Graphic File Types

Computers use two different types of graphics files: vector and bitmap.

Bitmap graphics are based on a pixel grid – they're made of squares of light on the screen. Pixel means PICture ELement.

  • If you take a small image from the Internet and resize it larger, the pixels get larger, and the image becomes jaggy or blurry. You can see the individual pixels.
  • Use bitmaps for photos.
  • Common bitmap file formats: GIF, JPG, TIFF (see below for more information).

Vector graphics are based on mathematics – they're made of lines, curves and fill colors or gradients:

  • Can be resized without losing quality.
  • When to use? logos, cartoons – simple shapes, few colors.
  • Common vector file formats: AI, EPS, PNG (see below for more information).

Most graphics programs work with one or the other – some use both:

  • Bitmap: Adobe Photoshop, Adobe Photoshop Elements, Corel Paint Shop Pro.
  • Vector: Adobe Illustrator, Adobe Photoshop, Corel Paint Shop Pro.

 

Vector artwork
zoomed in 500%

Bitmap artwork
zoomed in 500% 


Characteristics of different image file formats:

Bitmap

.bmp - Microsoft's Bitmap Format

  • Displays millions of colors.
  • Not capable of animation or transparency.
  • Uncompressed, so large file sizes.

.gif - Graphics Interchange Format

  • Designed to create the smallest possible file size for Internet download and display.
  • Can only display 256 colors – makes for jaggy photos.
  • Capable of animation – displays one image after another, each slightly different – like cartoons.
  • Capable of having transparent areas.
  • Uses lossless compression (see .jpg).
  • Use with images containing broad areas of flat color, such as logos, cartoons and clip art.

.jpg or .jpeg - Joint Photographic Expert Group

  • Can display millions of colors.
  • Can keep track of image camera exposure information.
  • Not capable of animation or transparency.
  • Uses lossy compression – throws away extra image info in order to minimize the file size. If you compress it too much, it starts to lose too much information, which becomes visible as artifacts – jaggy areas and ‘halos’ around transition areas.
  • Only save once in this format; every time a file is saved in jpg format, it is compressed again, which will degrade the image.
  • Convert to tiff for archives.
  • Use on screen (Internet or PowerPoint) for photographs and images with a combination of photos and other images.
  • Can print high-resolution files (at least 200 dpi) with this format, but do not save more than once.

.pdf - Adobe Portable Document Format

  • Adobe Acrobat is used to create and edit PDF files, for the purpose of sharing information independent of one's computer operating system or software installed.
  • PDFs can be converted to fillable forms and can be set to email data entered into a fillable form.
  • The free PDF Reader software is available for all operating systems and is pre-installed with modern Internet browsers, such as Internet Explorer, Firefox, Safari and Opera.
  • PDF files are minimally editable; edit the original file that was converted to PDF.

.psd - Photoshop document

  • Photoshop native image file format. If you're working in Photoshop, save the original files in this format; it maintains image characteristics (e.g., font type, size and color) in case they need to be edited later.
  • Can only be read by graphics software, such as Photoshop and Paint Shop Pro.

Raw (file extension varies depending on the camera or scanner manufacturer)

  • Contains minimally processed data from the image sensor of a digital camera, image scanner or motion picture film scanner. Raw files are so named because they are not yet processed; therefore, they are not ready to be printed or edited with a bitmap graphics editor.

  • The image must be processed by a converter where precise adjustments can be made before conversion to a file format such as TIFF or JPEG for storage, printing or further manipulation.

.tiff or .tif - Tagged Image File Format

  • Displays millions of colors.
  • Uncompressed, so they’re very large files.
  • Mac and Windows computers and most common software can use this format.
  • To prevent lossy artifacts (see .jpg, above), convert JPGs to TIFF for editing.
  • If preparing a print document, submit the TIFF to the printer.
  • If preparing a screen document (Web or PowerPoint), after editing, crop and resize appropriately, then convert to JPG.

Vector

.ai - Adobe Illustrator

  • Illustrator native image file format. If you're working in Illustrator, save the original files in this format; it maintains image characteristics in case they need to be edited later.
  • Can only be read by graphics software.

.eps - Encapsulated PostScript

  • Encapsulated PostScript (EPS) is a standard format for importing and exporting PostScript (printer) language files in all environments.
  • Can contain any combination of vector graphics, bitmap images and text.
  • Includes an embedded preview image in bitmap format.
  • Often used for transferring image data between different operating systems.
  • Can be created and opened by Adobe Illustrator, Acrobat and Photoshop.

.png -  Portable Network Graphics

  • Combines the best of .jpg and .gif:
    • displays millions of colors
    • uses lossless compression
    • capable of animation and transparency
  • Not commonly used on websites.
  • Use for PowerPoint.