Rastor Image Files
Raster images are created by a series of pixels, or individual blocks, to form an image. .JPEG, .GIF, and .PNG are all raster images. All the photos you find online or in print are a raster image.The pixels have a fixed ratio depending on the resolution (up or down), and when the pixels are stretched to fill the space, they were not originally intended to match become distorted, resulting in blurry or unclear images.
In order to retain pixel quality, you cannot resize raster images without compromising their resolution
Vector Image Files
Vector images are more flexible. They are created by proportional formulas rather than pixels. EPS, .AI and .PDF are perfect for creating constantly redesigned graphics. Your logo and brand graphics should be created as a vector, and you should always have a main file. The real beauty of vectors lies in their ability to be as small as a postage stamp or as big as an 18-wheeler!
If you’re not sure whether you have a vector version of your logo, here’s a little trick for you: Call the company that printed your business cards or the vendor that embroidered your logo on a shirt. Often they’ll have a vector file of your logo that they can send to you for your records.