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

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 and therefore 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

Examples of graphics software:

• Adobe Photoshop - the industry standard for print and screen graphics. Comprehensive, but expensive, with a high learning curve.
• Adobe Photoshop Elements - less expensive offering from Adobe; easier to learn, often comes with scanners or digital cameras.
• Corel Paint Shop Pro - about $100, easier to use, especially for screen graphics, such as for the Internet and PowerPoint.
• Picasa - free image editor from Google.
• Microsoft Paint - free; comes with Windows. Very limited capabilities; not recommended.