JHOVE : TIFF word-alignment requirement: current best-practice / thinking?
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Joseph Pawletko
Apr 24, 2012, 9:57:39 AM4/24/12
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*** apologies for cross-posting ***
I'm using JHOVE v1.6 to validate a set of TIFFs. Some of the files do not conform to the
word-alignment requirement, however JHOVE considers the files well-formed if the byteoffset
parameter is set to "true".
<module><class>edu.harvard.hul.ois.jhove.module.TiffModule</class><param>byteoffset=true</param></module>
In this thread from 2006, Stephen Abrams describes the long-term implications of accepting
non-word-aligned TIFFs :
What is the current thinking re: non-word-aligned TIFFs? Are there still preservation concerns
with accepting non-word-aligned TIFFs?
Thank you all for your time.
Best-
Joe
--
Joseph Pawletko
Digital Library Technology Services
Bobst Library
New York University
slabrams
Apr 24, 2012, 1:28:47 PM4/24/12
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Hi Joe:
In our local policies at the CDL we “prefer” to have TIFFs that are word aligned, but we accept those that are byte aligned. In fact our general policy is always to prefer objects that are fully valid to their underlying format specifications for the reasons articulated in my 2006 post. In practice, whenever we detect invalid objects there is always the question of whether there is any effective remediation that can be done. Sometimes the object owner/curator has the ability to regenerate or reacquire valid versions, but that is not always the case. Regardless, we’ll eventual take whatever we get, although we’re clear in stating that the long-term preservation outcome may vary significantly depending on the form, structure, and validity of the objects at hand.
Recognizing that local policies will legitimately vary, the JHOVE2 project provides a way for institutions to codify their policy decisions in the form of assessment rules. In essence, JHOVE2 is capable of reporting two independent properties: validity, which is meant to be an objective measurement based on format specification requirements; and acceptability, which is a subjective measurement based on local policy decisions. This mechanism permits institutions to implement enforceable service levels based on whether an object is:
Valid and acceptable
Valid and unacceptable
Invalid and acceptable
Invalid and unacceptable
The use of a standard JHOVE2 expression language for defining acceptable also may facilitate the freer exchange of local policy rules.
The default JHOVE2 distribution ships with a TIFF module assessment file (config / spring / module / assess / jhove2-ruleset-tiff-config.xml) that defines images that are invalid due to byte alignment to be nevertheless acceptable.
--sla
In our local policies at the CDL we “prefer” to have TIFFs that are word aligned, but we accept those that are byte aligned. In fact our general policy is always to prefer objects that are fully valid to their underlying format specifications for the reasons articulated in my 2006 post. In practice, whenever we detect invalid objects there is always the question of whether there is any effective remediation that can be done. Sometimes the object owner/curator has the ability to regenerate or reacquire valid versions, but that is not always the case. Regardless, we’ll eventual take whatever we get, although we’re clear in stating that the long-term preservation outcome may vary significantly depending on the form, structure, and validity of the objects at hand.
Recognizing that local policies will legitimately vary, the JHOVE2 project provides a way for institutions to codify their policy decisions in the form of assessment rules. In essence, JHOVE2 is capable of reporting two independent properties: validity, which is meant to be an objective measurement based on format specification requirements; and acceptability, which is a subjective measurement based on local policy decisions. This mechanism permits institutions to implement enforceable service levels based on whether an object is:
Valid and acceptable
Valid and unacceptable
Invalid and acceptable
Invalid and unacceptable
The use of a standard JHOVE2 expression language for defining acceptable also may facilitate the freer exchange of local policy rules.
The default JHOVE2 distribution ships with a TIFF module assessment file (config / spring / module / assess / jhove2-ruleset-tiff-config.xml) that defines images that are invalid due to byte alignment to be nevertheless acceptable.
--sla
Joseph Pawletko
Apr 24, 2012, 1:35:14 PM4/24/12
to digital-...@googlegroups.com
Thank you, Stephen.
Best-
Joe
--To view this discussion on the web visit https://groups.google.com/d/msg/digital-curation/-/G9_mk8uLajQJ.
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