One of the most frustrating things in graphic design is gathering source material and getting started. This difficulty stems from a lack of understanding about what the terms "high res" and "print ready" mean. In this post, I'll explain these terms and why the following statements torment your designer.
Let's talk about dots Resolution is a measurement of dots (or pixels) per inch. The more dots per inch (or higher DPI), the higher the image quality. The fewer dots per inch (lower the DPI) the lower the quality of the image. When an image is low resolution, it will look "pixilated" and edges will have "stair stepping." Basically, it will look terrible.
What DPI do you need? When giving images and logos to a designer, the bigger the file size the better. A good designer will know what to do with large files. Also, you can always go smaller. That is important enough to repeat: an image can always be reduced in size or quality, you cannot increase the quality of an image. Here's the rules:
Your screen needs significantly fewer dots per inch, that's why something can look great on your computer (at 72 DPI) and print out crappy (printing needs 300 DPI)
Vector vs Raster or Scalable vs Pixelated There are two types of images. Vector (math based) & Raster (pixel based) A pixel based image, or raster image, is made up of thousands of colored squares. Think of Monet's pointillism. These are typically photographs or digital paintings. If you zoom in on a raster image or enlarge it, it will degrade in quality and you'll start to see the squares of color (pixels) that make up the image. A good rule of thumb is don't enlarge pixel based images. One more thing to think about when talking about resolution of raster images. Resolution is a function of the number of dots per square inch. If you take a 300 DPI image and double the size (avoid doing this at all costs), then your Image is now 150 DPI. Where'd all your pixels go? There is still the same number of pixels, but you image is now bigger, so there are fewer of them in an inch. (now if you could figure out how to make an inch bigger, then you'd really be onto something)
A vector image is completely different. Instead of the image containing thousands of pixels, it has no pixels. Instead, a series of anchor points and lines. These make two things very different for vector files:
So, when vectors can be used, they should be.
So, which is best? That's kind of like asking what the best flavor or what kind of vehicle is the best. It all depends on what you're doing and what you're doing it for. If you don't know, hire a pro. Things go much better with the right designer on board.