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?
Thumbnail upload (or for that matter any rendition upload) is specific to that image and it will not apply to set of images.
If we want to apply some custom thumbnail instead of the default one either we need to override the default image or custom workflow step is required.
If we override the default image it will apply acroos the DAM.
Regarding custome workflow step. This step will be added after thumbnail creation step in DAM Update Asset workflow(this wf is responsible for creating all renditions). In this workflow step you can check whether thumbnail is created or not if not create thumbnail of your desire.
Thank you for the helpful suggestions!