Author Topic: Ingest changes MD5SUM of file?  (Read 5564 times)

Offline crunge

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Ingest changes MD5SUM of file?
« on: June 18, 2006, 01:53:44 PM »
Due to some white balances issues that I posted earlier, I'm now trying to use Photo Mechanic to ingest D2x RAW files without making any changes other than file renaming. I've disabled all IPTC writing and notice that the file after it has been imported and renamed has a different MD5SUM than it had prior to import. Since renaming a file doesn't change the MD5SUM, what else might be going on here?

PM 4.4.1 on Mac OS X 10.4 (Tiger)

Thanks,
Chris

Offline dennis

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Re: Ingest changes MD5SUM of file?
« Reply #1 on: June 19, 2006, 11:03:14 AM »
Chris,

Photo Mechanic adds a block of data to the end of files (except CRW and RAF) for storing its image preferences (rotation, tag, crop) and also for storing the "inferred frame number".  If you have your preferences set to not embed IPTC or XMP into TIFF-based RAW files (like NEF) then the original file is intact as shot other than data that is appended for our prefs.  If you were to checksum all but the last 2060 bytes then it would match the original file prior to ingest.

--dennis

Offline crunge

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Re: Ingest changes MD5SUM of file?
« Reply #2 on: June 19, 2006, 01:56:46 PM »
Hi Dennis:

Thanks for this information. In case it should become an issue, is it possible to easily reverse this process and return to the original NEF?

Chris

Offline dennis

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Re: Ingest changes MD5SUM of file?
« Reply #3 on: June 20, 2006, 12:53:45 PM »
In case it should become an issue, is it possible to easily reverse this process and return to the original NEF?

We don't have an easy way to remove image prefs at the EOF but I suppose we could add this.  Normally data appended to the end of file isn't problematic (unless the format is something like a CRW which parses from the end of file backwards).  But there are some brain dead parsers out there (e.g. Mac OS) that fail when even a single byte is appended to the end of file.  See the following topic for related info:

http://forums.camerabits.com/index.php?topic=193.msg902#msg902

--dennis