Paper on JPEG 2000 for preservation
The JPEG 2000 compression standard is steadily becoming more and more popular in the archival community. Several large (national) libraries are now using the JP2 format (which corresponds to Part 1 of the standard) as the master format in mass digitisation projects. However, some aspects of the JP2 file format are defined in ways that are open to multiple interpretations. This applies to the embedding of ICC profiles (which are used to define colour space information), and the definition of grid resolution. This situation has lead to a number of interoperability issues that are potential risks for long-term preservation.
I recently addressed this in a paper that has just been published in D-Lib Magazine. An earlier version of the paper was used as a ‘defect report’ by the JPEG committee. The paper gives a detailed description of the problems, and shows to what extent the most widely-used JPEG 2000 encoders are affected by these issues.
The paper also suggests some possible solutions. Importantly, none of the found problems require any changes to the actual file format; rather, some features should simply be defined slightly differently. In the case of the ICC profile issue this boils down to allowing a widely used class of ICC profiles that are currently prohibited in JPEG 2000. The resolution issue could be fixed by a more specific definition of the existing resolution fields.
Both issues will be addressed in an amendment to the standard. Rob Buckley provides more details on this (along with some interesting background information on colour space support in JP2) in a recent blog entry on the Wellcome Library’s JPEG 2000 blog. As Rob puts it:
“The final outcome of all this will be a JP2 file format standard that aligns with current practice; supports RGB spaces such as Adobe RGB 1998, ProPhoto RGB and eci RGB v2; and provides a smooth migration path from TIFF masters as JP2 increasingly becomes used as an image preservation format.”
So, some relatively small adjustments to the standard could result in a significant improvement of the suitability of JP2 for preservation purposes.
Since various institutions are using JPEG 2000 now, the paper also provides some practical recommendations that may help in mitigating the risks for existing collections.
Johan van der Knijff
KB / National Library of the Netherlands