Clipart vs. Photographs; The Vector-Raster Issue?

A common question is, “What’s the difference between clipart, a photograph, an illustration, and other image references?” Sometimes the question is there, but isn’t articulated, due to lack of nomenclature. Nomenclature is the root of understanding the differences. This article will help explain which words relate to which types of images and explain the differences between them.

There are two major groups to image types; Vectors and Rasters. A raster image is the image type we all see as the standard photograph and webpage image. A vector image is less usual, but is not acknowledged for what it is most of the time. Vector images are built with lines and fills that make up true “clipart” as well as real logos, etc. The best example of vectors are the common Microsoft Office © clipart characters that appear as drawings.

The Raster: A raster image is built from the composition of a multitude of individual dots in an array (matrix) and containing display information specific each unto itself. Think of the raster as a large collection of individual paint spots that can be defined as a unique entity within the collection as a whole. That spot contains information about what color it has, its saturation, the hue and so on. remove that spot and the image remains intact, minus a spot.

The Vector: A vector is built from the composition of one or more lines and fills defined by mathematical equations. Consider a simple circle of blue with a yellow fill. The image is created when the computer calculates a mathematical equation to decide how large the circle is, how thick the line is and then what color the fill is. Once calculated, the image is displayed as an array of dots on the monitor.

Defined: Although both rasters and vectors must be displayed as an array of monitor dots, they are created by different methods. If the vector image is to be doubled proportionally in height and width, the computer recalculates the original equations and redraws the image with the new magnitude. However, if you do the same to the raster image, the process is much different. The computer is working with a set number of dots from the original and must move the dots apart to create a larger size. Moving the dots apart means there are gaps between them both vertically and horizontally. This is where you must understand how the computer fills in those new gaps. The computer actually inspects the dots around the gaps, makes complex calculations based on surrounding information, and makes a best guess ass to what dot should fill the gap.

Quality: So why do rasters looks so much better than vectors? Think of it like this… Try and create the same image with two different methods. The raster method is to use an unlimited variety of colored sand. The vector method is to use an unlimited number or colored yarn. Obviously, the sand allows much more detail and the yarn does not. This is exactly why the different image types don’t display the same on screen. Yes, you could simply use a massive number of tiny vector lines to simulate dots as the raster does, but the tiny vectors would require much more information than the raster dots. remember, file size is still an issue in the majority of projects.

Usage: There are different applications for rasters and vectors. Photographs and similar images that need detailed quality to meet visual expectations should remain raster. Logos and clipart that don’t require such complexity, and may need quality resizing should remain vector. Rasters may be converted into vectors and vectors into rasters. This is referred to as Rasterization and Vectorization. We find Macromedia Flash does the best job of converting rasters to vectors, buy using the Convert Bitmap function. Almost every graphics application can convert vectors into rasters, even if by simply saving as a JPEG format!

Sometimes raster/vector image type is controlled (screwed up) by another application. Microsoft Office is an example of taking control away from you. If you try to import a vector image into Power Point, it will usually convert that image to a bitmap (raster) and you lose the ability to resize it. Workarounds for such problems require creative methods. Try and use Corel Draw to convert the raster image into a WMF format and Office will import it as a native vector, retaining its resizing qualities. If you have problems with vector/raster manipulation, email XtremeVisions and they’ll help.

Raster: Image defined by an array of unique dots.
Vector: Image constructed from mathematically defined lines and fills.

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