Re: Image types and related issues [was: Re: filetype extensions] (Chris Lilley, Computer Graphics Unit)
Date: Sun, 15 May 1994 04:43:19 +0200
Message-id: <>
Precedence: bulk
From: (Chris Lilley, Computer Graphics Unit)
To: Multiple recipients of list <>
Subject: Re: Image types and related issues [was: Re: filetype extensions]
X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas said:

[I said:]

>> [ Note for those who care; Iris RGB and Utah RLE (assumed linear
>> encoding) and TIFF (assumed generic RGB coding) are all 24 
>> bit lossless formats. Within the assumptions specified, these 
>> 3 can be freely and repeatedly interconverted without information 
>> loss, which is why I picked them as examples.]

> Well, often authors include other information in TIFF tags that will
> be lost when you convert to Iris RGB. For most purposes, you don't
> care about those tags, but in a few cases you will.

Sure - which is why I was careful to specify generic rgb. If you have stuff like 
scanner whitepoint, phosphor chromaticities, transfer functions etc in there 
then clearly that information will be lost. I was just trying not to make it too 

> Suddenly you might find that `loss' is a vector and not a single
> number. (presentation fidelity, structure retention, invertible
> conversion, etc.)

I agree with this assesment. Asking people to code this vector into every image 
URL is clearly asking tooo much unless intelligent editors are ubiquitous - 
which we cannot assume - or unless there are well chosen and documented defaults 
for when the user does not specify this vector.

Chris Lilley
| Technical Author, ITTI Computer Graphics and Visualisation Training Project |
| Computer Graphics Unit,        |  Internet:            |
| Manchester Computing Centre,   |     Janet:            |
| Oxford Road,                   |     Voice: +44 61 275 6045                 |
| Manchester, UK.  M13 9PL       |       Fax: +44 61 275 6040                 |
| X400:  /I=c/S=lilley/O=manchester-computing-centre/PRMD=UK.AC/ADMD= /C=GB/  |
|  <A HREF="">my page</A>   |