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Standards for Digitization in Cases of Maps, Documents, and other Relics in the Service of Cultural Heritage


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This paper discusses the analysis of correct digitization practices to follow for maximum performance of the technique. Although it is written for cases that fall within the broader context of culture and cultural heritage, it is ultimately about writing rules that are not limited to the above-mentioned cases, but can be used in more general situations, particularly printed materials. This paper will therefore discuss the technical characteristics of the choice of digital imaging devices and distinguish the types of quality calculation in the different cases of digitized text, digitized manuscript, digitized maps, and photographs.
Open Journal of Educational Research, 2021, 1, 24-31
DOI: 10.31586/ojer.2021.99
DOI: Open Journal of Educational Research
Standards for Digitization in Cases of Maps, Documents, and
other Relics in the Service of Cultural Heritage
George Malaperdas
Laboratory of Archaeometry, Department of History, Archaeology and Cultural Resources Management,
University of The Peloponnese, Kalamata, Greece
Abstract: This paper discusses the analysis of correct digitization practices to follow for maximum
performance of the technique. Although it is written for cases that fall within the broader context of
culture and cultural heritage, it is ultimately about writing rules that are not limited to the
above-mentioned cases, but can be used in more general situations, particularly printed materials.
This paper will therefore discuss the technical characteristics of the choice of digital imaging de-
vices and distinguish the types of quality calculation in the different cases of digitized text, digit-
ized manuscript, digitized maps, and photographs.
Keywords: Digitization, Maps and documents, Cultural Heritage, Mapping, GIS
1. Introduction
In the process of digitization, especially when it comes to cultural relics in printed
and written form- such as old maps and diagrams, old handwritten documents, rare
notes, and photographs- some important specifications must be met in order to achieve
the desired result. All the above-mentioned cases involve objects based on any type of
illustration or writing on paper surfaces; while after digitization they can change their
format and pass into cases of three-dimensional technologies, the whole digitization
process is based on so-called two-dimensional digitization.
Two-dimensional digitization is the most standardized and best-documented
method of digitization worldwide. It is divided into two main methods: scanning and
digital photography. The equipment for these two methods is different; while the first
form is mainly done through the choice of scanners, the second is done through pho-
tography and photographic techniques.
1.1. Main categories of deterioration
Discussing in general the objects that are part of the broader term of cultural herit-
age, they are usually objects that have stood the test of time. However, it would be ex-
tremely unlikely that we would encounter such objects without having suffered on a
smaller or larger scale due to the passage of time. These damages can be summarized in
three main categories:
I) Photochemical damage: due to the aging of the construction material and the ef-
fect of environmental parameters such as relative humidity, temperature, and radiation.
II) Mechanical damage: due to poor handling, storage, and transport practices. They
include significant damage such as tearing, bulging, loss of entire parts and loss of paper.
III) Deposits: due to mishandling and human carelessness, incorrect operations, and
inappropriate storage conditions [1].
How to cite this paper: Malaperdas,
G. (2021). Standards for Digitization
in Cases of Maps, Documents, and
other Relics in the Service of Cultur-
al Heritage. Open Journal of Educa-
tional Research, 1(1), 2431. Retrieved
Received: August 7, 2021
Accepted: September 22, 2021
Published: September 23, 2021
Copyright:© 2021by the authors.
Submitted for possible open access
publication under the terms and
conditions of the Creative Commons
Attribution (CC BY) license
George Malaperdas 2 of 8
2. Materials and Methods
The choice of method to be used must accounts for a number of factors that concern
the technical characteristics and affect the quality of the final result. The most important
factors are the resolution, the color depth, the dynamic field, and the signal to noise ratio
•Resolution: The resolution is directly related to the density of information that can
be captured by the scanner. This is expressed in dots per inch (DPI) or pixels per inch
(PPI). It is obvious that the higher the number of DPIs or PPIs respectively, the more in-
formation will be printed. There are three main factors in choosing the right resolution of
an object. These are:
A) Its dimensions. In a case where we want to digitize an object- such as a photo- of a
certain scale, which as an original maximum resolution to be printed on A5 paper; when
we want to enlarge the exact same photo, to print it on A4 paper, then we will we have
less information than in the original and therefore less analysis. On the contrary, in the
initial dimensions of A5, more resolution will be needed, as more imprinted detail will be
B) The detail it has. For example, a document requires much less resolution than a
photo on a page of the same size, as the photo has more detail.
C) The purpose for which the digitization will take place. When the purpose of a job
is, for example, to capture a map and digitize it in every detail in a design software; this is
completely different from needing the map to simply display it on the internet. In such a
case, obviously, the scan can be done in low resolution; as, on the one hand, we are not
interested in every detail and, on the other hand, we also need to reduce the file size.
•Color depth: The color depth is the direct function of color tones that can be cap-
tured. The tone for each pixel is represented in bits. For example, a 1-bit image is a
black-and-white image, where each pixel corresponds to a bit that can be either black or
white. In contrast, an 8-bit image has 256 shades (28 = 256) and a 24-bit image has millions
of shades (224 = 16,777,216).
Figure 1 shows the same image imprinted at different color depths. Capture at a
greater color depth helps reduce noise and extends the range of image shades without
loss of information; it is worth mentioning that the scanners on the market have a max-
imum color depth of 48-bit.The main rules regarding the color depth are the following:
1) For black and white documents, as in the case of photocopies, black and white
digital capture is recommended due to their high contrast.
2) As for black and white originals that have images with the mapping, it is prefer-
able to be in grayscale.
3) Concerning very valuable or very old prototypes (such as manuscripts, old pub-
lications, musical scores, maps and diagrams), it is preferable to be captured in grayscale,
or even colorized, so that all the details that may be related to the shade can be distin-
guished and the condition of the paper, including the marks that may be on them, can be
Figure 1. Color Depth 1-bit, 8-bit, 24-bit (from left to right)
George Malaperdas 3 of 8
Dynamic field: The dynamic field measuring range between the brightest and the
darkest point of an image. What triggers the dynamic field of a scanner or even a digital
camera is how it affects the ability to capture shadows and highlights in an image.
As a rule, scanners with greater color depth have the ability to capture higher optical
densities. The dynamic field arises as a function of the optical density logarithm. While
the value pair (0,0) is the absolute white, respectively, the absolute black is observed in
the value pair (4,0).If we were to specify all this, we would say that the dynamic field is
the range of optical density values, between 0 and 4, that a scanner can distinguish.
Flatbed scanners have a dynamic range of 2.5 to 3.5; while more expensive scanners,
which contain a drum, reach up to 3.8. The latest technology scanners also have a special
value for the darkest spot that can capture called dMax. The higher the dMax value a
scanner has, the better it captures shadows. This is especially important for all digitiza-
tion cases involving maps, slides, negatives of an old camera, and, in general, where there
is a lot of detail that we want to render as it is. The following table (Table 1) shows the
values for the dynamic field of different scan product sources.
Table 1.Dynamic field of different scan product sources
Dynamic Field Values
Other printed material
Photography (normal print)
Photography (high quality)
Negatives from old films
Maps and Diagrams
The ratio of the signal to the noise: Any unwanted component within the image
signal is considered noise. It is caused by failures in the design of the recording device
and, in general, you consider that the presence of noise is inevitable in all electronic de-
vices. However, the size of the noise is variable and always depends on the quality
characteristics of each electronic device.
In the case of digital images, the presence of noise appears as small dots at different
shading points and in instances where the signal is low.
In order to make this visible, there should be bold printing in areas that are brighter
in color or in areas where there is an increasing range of image contrast.
Noise is measured based on the ratio of the signal to the noise (SNR). A typical ratio
is 60 dB for a 24- bit color depth and at least 75 dB for a 36- bit color depth. As a general
principle, the higher the ratio, the better the quality of the digital image; this is very im-
portant in terms of digital processing, especially of color maps and diagrams.
3. Analysis
3.1. Limitations of Analysis
In the process of scanning any product that comes from it, it makes sense that as the
resolution and essentially the quality of the document increases, so does the volume oc-
cupied by the digital file. Nowadays, despite the fact that the storage space of computers
has increased significantly, a large amount of storage space is occupied by this type of
archival material, especially when we refer to digital scans of old and historical maps and
diagrams that may need a lot of detail. There is also a limit to the speed of the design
software we will use, as in all software the larger the file we want to open, the more dif-
ficult it is to both import and edit (due to the fact that it loads later).Finally, there is the
George Malaperdas 4 of 8
limitation of over-recording information. Increasing the resolution often does not have
the desired effect from the user, as it does not add any new information from the already
known ones that can be attributed to a lower resolution scan. In fact, in many cases, the
result obtained due to the excessive recording of information is the exact opposite, as of-
ten there is the recording of details due to noise which are not desirable (small dots, line
melanoma, etc.).A typical example for this is all the scanning effort of old post-
card-postcards. So, with these, the paper is of very poor quality and if someone tried to
scan them in very high resolution, the result would be the imprint outside the image and
texture of the paper resulting in the alteration of the desired scan result. In general, there
is a point of equilibrium, in which there is complete harmonization between the resolu-
tion and the color depth of the digital capture, with the information of the original. In
order for the result from the digital copy of the scanning to be ideal, this equilibrium
point must be found as the extra resolution has nothing more to offer. The general rec-
ommendation is that the digital capture should be done in the maximum possible reso-
lution that is allowed, by both the cost and the available resources, and that it is consid-
ered satisfactory for the specific object to be scanned. In this way, it is possible to extract
from the digital copy a file that may have a lower resolution and therefore be much
smaller in size. On the other hand, in no case will the opposite be true, i.e. to have a low
quality image and export it to a higher quality image.
3.2. Methods of quality calculation (Quality Index - QI).
The great majority of large format document scanning is done at resolutions of 200
to 500 dpi (dots per inch).While higher resolutions produce better images, they also in-
crease file size, often significantly; the file size would increase by 125 percent when the
resolution is increased from 200 to 300 dpi, from 40,000 to 90,000 pixels per square inch. A
grayscale scan requires more patience (Figure 2).
The scanner head must scan the same image for three different colors- namely red,
green, and blue- when scanning a color image. In early color scanners, this was accom-
plished by scanning the same area three times for the three separate colors. Three-pass
scanners are the name for this type of scanner.
Moreover, most color scanners now scan in one pass, using color filters to scan all
three colors in one pass. In theory, a color CCD works in the same way as a monochrome
CCD. Each color, on the other hand, is made by blending red, green, and blue. Each pixel
in a 24-bit RGB CCD, for example, has 24 bits of information. A scanner that uses these
three colors (in all 24 RGB modes) may output up to 16.8 million different colors.
Various researchers have developed, overtime, the issue of quality calculation for
the digitization of mainly printed material. Here, we present the calculation of quality
(Quality Index - QI) developed by the University of Cornell.
Figure 2. Scan settings
George Malaperdas 5 of 8
Α) Texts
In the case of digitized texts, there is an initial clear distinction between black and
white scanning and scanning in color or grayscale (Figure 3). It is now commonly ac-
cepted that scanning in black and white shows information loss (even infinitesimal).
Figure 3. Scanned text comparison 300 dpi (left) vs. 600 dpi (right)
There are two main factors that affect the quality of the text scanning process. These
are the function of the height of characters (h in mm), and the resolution (in dpi). In small
text (height 1 mm), the scan must be done at a resolution of 400 dpi in grayscale, so that
the resulting digital copy is of excellent quality. On the contrary, for a text in which the
characters have a height of 2 mm, it is enough to scan at half of the 200 dpi resolution, in
grayscale (Table 2).
Table 2. Types of quality calculation (for digitized text)
Black and white text
QI = (dpi*0.039*h)/3
h = (3*QI) /(0.039*dpi)
dpi = (3*QI)/(0.039*h)
Text in shades of gray or color
QI = (dpi*0.039*h)/2
h = (2*QI) /(0.039*dpi)
dpi = (2*QI)/(0.039*h)
Levels of Image Quality
(8.0) Excellent
(5.0) Good
(3.6) Poor
(3.0) Just Readable
Β) Prototypes including graphics
If we have prototypes that include graphic maps, sketches, engravings, and even
manuscripts, there are other types that take into consideration the width of the thinnest
line or point of the drawing (w in mm).In the case of the map, where the thinnest line
thickness is 0.2 mm, the resolution that should be scanned to have the desired result is at
least 400 dpi in shades of gray or color.
Table 3.Types of quality calculation (for prototypes with graphics)
Text in shades of gray or color
dpi = (1.5*QI)/(0.039*w)
Levels of Image Quality
(2.0) Excellent
(1.5) Good
(1.0) In dispute
(<1) Insufficient not acceptable
George Malaperdas 6 of 8
C) Photographic material
With regard to cases of photographs and photographic material, it should be em-
phasized that there is no specific type of calculation of its scan of the two previous cases.
This is mainly because the measure of detail is subjective to each photograph and there is
no single measure that could determine the smallest unit of detail above the line and
point on a map. The desired resolution is therefore determined by the dimensions of the
original. Halftones images
require very high resolutions as the way they were printed in
the past was done through repetitive patterns of dots and lines. Thus, even when scan-
ning, it is easier to deform due to the phenomena of the wavy lines (moiré effect).
The general rule for such cases is to scan in shades of gray and with a resolution four
times the scale of the sinusoidal image. In cases of aerial photo scanning, the minimum
resolution requirements are the same as in art, the minimum, ie 800 dpi, while for the rest
of the images; the minimum resolution is set at 400 dpi (Figure 4).
Figure 4. Scanning a halftone image in 150 dpi (left) and 400 dpi (right).
3.3. Scanning on digital cameras
The second scanning mode is made with the help of the cameras. The resolution in
this case is measured in Megapixels, which result from the number of pixels that the
digital camera can print. The following (Table 4) is a table of minimum resolution and
color depth requirements for scanning with a digital camera. What will determine the
final specifications for the best result depends mainly on the nature of the original object,
the objectives of the work, the degree of specialization of the users involved, and, finally,
the budget of the work.
Halftones are methods of graphic reproduction processes using dots (discrete locations) of different sizes or even distances from each other to simulate the smooth
tonal continuity of a natural image. This technique is also known as dithering. Non-dot image printing techniques are called contone prints, e.g. laser printing on pho-
tochemical papers or dye sublimation printing.
George Malaperdas 7 of 8
Table 4. Minimum scanning requirements through digital photography
Original Item
Minimum Resolution
Color Depth
Printed material
3264 * 2448 (8Mpixel)
4064 * 2 704 (11Mpixel)
(always depends on their scale)
4064 * 2 704 (11Mpixel)
Works of art and fabrics
4064 * 2 704 (11Mpixel)
3.4. The accuracy of scanned images in GIS
Scanned images have now become the main source of input for GIS; the increased
use of scanners in the GIS environment has prompted us to consider the scanners' limi-
tations in terms of scanned image accuracy. Since most GIS software has very strict ac-
curacy criteria, this accuracy of the input data must be quantified before the user uses it.
In practice, input data must be accurate to 0.4572 mm in order to be used in a GIS data-
base. This means that, at the scale of the map, an input data position must be within
0.4572 mm of its actual geographic location. As a result, a scanner cannot generate more
positional accuracy error than the GIS's maximum error limit. Standard accuracy prob-
lems, including media continuity, source accessibility, and gaps in data collection
methods which can be easily quantified; as such, the user can determine if the resulting
data is suitable for their GIS before integrating it. Presently, with the sudden wave of
scanned data, there is a new problem to address: the input scanner's accuracy. The ability
of a scanner to generate an image with output dimensions that are proportional to the
input document is known as accuracy. Since scanners are still relatively costly, scanning
large volumes of data that do not meet the GIS's accuracy criteria can be disastrous.
Within the defined tolerances, the scanned image can be dimensionally accurate, but
nothing can be said about the data within the image's body. Even if the scanner is work-
ing within specified accuracy requirements, features inside the image can be as far as 7-10
mm from their correct position at the scale of the map, even if the image has exactly the
same amount of pixels. Depending on the size of the source map, 7-10 mm will equate to
hundreds of meters of error on the field. This is unacceptably bad for any GIS. As a result,
it is important to know how accurate the scanned image is so that corrective steps can be
easily integrated into the study.
Although scanning and table digitizing can handle the majority of conversion needs-
from textual data to graphics and even image data and video images- special techniques
for entering material from other sources have been created. This includes everything
from basic programs that make entering survey coordinates on the keyboard easier to
technologies that reconcile aerial photographs with geographic data. Additional possible
input sources include photogrammetric, remotely sensed, and CAD-generated data [2-5].
4. Conclusions
Digitization and the whole process allowed to a wide audience to access both objects
and information they probably would not even know existed. The use of the internet
nowadays helps in this direction where even the so-called non-experts have access to
such cases.
Digitization is synonymous with extroversion as the most important thing it pro-
vides is that through digitization, the object or information is available to such a wide
range of audiences, while the use of authentic, original heirlooms is protected "by many"
That is the reason of why digitization is one of the most contradictory methods re-
garding extroversion; as it is at the same time, an extroverted process that gives
knowledge and information to such a large audience, but also with such great introver-
George Malaperdas 8 of 8
sion as the user who will digitize the object is often not even part of a working group but
is an individual user who as a modern Apostle aims to transmit this information around
the world.
Digital information depends mainly on machines for decoding and reproducing
data on digital screens. There are two critical factors that favor this process: appropriate
equipment and human intervention [7].
Nowadays, due to the increasing speed of the internet, but also due to the many free
(unpaid) software and websites that exist in the vast internet universe, there are websites
that can automatically calculate the best needs for the best quality for both printing, as
well as for scanning documents, texts, images, and maps [8].
However, before using our data, particularly with regard to cartographic ap-
proaches, we should be certain of its source (knowing the scan quality and estimating
any errors) or we have performed the scan ourselves according to the requirements of
each task assigned to us.
Acknowledgments: This project was implemented within the scope of the “Exceptional Laboratory
Practices in Cultural Heritage: Upgrading Infrastructure and Extending Research Perspectives of
the Laboratory of Archaeometry”, a co-financed by Greece and the European Union project under
the auspices of the program “Competitiveness, Entrepreneurship and Innovation” NSRF
[1] Kyriazi, E., Tataris, G. and Soulakellis, N. "Preservation and Digitization of Maps of the early 20th century of the city of Myti-
lene", 11th National Conference of Cartography, The Cartography of the Greek State, 2010.
[2] Available online: (accessed on
[3] Chiang, Yao-Yi &Leyk, Stefan &Knoblock, Craig. A Survey of Digital Map Processing Techniques” ACM Computing Surveys
2014, Vol.47 (1), pp. 1-44
[4] Malaperdas, G; Zacharias, N. “A Geospatial Analysis of Mycenaean Habitation Sites Using a Geocumulative versus Habitation
Approach” Journal of Geoscience and Environment Protection, 2018; 6, pp. 111-131.
[5] Anagnwstou, E. “Study and Methodology of Good Development Practices for Digitization of Culture Content” University of
Patras, 2005.
[6] Malaperdas, G. “Digitization in Archival Material Conservation Processes”, European Journal of Engineering and Technology
Research, 2021; 6(4), pp. 30-32. doi: 10.24018/ejers.2021.6.4.2444
[7] Smith, A. (1999) “Why Digitize?” Council on library and information resources, commission on preservation and access.
[8] Fulton, W. “A Few Scanning Tips” Available online: (accessed on 7/8/2021).
... Since they are usually kept in libraries to prevent further decay, a scan is of course very helpful to use these maps and make them accessible to a broader community (Livieratos and Koussoulakou, 2006), (Southhall and Pridal 2012). The problems that may occur by scanning maps are discussed by several researchers (Daniil et al 2003), (Boutoura and Livieratos 2006), (Cura et al 2018), (Malaperdas 2021). However, there is more potential than just using the scanned image (Tsorlini et al 2014), (Iosifescu et al 2016), (Uhl et al 2018). ...
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