Pros and cons of the JPEG2000 format for a digitisation project

Wednesday, January 11, 2017 09:00

Ed Pinsent by Ed Pinsent

When it comes to selecting file formats for a digitisation project, choosing the right ones may help with continuity and longevity, or even access to the content. It all depends on the type of resource, or your needs, or the needs of your users.

If you’re working with images (e.g. for digitised versions of books, texts, or photographs), there’s nothing wrong with using the TIFF standard file format for your master copies. We’re not here to advocate using the JPEG2000 format, but it does have its adherents (and its evangelists), and so in this post we want to briefly discuss some of the pros and cons of the JPEG2000 format.

Read more: Things to consider before undertaking a digitisation programme

PROS

May save storage space

This is a compelling reason and may be why a lot of projects opt for the JP2. Unlike the TIFF, it supports lossless compression. This means it can be compressed to leave a smaller “footprint” on the server, and yet not lose anything in terms of quality. How? It’s thanks to the magic codec.

jpeg2000_2.jpg

Versatility

In “old school” digitisation projects, we tended to produce at least two digital objects – a high resolution scan (the “archive” copy, as I would call it) and a low resolution version derived from it, which we’d serve to users as the access copy. Gluttons for punishment might even create a third object, a thumbnail, to exhibit on the web page / online catalogue. Conversely the JPEG2000 format could perform all three functions from a single object. It can do this because of the “scalable bitstream;" the image data is encoded so it only serves as much as is needed to meet the request, which could be for an image of any size.

Open standard with ISO support

As indicated above, a file format that’s recognised as an International Standard gives us more confidence in its longevity, and the prospects for continued support and development. An “open” standard in this instance refers to a file format whose specification has been published; this sort of documentation, although highly technical, can be useful to help us understand (and in some cases validate) the behaviour of a file format.

CONS

Codec dependency

We mentioned the scalable bitstream above and the capacity for lossless compression as two of this format’s strengths. However, to do these requires an extra bit of functionality above and beyond what most file formats are capable of (including the TIFF). This is the codec, which performs a compression-decompression action on the image data. Besides being a dependency – without the codec, the magic of the JPEG2000 won’t work. This is one part of the format which remains something of a “black box,” a lack of transparency which may make some developers reluctant to work with the format.

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Save As settings can be complex

In digitisation projects, the “Save As” action is crucial; you want your team to be producing consistent digitised resources which conform precisely to a pre-determined profile, for instance with regard to pixel size, resolution, and colour space. With a TIFF, these settings are relatively easy to apply; with the JPEG2000, there are many options and many possibilities, and it requires some expertise selecting the settings that will work for your project. Both the decision-making process, and the time spent applying them while scanning, might add a burden to your project.

jpeg2000_3.jpg

Not yet the de facto standard

The “digital image industry,” if indeed there is such an entity, has not yet adopted the JPEG 2000 file format as a de facto standard. If you’re inclined to doubt this, look at the hardware; most digital cameras and digital scanners tend to save to TIFF or JPEG, not JPEG2000.

In conclusion, this post is not aiming to “sell” you on one format over another; the process that is relevant is going through a series of decisions, and informing yourself as best you can about the suitability of any given file format. Neither is it a case of either/or; we are aware of at least one major digitisation project that makes judicious use of both the TIFF and the JPEG2000, exploiting the salient features of both. 

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Posted in Digital Preservation, IT and Digital