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GRAPHICS

Home >> Communications Guidline >> Graphics

Graphics

File types—and when to use them

The most common image file formats are JPG, TIF and GIF.

JPGs are useful when you need to keep the file size small and don't mind giving up some quality for this.
Use JPG:

  • for photos on the Web
  • for digital photos

Don’t use JPG:

  • for line art, logos, images with text, large blocks of color or simple shapes. In JPG files, crisp lines will blur and colors can shift.

TIFs are used when very high quality images are necessary and file size isn't an issue.
Use TIF:

  • for logos
  • when high quality images are desired
  • as the working storage format (because quality of images doesn’t degrade with new saves, as do JPG files).

Don’t use TIF:

  • for Web images: they produce big files and most Web browsers won’t display TIFs

GIF files are always reduced to 256 unique colors, or less, so are good for images with few colors.
Use GIF:

  • for simple Web graphics having limited colors
  • for small, fast-loading Web graphics, like Web buttons, charts, diagrams, cartoon-like drawings, banners, text headings
  • for small compact Web animations

Don’t use GIF for photos.

BMP is a proprietary format invented by Microsoft. It can be used for any type of pixel-based images, but BMPs are huge files and have no real benefits over TIFF.

Sources for graphic images

Non-copyrighted photos can be obtained from the following sources:

  • i-Stock: www.iStockPhoto.com is a Web site that provides thousands of royalty-free downloadable photos and other graphic images. The site can be searched by topic. (A search for ‘trees’, for example, yields 126,000 photos.) Photos suitable for Web sites and small publications cost $1 each. Larger, higher resolution photos cost $5 to $10 each.
  • King County: Ned Ahrens has archived hundreds (thousands) of photos for use by King County staff. Go to http://photoarchive/res/sites/search/ and search for images. To obtain an image, contact Ned at ned.ahrens@kingcounty.gov, provide him with billing numbers and he will provide the image(s) at the proper resolution.
  • Seattle Municipal Archives (www.cityofseattle.net/cityarchives): The City of Seattle maintains archival photos that can be accessed electronically or in person. Photos in the collection date from the 1880s to the present, and there are more than 110,000 records. Digital images are available for 95% of the photos.

Resolution

Resolution is a measurement of the output quality of an image—that is, how clear it is. Resolution is usually expressed in terms of dots, pixels or lines per inch. “PPI”, or pixels per inch, refers to screen resolution. “DPI”, or dots per inch, refers to print resolution.

Images are referred to as high resolution (hi-res) or low resolution (low-res). High resolution images are intended for print and are usually 300 dpi, or greater. Low resolution images are intended for screen display; the standard is 72 ppi.

The higher the resolution of the image, the larger the file. The optimal resolution depends on how the graphic will be used.