Computer Graphics

Pixel Graphics

As many people are aware, the screen of a computer monitor is composed of a grid of dots. These dots, called pixels, have red, green and blue elements, which combine to produce a single color per pixel. Pixel graphics are those 2D images that concern themselves with the exact color of each pixel on the screen.
This kind of image is useful primarily because it can store exact information about each pixel. This is good for complicated images such as photographs and detailed drawings.

Color Palettes

A color palette is the set of colors from which a bitmap is composed. Technically, it defines the mapping from the numbers in the bitmap to the colors of the pixels on the screen. Ideally, of course, there should be a continuum of color values encompassing every possible color in nature. However, the computer would therefore have to assign each of these infinite colors an individual number, so that it could represent them internally, which would require either a continuous domain representation, or the entire set of integers. This cannot be done because the modern digital computer cannot represent an infinite number of values.

Image Compression Formats

A major element of the computer graphics industry is image compression. The largest and most complete format for an image is the bitmap form, for which each pixel has a unique color value stored. Ultimately, every image becomes a bitmap when it is displayed, but often it is convenient to store and transfer images in a compressed format, in which the file size is smaller than that which would arise when stored in a bitmap format.
It is important to know a little about image compression formats, because their characteristics can determine the quality of a final displayed image, and some are more appropriate for different types of images than others.

Vector Graphics

Vector graphics store the information about the picture to be displayed in the form of geometric objects described by coordinates. The description ‘vector’ arises from the fact that each coordinate can be thought of as a vector from the origin to the coordinate point. The geometric objects included are highly dependant upon the file format used, but can conceivably be any object which can be well defined by a small set of coordinate points. Examples of objects stored can include lines, ellipses, spline curves, text glyphs, etc.

There are also many difference forms of vector graphic file formats available. Examples include MS Windows metafiles, Autodesk DXF files and Macromedia Shockwave objects. There is no widely accepted vector graphic format available, and most are proprietary formats that are not available for incorporation into other products. The DXF format is debatably the most commonly used.


3D Graphics

Beyond the world of 2-dimensional, flat graphics, exists the exciting world of 3-dimensional graphics. More often than not, these 3D graphics are displayed on a 2-dimensional computer screen, by projection from the 3D volume to the 2D plane.

Polygons and Primitives

Using current technology, 3D graphics are rendered, that is placed upon the screen, by evaluating a scene that is described by a set of primitives and polygons. Broadly, a primitive can be thought of as a basic element of a scene description language. A primitive can be such things as a sphere, box, cone, cylinder, NURBS curve, and even a polygon. Polygons are many-sided shapes (starting with triangles) which represent a single face on a multi-faceted object.