I understand that when I upload an asset to the DAM of a file type for which CQ5 doesn't support thumbnail generation (Excel .xls and .xlsx, in my case), CQ5 will use a default dogeared-page icon for the thumbnail. it also writes an error-level message to the log to the effect that it can't generate a thumbnail. E.g.,
15.10.2012 12:03:47.078 ERROR [JobHandler: /etc/workflow/instances/2012-10-15/model_1135358760340484:/content/dam/FY06NIVDetailTable1.xls/jcr:content/renditions/original] com.day.cq.dam.commons.handler.AbstractAssetHandler createThumbnails: cannot create thumbnails for asset [/content/dam/FY06NIVDetailTable1.xls], failed loading graphical representation for rendition [/content/dam/FY06NIVDetailTable1.xls/jcr:content/renditions/original].
The error message is mostly harmless, but I would like to prevent it.
And I understand that I can add a thumbnail after the fact. But despite the language in the document, apparently this thumbnail does not apply to subsequent uploads (for all files of the same type).
Is there a way to establish a thumbnail image that applies to subsequent uploads?