The Favicon Gallery

What is a Favicon ?

A favicon (short for "Favorites icon"), also known as a page icon, is an icon associated with a particular website or webpage. A web designer can create such an icon, and many graphical web browsers - such as recent versions of Internet Explorer, Firefox, Mozilla, Opera, Safari, and Konqueror - can then make use of them. Browsers that support favicons may display them in the browser's URL bar, next to the site's name in lists of bookmarks, and next to the page's title in a tabbed document interface.

The original means of defining a favicon was by placing a file called favicon.ico in the root directory of a webserver. This would then automatically be used in Internet Explorer's favorites (bookmarks) display. Later, however, a more flexible system was created, using HTML to indicate the location of an icon for any given page. This is achieved using the link element like: <link rel="shortcut icon" href="/favicon.ico" /> in the <head> section of the document. In this way, any appropriately sized (16x16 pixels or larger) image can be used, and although many still use the .ico format, other browsers now also support the GIF and PNG image formats.

Most modern browsers implement both methods. Because of this, web servers receive many requests for the file "favicon.ico" even if it doesn't exist. Another common problem is that the favicons may disappear if the browser's cache is emptied.

Originally, Internet Explorer only used favicons for bookmarks, which created a minor privacy concern in that a site owner could tell how many people had bookmarked their site by checking the access logs to see how many people downloaded the favicon.ico file. However, since modern browsers - including Internet Explorer - also display the favicon in the address bar on every visit, that concern is no longer relevant.
 

Guidelines

For optimal browser support, the following rules should be obeyed:

  • Include all element types:
    <link rel="icon" href="http://example.com/favicon.ico" />
    <link rel="shortcut icon" href="http://example.com/favicon.ico" />
  • The link elements must be inside the head element (between <head> and </head>) in the HTML.
  • For XHTML, the link element must be empty (terminated by /> )
  • The href can, but need not, point to the location /favicon.ico. It could equally well point anywhere else on your site that is convenient.
  • The image can usually be in any image format supported by the web browser, the major exception is IE, which only supports ICO.
  • The .ico file format will be read correctly by most browsers.
  • Configure the webserver to send the correct MIME identifier:
    • ICO files image/vnd.microsoft.icon
    • GIF files image/gif
    • PNG files image/png
  • Use the appropriate resolution and colordepth.
    • ICO: include multiple resolutions (most commonly used being 16x16 and 32x32, with 64x64 and 128x128 sometimes used by Mac OS X) and bit-depths (most common being 4, 8, 24 bpp - i.e. 16, 256 and 16 million colours) in the file.
    • GIF: use 16x16 in 256 colors.
    • PNG: use 16x16 in either 256 colors or 24-bit.

Note: A file called favicon.ico and located in the document root directory will also be found by some browsers which do not process the link elements, even if it is not linked from anywhere on your site.
 

Standardization

The original favicon feature was created by Microsoft, and Microsoft's Internet Explorer web browser would request a favicon from a set URL (/favicon.ico) on every website. Microsoft's supported format for the link tag did not conform to the World Wide Web Consortium (W3C) HTML recommendation because:

  • The rel attribute must contain a space-delimited list of link types, so a two-word link type would not be understood correctly by conforming web browsers.
  • The ".ico" file format (a raster format used for icons on Microsoft Windows) did not have a registered MIME type, and wasn't likely to be automatically understood by most web browsers. In 2003, however, the format was registered with the Internet Assigned Numbers Authority (IANA) under the MIME type image/vnd.microsoft.icon, eliminating the first part of this problem.
  • The use of a reserved location on a website conflicts with the Architecture of the World Wide Web, and is known as link squatting or URI squatting.

The Mozilla web browser added support for favicons, including a version that conformed to web standards: the use of rel="icon" and optional mime-type (e.g., image/png) let web designers add favicons in any supported graphics format while conforming to W3C standards. e.g. <link rel="icon" type="image/png" href="/path/image.png" /> Most web browsers have since added support for this feature, which should be used for all new content.
 

Source: Wikipedia

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