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Subject: Re: [office-comment] thumbnail shouldn't be stored inside the document file

Hello Jerome,

Thanks for submitting your note.  We discussed it in our last meeting of the ODF Technical Committee.  

The thumbnail image is specified in ODF 1.2 Part 3, Section 3.8.  As stated there, the use of the thumbnail is recommended but not required. In other words the text says "should", not "shall".   So a vendor has the ability to implement this or not, or even to make the use of thumbnails be a matter of user configuration.    

Not all ODF applications are full editors with the ability to layout a document and generate their own preview.  Some are simple XSLT transforms or similar.  For example, I once saw a demo of one application that would scan a directory full of ODF text documents and extract metadata from it, including the preview image, and generate a new document that was a catalog of the other documents, showing the image, author, keywords, etc.  This was all done from with scripts operating on the ODF document.

In the end these are cpu/storage/time trade-offs that the vendors and implementers are best able to make.  The ODF standard defines an interoperable way to store such thumbnails in cases where the implementers thinks they are appropriate.  


Rob Weir

Jérôme Bouat <jerome.bouat@wanadoo.fr> wrote on 07/14/2013 12:21:19 PM:

> I think that the thumbnail image shouldn't be stored inside the document file.
> It could be handled by the file browser cache (Nautilus, Dolphin,
> Thunar, Microsoft Windows file explorer, etc) or any application
> using a preview instead of storing the preview into the document
> file. Each application could use a fast check of a modification
> (modification of the date and the size for example) in order to
> refresh the thumbnail. Each application could use a Open Document
> producer component in order to quickly generate an image preview
> with the right format (file format and image dimension).
> Storing a thumbnail into the document file :
> - increases the used space on expensive storage
> - increases the cpu usage (and the energy consumption)
> Note  that the storage cost depends on the usage :
> - the local desktop disk is a cheap storage with possibly no backup
> (in enterprise for example),
> - the network storage of a user or a group is an expensive storage
> (the final archived size can be multiplied by ~20 with archives
> rotation, humans are paid to perform the storage and check it, ...).
> Note that a document sent by email will use the network bandwidth
> for image preview which can be easily created by the recipient.
> Moreover, the document will be copied into the "inbox" folder of the
> recipient and also into the "sent" folder of the sender. The
> mailboxes of the sender and the recipient will be possibly backed up
> (expensive storage).
> Note that the preview image file size can be roughly up to ~30% of
> the compressed office document (see the small Draw document I
> attached for example).
> Note that there are users who never use preview image (detailed view
> of the Microsoft Windows file explorer for example).
> The CPU usage increases with thumbnail into the documents because :
> - of additional work for saving (and reading) a file, especially
> when the automatic saving is performed often or when the user is cautious,
> - of possible useless format conversion between the document preview
> format and the application underlying image format,
> - of resizing between the preview image dimensions inside the
> document and any application using the preview with other dimensions.
> However I think there were reason of using the preview inside the
> document. Could you please explain those reasons ? Thanks.
> Regards.
> [attachment "test.odg" deleted by Robert Weir/Cambridge/IBM]
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