Raster Images vs. Vector Graphics

Computer graphics are created as either vector or raster images. The method selected depends on the type of project. Raster graphics are better suited for non-line art imagery, such as scanned artwork, digitized photos, or detailed graphics. This is because those types of images tend to contain complex composition, subtle chromatic gradation, and undefined lines and shapes.

Raster Images

Raster graphics are bitmaps. A bitmap is a grid of separate, individual pixels that collectively make up an image. A raster graphic renders an image as a vast group of numerous tiny squares, or pixels. Each pixel is coded in a particular shade or hue. Separately the pixels are worthless, but collectively they form a picture, which as we know is worth a thousand words.

The Problem of Image Degradation

Raster imagery is a great example of technological advancement in graphics. But here’s the catch: pixel -based imagery, such as raster, tends to experience image degradation when the graphic is enlarged or blown up. This is similar to the way a photograph can appear blurry when blown up. Upon magnification the raster image becomes irregular and coarse because you can begin to see the individual pixels. It’s true that raster images can be easily scaled down, but then the images have a tendency to appear softer, or less crisp, than the original image.

In order to maximize the quality of a raster image, it’s vital to understand that this format is resolution-specific. That means the images are classified and displayed at one particular resolution. Raster resolution is measured in dots per inch, or dpi; the higher the dpi the clearer the resolution. Keep in mind that the resolution you view on any output device is not a function of the file’s own internal specs, but rather the output capability of the device itself. Therefore you should only use high resolution imagery if your equipment has the capacity to display them at high resolution.

There is a price to be paid for better resolution. Just as raster files are considerably larger than comparable vector files, high- resolution raster files are considerably larger than low- resolution raster files. Raster graphics are less economical than vector graphics, as well as less versatile, slower to display and print, and more awkward to work with. Certain images, however, such as photos, are still better suited to the raster format. Some of the more common raster formats are JPEG, TIFF, GIF, PCX, and BMP files. Raster formatting is still the web standard in spite of its shortcomings. But within a few years raster graphics most likely will be surpassed by vector graphics in terms of popularity and prevalence.

Vector Graphics

While raster images are pixel-based, vector graphics are based on mathematic formulas that delineate geometric primitives such as lines, curves, polygons, circles and rectangles. Since vector graphics are comprised of true geometric primitives, they’re best suited for structured imagery such as line art graphics with flat, uniform coloration. Most produced images, (as opposed to natural images), meet these qualifications, including letterhead, logos, and fonts.

Since vector graphics are more malleable than raster graphics, they’re a lot more flexible, versatile, and easier to use.. One of the most obvious benefits of vector graphics over raster is that vector images are faster and precisely scalable. There is no higher or lower limit for sizing vector images. Just as the rules of mathematics are identical whether calculating two-digit numbers or two hundred- digit numbers, the mathematical formulas that govern the rendering of vector images are applied identically to any size graphics.

Another important advantage is that unlike raster images, vector graphics are not resolution-dependant. Rather than having a fixed intrinsic resolution, vector images display at the resolution capacity of whatever output device (meaning monitor and/or printer) is rendering them.

Furthermore, vector graphics don’t have the burden of memorizing the contents of millions of pixels, so vector files have a tendency to be significantly smaller than comparable raster files. Essentially, vector graphics are more economical and more efficient than raster graphics.

Some of the common vector formats are AI, CGM, EPS, WMF and PICT (Mac).