Have you ever had a graphics artist ask you about raster and vector images? Like most people not involved in graphics you were probably a little confused by the question. The fact is, that the proper use of vector and raster (or bitmap) images is very significant to the final outcome of large dimension printing like full color banners. If you have seen a printed image that was pixilated, out of proportion or lacked precise definition, then they most likely used a bitmap imagery and enlarged that image until it lost its crisp definition. Speaking of crisp definitions, lets define vector and raster.
- Vector images are composed of paths, which are defined by a start and end points, along with other points, curves, and angles. A path may take the form of a line, a square, a triangle, or a curved shape. These paths may be combined to create simple drawings or complex diagrams. Due to vector images not being composed of a specific number of dots, but formula representing the curves and paths, they can be scaled to a larger size and not lose any image quality. Vector images are stored in a good deal smaller files than raster images. Vector images are generally unsuitable for photo-realistic, extremely complex images, but are best suited for graphs, diagrams, logos or images composed of basic shapes, such as cartoon-style characters. Common types of vector graphics editors include Adobe Illustrator, and Macromedia Freehand. Their file designators are ai and eps.
- Bitmap images are exactly what their name implies, a collection of bits that form an image. The image consists of a matrix of individual dots or pixels that all have their own color. Bitmap images are not the best candidates for resizing, rotating, or stretching. Their best representation is in the size and orientation they were originally developed. They may be cropped, colorized, converted to black and white, or combined with other images using an image editing program such as Adobe Photoshop, Adobe Photoshop Elements or Corel Photo-paint. When modifying bitmap graphics you are modifying at the pixel level; in other words, the color of any one pixel may be modified. The size of the file is based on the image’s resolution. Bitmap images are used for photorealistic images and, therefore, may include involved color variations.
After enlarging a vector image, the edges remain smooth and distinct. As a result, vector images are great for large graphics like full color banners. Vector graphics, like a logo, can be compressed small enough to appear on a 3.5″ X 2″ business card, but can also be enlarged up to size for a 6′ H X 30′ W full color banner with no loss of resolution or definition. If you use a digital photograph on a large banner, it must be taken at extremely high resolution. This results in using a very large file providing sufficient pixels to not lose definition when the photograph is enlarged.
You can still use photos, with good results. on full color banners. The file sizes become so large they are difficult to work with and the equipment that must be used is very expensive. Conversions of raster to vector is getting more popular. The result may not look like a real photo, but in most instances has a striking and dynamic impact. For example, conversion of a bitmap image of a political candidate to a vector image to place on a large banner has a unique effect. The reader still recognizes the characteristics of the politician, but the resulting image has a “dynamic” almost surreal feel to it.
The bottom line is that both raster and vector may used with success on large full color banners. Make sure the person doing it knows what they are doing and that you ask to see samples of their work.