Re: Image types and related issues [was: Re: filetype extensions]

Chris Lilley, Computer Graphics Unit (
Fri, 13 May 1994 14:29:33 GMT 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
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