(6) Graphic Interchange Format (GIF)

• RFC 2046 [http://dret.net/rfc-index/reference/RFC2046] registers the oldest graphics format on the Web
• GIF was subject of a long patent debate
  • the compression technique of GIF (LZW [http://en.wikipedia.org/wiki/Lzw]) had been patented by Unisys (1983)
  • Unisys wanted to get licensing fees from all commercial online uses of GIF
  • Portable Network Graphics (PNG) [Portable Network Graphics (PNG) (1)] was developed as an effort to develop a copyright-free format
  • in 1999, Unisys changed its tactics and wanted to collect one-time fees ($5000-$7500) from all users
  • all GIF-related LZW expired in 2003/2004, so GIF is freely available now
• GIF's poor features make PNG the better choice anyway
  • 8 bit color (requires dithering for photographs), binary transparency
  • GIF's animation feature is the only thing that is not available in PNG …

(8) Joint Photographic Experts Group (JPEG)

• RFC 2046 [http://dret.net/rfc-index/reference/RFC2046] standardizes the second popular image format for the Web
  • ISO 10918 [http://dret.net/biblio/reference/iso10918] is the standard for the actual image format
• JPEG has been specifically designed for photographs
  • it always is lossy (it cannot preserve the complete information from a random bitmap)
  • it uses perception-based compression (for example, color precision is sacrificed for brightness)

Q = 50, filesize 15,138 bytes	Q = 10, filesize 4,787 bytes	Q = 1, filesize 1,523 bytes

(9) JPEG 2000

• JPEG has some problems (for example, it is never lossless)
  • compression technology has advanced since JPEG (DCT → Wavelets [http://www.acm.org/crossroads/xrds6-3/sahaimgcoding.html])
• JPEG 2000 is a completely new standard
  • it uses wavelets instead of DCT as the compression algorithm
  • it includes support for lossless encoding (JPEG is always lossy)
  • it even comes with its own transmission protocol (JPIP [http://en.wikipedia.org/wiki/JPIP])
  • image/jp2 (JP2 [http://dret.net/glossary/jp2]) and image/jpx (JPX [http://dret.net/glossary/jpx]) are the two JPEG 2000 MIME types
• Support for JPEG 2000 is good but not universal

(11) Portable Network Graphics (PNG)

• PNG is registered as image/png and is the third major image format
  • PNG was intended to be a royalty- and copyright-free replacement of GIF [Graphics Interchange Format (GIF) (1)]
  • image formats need to supported by browsers and thus take a long time until they are established
  • IE6 implements PNG in a very rudimentary form, IE7 handles PNG correctly
• PNG has some advantages over GIF and JPEG
  • lossless, compressed palette, grayscale, or true color images
  • 8 bit alpha channel for gradual opacity (blending into the background)
• JPEG still is the preferred format for photographic pictures
• GIF still is the preferred format for animated images
  • MNG [http://en.wikipedia.org/wiki/Mng] and APNG [http://en.wikipedia.org/wiki/APNG] are two available but not widely supported PNG animation formats

(12) Alpha Channel Effects

(14) Tagged Image File Format (TIFF)

• Standard file format format for scanned images
  • none of the limitations of Graphics Interchange Format (GIF) [Graphics Interchange Format (GIF) (1)]
  • ability to represent any kind of bitmapped image information
  • compression is supported but always lossless (not as effective as JPEG [Joint Photographic Experts Group (JPEG) (1)])
• Popular for scanned images and similar applications
  • native support in browsers is the exception (only Safari)

(15) Icons

• Original favicon (a.k.a. page icon or urlicon) format
  • the image format used by Windows for its icons (which is identical to the cursor format)
• Important on the Web only for Web site icons
  • most browsers will display the icons in the address bar
  • most browsers will remember the icon for bookmarks and shortcuts
• Icons appear as meta information of a Web page
  • standards are not really tight and based on best practices and browsers

  <link rel="icon" href="/favicon.ico" type="image/x-icon" />
  <link rel="shortcut icon" href="/favicon.ico" type="image/x-icon" />

(19) Graphics for the Web

• Identified as important media type a long time ago
  • W3C work on SVG for a long time
  • complex format with little support and little success on the Web
• Embedding SVG in HTML is more art than science [http://www.carto.net/papers/svg/samples/svg_html.shtml]
  • using SVG requires browser-specific HTML code
  • backwards compatibility must support bitmapped version of the SVG pictures
• Support for SVG is provided by many newer tools
  • the SVG code produced not always is a very good version of SVG
  • SVG has not yet been adopted as something that people really care about

(20) Image vs. Graphics