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Digitized images can saved in a multitude of file formats. Many formats compress the image in some way to make the file size smaller. Several graphics formats provide reasonable compression and are cross-platform compatible. Not every format is compatible with every program.

Graphics compression can be lossless or lossy. Lossless compression looks for repetitive patterns, but doesn't change the image. Lossy compression also looks for repetitive patterns and averages parts of the image to make it smaller. All images should be saved with a lossless compression if further editing is required as averaged information can never be fully recovered.

One of the best cross platform graphics formats is TIFF (Tagged Image File Format) which has both Mac & PC subformats but is usually readable on both and uses LZW compression (a lossless very efficient compression algorithm). For Internet use files should be saved in .gif or .jpg formats.

Below is a list of some of the common file types for output.

File Extension	Description	Example
.txt	ASCII text file; basic text without any formatting like bold or italic.	Click
.gif	Graphic files often used for fancy text, graphics, logos, and animations. GIF (Graphics Interchange Format) is a 256 color or less representation of the original with no image alteration except for reduced number of colors. GIF compresses left to right, top to bottom and looks for repetitive patterns. GIF defaults to 256 colors, but some images will still look fine with as little as 3 bits of color information per pixel. Trying lower bit settings will make the file smaller but can severely distort color rendition. Convert images to Indexed color before saving as a GIF or use Photoshop's Gif89a export feature. You can always use the one step undo to get back to a true color image and try again if there is too much color distortion by trying a lower bit setting when using indexed color. Areas with subtle gradation usually don't index very well. Believe it or not selecting the graded area and adding about 10% noise to it before indexed color produces acceptable results.	Click
.jpg	Image file often used for full-color photographs. JPEG files can be made from grayscale images or true color, 24 bit, 16.7 million color images. Files are compressed using a lossy compression algorithm. JPEG looks for areas of the image that are about the same and creates blocks that are reconstructed to create an image. JPEG has adjustable percentages of compression when saving and compresses very well. Photos compress with acceptable distortion via JPEG but text and lines usually suffer from jaggy & fuzzy edges. A new variation of JPEG is Progressive JPEG, which loads at successively higher resolutions (out of focus) until the entire file is loaded.	Click
.pdf	Portable Document File for displaying facsimiles of documents including fonts, graphics, layouts, etc. Files are not digitally editable.	Click

Web Browser

Web browser (such as Netscape and Internet Explorer) standard graphics formats are:

• .gif (normal, interlaced, transparent and animated)
  • for logos and buttons
    
• .jpg (normal and progressive)
  • for photographic continuous tone images

Microsoft Word

• .tif (PC and Mac)
• .gif (PC and Mac)
• .jpg standard, but not progressive
• .bmp (PC only)
• .pct or .pict (Mac only)

Powerpoint 4.0 for Macintosh

• .pct or .pict
• .tif (must be indexed color)

Powerpoint 4.0 or 97 for the PC

• .tif
• .gif
• .jpg standard, but not progressive

Adobe Pagemaker

• .tif
• .eps
• .jpg

Hyperstudio

• .pct or .pict indexed color @ 72dpi
  • usually image about 2 x 3 inches

Maintained by: Gene Gatlin (gatlinet@plu.edu)
Last Update: 09/23/97