Patent Publication Number: US-8115774-B2

Title: Application of selective regions of a normal map based on joint position in a three-dimensional model

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to computer graphics and animation, and more specifically to the use of normal maps in lighting pixels when rendering three-dimensional computer models in real-time. 
     2. Discussion of the Related Art 
     The process of per-pixel lighting in a three-dimensional computer model uses the surface normal and the light vector at each pixel to calculate the brightness of the pixel. A surface normal is like an arrow that points in the direction that the surface of the model is facing. A light vector is a line from the point on the surface to the position of the light. As the angle between the surface normal and the light vector gets greater, the color of the pixel gets darker (and vice versa). 
     Texture mapping is the process of applying a texture, i.e. an image, to the surface of a computer model during rendering wherein the texture gets mapped onto the surface. The surface normal at each pixel is used along with the color values in the texture map to determine the lighting for each pixel. 
     A normal map is similar to a texture map but includes surface normal data instead of color values. More specifically, a normal map includes data that alters the original surface normals of the model. 
     It is with respect to these and other background information factors that the present invention has evolved. 
     SUMMARY OF THE INVENTION 
     One embodiment provides a method for use in animation, comprising the steps of: establishing a model having a plurality of joints; exposing a region of a first normal map based on a position of one or more of the joints; and applying the exposed region of the first normal map to the model. 
     Another embodiment provides a system for use in animation, comprising: means for establishing a model having a plurality of joints; means for exposing a region of a first normal map based on a position of one or more of the joints; and means for applying the exposed region of the first normal map to the model. 
     Another embodiment provides a computer program product comprising a medium for embodying a computer program for input to a computer and a computer program embodied in the medium for causing the computer to perform steps of: establishing a model having a plurality of joints; exposing a region of a first normal map based on a position of one or more of the joints; and applying the exposed region of the first normal map to the model. 
     A better understanding of the features and advantages of various embodiments of the present invention will be obtained by reference to the following detailed description and accompanying drawings which set forth an illustrative embodiment in which principles of embodiments of the invention are utilized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and advantages of embodiments of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1  is a flow diagram illustrating a method for use in animation in accordance with an embodiment of the present invention; 
         FIG. 2  is an exploded, pictorial view illustrating an application of the method shown in  FIG. 1  in accordance with an embodiment of the present invention; 
         FIGS. 3A ,  3 B,  3 C, and  3 D are screen shots illustrating a neutral pose for an application of the method shown in  FIG. 1  in accordance with an embodiment of the present invention; 
         FIGS. 4A ,  4 B,  4 C, and  4 D are screen shots illustrating a “brows up” pose for an application of the method shown in  FIG. 1  in accordance with an embodiment of the present invention; 
         FIGS. 5A ,  5 B,  5 C, and  5 D are screen shots illustrating a smile pose for an application of the method shown in  FIG. 1  in accordance with an embodiment of the present invention; and 
         FIG. 6  is a block diagram illustrating a system that may be used to run, implement and/or execute the methods and techniques shown and described herein in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Computer animation involves building an animated three-dimensional (3D) figure on the computer monitor that is rigged with a virtual skeleton. A full wire frame model, or a model built of polygons, is formed that typically includes a plurality of joints (sometimes called “bones”) that allow the model to move into different positions or poses. Surfaces, such as skin, eyes, mouth, etc., are added to the model during the rendering process. 
     The three-dimensional models used in video games are typically limited to being relatively low resolution, i.e. having a low polygon count, due to the models having to be rendered in real-time. Normal maps can be used to give a low resolution model the appearance of a high resolution model, i.e. a model having a high polygon count. In general, this can be done by taking surface detail from an actual high resolution model and putting it into a normal map, and then applying the normal map to the low resolution model similar to the way a texture map would be applied. 
     More specifically, the normal map in this scenario includes the direction information for the surface normals from the actual, more detailed high resolution model. When the normal map is applied to the low resolution model, the direction information in the normal map is used to alter the original surface normals of the low resolution model. The surface normals are altered in a manner which mimics the surface normals of the more detailed high resolution model. This fools the eye into believing that the surface has more detail than it really does because of the way the lighting reacts with the normal at each pixel. The surface does not really include the extra detail, but it appears like it does because of the changes in the lighting equation due to the change in the normal direction of the surface. This technique can be applied in real-time to significantly improve the appearance of the relatively low resolution models used in video games. 
     In general, one embodiment of the present invention provides a method of adding features and/or details to three-dimensional models that is driven by alpha blending a normal map based off of bone or joint translation/position. In some embodiments, a normal map is used to add details to specific regions of three-dimensional models based on the movements of one or more joints in the model. And in some embodiments, the locations of the specific regions for which detail is to be added are determined based on the positions or movements of one or more joints in the model. 
     Referring to  FIG. 1 , there is a method  30  in accordance with an embodiment of the present invention. In step  32  a model is establishing having a plurality of joints. In step  34  a region of a first normal map is exposed based on a position of one or more of the joints. And in step  36  the exposed region of the first normal map is applied to the model. 
     An example application of the method  30  in accordance with an embodiment of the present invention will be described with reference to  FIG. 2 . This example application may be used in animation for applying wrinkles or other details to specific regions of a character&#39;s face. 
     Specifically, a three-dimensional model  50  of a character&#39;s head is established. The model  50  includes a plurality of joints  52  that control the character&#39;s facial movements. A neutral normal map  54  containing static details, such as for example permanent wrinkle traces, pores, etc., may optionally be applied to the model  50 . 
     A normal map  56  containing dynamic wrinkles or other details that would appear on an average face in various contractions is layered on top of or above the neutral normal map  54 . This normal map  56  may also be referred to as a “wrinkle map” or “detail map”. In accordance with an embodiment of the present invention, a specific region of the normal map  56 , such as for example the region indicated at  58 , may be exposed based on a position of one or more of the joints  52  in the model  50 . The locations of the specific regions of the normal map  56  that get exposed may be determined based on the positions or movements of one or more joints  52  in the model  50 . Thus, the positions or movements of one or more joints  52  may be used to select the regions of the normal map  56  to be applied. 
     The exposed region  58  of the normal map  56  is then applied to the model  50 . For example, the model  50  may be rendered using the exposed region  58  of the normal map  56  in lighting pixels. In the illustrated example this results in wrinkles or other details being provided in the forehead region  60  of the model  50 . In embodiments where the neutral normal map  54  is used, the exposed regions of the normal map  56  may be superimposed onto the neutral normal map  54 . Thus, application of various different exposed regions of the normal map  56  to the model  50  may be used to provide wrinkles in specific regions of the face to create different facial expressions. 
     In some embodiments an alpha map  62  may be used to expose the specific regions of the normal map  56 . Furthermore, the alpha map  62  may be used to control the locations of the exposed regions of the normal map  56 . This may be accomplished by controlling an opacity value of the alpha map  62  based on the position of one or more of the joints  52  in the model  50 . Namely, the position of one or more of the joints  52  in the model  50  may be used to control the opacity value of a specific region of the alpha map  62 . For example, changing the opacity value of the specific region  64  of the alpha map  62  may be used to allow the corresponding region  58  of the normal map  56  to be exposed to the model  50 . 
     In some embodiments the method  30  ( FIG. 1 ) may, for example, be used in real-time applications, such as video games or the like. For example, the model may be rendered in real-time using the exposed region of the normal map in lighting pixels. In some embodiments, specific regions of the normal map may be dynamically exposed in real-time based on the movements of one or more of the joints in the model. Then, the exposed regions of the normal map may be dynamically applied in real-time to the model. This allows wrinkles or other details to be applied to specific regions of the face in real-time based on facial movements. 
     With respect to real-time applications, the method  30  may be used to provide a real-time dynamic shader that may be used in computer animation in accordance with an embodiment of the present invention. An example of such a shader will now be described for a scenario similar to as described above where wrinkles or other details are applied to specific regions of a character&#39;s face. It should be well understood, however, that in other embodiments of the present invention the teachings and techniques described herein may be used to apply any type of features or details to models representing any type of structure, whether animate or inanimate. 
     The embodiment of the real-time dynamic “wrinkle” shader described herein animates high frequency details, such as dynamic wrinkle-patterns, that cannot otherwise be efficiently generated using conventional geometry deformation techniques. The low frequency deformations are separated from the high frequency details by using low resolution geometry for the broad facial deformations and dynamic texture maps (normal maps) for the finer details. It has been found to be efficient to create the broad facial movements by actually transforming vertices via skin clusters on a fairly low resolution geometry and to generate finer details such as dynamic wrinkles using normal maps. The shader may be used in conjunction with computer generated (CG) characters that employ common smooth skin deformations. 
     The embodiment of the real-time dynamic wrinkle shader described herein uses a defined set of key “facial expressions” that would each benefit from detailed wrinkles or other details in order to be more readable and more effectively convey emotion. A normal or “wrinkle” map is generated that includes the data for these expressions. In some embodiments, a single normal map may contain all of the different dynamic wrinkles that would appear on an average face in various contractions. 
     For example, such a normal or wrinkle map may be created utilizing the following workflow. First, a blendshape of the desired facial expression that is to be detailed is generated. For example, for a “brows up” facial movement the animation controls of the facial rig are used to raise the eyebrows of the model into their extreme position. The resulting shape is exported into a high resolution modeling package to be used as a template for an artist to add the high frequency details that the particular expression requires, i.e. forehead wrinkles. By way of example, a modeling package that may be used for this task is ZBRUSH® available from Pixologic, Inc. The added geometric details are then exported as a normal or wrinkle map. The wrinkle map may be layered on top of a neutral normal map containing all the static details, such as permanent wrinkle traces, pores, etc. 
     In some embodiments, in order to locally control the appearance of the details in the wrinkle map, greyscale alpha maps may be used similar to as described above. Such alpha maps may be generated or created using a two-dimensional (2D) image processing package, such as for example PHOTOSHOP® available from Adobe Systems Incorporated. The alpha maps are created to locally expose the particular facial region of the wrinkle map, such as for example the forehead so that the forehead wrinkles may be applied to the model. 
     The system utilizes the joint transformations in the three-dimensional model which generate the broader facial movements to animate shader attributes, which in turn control the wrinkle display. In some embodiments the joint transformations may be used to control the alpha maps so that the shader regulates the display of predefined areas of the wrinkle map using blended alpha maps. That is, the alpha blending may be controlled directly by the translation of the joints in the facial rig. The translation value of selected control joints animates the opacity of their related alpha map. Based on the opacity value of a given alpha map, the wrinkle map is locally superimposed on the neutral map. In this way the set of alpha maps may be used to precisely control which region of the dynamic wrinkle map is revealed or masked. This provides for a dynamic and reactive wrinkle system. 
     In some embodiments, the character&#39;s face may be divided into a predefined number of regions which may show wrinkles independently. In the present example, the character&#39;s face is divided into seven regions in UV-space which may show wrinkles independently. Table 1 below is an example breakdown that may be used as a guideline. The table illustrates the alpha regions along with their related controllers. It should be well understood, however, that the choice and number of wrinkle-zones in other embodiments of the present invention may be reduced or increased based on the specific requirements and limitations of a given project. 
                             TABLE 1                       Translation       Alpha Region   Control Joints   Vector                  1) horizontal forehead wrinkles LEFT   Left Outer Brow   +Y       2) horizontal forehead wrinkles RIGHT   Right Outer Brow   +Y       3) angry Brow (vertical wrinkles   Inner Brow   −Y       between the brows)       4) crows feet wrinkles surrounding eyes   Left Cheek   +Y       LEFT       5) crows feet wrinkles surrounding eyes   Right Cheek   +Y       RIGHT       6) deepening of nasolabial folds LEFT   Left Mouth   −Z           Corner       7) deepening of nasolabial folds RIGHT   Right Mouth   −Z           Corner                    
The translation vector indicates the direction of the movement of the control joint, examples of which are provided below.
 
     An example operation of the real-time dynamic wrinkle shader will now be described. Specifically,  FIG. 3A  illustrates a three-dimensional model of a character&#39;s head that includes a plurality of joints that control the character&#39;s facial movements. In this figure the character&#39;s face is in a neutral pose, i.e. there is no translation of any of the joints. For example, the brow joint is neutral in this pose. 
     Because the character&#39;s face is in a neutral pose there is no need for the addition of any wrinkles from the wrinkle map. As such, the alpha map is invisible so that no portion of the wrinkle map is exposed.  FIG. 3B  illustrates the alpha map being invisible and also illustrates the UV-Map as reference. 
       FIG. 3C  illustrates the base or neutral normal map. The neutral normal map may contain the static details, such as for example permanent wrinkle traces, pores, etc. In the illustrated neutral pose it may be the only normal map that is applied. Again, in this example the wrinkle map is transparent for the neutral pose. 
       FIG. 3D  illustrates the final result. As shown no dynamic wrinkles are added or show in the neutral expression or pose. 
       FIGS. 4A ,  4 B,  4 C and  4 D illustrate the manner in which relationships may be defined between the joint configuration of a given facial movement and the appearance of specific, related wrinkle patterns in the appropriate region in accordance with an embodiment of the present invention. For example,  FIG. 4A  illustrates the joint translation for a “brows up” or “brow raise” pose. As shown, this pose transforms the brow joint upwards, which corresponds to a positive Y movement, which lifts up the skinned forehead geometry. Thus, the outer brow joint translates in the +Y direction. 
       FIG. 4B  illustrates the alpha map fading for the “brows up” pose. Namely, the positive Y joint translation value is input into the shader to control the alpha map for the brow region, which makes the “brows” portion of the alpha map visible. 
       FIG. 4C  illustrates the wrinkle map emergence. That is, the brow region of the wrinkle map is exposed by the alpha map. Namely, the alpha map is controlled in such a way that the dynamic wrinkle map becomes opaque only in the brow region, causing the forehead wrinkles to display. 
       FIG. 4D  illustrates the final result, namely, the brow wrinkles show on the three-dimensional model. 
       FIGS. 5A ,  5 B,  5 C and  5 D illustrate another example relationship between the joint configuration of a given facial movement and the appearance of specific, related wrinkle patterns in the appropriate region in accordance with an embodiment of the present invention. Namely,  FIG. 5A  illustrates the joint translation for a smile, which is a compound expression. As shown, the cheek joint translates in the +Y direction and the mouth corner joint translates in the −Z direction. 
       FIG. 5B  illustrates the alpha map fading for the smile pose. As shown, “crows feet” and “smile fold” alpha maps become visible. 
       FIG. 5C  illustrates the wrinkle map emergence. As shown, the eye region and cheek folds of the wrinkle map are exposed by the alpha map. 
     The final result is illustrated in  FIG. 5D , which shows the crows feet and smile folds showing on the three-dimensional model. 
     The relationships between the joint configurations and their appropriate wrinkle-patterns may be fine-tuned by an artist/animator going through an iterative process of setting extreme facial poses and testing the wrinkle behaviors. For each key pose that is to be set up for wrinkles, it may be desirable in some embodiments to find the most logical relationship between the joint position of the control rig and the related intensity value of its alpha map. In such embodiments the validity of this relationship may help to ensure that anytime the geometry is deformed by the joints the correct wrinkles will be displayed. 
     The timing of the wrinkle display in relation to the geometric deformation of the model may also be considered in accordance with embodiments of the present invention. For example, in some embodiments having the timing of the wrinkle display in relation to the geometric deformation be nonlinear may help it to appear more realistic. Namely, it has been observed that wrinkle patterns may not emerge in a linear fashion. Instead, wrinkle patterns may have a natural “ease in” that in some cases may cause them to only start emerging after about half the distance of the joint translation has already been covered. It is believed that as a rule of thumb, with relation to the broad movements of the face, wrinkles display at a slower rate first and become intense more quickly at the peak of the slope of the joint translation. Therefore, in some embodiments more believable results may be achieved if the attack and decay of the wrinkle display are regulated with curve relationships. 
     The methods and techniques outlined above may be used for the efficient generation of animated characters having highly detailed features, such as for example highly detailed facial expressions. The automated, reactive setup of the “wrinkle maps” and the relationships set up between the broad facial movements (joint transformations) and the emergence of the finer details (alpha-blended normal maps) help to create cohesive facial expressions that naturally contain all the characteristic elements necessary to be read correctly. The methods, techniques and solutions described herein, such as the above-described dynamic shader, are suitable for use in advanced real-time applications and engines, such as a cinematic game engine. Moreover, the methods and techniques described herein may be used with motion capture data as well as keyframe animation since the wrinkle maps are controlled on the deformer level (i.e. the joints). 
     It should be well understood that in other embodiments of the present invention the methods and techniques described herein may be used in many other types of applications and scenarios in addition to the examples provided herein. For example, the methods and techniques described herein may also be utilized to enhance other deformations of the face or body that cause subtle changes beyond wrinkles, such as adding and subtracting volume in controlled and subtle ways. For example, the methods and techniques may be used to make the eyelid pouches fuller when smiling. Other potential uses include veins popping around the neck, arms, and hands, and even neck folds appearing when turning the head. In addition to character animation, the methods and techniques described herein may also be utilized to detail cloth deformations by adding intricate fold patterns. Thus, the methods and techniques described herein have many other uses in addition to the wrinkle-solution described herein. 
     The methods and techniques described herein may be utilized, implemented and/or run on many different types of computers, graphics workstations, televisions, entertainment systems, video game systems, DVD players, DVRs, media players, home servers, video game consoles, and the like. Referring to  FIG. 6 , there is illustrated an example system  200  that may be used for such implementation. It should be well understood, however, the use of the system  200  in any of the embodiments described herein is certainly not required. 
     By way of example, the system  200  may include, but is not required to include, a central processing unit (CPU)  202 , a graphics processing unit (GPU)  204 , digital differential analysis (DDA) hardware  206 , a random access memory (RAM)  208 , and a mass storage unit  210 , such as a disk drive. The system  200  may be coupled to, or integrated with, a display  212 , such as for example any type of display. 
     The CPU  202  and/or GPU  204  can be used to execute or assist in executing the steps of the methods and techniques described herein, and various program content, images, models, animations, characters, video games, etc., can be rendered on the display  212 . Removable storage media  214  may optionally be used with the mass storage unit  210 , which may be used for storing code that implements the methods and techniques described herein. However, any of the storage devices, such as the RAM  208  or mass storage unit  210 , may be used for storing such code. Either all or a portion of the system  200  may be embodied in any type of device, such as for example a computer, workstation, television, video game console or system, or any other type of device, including any type of device mentioned herein. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.