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

David Seibert (seibert@hep.physics.mcgill.ca)
Tue, 5 Dec 1995 12:18:08 -0500 (EST)


Date: Tue, 5 Dec 1995 12:18:08 -0500 (EST)
From: David Seibert <seibert@hep.physics.mcgill.ca>
To: lilley <lilley@afs.mcc.ac.uk>
Cc: "Scott E. Preece" <preece@predator.urbana.mcd.mot.com>,
Subject: Re: style sheet scalability (was: Specifying style notation in <link>)
In-Reply-To: <26628.9512051553@afs.mcc.ac.uk>
Message-Id: <Pine.ULT.3.91.951205120232.24409C-100000@prism.physics.mcgill.ca>

On Tue, 5 Dec 1995, lilley wrote:

> 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.
> 

Legibility should normally be increased with a larger display area, 
assuming you don't get make the image too big for your display ;), as 
long as the number of pixels you use on your screen is an integral 
multiple of the number in the bitmap.  If the author specifies a minimum 
display size for an image, that should not be a problem to honour; if the 
granularity of the image is higher than the granularity of your screen, 
you could expand the image (probably by order 20% or so) to cover the 
same number of pixels, while if the screen has a higher granularity you 
could remap each pixel to an N x N block of pixels, where N is the minimum 
number to make the image larger than the desired minimum size.  This 
should preserve the minimum size and maintain legibility.  As Chris 
pointed out, a fixed size is obviously much harder to render, but it 
would be good to be able to prescribe a minimum.

David

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