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April 2006
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2006.04.04 22:42 "Re: BigTIFF Suggestion", by Joris Van Damme
Larry, Please keep stuff on the list... You are likely not unique in this situation. Larry Michaels wrote: > I currently keep the offset of the last IFD in memory as long as I > have a particular TIFF open and use and update that offset value when > I append an image. The main challenge is determining that offset > value when I first open the file without having to do hundreds or > thousands of seeks. I therefore started writing the offset value, > along with a signature and CRC, to the end of the TIFF file, so that > as long as I am opening a file which my app created, I will find that > offset. Dangerous tactics. I would really recommend you write that stuff in a seperate file, like Frank and I suggested. Also, consider not using the CRC, as that implies you scan through the complete file anyway, but a file size and date. (OK, agreed, that is dangerous too...) Maybe you ought to look at other file formats? Like I said, TIFF's strong point is its simplicity. That is also its weakness, as is continuously proven when needs like yours arise. PDF's weak point is its elaborate complexity. But that is also its main strength, and your need might prove that too. I'm not a PDF expert, but if I remember correctly, PDF can contain a sortoff hash table for page offsets, that allows you to quickly locate last page and all. In addition to that, PDF is also very suitable for update as opposed to rewrite. I don't think there's a lot of processing required to append a page to a 10.000 page PDF. But I'm no PDF expert, I could be mistaking. Joris Van Damme info@awaresystems.be http://www.awaresystems.be/ Download your free TIFF tag viewer for windows here: http://www.awaresystems.be/imaging/tiff/astifftagviewer.html