Hi Louise,
Certainly there is no need to store raw TIF files. LZW compressed TIF is a good format - it is "lossless" compression so all data is retained. You can use JPEG compression with TIF files, but JPEG is a "lossy" compression so some data is lost - though often this is not noticeable (particularly with photographs) to the naked eye. JPEG compressed TIF files will be smaller than LZW compressed TIF. There used to be legal issues (patents) preventing the use of LZW but this isn't a problem now. Some more information here: http://www.alliancegroup.co.uk/tiff.htm
PNG isn't widely used for archiving. You may also consider PDF/A (the archiving format of PDF), though you have the same issues with compression here - and LZW compression isn't available in PDF/A.
It is this question of "lossy" or "lossless" compression that is the key to the issue. Lossless compression (such as LZW) shouldn't be an issue for legal admissibility. Lossy compression is more questionable. The Code of Practice for Legal Admissibility shows that scanned documents will be accepted by a court, but they can be challenged. Can you therefore show that your scanned copy is a 'true copy' of the original ? With lossless compression this is more straightforward, with lossy compression it may be more difficult to prove. Lossy compression reduces the evidential weight of the image.
Best regards,
Steve
-----Original Message-----
From: The Information and Records Management Society mailing list
[mailto:[log in to unmask]]On Behalf Of Louise Pichel
Sent: 25 October 2012 09:28
To: [log in to unmask]
Subject: Legal admissibility of compressed images in EDRMS
Dear all,
We are currently investigating long term storage of colour images in our EDRMS and the potential storage implications.
Storing the raw TIFF files for the required 7 year retention period has been rejected due to the large amount of storage space required, and we have been pointed towards both the LZW compression algorithm and/or storage as PNG files instead.
I would be very grateful for any comments/suggestions on both the use of LZW compression and PNG's for long term storage in terms of legal admissibility. I have looked at the Code of Practice for Legal Admissibility but it doesn't go into much detail about compression specifically.
I would be more than happy to summarise responses to the list.
Many thanks.
Louise
Assistant Archivist
Library and Museum of Freemasonry
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