Digital Film: Vector v. Raster

"Displays" vs "Logic" ... A Little Difficulty ...

The difference between vector and raster graphics is a little difficult to illustrate because the actual display on your computer screen, your printer, and your phone is almost certainly a raster display. Vector-based computer displays have existed in the past but are very rare these days. The best example of a vector display is a human hand writing notes or making a drawing with a pen on paper.

While all modern digital displays are raster, the logic just "behind" the screen may be either vector or raster, similar to the way paint brushes can be used to make stokes of color, or daubed to make patches of color. These two approaches to graphic display influence available program operations, visual characteristics of the results, and ease of use. That's why the distinction is important.

The Graphics Pipeline: Two kinds of digital "Film"

The figure at right illustrates both ways to store and process 2D computer graphics. You may have encountered this distinction in the past, in some form or another, using various dualities, the most common pairings being

• raster and vector
• paint and draw
• pixel and object

Each of these pairings describes the same fundamental distinction. One (on the left) involves thinking of an image as constructed through a series of mathematically defined and geometrically precise pen, pencil or brush strokes using special geometrical concepts or primitives (such as "circle"). The other (on the right) requires thinking of the image as a rectangular grid of colored picture elements (pixels) that collectively approximate the final result--all you need to know is where they are and what color they are.

Consequences

It may not be obvious, but it follows that there are two sets of algorithms for rendering 3D data into a 2D image, those which process and produce vector data, and those which process and produce raster data. The distinction will not always be clear, but the difference will be quite apparent in such things as line quality when sending images to a laser printer. Similarly, should you wish to modify the digital image, you will have different options depending on the kind of algorithm used to produce the original image data. Finally, the two technologies for storing and manipulating 2D graphics are linked to different hardcopy technologies, so it should be no suprise that the kind of image has an impact on what devices can print the image as well (or what CNC output options exist). We will attempt to ellucidate these differences throughout the quarter, but you should start looking for them immediately.

[report bug]