Re: Alternate images for different media

Jacques Steyn writes:
 > Problem:
 > Images designed for display on computer screens are too small to be used
 > on video/TV screens. When such images contain text, they can be read due
 > to the closeness of the computer screen. These words disappear at the
 > larger distance of video/TV screens.
 > 
 > Web documents designed for computer screens can be adapted by using
 > style sheets for different visual media, but the problem is that such
 > images cannot be resized without sacrificing too much resolution. There
 > is something missing.
 > 
 > Solution?:
 > One solution would of course be vector images. But this cannot be
 > applied across the board.

Yes, that's one solution. W3C is working on scalable vector graphics
(SVG).

 > 
 > Another solution would be to match copies of images in different sizes
 > to specific media. 
 > Here one strategy could be to dump all small screen images in one
 > directory, and all large images in another. Then we need a way to
 > declare a BASE element related to a path and image declarations in the
 > body of the document.
 > 
 > OR
 >  when an IMG is declared in a document, there should be the possibility
 > to declare alternatives. Then we would need an additional attribute,
 > perhaps an extension of the functionality of the "media" attribute?

Another possibility is to use the LINK element of HTML, which allows
links to alternative versions of the HTML document itself
(REL="alternate").

SMIL has a slightly different mechanism. It has SWITCH elements with
attributes for, e.g., bandwidth requirements. You put such a SWITCH
around a group of images (or other objects) that are each other's
alternatives.

Yet another solution is HTTP content negotiation. There are ideas
about so-called "client profiles" on which a browser and a server can
agree: the browser sends in its HTTP "accept" headers or in a similar
mechanism what profiles/media it supports and the server sends the
corresponding image (or a redirect to the corresponding image). No
URLs need to be changed.

 > 
 > I am not sure what the solution would be, but I cannot find any solution
 > in the present recommendations. Is there something I've missed?
 > 
 > I guess there may even be an application of such a feature for TV-Web
 > and SMIL applications.

... and don't forget mobile devices.


Bert
-- 
  Bert Bos                                ( W 3 C ) http://www.w3.org/
  http://www.w3.org/people/bos/                              W3C/INRIA
  bert@w3.org                             2004 Rt des Lucioles / BP 93
  +33 (0)4 92 38 76 92            06902 Sophia Antipolis Cedex, France

Received on Saturday, 2 January 1999 10:50:16 UTC