discussion, preview images of embedded objects

[Hanssens Bart <Bart.Hanssens@fedict.be>]

Hi,


during the conference call we've briefly discussed preview images, see
also http://tools.oasis-open.org/issues/browse/OIC-26 and previous
discussions on the mailing list.

And of course, the Interop profile working draft itself:

http://www.oasis-open.org/committees/document.php?document_id=34166&wg_abbrev=oic




General observation:

- previews and thumbnails are always a burden for Producers (more work),
while they can benefit Consumers. It will always be a trade-off.

- only humans benefit from previews, machines don't need them to process
ODF files



** First and foremost, I'm _not_ talking about the Thumbnail.png in 17.6

IMHO, this image doesn't buy you much in terms of interoperability:

- your desktop / file manager is likely to ignore the preview and display another
icon anyway,

- in a corporate environment, it's common to have a cover page for all your
documents, so it might be hard to see the difference between documents using
a 128x128 preview that probably is going to be displayed as 64x64 or smaller...



** This is about 9.3.3 Objects, in the "Object Data" section, the last sentence
reads

"It is recommended to include an image representation of the object into the
frame in addition to the object itself."

Thus:

<draw:frame...
   <draw:object...
   <draw:image...


This is commonly used in charts in spreadsheets where draw:object links to
the XML elements with chart data, and a draw:image is used for including a
preview.

Other cases where this might be useful:
- tables in ODF 1.1 presentations
- MathML formulas in word processor without equation editor

Preview images are useful for consumers that don't support the embedded
object type (viewer on a cell phone, lightweight word processor etc)


And ODF 1.1, 9.3.2 states

"While the image data may have an arbitrary format, it is recommended that
vector graphics are stored in the [SVG] format and bitmap graphics in the
[PNG] form"


In reality, it is observed that 

a) some implementations use a proprietary image format
b) some implementations don't insert preview images at all
 


** So the questions:

- do we want Producers to always insert a preview image (whatever that
may be, it could be an overly simplified SVG thingie)

- if not, do we want to add a requirement that an Implementation updating an
existing embedded object shall either update or remove the existing preview
(if present). Otherwise we might indeed end up with a preview that no longer
represents the embedded object


I do realize that at some point we have to split this up into different profiles
for different applications: "Interop Profile Core", "Dedicated Spreadsheet"
"Everything-and-Kitchensink-Office-Suite" etc... but I'd like to start with the
"core" part, that improves interoperability / raises the floor for each and
every application type.


Best regards,

Bart