By James, Design Development.
In this discussion we will use the word “vector” when discussing Illustrator files and “raster” when talking about Photoshop files.
A vector image is made up of paths, each with a mathematical formula (vector) that tells the path how it is shaped and what color it is bordered with or filled by. Logos, letterhead, and other graphic elements are typically best created as vectors; while photographs are best left for rasters. Adobe Illustrator is the most common vector drawing program.
*example of Illustrator (Vector) Art. Note crisp clean edges and “bezier” curve handles.
A raster image is made of up pixels, each a different color, arranged to display an image. Raster images are primarily used with photos. Pixel painting programs have been around since Apple introduced the first Macintosh. Most people are familiar with the programs and do minor editing to digital photos. Photoshop is a full featured raster editing program.
*example of Photoshop (Raster) Art. Note soft, blurry edges.
The major difference is that raster image pixels do not retain their appearance as size increases – when you blow a photograph up, it becomes blurry for this reason. Vector images do retain appearance regardless of size, since the mathematical formulas dictate how the image is rendered.
Pros and cons of rasters & vectors
Raster images are capable of displaying millions of colors in a single image and allow for color editing beyond that of a vector image. They can display finer nuances in light and shading at the right resolution. Vector images are scalable, so that the same image can be designed once and resized infinitely for any size application – from business card to billboard.
Raster images cannot be made larger without sacrificing quality. Vector images cannot display the natural qualities of photographs. Raster images are often large files, while vector images are relatively lightweight. Raster images are used in web and print, vector images cannot as of this writing be used in electronic format – they must be converted to a raster first. Vectors display at the highest resolution allowed by the output device, while rasters blur when blown up. I like to use the example of a photocopier when scaling up raster images… when you blow something up on a copier and the images gets distorted, it’s the same with scaling up raster images.
Using the Adobe Suite of applications allows for smooth transitioning from raster to vector images. You can create a design in Illustrator and export it in many formats to create raster images. Conversely you can also use an option in Adobe Illustrator to “Live Trace” SOME raster images to make them vector, BUT there are a handful of issues that need to be address when doing this which shall be address here in the future.