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Subject: Re: [office] Proposal for modification of preview image description


first of all, thank you very much for all the feedback to the proposal. 
I'm answering to this particular mail, because I think the suggestion 
from Florian/Hubert Figuiere provided a very good basis for refining my 
proposal. However, this mail should be seen as a reply to the other 
mails regarding this topic as well.

Actually, I think I should have provided some more rationales for the 
proposal: The reason for proposing to change the specification at all 
was that it turned out that some operating systems allow to display 
thumbnails in boxes that are larger than 128x128 pixels. As 
Florian/Hubert Figuiere correctly mention, the thumbnail specification 
at freedesktop.org allows 128x128 and 256x256 pixels. Microsoft Windows 
Vista also allows thumbnail boxes up to 256x256 (at least that is what I 
have been told). And 128x128 pixel thumbnail upscaled to 256x256 simply 
look bad. Therefore, the rational behind the proposal actually was to 
support larger thumbnail images than 128x128 pixels. The idea never was 
to support smaller ones.

I thirst thought about adding 256x256 pixels as an option, but decided 
against that. The reason is that the two examples provided above are 
just two examples. Other operating systems may use other thumbnail 
sizes, and who knows what sizes will be used in future OS versions, 
let's say in a year or two? In addition, the thumbnail image size has an 
impact on the document size. The larger the image gets, the larger the 
documents get. That may not be an issue for desktop systems, but may be 
for small devices storing many small documents. So, taking it all 
together, the "optimal" thumbnail image size depends on many factors, 
and it seems to be reasonable to me to allow implementors/users to 
choose an image size that is appropriate for their use case and 
platform, rather than to require a certain one in the specification. The 
same applies to other PNG parameters that we have in the specification.

However, I also agree that with the text I have proposed, any guidance 
what an appropriate image size may be is lost, and that this may be an 
issue. To resolve this issue, I like Hubert Figuiere's idea to say in 
which resolution thumbnail images are typically displayed, rather than 
recommending any image sizes. I therefore suggest to add a the following 
(non-normative) note to the (normative) text I have proposed:

"Note: Current desktops display thumbnail images within squares of up to 
256 pixel width and height. While this specification does not define 
upper or lower limits for thumbnail image sizes, implementations should 
only use image sizes that are displayed with a reasonable quality if 
scaled to fit into 256x256 pixel square."

Well, this probably can be said in better words. I'm very open for 

A normative minimum size seems not to be required in that case, because 
the note makes already clear that a 33x32 pixel image will not be the 
best choice.

Some more comments are inline.

Florian Reuter wrote:
> Dear TC,
> here a some comments from my colleague Hubert Figuiere who knows more about this then me:
> <snip>
> The thumbnail size shouldn't be limited by the spec, because it does not
> make sense to do so.
> On the other hand, the file format MUST be PNG. (MUST is stronger that
> SHALL, isn't it?)

MUST equals SHALL, but the ISO directives ODF is using does only know 
SHALL. The less strong term is SHOULD.

> Ideally the spec could state that the recommended size is, for now, to
> be enclosed in a 256x256 rectangle (document pages are not square) in
> order to allow down-scaling the original thumbnail, but the size is to
> be implementation specific and thumbnailer should NOT depend on it. This
> would allow increasing the default size without changing the spec. I
> don't see why we would need alpha transparency.
> Below is a link to the thumbnail spec which give a good idea of what is
> going on on the freedesktop.org side:
>  http://jens.triq.net/thumbnail-spec/index.html
> IMHO this spec should be used as a guide.

Well, it has been used as a guide, and the ODF 1.0 specification 
actually referenced freedesktop.org. However, because this is not really 
a standard, the reference has been removed for formal reasons.

> Hub
> </snip>
> Best regards,
> ~Florian

Best regards

Michael Brauer, Technical Architect Software Engineering
Sun Microsystems GmbH             Nagelsweg 55
D-20097 Hamburg, Germany          michael.brauer@sun.com
http://sun.com/staroffice         +49 40 23646 500

Sitz der Gesellschaft: Sun Microsystems GmbH, Sonnenallee 1,
        D-85551 Kirchheim-Heimstetten
Amtsgericht Muenchen: HRB 161028
Geschaeftsfuehrer: Wolfgang Engels, Dr. Roland Boemer
Vorsitzender des Aufsichtsrates: Martin Haering

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