Understanding Image Formats Part 1

by Bruce Hitchen

Do you know the difference between a jpeg, png, tiff, or a bitmap? Many people struggle to understand the differences between these file formats and which is best for their application. With so many image formats and resolutions, the topic is too much information to cover in just one blog post. Therefore, I am dedicating the next few posts to providing a basic understanding of the most common image formats, the difference between raster and vector images, and an overview of acceptable resolutions.

In this first of the three-part series, I will explain the difference between raster and vector graphics.

Vector images are graphics that are not resolution dependent. That means you can expand or blow-up a vector graphic to any size and it will retain it’s sharp edges and crisp appearance because the program uses the mathematical coordinates of each shape to redraw it whenever its size is changed. This is particularly important with logos and graphic shapes. Vector graphics are created in programs like Adobe Illustrator, Corel Draw, and InDesign. The most common request that a graphics developer will have for their client is for an “.eps” version of their logo. EPS is short for Encapsulated Postscript. Many business professionals have an .eps version of their logo but are often unable to open it because they don’t have a program like Photoshop or one of the other vector based programs mentioned above. A little-known secret is that you can view an .eps file in the latest versions of PowerPoint and Keynote. Neither of these programs will open an .eps file but when a presentation is open you can choose to insert a photo and then select the .eps file you want to view.

Raster images, sometimes known as bitmaps, are different from vector images in that their resolution is finite. Photographs are a good example of raster images, which have a set resolution. Resolution is represented by pixels so if a photograph is 2,500 pixels wide then once you increase its size beyond 2,500 pixels, you will start to see a loss in quality.

Pictures found on the Web and photos you import from your digital camera are raster images made up of pixels. The larger the image, the more disk space the image file will take up. For example, a 640 x 480 image contains 307,200 pixels, while a 3072 x 2048 contains 6,291,456 pixels. Since raster graphics need to store so much information, developers have created image compression algorithms that reduce these file sizes. JPEG and GIF are the common compression formats but there are several other types of image compression formats that I will discuss in the next blog post.