Types of Image Files

Image files come in two basic types, vector or raster. Consider how you anticipate using an image when deciding in which format to save an image.  The information below will also help you understand the different file formats that you are likely to encounter when receiving or requesting images from others.

• Raster images are pixel-based images, meaning the images is formed using a series of colored blocks (pixels). Pixels have a defined proportion and do not resize well – enlarging the image size will cause gaps in the pixels and reducing the image size requires the removal of pixels. Both will result in a ‘pixelated’ image. Raster file types, such as JPEG, PNG, and GIF, should be created at the precise dimensions needed for its use.
• Vector images are created using mathematical formulas rather than pixels. These images are best for things that need frequent resizing, like logos and other marketing graphics. Vector files, such as EPS, SVG, and some PDFs, can reduce your image down to a very small size, like a stamp, or a super large size, like a banner or billboard, without pixelation.
  • Vector files can be saved as raster images at any size or resolution, but the opposite is hardly ever possible

Resolution

You have likely encountered someone asking for a high resolution image, but what does that mean?

• High resolution is defined as 300ppi (pixels per inch – digital term) or 300dpi (dots per inch – printing term) or larger. This resolution is best for printing or use of an ‘expandable’ image (one that someone may want to zoom in on) on the web.
• Low resolution is defined as 72ppi, but can range from 72-150ppi, and is best for a digital use, like the web. We recommend 96ppi or more for use on the web. Smaller image resolution will load quicker than high resolution images.

Common File Types

1. JPEG (or JPG):
   • JPEGs are raster images saved in a compressed file format standardized by the Joint Photographic Experts Group. JPEGs are known for their “lossy” compression, which can significantly reduce image quality, especially as the size of the image is reduced
   • JPEGs are great for use on the web or other digital modalities. I recommend that you pay attention to both the file size and resolution of your file for best results
   • Large JPEGs can be used for print, but a different file type is generally requested
   • These files do not support transparency
   • JPEG = Joint Photographic Experts Group
2. TIF (or TIFF):
   • TIF files are large raster files that have no loss in quality – they use “lossless compression”. This means that the original image data is retained, no matter how often it’s compressed or copied
   • These files are great for print because of its lossless compression, but are usually not great for the web because of very slow loading times
   • Generally does not support transparency
   • TIF = Tagged Image File
3. PNG:
   • PNGs are raster files that are great for use on the web or other digital formats. Like TIFs, PNGs are lossless files, but are still considered low resolution files, so are not good for printing
   • *This is your go-to raster file for images that need a transparent background*
   • PNG = Portable Network Graphics
4. GIF:
   • GIFs are a great low-resolution alternative for short animations. They are generally used for short, eye-catching, moving images that will load quickly. Because they are an animated series of images, they are used for web only, not for print
   • GIFs usually loop infinitely, but in some software programs can be programmed for a set number of loops
   • GIF = Graphics Interchange Format
5. EPS:
   • EPS files are vector files that are perfect for high-resolution print
   • EPS files can be used to open vector-based artwork in more programs than those in the Adobe suite, so it is a great way for sharing editable files without worrying about what program your counterpart uses
     • Use caution when saving EPS files! If you do not want the recipient of your file to have editing permissions, change the settings of your EPS file before saving so that it is view-only
   • EPS = Encapsulated Postscript
6. SVG:
   • SVGs are another great vector file for artwork, although they are not as widely supported as EPS files
   • SVG = Scalable Vector Graphics
7. PDF:
   • PDFs are a vector file format that are perfect for sharing graphics with others that you don’t want to have editing permissions. PDFs were created by Adobe, so Acrobat Reader is required to view them, but it is a free software available on any platform
   • PDFs are best for print
   • PDF = Portable Document Format
8. PSD:
   • PSD files are source files created in Adobe Photoshop. This file contains all of the layers and components of your image that you create
   • Photoshop is a robust program for editing photographs and creating original work, but its downfall is that it is a raster-based program
   • PSD = Photoshop Document
9. AI:
   • AI files are source files created in Adobe Illustrator. This file contains all of the layers and components of your image that you create
   • Illustrator is the gold-standard software for making vector work, but does not contain the photo-editing qualities found in Photoshop
   • AI = Adobe Illustrator Document

If you have questions, or want to suggest an additional file type for this list, please contact ESS at vet-ess-e@cornell.edu