Object-based ImageryThe figure at right illustrates the two known ways to store and process 2D computer graphics. You may have encountered this distinction in the past, in some form or another. They go by various names, 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.
The individual strokes of the vector, or draw graphic are sometimes called "objects" (hence the alternative name, "object graphics"). These objects consist of a fundamental data descriptor (such as "line", "circle", "arc" or "text") and modifying parameters (line width, color, layer, etc.). The different geometric elements are called primitives. The different qualities are called attributes. The completed graphic is represented by a list of these objects, sometimes (less commonly) called a display list.
Draw graphics can be enlarged or reduced in size without loss of detail. They can be quite compact (in terms of memory requirements), but the amount of memory required to store the graphic grows as the graphic grows in complexity. They are also dependant on the particular primitives of each program. A graphic containing only straight lines, for example, but representing complex curves, can do so only through the use of a great many short line segments. Such a graphic may well take significant amounts of space. This makes translating between object-graphic formats more complicated than translating between raster-graphic formats.
Since your object-based digital image consists of a list of drawing commands, the image is more likely to resemble a line drawing than a photograph. If it has areas of tone, they will probably be uniform.
Image manipulation (scaling, editing, etc.)
The benefits of the vector data format will become most apparent if you need to adjust line weights or colors in the image, or when sending images to a laser printer or other high-resolution device, or blowing it up to wall-size. A vector graphic will have the best resolution available, at any plot size, on whatever device you print to.
An object-based image can often be imported into a CAD or illustration system and rotated, stretched, or trimmed, and are readily plotted to a precise scale, so if you are creating traditional 2D CAD drawings from your 3D model and your software doesn't do this automatically, you'll want to use a vector data format for the output.
Common Vector File Formats
- Autocad drawing file: DWG
- Autocad drawing exchange format: DXF
- Adobe Illustrator file: AI
- Adobe Postscript format: PS
Hybrid File Formats
Object-based formats may well include a "raster image" primitive, making it possible to include raster data in what is ostensibly a vector format. The exact nature of the resulting image may only be determined by testing.
- Adobe Illustrator: AI
- Portable Document Format: PDF
- Windows Metafile format: WMF
Last updated: April, 2014