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“A consistently high image quality can only be achieved with standards”

The basic aim of digitizing cultural heritage materials is to create a digital copy of the original. In order to achieve this, the quality of the digitization must be verified and classified. This is achieved through image quality measurements based on quality standards and guidelines for cultural heritage imaging . However, it is important to understand the fundamental elements of image quality first, as given by Volker Jansen, Head of Development and Research at Zeutschel. We spoke to him about the content, differences, practical implementation, helpful tools and Zeutschel’s active role.

Mr. Jansen, why is it important to consider standards and guidelines in digitization projects?

Volker Jansen: Every digitization project has the common goal of capturing the original in all its details as comprehensible and reproducible as possible. Such a digitized copy is basically a digital representative of the original. Thus can be used for tasks such as digital long-term archiving or for remote access for research purposes. There are a number of quality requirements; for example: the image sharpness must match the pixel resolution evenly across the entire image area. The quality of the digital copy depends on the condition of the original, but above all on the performance of the imaging system. A subjective evaluation, which is in the eye of the observer and this is not acceptable. Rather, the image quality achieved with a digital camera or scanner must be fully defined and, above all it has to be measurable.

But is image quality objectively measurable?

Volker Jansen: Yes, image quality can be measured. There is a series of ISO standards for the objective measurement of the different quality parameters. the methods are bundled sn described in ISO 19264-1 especially for the area of cultural heritage imaging. Firstly, the standard defines the most important parameters – such as resolution, noise, dynamic range and color reproduction. And secondly, the standard describes the measurement methods. The performance of the system can be assessed by measuring the parameters using a test chart and analysis software. Likewise the ISO standard also contains a table in the appendix that divides the measurement results into three A, B and C quality levels. Those quality levels have an informal status . To summarize: The ISO standard provides users with a comprehensive compendium, to analyze the performance of the imaging systems used for cultural heritage digitization.

What significance does the ISO standard have for the digitization of cultural assets and how will it continue to develop?

Volker Jansen: It is highly recommended to adopt the methods ofthe ISO 19264-1 standard when digitizing cultural heritage. Libraries, archives and other public institutions are increasingly implementing quality control in accordance to the standard as mandatory in their tenders. This applies in particular to cultural heritage projects. This makes the ISO standard legally binding for external digitization companies. Currently, the ISO standard relates to originals such as books, magazines and maps. A separate standard for transparent materials – for example slides, glass negatives and other film formats – is expected to be released within 2025.

How does the ISO standard differ from the digitization guidelines?

Volker Jansen: The two technical guidelines Metamorfoze and FADGI are helping to implement the ISO standard in the daily workflows of digitization projects. To this end, they take up the measurement methods and quality parameters defined in the ISO standard and define their own quality aims and tolerances. Both Metamorfoze and FADGI divide the image quality into different quality levels with the corresponding limit values. Depending on the area of application, Metamorfoze provides three levels: First, Metamorfoze full with a very high tonal and color accuracy, as required for unique works of art such as paintings and art prints or historically valuable documents such as handwritten letters from historical personalities. Secondly, Metamorfoze Light with high color accuracy; examples of applications are historical books, newspapers or manuscripts. And finally, Metamorfoze Extra Light with high color accuracy for digitizing individual documents and originals with feed through scanners.

Does FADGI take a different approach?

Volker Jansen: The FADGI guideline describes and sets the limits based on use cases.
This means that it is divided into 17 different typical applications, and in each application area there are three to four quality levels, marked with stars in FADGI. Not all quality parameters of the ISO standard are taken into account in the FADGI guideline. ISO 19264-1 is an international standard and therefore applies worldwide. Metamorfoze has established itself among European and Asian users, while FADGI is widely used in the North Americas.

How is it implemented in practice? And how can image quality be measured in concrete terms?

Volker Jansen: Measurement methods and limit values for the required applications are described in the standards and guidelines. The limits and tolerances that are important for the project can be verified by quality analysis software such as the OS QM Tool from Zeutschel. Test charts such as the UTT (Universal Test Target) are available for determining the image quality. The user first digitizes the UTT with the imaging system to be used. The evaluation is done by the software on the image of the test chart analyzing the chart structures. The software compares the measurement results obtained with the defined limit values and tolerances. Within a few seconds, it is thus possible to determine whether the image quality achieved meets the defined requirements or not. At the same time, a statement is also made about the performance of the imaging system and whether recalibration may be necessary.

What role does Zeutschel play in the development and practical implementation of standards and guidelines?

Volker Jansen: Zeutschel has been involved in global standardization initiatives for many years. For example, Zeutschel is actively involved in the working group of international experts that drafted the ISO standard and is currently developing it further. Zeutschel also played an important role in the development of the UTT test chart, which was created as part of an international collaboration between Zeutschel and other experts. We also want to raise digitization expertise in our marked. To this end, we conduct training and courses not only for our employees, but also for partners and users. Video tutorials on important image quality topics are another component of our know-how transfer. And we develop tools that make regular image quality assurance easy and convenient.

Can you give us an example?

Volker Jansen: In practice, quality control usually is done randomly. This at the beginning and end of the digitization project; for larger projects, it is also done at defined intervals such as the start and end of shifts and when changes are made to the project schedule. However, this random sampling approach does not lead to a 100% reliable results. Quality fails in production can be overlooked and mismatch the quality specifications. Zeutschel has therefore developed the “Permanent Image Quality Control” software module. The result is constant monitoring of the image quality in production. The quality check is carried out ‘on-the-fly’ during scanning. Scans that fall outside the defined quality are detected immediately.

In a nutshell: Are standards and guidelines optional or mandatory in digitization projects?

Volker Jansen: ISO 19264-1 is part of the German body of standards and an important set of rules for the implementation of digitization projects. Users recognize that consistently high image quality can only be achieved if control is carried out in accordance with the standards and guidelines. The focus to digitize each original in the best possible quality, if possible only once. The measurement methods and practical limit values for this are available. There are also software tools for an efficient and uncomplicated digitization workflow. And companies like Zeutschel support users with know-how transfer and training. So the answer is clear: standards and guidelines are mandatory for best imaging results.

About Volker Jansen:

Volker Jansen leads Technology and Development at Zeutschel. The graduate engineer specializing in photo engineering has held a key position since 2003, developing all camera, scanner, and microfilm systems. As a member of the ISO TC 42 JWG 26 standardization committee, he actively contributes to the advancement of standards. He co-invented and established the UTT test target and the associated workflow for quality assurance in cultural heritage digitization. In addition to developing new solutions, his current focus is on defining a digitization standard for historical transmissive materials, which is being developed by ISO TC 42 JWG 26.