained by dividing a bounding volume (BV) of an object using a plurality of sampling lines; 
         FIGS. 6A and 6B  are diagrams illustrating a process of determining whether a vertex of a 3D grid projected onto a polygonal plane is a valid vertex performed in the method illustrated in  FIG. 4 ; 
         FIG. 7  is a magnified view of a portion  50  of  FIG. 5 ; 
         FIG. 8  is a diagram illustrating a texture map of a 3D polygonal mesh; 
         FIG. 9  is a flowchart illustrating a DIBR modeling method according to another exemplary embodiment of the present invention; 
         FIG. 10A  is a diagram illustrating a grid laid over part of a texture map; and 
         FIG. 10B  is a magnified view of a portion  100  of  FIG. 10A . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
       FIG. 3  is a block diagram of a DIBR modeling apparatus according to an exemplary embodiment of the present invention. Referring to  FIG. 3 , the DIBR modeling apparatus includes a division unit  30 , a vertex extraction unit  31 , a depth information extraction unit  32 , a color information extraction unit  33 , and a DIBR unit  34 . The operation of the DIBR modeling apparatus will now be described in detail with reference to  FIG. 4 . 
       FIG. 4  is a flowchart illustrating a DIBR modeling method according to an exemplary embodiment of the present invention. Referring to  FIGS. 3 and 4 , in operation  40 , the division unit  30  extracts a bounding volume (BV) from a 3D polygonal mesh obtained using an authoring tool. The BV is generated to have such a minimum size while still surrounding boundaries of an object because, in the present embodiment, unlike in the conventional art, a plurality of virtual cameras does not need to be installed. In operation  41 , the division unit  30  obtains a 3D grid by dividing the extracted BV using a plurality of sampling lines. The number of sampling lines used to divide the extracted BV is determined based on a volume resolution, which is proportional to a point resolution. In detail, a DIBR format used in the present embodiment is a point texture format. In the point texture format, each of a plurality of intersection points between the sampling lines and the object has depth information and color information. Therefore, in the present embodiment, once a point resolution of a final 3D DIBR image is set, the number of sampling lines used to divide the extracted BV is automatically determined based on the point resolution.  FIG. 5  is a diagram illustrating a 3D grid obtained by dividing a BV using a plurality of sampling lines. The authoring tool used to generate the 3D polygonal mesh may be any conventional 3D graphics tool, such as 3DS Max or Maya. 
     The vertex extraction unit  31  selects some of a plurality of vertices extracted from the 3D grid that intersect the 3D polygonal mesh as valid vertices. In detail, in operation  42 , the vertex extraction unit  31  extracts vertices from a plurality of cubes of the 3D grid that contain polygonal planes of the 3D polygonal mesh. Here, if the distance between the center of a cube of the 3D grid and a polygonal plane of the 3D polygonal mesh is smaller than the distance between the center of the cube of the 3D grid and a vertex of the cube of the 3D grid, the cube of the 3D grid is determined to contain the polygonal plane of the 3D polygonal mesh. Then, in operation  43 , the vertex extraction unit  31  selects some of the vertices extracted in operation  42  as valid vertices. It is determined whether a vertex is valid by determining whether a projection of the vertex onto a corresponding polygonal plane exists inside the corresponding polygonal plane. It is determined whether the projection of the vertex exists inside the corresponding polygonal plane by determining whether the sum of the areas of polygons into which the corresponding polygonal plane is divided by connecting the projection of the vertex to the corners of the polygonal plane is equal to the area of the corresponding polygonal plane. For example, referring to  FIGS. 6A and 6B , D is a projection of a vertex onto the triangle ABC. If the projected vertex D is located inside triangle ABC as illustrated in  6 A, the area of ΔABC is equal to the sum of the areas of ΔABD, ΔADC, and ΔBDC. However, if the projected vertex D is located outside triangle ABC as illustrated in  FIG. 6B , the area of ΔABC is not equal to the sum of the areas of ΔABD, ΔADC, and ΔBDC. 
     In operation  44 , the depth information extraction unit  32  extracts depth information from the valid vertices, and the color information extraction unit  33  extracts color information from the valid vertices. 
     The depth information of the valid vertices may be replaced by depth information of vertices of the 3D polygonal mesh that are closest to the respective valid vertices, as illustrated in  FIG. 7 .  FIG. 7  is a magnified view of a portion  50  of  FIG. 5 . In  FIG. 7 , reference numeral  70  indicates a grid vertex and reference numeral  71  indicates a polygonal mesh vertex. 
     The color information of the valid vertices may be obtained, as shown in  FIG. 8 , by converting the coordinates (x, y, z) of each of the valid vertices into texture coordinates (U, V) on a texture map  80  with the use of a Barycentric coordinate system and then converting the texture coordinates (U, V) of each of the valid vertices into a set of RGB values. 
     In operation  45 , the DIBR unit  34  converts the depth information and the color information of the valid vertices into DIBR format information and models the DIBR format information, thereby generating a 3D DIBR image. 
       FIG. 9  is a flowchart illustrating a DIBR modeling method according to another exemplary embodiment of the present invention. Referring to  FIG. 9 , in operation  90 , a texture map for a 3D polygonal mesh is generated using the authoring tool that has been described above. In operation  91 , a grid is laid over a 2D polygonal mesh contained in the texture map. Here, the grid is generated by using a plurality of sampling lines, as described above. In the present embodiment, like in the previous embodiment, once a point resolution of a final 3D DIBR image is set, the number of sampling lines used to generate the grid is automatically determined proportionally to the point resolution.  FIG. 10A  illustrates a grid laid over part of a texture map. Even though the sampling lines of the grid are illustrated in  FIG. 10A  as being spaced a large distance apart, the distance between a pair of adjacent sampling lines of the grid is preferably smaller than the resolution of the 2D polygonal mesh. 
     In operation  92 , depth information and color information of a plurality of vertices of the 2D polygonal mesh are replaced by depth information and color information of respective closest vertices of the grid.  FIG. 10B  is a magnified view of a portion  100  of  FIG. 10A . Reference numeral  101  indicates a grid vertex. Reference numerals  102  and  103  indicate polygonal mesh vertices, respectively. Depth information and color information of a grid vertex  101  is obtained by using texture coordinates (U, V) of a polygonal mesh vertex  102  that is closest to the grid vertex  101 . Color information of the polygonal mesh vertex  102  can be obtained by converting the texture coordinates (U, V) into a set of RGB values, and depth information of the polygonal mesh vertex  102  can be obtained by inversely converting the texture coordinates (U, V) into 3D coordinates (x, y, z) using a Barycentric coordinate system. 
     In operation  93 , the color information and the depth information of each of the vertices of the grid is converted into DIBR format information, thereby generating a 3D DIBR image. 
     Embodiments of the present invention can be realized as computer-readable code written on a computer-readable recording medium. The computer-readable recording medium may be any type of recording device in which data is stored in a computer-readable manner. Examples of the computer-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disc, and an optical data storage device. The computer-readable recording medium can be distributed over a plurality of computer systems connected to a network so that a computer-readable code is written thereto and executed therefrom in a decentralized manner. 
     According to the above-described embodiments of the present invention, depth information is directly obtained from a polygonal mesh without the need to synthesize a plurality of depth images, and thus is highly precise. In addition, since, in the above-described embodiments of the present invention, there is no need to install a plurality of virtual cameras, it is possible to simplify the overall rendering operation. Moreover, it is possible to extract depth information even from dead angles of the virtual cameras. Furthermore, since, in the above-described embodiments of the present invention, a BV is automatically determined proportionally to a point resolution, a manual adjustment of the BV is unnecessary, and it is possible to improve the quality of a DIBR image. 
     Although a few embodiments of the present invention have been shown and described, the present invention is not limited to the described embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.