|Publication number||US20050190181 A1|
|Application number||US 11/115,162|
|Publication date||Sep 1, 2005|
|Filing date||Apr 27, 2005|
|Priority date||Aug 6, 1999|
|Also published as||EP1074943A2, EP1074943A3, US6930685, US20050195332|
|Publication number||11115162, 115162, US 2005/0190181 A1, US 2005/190181 A1, US 20050190181 A1, US 20050190181A1, US 2005190181 A1, US 2005190181A1, US-A1-20050190181, US-A1-2005190181, US2005/0190181A1, US2005/190181A1, US20050190181 A1, US20050190181A1, US2005190181 A1, US2005190181A1|
|Inventors||Yukio Sakagawa, Akihiro Katayama, Daisuke Kotake, Masakazu Fujiki|
|Original Assignee||Canon Kabushiki Kaisha|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (37), Referenced by (13), Classifications (7)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to an image processing apparatus and method for shading or shadowing a virtual object using a virtual light source upon expressing a virtual space on the basis of photo image data.
The present invention also relates to an image processing apparatus and method for changing a real illumination condition in real time and generating a mixed reality image in accordance with the changed condition.
Many schemes for describing a virtual space based not on a three-dimensional geometric shape but on a photo image have been proposed. Such schemes are called Image Based Rendering (to be abbreviated as IBR hereinafter), and can express a virtual space with high reality that cannot be obtained by a scheme based on a three-dimensional geometric shape.
Attempts to describe a virtual space on the basis of the ray space theory as one IBR scheme have been proposed. See, for example, “Implementation of Virtual Environment by Mixing CG model and Ray Space Data”, IEICE Journal D-11, Vol. J80-D-11 No. 11, pp. 3048-3057, November 1997, or “Manual Conversion between Hologram and Ray Space Aiming at 3D Integrated Image Communication”, 3D Image Conference, and the like.
The ray space theory will be explained below.
As shown in
If the reference plane P is set at z=0, and disparity information of a light ray in the vertical direction, i.e., the degree of freedom in the φ direction is omitted, the degree of freedom of the light ray can be reduced to two dimensions. This x-θ two-dimensional space is a partial space of the ray space. As shown in
Image sensing by a camera corresponds to registering in an imaging plane the rays that passes through the lens focal point of the camera, and the intensity and color of the ray is represented as an image. In other words, the set of light rays that passes through one point in the real space, i.e., the focal point position, corresponds to the set of captured pixels. In this, since the degree of freedom in the φ direction is omitted, and the behavior of a light ray is examined in only the X-Z plane, only pixels on a line segment that intersects a plane perpendicular to the Y-axis need be considered. In this manner, by sensing an image, light rays that pass through one point can be collected, and data on a single line segment in the x-u space can be captured by single image sensing.
When an image is sensed a large number of times by changing the viewpoint position, light ray groups which pass through a large number of points can be captured. When the real space is sensed using N cameras, as shown in
x+Z n u=X n (2)
can be input in correspondence with a focal point position (Xn, Zn) of the n-th camera (n=1, 2, . . . , N), as shown in
Conversely, an image observed from a new arbitrary viewpoint position can be generated (
In the mixed reality space that takes a photo image into a virtual space, real and virtual spaces are mixed. For this reason, image processes which are easy to implement in a real or virtual space alone may become hard to implement.
Image processes using photo image data do not excel in addition of shades and generation of a shadow by means of virtual illumination. This is because although shades or shadow change in accordance with the three-dimensional pattern of an object, it is hard to reconstruct shades or shadow since photo image data does not have any information pertaining to the geometric shape of the object. That is, a technique for rendering a virtual object on the basis of space data including geometric shape information, rendering shades to be added to that object or rendering a shadow formed by the object is known to those skilled in an image processing field based on geometric shape information (e.g., computer graphics (to be abbreviated as CG hereinafter)), but is unknown in an image processing field using a photo image such as a ray space or the like.
One difficulty in generation of a mixed reality space involves changing a real illumination condition and mixing a virtual image with a real space in real time in correspondence with the change in illumination condition.
Conventionally, the brightness of a real space is measured by a batch method, and the detected illumination condition is reflected in the mixed reality space.
The present invention has been proposed to solve the conventional problems, and has as its object to provide an image processing method and apparatus suitable for recording space data, which is suitable for generating shades of a virtual object from space data based on a photo image.
It is another object of the present invention to provide an image processing method and apparatus for generating shades of a virtual object from space data based on a photo image at high speed.
It is still another object of the present invention to provide an image processing method and apparatus capable of appropriately generating shades even when the position or condition of a virtual light source is arbitrarily-changed.
It is still another object of the present invention to provide an image processing method and apparatus capable of generating shades for a virtual object described in space data based on a photo image.
It is still another object of the present invention to provide an image processing method and apparatus capable of pasting a shadow image to a virtual object image from space data based on a photo image.
It is still another object of the present invention to provide an image processing method and apparatus suitable for real-time processes for directly generating a shadow image from space data, and pasting the shadow image in a virtual space.
It is still another object of the present invention to provide a mixed reality presentation apparatus for constructing a mixed reality space in response to a change in real illumination condition in real time.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.
An image processing apparatus and method according to the first embodiment of the present invention will be described in detail below with reference to the accompanying drawings. The image processing apparatus and method have a function of rendering shades to be added to a virtual object by a virtual illumination from ray space data, and rendering a shadow by the virtual illumination.
This system presents a virtual space to the user on a CRT 23. The user can freely walk through that virtual space or can manipulate (move, rotate, enlarge, or the like) an object in the virtual space by operating a mouse 28. More specifically, an object in the real space is converted into ray space data on the basis of a photo image, and the converted data is stored in advance in a disk 25. When the viewpoint position moves as the user walks through, a ray space data object image at the moved viewpoint position is generated, as has been explained with reference to
The camera 29 and, especially, the illumination light source 32 are movable to sense shades generated by illuminations (real illuminations) at a plurality of known positions. This system generates ray space data with shades in advance on the basis of real shade images. Also, this system holds silhouette images of an object viewed from the light source positions as a shadow image database.
<Generation of Shades by Virtual Illumination>
As will be described later, the number of illumination positions influences the precision of the shapes of shades and shadow. Hence, the 10° increment width along each of the horizontal and vertical image sensing routes is merely an example, and the increment width can be arbitrarily increased/decreased as needed.
In this example, ray space data are respectively generated at 36 points of illumination positions. Each ray space data are generated from 36 images. If RS represents one object, the object RS can be expressed by RS(L) since it has an argument L of an illumination position.
As explained later, appropriate ray space data can be obtained by searching the table shown in
In step S30, viewpoint position i to be rendered is determined. It is checked in step S32 if rendering of ray space data objects pre-stored in correspondence with viewpoint position i of interest is complete. If rendering is not complete, the flow advances to step S34, the table shown in
If Ln represents the number of the ON illumination, steps S60 to S64 process an object RS(Ln). That is, the relative position of the object with respect to the illumination Ln is computed in step S60, and object data is acquired by searching the table shown in
P x =f(P, D x, D0, Rx, R0)
where P is the pixel value of a real image, and f is a predetermined function.
In this manner, rendering of an object is completed.
Referring back to
Upon completion of the process in step S38 for all ON virtual illuminations, the flow advances to step S42 to compute the sum of pixel values of that pixel computed for the respective virtual illuminations. In this case, the sum of pixel values can be obtained by simply adding the pixel values of the respective generated images at the corresponding pixel position. It is checked in step S44 if the sum of pixel values computed in step S42 overflows, i.e., exceeds the gamut of the display device (CRT 23). If 12S in step A44 restart process is done in step S46. In the restart process, the illuminance of the virtual illumination is decreased not to cause any overflow, and rendering is redone.
In step S66, objects are marked to indicate overflow. In step S68, the set illuminance values of all the virtual illuminations (see the table in
On the other hand, if it is determined in step S44 that no overflow is detected, the next object is referred to in step S50, and the flow returns to step S32. If YES is determined in step S32, ray space data have been processed for all pixels for one frame, and as a result, a virtual image under a condition that two virtual illuminations are ON (
<Effect of Shade Addition>
As described above, according to shade generation of this embodiment, shades from an illumination at a desired position can be appropriately generated even for a virtual object expressed by IBR data (having no geometric shape information) of the ray space theory or the like.
<Addition of Shadow by Virtual Illumination>
The image processing apparatus of this embodiment also has a function of adding a shadow by a virtual illumination in addition to addition of shades by the virtual illumination. The shape of a shadow is dominated by the geometric shape of an object and the shape of a plane (to be referred to as a “mapping plane” hereinafter) on which the shadow is projected. However, since an IBR image such as ray space data or the like does not have any geometric shape for an object, it is conventionally difficult to implement processes pertaining to a shadow, as described early. The image processing apparatus of this embodiment generates a shadow image in advance like in shading. The mapping plane is generated using a so-called “bounding box” known to those who are skilled in the CG art.
More specifically, when an illumination 32 illuminates a real circular cone 100 from the position in
The silhouette 121 serves as a basis of a shadow image, and will be simply referred to as an “Hedge shape” hereinafter. A shadow formed by a virtual illumination (i.e., a virtual shadow) can be obtained by computing the coordinate transform of the silhouette to have the viewpoint position of the virtual illumination as a coordinate axis, i.e., the affine transform. For example, when the angle of elevation of the virtual illumination is low, an elongated shadow should be generated, as shown in
The shape of a shadow is influenced by the shape of the mapping plane in addition to the silhouette shape. When the mapping plane is determined, the shadow shape is obtained by projecting the silhouette onto the mapping plane. This projected shape is expressed by an affine transform.
The principle of generating the mapping plane will be explained below.
A shadow of an object has a shape corresponding to the shape of said object. That is, a shadow is formed within a range corresponding to the shape of an object. A feature of this embodiment is to limit the shape (i.e., range) of the mapping plane to that of the mapping plane of the bounding box of an object (virtual object).
For example, when virtual images of two animal toys 301 having complicated geometric shapes in practice are present, as shown in
In step S100, the camera 29 and illumination device 32 are set at an arbitrary position L. In step S102, a real object is illuminated by the illumination 32 at this position L to capture its image. In step S104, a silhouette is acquired from that image. In step S106, pixel values in that silhouette are set to be black. Also, the transparency is set at a predetermined value (which does not indicate 100% transparency but allows to see through the surface of the virtual object).
A process in step S108 is selectively done. That is, if the image sensing plane (the camera position/posture) is not parallel to the projective plane (illumination position/posture), a re-projection process of a shadow image is required. However, in the example shown in
A blur process in step S108 considers the fact that an actual shadow is blurred at its edge portion. That is, by adding the blur process, a shadow image can look more natural. Furthermore, by increasing the blur value for a shadow projected at a position farther from the object, the natural feel can be further enhanced. When this blur process is done for an silhouette image generated from an image of a virtual object, it can be implemented using a viewing volume used upon rendering an image using a depth-of-field effect.
In step S110, the obtained shadow image data is saved. In step S112, the next image sensing position (illumination position) L+1 is selected, and the processes in steps S100 to S112 are repeated until the processes are done for all the illumination positions.
Note that the shadow data is saved in step S110 to be indexed by the relative position value between the illumination and object as shown in
In this manner, silhouettes obtained upon illuminating an object from a plurality of illumination positions can be prepared as shadow images.
More specifically, ray space data of a virtual object for which a shadow is to be generated is read out from the memory in step S120.
In step S122, all virtual illuminations that may generate shadows are detected. Steps S126 to S134 implement a rendering process of a shadow image formed by an ON illumination of those detected virtual illuminations. More specifically, one ON illumination L is found in step S126. In step S128, the shape of the mapping plane is computed. The shape of the mapping plane can be computed if the geometric shape of the bounding box of virtual object and the relative position of a light source are given, as described above. The geometric shape of the shadow mapping plane can be set so that an arbitrary element in its bounding box has a shadow projected onto that mapping plane.
Note that the bounding box used to determine the mapping plane can be used to create a simple shadow image in some cases. For example, when light reflected by a ceiling or external light serves as a light source, a very simple shadow image like an ellipse 305 that inscribes the bounding box can be used, as shown in
In step S130, a shadow image is rendered in correspondence with the relative position of the object with respect to the illumination L. As has been described above in step S110, the shadow image is indexed by the value of the relative position of the real object (virtual object) with respect to the illumination L (see
In step S124, the flow returns to step S124 to consider another illumination. If another ON illumination is available, in other words, if shadows formed by a plurality of illuminations may exist, the shadow images generated by the aforementioned scheme are mixed by known CG rendering (in consideration of semi-transparency of an image).
<Effect of Shadow Generation>
According to shadow generation of the above embodiment, a shadow formed by an illumination at a desired position can be appropriately generated even for a virtual object expressed by IBR data (having no geometric shape information) of the ray space theory or the like.
Various modifications of the present invention can be made.
In the above embodiment, ray space data are obtained by computations, but a RAM or ROM that stores them as a table may be used.
The display device is not limited to the CRT. For example, a lenticular or HMD type display device may be used.
The above embodiment has exemplified a method of holding in advance images sensed from all possible illumination positions. This is because ray space data objects used have only horizontal disparities but ignore vertical disparities. If a ray space data object can be generated in also consideration of the vertical disparity, an image of an object viewed from a given position of an illumination is generated using that ray space data object, and a silhouette can be rendered. In the ray space theory, not only the horizontal disparity but also vertical disparity can be provided, and such process can be implemented by expanding the aforementioned ray space data process pertaining to the horizontal disparity in the vertical direction. Hence, even when shadow data are not sensed in advance, the silhouette of an image viewed from an illumination position can be generated in real time using ray space data objects, and a shadow can be expressed by re-projecting the generated image.
When a plurality of illuminations are used, a silhouette image is generated at each illumination position, and shadows can be mixed by the scheme described in the above embodiment.
To restate, according to the present invention, shades can be appropriately added to a virtual object defined by space data based on a photo image.
Also, according to the present invention, a shadow can be appropriately mapped on a virtual object defined by space data based on a photo image.
A mixed reality presentation apparatus according to the second embodiment of the present invention will be described in detail below with reference to the accompanying drawings.
On the other hand, an image sensing device 105 uses a video camera or the like for sensing an image of a real space. The image sensing device 105 is preferably attached to the head of the user when the viewpoint position and line-of-sight direction of the user change. An image input module 104 converts an image sensed by the image sensing device 105 into an object, also generates a depth value of a given in that image, and passes them on to an image mixing module 102.
The image mixing module 102 mixes the CG image generated by the image generation module 103 with the video image from the image input module 104. In this mixing, as is well known, occlusion is determined by comparing the depth values of the CG image and video image, and a mask corresponding to a portion to be hidden of a behind object is generated, thus mixing the video and CG images.
Note that the image generation module 103 receives information that pertains to illumination conditions from a mixed reality space management module 108. That is, the image generation module 103 generates a CG with shades in accordance with the illumination conditions.
In this embodiment, a real illumination device 107 is used to illuminate an object. The management module 108 can change the illuminance, illumination direction, and the like of the illumination device. The management module 108 converts changed conditions of the illumination device 107 into predetermined parameter values, and passes them on to the image generation module 103.
A GUI 120 is a graphic user interface which is displayed on a display device by the management module to change illumination conditions.
The illumination conditions set by the user via this GUI are sent to a controller 107 b in the illumination device 107. The controller 107 b converts the illumination conditions into drive amounts of the motors and the like of the illumination device 107, and outputs them. In this manner, the illumination device 107 is set at illuminance and the like set by the user via the GUI.
On the other hand, the illumination conditions set via the GUI are converted into illumination condition parameters, e.g., angle, specular, ambient, position, diffusion, and the like defined by a space language used in the generation module 103. Note that these parameter values are determined in advance by experiments under various illumination conditions. The image generation module 103 sets the received parameter values in a rendering routine.
In the flow chart shown in
The states of such changes of a CG image are shown in
Various modifications of this embodiment may be made within the scope of the present invention.
In the above embodiment, the GUI is used to change illumination conditions. Instead, hardware devices such as a volume, slide switch, joystick, and the like may be used. When such hardware devices are used, output signals from these devices must be sent to the apparatus having the management module.
In the apparatus of the above embodiment, the illumination conditions are changed under the control of a computer. The present invention is not limited to such specific control. For example, the present invention can be applied when the illumination conditions are manually changed. On the other hand, condition change values on the GUI 120 may be read by the controller 107 b in a software manner. In this modification, the need for the rotary encoder in the above embodiment can be obviated. In order to detect changes in illumination conditions, an illuminance sensor, a sensor for detecting illumination direction, and the like are provided, and these sensor outputs are supplied to the management module.
In the above embodiment, illumination program parameters are pre-stored in a predetermined memory 121, but may be computed in real time on the basis of the detected illuminance, illumination direction, and the like. For this purpose, conversion formulas for deriving parameter values from the detection values of the illumination conditions may be pre-stored in the memory, and parameters may be computed using these conversion formulas in real time.
To recapitulate, according to the present invention, the illumination conditions of a virtual image can be acquired in real time in correspondence with changes in real illumination. For this reason, deviation of image quality between real and virtual images due to structural differences of the illumination conditions can be minimized.
As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the claims.
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