Have you ever found a picture on the internet, downloaded, and tried enlarge it?
Ever use that image in a document, and wonder why it prints out with jagged edges?
Ever use that image in a brochure or sign, and have it come out looking really bad?
Here’s how you can save yourself alot of embarrassment and rework.
There are basically two kinds of digital still images: raster (also known as bitmap) and vector.
Raster images are made up of pixels, tiny colored squares arranged in a rectangular grid, forming an image. The quality of a raster image is determined by resolution, or the number of pixels (“Dots”) per inch that the image is broken down into. The more dots per inch (DPI) the image is broken down into, the more detail is captured. Most photographs are raster images.
The reason why images look different on your screen than they do when you print them is because your eye sees things differently on a monitor than it does on paper. An image only requires a minimum of 72 DPI to appear clear on a monitor (called screen resolution), while the same image when printed on paper must be 300 DPI in order to look as good. When you print a 72 DPI image on paper, you see the pixels as jagged edges on the image.
Vector graphics, on the other hand, use points and paths — mathematical calculations — to describe the image. The resulting shapes, or objects, can be easily manipulated, colored and re-sized without loss of quality. Whereas a raster image may have, say, 1895 pixels from point A to point B, a vector graphic simply plots the two points, calculates the distance between them and draws a line (for this reason, vector files are typically much smaller than bitmap images). Whether you print the image on a business card or a billboard, it will always appear sharp and crisp.