Re: style sheet scalability (was: Specifying style notation in <link>)

scott preece said:

>    From: lilley <lilley@afs.mcc.ac.uk>
> |   Some image formats, such as TIFF and PNG, can give the desired display
> |   dimensions of an image (and by implication, the number of pixels per
> |   inch).  Should this size be honoured?
> |   I would say no, if the browser is going to do a quick and dirty
> |   rescaling job and mess up the image.  (Then again browser do quick and
> |   dirty colour reduction jobs and further screw up the image quality, so
> |   why not?)

> While the discussion of image quality is important and needs to be
> considered in answering the question, it's also important to remember
> the reason for the original question [...]
> While the quality of the rendering is probably important
> to people using images for this purpose, making sure the text is large
> enough to be read is *critical*. 

You appear to me to be making these assumptions:

a) image quality is nice but inessential
b) legibility is paramount (fine) but largely independent of graphic quality
c) legibility is increased by rendering the image in a larger display area.

However, as image quality falls, the first thing to be lost is legibility.

Further, a well constructed antialiased image (at, say, 72dpi) containing 
text will be more legible if displayed 1:1 on a 110 dpi screen - thus making 
it too small - than if it were scaled by a factor of 110/72 by pixel 
replication  - which would make it bigger, but drop the quality right down.

> In that context it makes a lot of
> sense to be able to specify a preferred display size for an image (and,
> perhaps, an indication of how much the author cares about variation.

Try actually doing that, and see how the legibility suffers. Remember 
we are talking about scaling factors of at most 50 - 200% and more 
likely 80 - 125% so Walter's suggested hints of integer scaling do 
not apply.

In summary, if you believe legibility is critical - and I have no problem 
with that - then you cannot just dismiss image quality as an optional extra.

Chris Lilley, Technical Author and JISC representative to W3C 
|       Manchester and North HPC Training & Education Centre        |
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