Category Archives: D

Delta E (dE or ∆E) is a measurand for determining color accuracy, i.e. for quantifying the distance, colloquially difference, between a given color value and the value achieved in reproduction by print media or displays.

Since visual color perception is strongly dependent on the viewer, a quantification by mathematically measurable reference values offers the possibility of an objective evaluation.

When specifying color distances according to the dE formal, the value denotes a difference that the human eye no longer perceives.

Generally applies: the smaller the distance, the smaller the color differences. A color distance of dE <0.2 is considered invisible, a distance below dE 1.0 still as small.

Delta E is frequently used in the field of digitization as an objective measurement variable in the color profiling of grayscale and RGB primary colors for quality determination.

In photography, the dynamic range describes the difference between the lightest and darkest point within an image. It is given as the ratio of the darkest to the lightest point.

In an original (slide, negative, photo), the brightest point has a so-called minimum density and the darkest point has a maximum density. The difference between the maximum density and the minimum density is then the so-called density range, or dynamic range.

The dynamic range of the subject or the original is crucial for determining the correct exposure: Only if the exposure range of the sensor or film is greater than or equal to the dynamic range of the subject can all the details of the subject be captured. Otherwise, parts of the subject will be imaged in black and/or white.

When digitizing, one speaks of distortion whenever the geometry of the original is not reproduced true to the original. The most common templates for scanning are documents, books, files or single pages. These usually consist of right-angled pages, the exactness of which should of course be maintained during the digitization process. However, depending on the optics used, it can happen that an actually rectangular A4 page looks, for example, “bulbous” or “pillow-shaped” in the scan. The edges and angles are then no longer straight and right-angled, but rather curved, too pointed or too blunt.

For this reason, it is imperative to use high-quality lenses for digitization that counteract this effect. In our scanning systems, the lens and sensor are matched to one another in such a way that a distortion-free capturing is guaranteed and no subsequent image processing or correction calculations are carried out using software.

Document scanners are generally sheetfed scanners that are designed for productivity in order to scan the highest possible throughput of documents at high speed. They are essentially structured like a fax machine, but nowadays they work with additional functions such as grayscale, color recognition, feed control, etc.

The most obvious disadvantage of the sheetfed scanner is that it only processes single pages (front and back). Document scanners therefore score particularly well when it comes to the mass digitization of high-volume stacks of documents consisting of loose pages. However, bound originals cannot be digitized with this type of scanner. In addition, sheetfed scanners usually require the documents to be in good condition, since the originals are exposed to greater stress than with contactless scanning by planetary scanners operating with incident light. In addition, when feeding smooth documents, such as photos, there are unpleasant edge distortions.

With the SCAMIG series, book2net offers document scanners in the high-end area, which have unique features such as sensory feed and flow control, slow-down option, paper-friendly tape transport, gentle LED lighting and maximum color fidelity in accordance with the ISO 19264-1 standard. This makes it possible to digitize even sensitive templates and documents of various sizes, such as archive material, gently and efficiently at the same time.

With the combination of our document scanner SCAMIG 210 with various models of our book2net book scanners, we also offer our customers a uniquely variable and productive hybrid scanning system with shared user software.

The depth of field indicates the range in which images are displayed sharply when photographing or scanning. For example, if you work with a shallow depth of field and focus on an object that is, say, 30 cm away from the lens, everything closer (15 cm) or farther away (35 cm) will appear out of focus.

When digitizing, however, one works mainly with flat, two-dimensional originals, for which a shallow depth of field is supposedly required. However, if you want to digitize three-dimensional objects, such as books with a deep book fold or seal letters with a structure, it quickly becomes clear why a high depth of field is necessary: here, all areas should be displayed sharply and legibly so that no information is lost.

The further away the lens is from an object, the greater the depth of field. In macro photography, where the distance between the optics and the subject can be less than 5 cm, it is self-explanatory that the depth of field decreases accordingly or is barely present.

Thanks to the special optics and the area sensor used, our systems are able to provide a depth of field of 8-15 cm, depending on the format.

Why are guidelines for digitization important to your project?

The quality of a digitization process is subject to a wide variety of factors. It depends on components such as the scanner hardware used (sensor technology and quality of the lens), but also crucially on the light irradiation (internal, controllable lighting in the scanning system, external, often uncontrollable irradiation from natural or artificial room light). Wall colors, the color of the scanning system itself or even the clothing of the user can also influence the quality of the results. Further factors concern upstream or downstream algorithms for image processing or color management.

In particular, the digitization of valuable cultural objects should be carried out as gently and with the highest quality as possible in order to enable future generations to benefit from the data. This raises the question of the best possible concepts and methods that guarantee a constant quality of the scan results with the least physical stress. The development of and compliance with guidelines should therefore be a mandatory prerequisite for every project for the digitization of cultural property. However, navigating through the multitude of scan systems and analysis tools available on the market can be an enormous challenge for the user.

The two currently most popular digitization guidelines, which also define the relevant standards for us, come from the United States (FADGI – Federal Agencies Digitization Guidelines Initiative) and the Netherlands (Metamorfoze Preservation Imaging Guidelines – a cooperation project between the National Library and the National Archives of the Netherlands). They arose out of the need to create an objective catalog of requirements which state and public institutions can use as criteria for the procurement of scanning systems.

To standardize these two different approaches, the ISO (International Organization for Standardization) has been developing a new standard since 2012, which can be found in the three documents ISO 19262, ISO 19263 and ISO 19264. ISO 19262 documents the terms that are used in the field of image capturing in order to generate a standardized vocabulary. ISO 19263 describes the technical work processes and provides detailed information on how the measurements are best carried out. Finally, ISO 19264 describes the measurements in detail as well as goals and tolerance values for various aspects. Among other things, the main features of image quality, the metrics for evaluating these quality features, the procedure for the image quality analysis and the documentation of the results are specified.

We encourage you to review these documents in order to carry out your projects, even if you are not required to adhere to certain guidelines.

Get more information:

FADGI
Website: http://www.digitizationguidelines.gov/
PDF digitization guidelines for download: http://www.digitizationguidelines.gov/guidelines/FADGI_Still_Image_Tech_Guidelines_2016.pdf

METAMORFOZE

Website: https://www.metamorfoze.nl/
PDF digitization guidelines for download: https://www.metamorfoze.nl/sites/default/files/publicatie_documenten/Metamorfoze_Preservation_Imaging_Guidelines_1.0.pdf

ISO-Standard
PDF digitization guidelines for download: Standardization of Image Quality Analysis – ISO 19264

PDF vocabulary: ISO 19262 : 2015 Photography-Archiving Systems – Vocabulary http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=64219

The standardized values for paper sizes known today as DIN formats were first defined by the German Institute for Standardization (DIN) on August 18, 1922, in the DIN standard DIN 476. They classify the ratio between the width and height of a sheet of paper, which is the same for all sheet sizes, namely 1: √2.

Only with this ratio does the next smaller sheet created by folding centrally over the long side remain geometrically similar to the original sheet.

This aspect ratio, on which the DIN standards are based, goes back historically to the 18th century and was already specified by Georg Christoph Lichtenberg in 1786. Forgotten for a long time, it was taken up again in 1910 by Wilhelm Ostwald and subsequently disseminated by Walter Porstmann and enforced as a DIN standard in 1922.

With its specifications on the A and B series, the German standard served as the basis for the European and international equivalent EN ISO 216, which in turn has been adapted in almost all countries. The only differences are usually in the permitted tolerances. As a purely national standard, DIN 476-2:2008-02 Paper end sizes – C series is still valid.

ISO and DIN paper sizes

There are four series (A and B according to ISO and DIN, C and the original D according to DIN), each of which is divided into eleven classes numbered in descending order of size from 0 to 10.

The nominal area of an A0 sheet is one square meter, but due to the rounding of the side lengths to whole millimeters, the real areas in the A series deviate from one square meter or whole fractions thereof. The same applies to whole multiples of √2 for the other series. Because of the permitted length tolerances, the real areas can deviate even further.

DPI stands for ‘Dots per Inch’ “, more precisely the print-dots per inch and describes the dot density. So 300 dpi means a printer puts out 300 tiny dots of ink to fill in every inch of the print. In image reproduction, the dot density is a measure of the level of detail in a rasterized, visual reproduction and thus one of the quality aspects of the technical reproduction process.. This means that dpi is the technical printing resolution with which the print data is handled on a carrier medium. The dpi number depends on the specific printer.

In common parlance, there is no longer a distinction between dpi and ppi. In fact, even in the technical jargon of media designers, the terms are largely used synonymously. PPI describes the resolution in pixels in a digital image, whereas dpi describes the number of (print-)dots in a printed image.

As physical stacks are needed to be well managed and well organized, so is the case with online information. One wants online resources to be researchable and organized, just like hard copies.

A digital repository provides you a hub of online resources that one might need for a variety of different functions and purposes. In addition, the digital repository is responsible for preserving digital content.

How do digital repositories work?

Digital repository is a broader term that includes the journey from a single software system to the overall management and planning of online materials. This stewardship is not restricted to hardware or software solely but extends to services, processes, content, rules, regulations, and metadata.

While keeping up intelligent control, digital repositories hold a particular and permanent location so that researchers may not face any difficulty in finding the digital materials they are looking for.

We can find two basic types of digital repositories:

1) Institutional Repository

2) Disciplinary Repository

As evident by its title, an institutional repository is a repository or collection of an institution’s particular resources.
On the other hand, some repositories work as subject-based online archives maintained by a subject community. Such a disciplinary repository contains the data associated with scholars in a specific area.

Advantages of digital repositories

• A digital repository deals with intellectual stuff and metadata in the same area.
• It allows user-friendly remote access to resources. It works as a valuable tool for RAE (Research Assessment Exercise).
• A digital repository allows organizations and institutions to preserve the integrity of their intellectual assets efficiently.
• These repositories allow the deposits in bulks, thus reducing the need for physical storage.