I have included these terms to ease your understanding of this material. If you find any of this confusing, please send me mail.
| alpha | Can be thought of as how clear a pixel is. Often added to the RGB values of a pixel to create a new RGBA value. |
| alpha blending | Method used to calculate the transparency of a pixel. Transparency value is added to the pixel's red, green, and blue color values and can be contained as a part of the pixel's properties. |
| antaliasing | The process used to reduce the appearance of jagged lines in a bit map by sampling nearby pixels and "blurring" them together. The process usually makes the image look hazier but increases it's realism. |
| atmospheric effects | Refers to the effects of applying fogging and depth cueing to a scene. Can range from precipitation such as snow and rain to effects that make the scene seem emerged in water. |
| bilinear filtering | A method of filtering that uses four adjacent texels to create a smoother textured polygon. The drawback is that it quadruples the amount of memory access. |
| bit map | A bit map is a two-dimensional array of color values usually used to represent an image. The image size as well as the number of colors can vary widely and extra information such as transparency can be contained internally. |
| clipping | When rendering a scene, parts of polygons may be hidden by polygons closer to the viewer. Clipping is the process by which obscured polygons are 'cut' out of the scene. |
| color look up table (CLUT) | A table that maintains a subset of a global set of colors. The table may contain 256 entries (8 bits) any one of which may point to a larger set of colors. The table allows objects the luxury of having small color tables, but still allows for a wide range of colors in a scene. |
| depth cueing | An atmospheric effect that gives the appearance of depth in a scene. It is analogous to the effect of haze on a humid day. It is different from fogging in that it is a much more subtle. |
| dithering | The process of representing a larger number of colors by creating patterns of dots with a smaller number of colors. For example, a black and white image can give the impression of shades of gray by increasing or decreasing the space between black pixels. So, a 4-bit, 16 color image can represent an 8-bit, 256 color image. |
| fill rate | The rate at which a graphics accelerator can draw pixels on the screen. Many accelerators can provide anywhere from 20 million pixels per second up to 90 million pixels per second. |
| filtering | Filtering determines the color of a pixel based on texture maps. As filtering increases in memory lookups, point filtering, bilinear filtering, and trilinear filtering also increase in scene realism. |
| fogging | The atmospheric effect that gives the illusion of fog. Like depth cueing, fogging obscures objects that are further away from the viewer. Unlike depth cueing, however, fogging can be irregular and vary its appearance. |
| frame buffer | When the computer is rendering a frame, it most likely is rendering to a frame buffer. The frame buffer is a temporary storage location for the frame's pixels. Most applications make use of two or more frame buffers to increase the speed at which rendering can occur. By maintaing two frame buffers, one can be sent to the video display hardware while the other is being written to. This new technique is called 'double buffering.' |
| graphics accelerator | For a few years, consumers have wanted more elaborate and
sophisticated looking applications and games. This has led to an increase in expansion
cards that fit into PCs that remove much of the load of rendering
from the computer's CPU and re-routed it to a card called the 'graphics accelerator.'
Graphics Accelerators are actually small computers in themselves. Capable of geometry
processing, bilinear filtering, atmospheric effects, hidden
surface removal, texture mapping, shading
and lighting effects, z-buffering, and other
computationally-intensive tasks, graphics accelerators take the burden off of CPUs while
still increasing the realism of the application. There is a page on the architecture of graphics accelerators in this report. |
| hidden surface removal | Three dimensional objects are collections of vertices and polygons. Any of these polygons that face away from the viewer are removed from the scene to increase the speed of the application. This technique is known as hidden surface removal. It is calculated by finding the normal of the polygon; if the normal faces away from the viewer, it is not drawn. |
| line segment | A one-dimensional region of space bounded by two points. |
| MIP mapping | A method of using multiple texture maps for different viewing distance, i.e., larger, more detailed texture maps are used when the viewer is close, smaller texture maps are used when the viewer is further away. |
| model | Generally, the process of representing a real-world object or phenomenon as a set of mathematical equations. More specifically, the term is often used to describe the process of representing 3-dimensional objects in a computer. All 3-D applications, including CAD/CAM and animation software, perform modeling |
| perspective correction | When textures are applied to objects, distortion in the form of extreme jaggedness and irregularity can sometimes occur. Perspective correction eliminates these unwanted jaggedness and smoothes the texture on the object. |
| pixel | A single point on your monitor. (I have not found an adequate definition for this term.) |
| point | A point is a singular coordinate that contains values that determine its location in space. For example, a three dimensional point would contain an (x, y, z) coordinate. |
| polygon | A region of a plane bounded by a finite collection of line segments. The term is used in any number of n-dimensional surface representations. |
| ray tracing | In computer graphics, an advanced technique for adding realism to an image by including variations in shade, color intensity, and shadows that would be produced by having one or more light sources. Ray tracing software works by simulating the path of a single light ray as it would be absorbed or reflected by various objects in the image. To work properly, the artist must specify parameters of the light source (intensity, color, etc.) as well as all the objects (how reflective or absorbent the materials are). |
| rasterization | The process of determining the color of a pixel in a scene. During the rendering of a scene, factors such as light levels, fog and distance, and reflections can affect the color of a pixel. |
| refresh rate | The rate at which a computer can redraw the screen. Usually in frames per second, refresh rate is critical in the realism factor in a computer application. The human brain can see individual frames if the refresh rate is less than 10 frames per second. For reference, television refreshes the screen 24 frames per second and movies are around 30 frames per second. Most good games try to shoot for around 30 frames per second. |
| rendering | Refers to the process of adding realism to a scene by adding three-dimensional qualities such as shadows and variations in color and shade. One technique for rendering graphics is called ray tracing. Another type of rendering is scanline rendering, which renders images one vertical line at a time instead of object-by-object as in ray tracing. In general, scanline rendering doesn't produce as good results as ray tracing, but it is used frequently in animation packages where the image quality of each individual frame isn't so important. |
| scene | A scene can be referred to as the entire collection of objects, polygons, and vertices in the computer at run-time. The author has used this convention to refer to all of the objects being interacted with in the program. |
| gourad shading | A rendering method to produce color gradual shading over the entire surface of a polygon. Performed by determining brightness with the normal vector at each vertex of a polygon and the position of the light source, and performing linear interpolation between vertices. |
| flat shading | A rendering method to determine brightness by the normal vector on a polygon and the position of the light source and to shade the entire surface of a polygon with the color of the brightness. This rendering method produces a clear difference in the colors of adjacent polygons, making their boundary lines visible, so it is unsuitable for rendering smooth surfaces. |
| tessellation | Tessellation is the total coverage of an area by geometric figures of the same size and shape, with no overlaps. Tessellation is regular if it is formed by repeating a regular polygon such as a square, equilateral triangle, or regular hexagon. The tessellation is nearly regular if formed by repeating the pattern of an "almost" regular polygon, such as a non-square rectangle, non-rectangular parallelogram, or non-equilateral triangle. Tessellation is really a complex way of referring to a quilt of patterns. |
| texture | A bit map image used to increase the detail on an object. Can be thought of as a stencil that is painted on the side of a polygon. |
| texture mapping | The act of applying a texture to an object. Process includes antialiasing and perspective correction as well as other image correction techniques. |
| texture memory | Specialized, high-speed memory that is used to hold texture maps. |
| transformation | The math used to adjust for motion, scaling, and rotation of geometrical objects. Transformations are basically well known matrix functions which can correct for perspective and distance. |
| transparency | How clear a pixel is. (I have not found an adequate definition for this term.) |
| trilinear filtering | I have not found an adequate definition for this term. |
| vertex | A vertex is a point where two line segments meet. |
| viewer | The perspective in which the scene is being used. I have assumed that the viewer is either a user using the computer or a camera in the scene itself. |
| voxel | I have not found an adequate definition for this term. |
| z-buffer | An extension of memory where the depth (z-axis) value of a pixel is stored. The z-buffer is a portion of memory used to store the coordinate on the z-axis of the closest opaque point for each value of x and y. The value of the z-axis allows the graphic accelerator card to determine whether a pixel is visible or not. |