Low Vision and Image Sizes

copied to ER

Image with sizes expressed in pixels can be a problem for a person with low 
vision because it can force an enclosing table cell to be wider than the 
screen when the user sets screen resolution low, e.g. to 480x640  (done to 
increase font and image sizes).  Thus, the image, and other contents of the 
cell, lie off screen.  At best, this requires horizontal scrolling.  At 
worst, if the author has turned off scroll bars, those portions of the 
screen become unviewable.

Now Checkpoint 3.4, which requires relative units, theoretically addresses 
this since image sizes... and coordinates of image maps... can be set as 
percentages, not merely pixels.  However, with current browsers, presenting 
images at any size other then their natural pixel width can degrade their 
appearance because of aliasing, especially for fine detail.  There's also 
the question of whether browsers have good support for image map 
coordinates set as percentages.   Was 3.4 really intended to apply to image 
sizes and image map coordinates?

If not, how do we handle this situation?

One way, in wcag 2, is to simply say that screens shall read sensibly at 
any pixel resolution.  Problem is, that may be overkill... does it apply 
e.g. to screens 48 x 64 pixels large.


Leonard R. Kasday, Ph.D.
Institute on Disabilities/UAP, and
Department of Electrical Engineering
Temple University
423 Ritter Annex, Philadelphia, PA 19122


(215) 204-2247 (voice)
(800) 750-7428 (TTY)

Received on Wednesday, 3 May 2000 14:03:40 UTC