JP4287013B2 - Method for embedding digital watermark in 3D shape model - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital watermark technique for embedding copyright display information or the like in three-dimensional shape model data. In recent years, the use of technology for distributing and distributing digital data expressing a three-dimensional shape through the Internet or a CD-ROM medium has increased in the industry, and the present invention can be used in such a field.
[0002]
[Prior art]
As in the case of electronic museums on the Internet, there are an increasing number of cases in which three-dimensional digital data is distributed in addition to text, images, and sounds. Since such data can be easily copied illegally like an image or the like, a means for protecting the ownership is desired.
[0003]
Currently, embedding copyright information as a text comment in a data file of a 3D shape model is a common method, but information embedded in text can be easily removed by a text editor or the like. I can do it. In addition, copyright information embedded as a text comment is often removed even if the file is saved in a different file format after being read into editing software having a three-dimensional shape. Under such circumstances, there has been no effective means for protecting the three-dimensional shape model from theft such as illegal copying.
[0004]
[Problems to be solved by the invention]
The present invention has been made in consideration of such problems, and an object of the present invention is to provide a method that enables embedding of an invisible digital watermark into three-dimensional shape model data. It is. By embedding appropriate information according to the purpose, it becomes possible to prove the creator of the data, and to check the act of duplicating the data without permission from the creator for secondary use.
[0005]
[Means for Solving the Problems]
FIG. 1 is a flowchart showing the method of the present invention devised to solve the above problems. That is, according to the method of the present invention, a part of the three-dimensional shape data is selected as a watermark embedding part, a required number of vertices are selected from vertices constituting the watermark embedding part, and a new vertex obtained by duplicating this is used as a watermark. A first step (S1) for constructing the three-dimensional shape data for the first, a second step of inverting the orientation of each surface constituting the watermark shape to the opposite direction of the corresponding surface of the original three-dimensional shape data Step (S2), a third step (S3) in which a watermark shape is arranged in the embedded portion of the original three-dimensional shape data and both are combined to be the same node (S3), and the watermark shape and the embedded portion This is a method for embedding a digital watermark in a three-dimensional shape model, comprising a fourth step (S4) excluding overlapping vertices.
[0006]
In the method of the present invention, in the first step, watermark three-dimensional shape data is created from vertices having the same coordinate values as the number of vertices selected from the watermark embedding portion. At this time, in order to prevent the watermark from appearing when displayed in the wire frame model, the line segment constituting the created watermark shape data is configured not to protrude from the watermark embedding portion. In other words, the created watermark shape data is configured not to have a side (a line segment defined as a graphic element or a series of such line segments) that does not exist in the embedded portion.
[0007]
In a computer graphics (CG) rendering calculation, a process called hidden surface removal is performed. It is determined whether each surface of the CG object is face-up or face-down, and the face-down surface is made invisible. The orientation of the surface is determined by the sign of the inner product of the surface normal vector N and the line-of-sight vector V as shown in FIG. That is, if the inner product is positive (the angle formed by N and V is an acute angle), it is facing forward, and if the inner product is negative (the angle formed by N and V is an obtuse angle), it is facing backward. If there are no other front faces before the front face, the face is displayed. In the method of the present invention, using this principle, in the second step, the normal vector of each surface of the component of the watermark shape has a normal vector opposite to the surface to which it is pasted. Define.
[0008]
In the third step, the watermark embedded portion of the original 3D shape and the embedded watermark shape are set to the same node, so that the 3D shape model in which the watermark is embedded is read into the 3D modeling tool. This is a procedure for preventing the presence of a watermark from being perceived on the scene graph.
[0009]
In the fourth step, by removing the overlapping vertexes of the coordinate values of the watermark shape and the shape of the embedded portion, the embedded watermark data has resistance to data processing. What this means is that if the user of the 3D model data can extract the watermark shape data by some method or accidentally, even if trying to remove the extracted watermark shape portion, Since the watermark shape shares one or more vertices with the original three-dimensional shape data, a part of the original three-dimensional shape data is necessarily lost, so it is not possible to remove only the watermark shape. That is not possible. As a result, some vertices are shared with the watermark embedding portion of the original three-dimensional shape, and each surface constituting the watermark shape is connected to the watermark embedding portion from the same side (shared side). A watermark shape that is defined so that there is always a reverse surface to be formed is created.
[0010]
As another preferred embodiment of the present invention, after the first to fourth steps of the method of the present invention, a fifth step of setting the surface attribute of the watermark shape to be the same as that of the surface shape to be embedded is performed. Additional methods are possible. This procedure is shown in the flowchart of FIG. By adding the fifth step (S5), the watermark shape is more difficult to be recognized, which is more preferable.
[0011]
In addition, the second invention is a three-dimensional shape displayed by hidden surface removal processing having a normal vector attribute representing the orientation of each polygon surface defined by a plurality of polygon vertices and defined by those vertices. a computer readable recording medium storing modeling data, the three-dimensional geometric modeling data is configured to include a three-dimensional shape data, and a watermark for the shape data, the three-dimensional shape data, of that one in part, be those containing shape data portion to be watermark embedding section share some polygon vertices constituting the watermark for shape data, each polygonal surface constituting the watermark for shape, the watermark a surface composed of edges to be shared with the implanted portion, such as with a normal vector attribute opposite to the normal vector of the surface, the watermark embedding A computer-readable recording medium a three-dimensional shape modeling data, wherein a polygonal surface constituting a write portion and is configured to always correspond. Such a watermark shape can, of course, be created by the method of the first invention, but may be created by other methods.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the method of the present invention will be described by way of specific examples.
[0013]
(Original three-dimensional shape) A three-dimensional shape model in which a digital watermark is embedded to prevent unauthorized copying is formed as shown in FIG. Here, the watermark is defined by the front meshed surface, that is, the vertex (1,1,1) (-1,1,1) (-1, -1,1) (1, -1,1) FIG. 3 shows an example of the polygon structure of the surface 100 that is embedded in the surface 100 to be processed. In FIG. 3, it consists of many small square polygons. The figure shown in FIG. 3 corresponds to the embedded portion in this case.
[0014]
(Creation of Watermark Shape) A procedure for creating a watermark shape to be embedded as a digital watermark is described below. First, information to be embedded in a three-dimensional shape is prepared as a digital watermark. The information to be embedded may be a character representing a creator of a three-dimensional shape data, a copyright holder, a logo, or a figure as shown in FIG. Such information is replaced with an appropriate polygonal figure. At this time, in order to prevent the watermark from appearing when the wire frame is displayed, the information to be embedded is replaced with a polygonal figure having vertices having the same coordinate values as the vertices of the polygon in FIG. 3 as shown in FIG. This work can be performed interactively on, for example, a three-dimensional shape modeling system normally used by a CG production worker. FIG. 6 shows that the embedding information is replaced with a polygonal figure in which all the vertices and sides coincide with the mesh of the surface 100 in this way. The polygonal figure in FIG.
[0015]
(Reversal of Normal Vector) In order to paste the created watermark shape 200 on the back surface of the original three-dimensional shape data, the normal vector of the polygonal surface constituting the watermark shape 200 is reversed. Specifically, this inversion is to redefine the surface by reversing the order of the vertex rows defining the polygonal surface, or to rewrite the attribute of the surface as a normal vector. Which one is performed depends on the description format of the 3D shape model of the 3D graphic system to be used. In either case, the inversion of the normal vector can be described as a fixed algorithm, which can be automatically processed by a program. It is.
[0016]
(Combination of Watermark Shapes) The created watermark shape 200 is made up of vertices having the same coordinate values as the vertices of the polygons in FIG. 3 constituting the embedding surface 100 in a mesh shape, and the normal vectors are opposite to those polygons. Since it is a direction, it is defined in a form pasted on the back surface of the surface 100. Next, in order that the watermark shape 200 is always displayed together with the surface 100 on the three-dimensional graphic system, the surface 100 (a large number of polygon sets of FIG. 3 constituting the surface 100) and the watermark shape 200 are displayed. Are combined (redefined) as the same node in the scene graph.
[0017]
Here, a node is one graphic unit handled by the graphics system, and the graphics system controls whether or not to display one node unit when a certain screen is displayed. The specific method of connecting as the same node depends on the description format of the three-dimensional shape model of the graphics system to be adopted, but this can also be described in a certain procedure.
[0018]
(Embedding of watermark shape) There are some of which the coordinate values overlap between the vertices of many polygons of the surface 100 and the vertex of the watermark shape 200. One of these overlapping vertices is removed, and the necessary figure is redefined with the remaining vertices. In this way, if all or part of the watermark shape figure is extracted by extracting the figure with respect to the direction of the normal vector, the original figure will always be damaged when the extracted figure is deleted. The part that will be generated.
[0019]
(Setting of surface attribute of watermark shape) Finally, specular reflection light, diffuse reflection light, ambient light, etc. of the watermark shape 200 are set to the same value and attribute value as the original three-dimensional shape. By doing so, the presence of the watermark shape 200 is more difficult to be recognized.
[0020]
FIG. 8 shows a state in which the watermark shape 200 of FIG. 6 is embedded in the original shape surface 100 in this way. The rendering result of FIG. 8 is shown in FIG. FIG. 9A shows a case where the viewpoint is on the surface table (Z> 1). In this case, the watermark shape 200 is not displayed because it is located on the back side of the surface and the normal line is opposite to the line-of-sight direction. FIG. 9B shows a case where the viewpoint is behind the surface (Z <1). In this case, since it is the reverse of FIG. 9A, only the watermark shape is displayed. In addition, when a wire frame is displayed, only the polygon mesh is displayed for both directions of view.
[0021]
In order to improve the watermark resistance against partial modification to the original three-dimensional shape figure, it is only necessary to select a plurality of embedding parts and create and embed a watermark shape for each embedding part. (If the embedding parts at multiple locations are congruent with each other, the creation of the watermark shape only needs to be done once).
[0022]
In order to check the watermark information inserted by the method of the present invention, a special viewer is used that renders and displays all figures regardless of the orientation of the face with a transparency of about 50%. In this viewer, the portion in which the watermark shape is embedded has different transparency (the surface overlaps with the original three-dimensional shape), so that the information embedded as a watermark appears to float. Such a viewer system is generally not commercially available, but can be created by those who are familiar with the three-dimensional CG technology.
[0023]
The method of the present invention has been described above using the specific example of the original three-dimensional shape data of FIG. 2 and the watermark shape 200 of FIG. In this specific example, the embedding portion 100 (actually a set of many small polygons) forms one plane, but in general, a watermark is embedded, and the embedding portion may not be a single plane. Good. In other words, the vertices forming the figure constituting the embedded portion do not need to be on the same plane. This is because the essential idea of the present invention is to form a watermark shape having a surface opposite to the embedded portion by using a necessary number of vertices from the vertices forming the figure of the embedded portion (such as The configuration can be created interactively on the 3D shape modeling system, or a dedicated program can be created that automatically configures by providing the embedded part data). Therefore, the watermark shape cannot be detected by wire frame display. However, in general, the watermark shape cannot be created unless the embedding portion is determined.
[0024]
The three-dimensional shape modeling data created by the method of the present invention and the recording medium on which this is recorded are defined to have a normal vector in the reverse direction using the surface constituting the watermark embedding portion and the vertex of the surface. A watermark shape composed of faces is included.
[0025]
【The invention's effect】
As described above in detail, according to the method of the present invention, an invisible watermark can be embedded in a three-dimensional shape model by a simple procedure. There has never been a simple and practical method for inserting a digital watermark into 3D shape model data. Therefore, in the case of distributing three-dimensional digital data, such as an electronic catalog on the Internet, the present invention is the proof of the creator of the data, and the act of replicating the data without permission from the creator for secondary use. This is an epoch-making invention that is extremely practical and can be used as a means of inhibiting illegal copying and protecting ownership.
[Brief description of the drawings]
FIG. 1 is a flowchart illustrating the procedure of a method of the present invention.
FIG. 2 is an example of a three-dimensional shape model.
FIG. 3 is an enlarged view of a surface 100 which is an embedded portion.
FIG. 4 is character / graphic information embedded as a digital watermark.
FIG. 5 is a diagram illustrating a process of creating a watermark shape 200. FIG.
6 is a created watermark shape 200. FIG.
FIG. 7 shows a watermark shape 200 with the normals inverted.
8 is a diagram showing a state in which a watermark shape 200 is embedded in a surface 100. FIG.
FIG. 9 is a rendering result of a figure in which a watermark shape 200 is embedded.
FIG. 10 is a flowchart illustrating the procedure of the method of the present invention.
FIG. 11 is a diagram for explaining a method for determining a surface normal vector and a surface front and back.
[Explanation of symbols]
100 Three-dimensional watermark embedding portion 200 of embodiment 200 Watermark shape

Claims (3)

  A part of the three-dimensional shape data is selected as a watermark embedding part, a necessary number of vertices are selected from the vertices constituting the watermark embedding part, and the three-dimensional shape data for the watermark is obtained from the new vertices duplicated. A first step of configuring, a second step of reversing the direction of each surface constituting the watermark shape to the opposite direction of the corresponding surface of the original three-dimensional shape data, A three-dimensional shape comprising a third step of arranging the watermark shape obtained in the second step in the embedding portion and combining the two, and a fourth step excluding the watermark shape and the overlapping vertex of the embedding portion How to embed a digital watermark in a model. The method for embedding a digital watermark in a three-dimensional shape model according to claim 1,
A method for embedding a digital watermark in a three-dimensional shape model, wherein a fifth step of setting a surface attribute of a watermark shape to be the same as a surface attribute of a surface of an embedding portion after the first to fourth steps is added. A computer-readable recording of 3D shape modeling data displayed by hidden surface removal processing, which has a normal vector attribute that represents the orientation of the surface for each polygon surface defined by multiple vertexes. Recording medium,
The three-dimensional shape modeling data includes three-dimensional shape data and watermark shape data,
The three-dimensional shape data, a part of its, be those containing shape data portion to be watermark embedding section share some polygon vertices constituting the watermark for shape data,
Each polygonal surface constituting the watermark for shape is a surface formed from the side shared with the watermark embedding portion, such as with a normal vector attribute opposite to the normal vector of the surface, watermarks It must be configured to always correspond to the polygon faces that make up the embedded part.
Computer readable recording medium storing a three-dimensional geometric modeling data, wherein.

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