Are you confused by the files that are on your web site? Files that are on a web site are called bitmap images (also known as raster). These bitmaps are broken up into a series of pixels. For example a graphic that is 150x150 pixels has a total of 22,500 individual pixels. (This translates to about a 2 inch square.) The make up of pixels is referred to as the resolution of the image. Resolution is measured by pixels per inch (ppi); the more pixels there are in each inch, the higher the resolution. The high resolution causes the file size to be larger as well. In order to keep the file size down for faster loading on a web site, we optimize the images to make sure they are all down to 72 ppi, standard screen resolution for the web.

These are the most common pixel based files:

  • .bmp (Bitmap file)
  • .gif (Graphic Interchange Format)
  • .png (Portable Network Graphic).
  • .jpg (The most common format for bitmap images these days)
  • .tiff

If printing is what you want to do with an image then you will need to save your photographs at (a high resolution) 300 ppi. If its artwork (like a logo) that needs to be printed it should be created and saved in a vector file format. Vector is different than bitmap. Vector is a mathematical formula that makes up the image. This allows the image to be printed as small as a business card or as large as a billboard with out losing any quality. In other words vector images are solid shapes, not separate pieces. These files are usually created with a drawing program such as Adobe Illustrator.


Some common vector graphic file formats are listed below.

  • .ps (PostScript) used to describe a full page or multi-page document
  • .eps (Encapsulated PostScript) used to describe a specific free-standing diagram or figure
  • .pdf (Adobe's Portable Document Format) can be read and printed on almost all operating systems. Can be used to describe an individual, free-standing diagram, or an entire page layout.
  • .ai (Adobe Illustrator Files)
  • .wmf (Window's MetaFile-only partially vector)
  • .svg (Scalable Vector Graphic) this is a relatively new format, designed especially to provide vector graphics on web pages.