3D computer graphics are works of graphic art that were created with the aid of digital computers and specialized 3D software. In general, the term may also refer to the process of creating such graphics, or the field of study of 3D computer graphic techniques and its related technology.
3D computer graphics are different from 2D computer graphics in that a three-dimensional representation of geometric data is stored in the computer for the purposes of performing calculations and rendering 2D images. Sometimes these images are later displayed in a pre-rendered form, and sometimes they are rendered in real-time.
In general, the art of 3D modeling, which prepares geometric data for 3D computer graphics is akin to sculpting or photography, while the art of 2D graphics is analogous to painting. However, 3D computer graphics rely on many of the same algorithms as 2D computer graphics. In computer graphics software, this distinction is occasionally blurred; some 2D applications use 3D techniques to achieve certain effects such as lighting, while some primarily 3D applications make use of 2D visual techniques.
Creation of 3D Computer Graphics
The process of creating 3D computer graphics can be sequentially divided into three basic phases:
- Modeling
- Scene layout setup
- Rendering
Modeling
The modeling stage could be described as shaping individual objects that are later used in the scene. A number of modeling techniques exist, including, but not limited to, the following:
- constructive solid geometry
- NURBS modeling
- polygonal modeling
- subdivision surfaces
- implicit surfaces
Modeling processes may also include editing object surface or material properties (e.g., color, luminosity, diffuse and specular shading components — more commonly called roughness and shininess, reflection characteristics, transparency or opacity, or index of refraction), adding textures, bump-maps and other features.
Modeling may also include various activities related to preparing a 3D model for animation (although in a complex character model this will become a stage of its own, known as rigging). Objects may be fitted with a skeleton, a central framework of an object with the capability to effect the shape or movements of that object. This aids in the process of animation, in that the movement of the skeleton will automatically effect the corresponding portions of the model. See also Forward kinematic animation and Inverse kinematic animation.
At the rigging stage, the model can also be given specific controls to make animation easier and more intuitive, such as facial expression controls and mouth shapes (phonemes) for lipsyncing.
Modeling can be performed by means of a dedicated program (e.g., Lightwave Modeler, Rhinoceros 3D, Moray), an application component (Shaper, Lofter in 3D Studio) or some scene description language (as in POV-Ray). In some cases, there is no strict distinction between these phases; in such cases modelling is just part of the scene creation process (this is the case, for example, with Caligari trueSpace)
3D ANIMATION PROCESS
Scene layout setup
Scene setup involves arranging virtual objects, lights, cameras and other entities on a scene which will later be used to produce a still image or an animation. If used for animation, this phase usually makes use of a technique called "keyframing", which facilitates creation of complicated movement in the scene. With the aid of keyframing, instead of having to fix an object's position, rotation, or scaling for each frame in an animation, one needs only to set up some key frames between which states in every frame are interpolated.
Lighting is an important aspect of scene setup. As is the case in real-world scene arrangement, lighting is a significant contributing factor to the resulting aesthetic and visual quality of the finished work. As such, it can be a difficult art to master. Lighting effects can contribute greatly to the mood and emotional response effected by a scene, a fact which is well-known to photographers and theatrical lighting technicians.
Tessellation and meshes
The process of transforming representations of objects, such as the middle point coordinate of a sphere and a point on its circumference into a polygon representation of a sphere, is called tessellation. This step is used in polygon-based rendering, where objects are broken down from abstract representations ("primitives") such as spheres, cones etc, to so-called meshes, which are nets of interconnected triangles. Meshes of triangles (instead of, for example, squares) are popular, because they have proved to be easy to render using scanline rendering. Polygon representations are not used in all rendering techniques, and in these cases the tessellation step is not included in the transition from abstract representation to rendered scene.
Rendering: Putting It All Together
Rendering is the final process of creating the actual 2D image or animation from the prepared scene. This can be compared to taking a photo or filming the scene after the setup is finished in real life. Rendering for interactive media, such as games and simulations, is calculated and displayed in real time, at rates of approximately 20 to 120 frames per second. Animations for non-interactive media, such as video and film, are rendered much more slowly. Non-real time rendering enables the leveraging of limited processing power in order to obtain higher image quality.
Rendering times for individual frames may vary from a few seconds to an hour or more for complex scenes. Rendered frames are stored on a hard disk, then possibly transferred to other media such as motion picture film or optical disk. These frames are then displayed sequentially at high frame rates, typically 24, 25, or 30 frames per second, to achieve the illusion of movement.
Several different, and often specialized, rendering methods have been developed. These range from the distinctly non-realistic wireframe rendering through polygon-based rendering, to more advanced techniques such as: scanline rendering, ray tracing, or radiosity. In general, different methods are better suited for either photo-realistic rendering, or real-time rendering. In real-time rendering, the goal is to show as much information as the eye can process in a thirtieth of a second.
The goal here is primarily speed and not photo-realism. In fact, here exploitations are made in the way the eye 'perceives' the world, and thus the final image presented is not necessarily that of the real-world, but one which the eye can closely associate to. This is the basic method employed in games, interactive worlds, VRML. However, the rapid increase in computer processing power, allowed a progressively higher degree of realism even for real-time rendering, including techniques such as HDR rendering. Real-time rendering is often polygonal and aided by the computer's GPU.