Category Archives: C

RGB color space

What is a color space?

Most likely you are reading this article on the screen of your computer, laptop or your smartphone. Do you see the colors in the illustrations? These colors are defined on your screen by the use of a color space. A color space is a defined range of colors. Color space means the use of a specific color model. A color model is a method of generating many colors from a defined group of primary colors. Each color model has a range of colors that it can generate. This area is the color space. The most common systems are RGB and CMYK.

When choosing which color space to use, the basic question is: Are you working in digital or print format? Digital devices such as cameras and monitors use a color space called RGB.

The RGB color space is composed of three basic colors to which the light-sensitive cones in the human eye react most sensitively: red, green and blue. Theoretically it is possible to decompose every visible color into combinations of these three “primary colors.” Color monitors, for instance, can display millions of colors simply by mixing different intensities of red, green and blue. It is most common to place the range of intensity for each color on a scale from 0 to 255 (one byte). The range of intensity is also known as the “color depth”. Multiplying all available color gradations per channel results in 2563 or 16,777,216 color combinations. One often finds the statement: 16.7 million colors.

The possibilities for mixing the three primary colors together can be represented as a three-dimensional coordinate plane with the values for R (red), G (green) and B (blue) on each axis. This coordinate plane results a cube called the RGB color space.

Source: Wikimedia Commmons Copyright: GNU-Lizenz für freie Dokumentation. 

The RGB color space is based on colored light. The three colors of light combine in different ways to create color. It is an additive process, a look at the pictures shows why:


If all three color channels are set to their maximum values (255 at a one byte color depth), the resulting color is white.

If all three color channels have a value of zero, it means that no light is emitted and the resulting color is black (on a monitor, for example, it cannot be blacker than the surface of the monitor producing 0 light).

This type of color mixing is also called “additive color mixing”.


What types of RGB color spaces are existing?

Source: Wikimedia Commons (unbearbeitet)
Copyright: Creative Commons Attribution-Share Alike 3.0 Unported 

Different color spaces allow for you to use a broader or narrower range of those 16.7 million colors used in an image. If you think about it, there is a nearly infinite number of ways you can mix different colors together. If you add just a little more green here or there, you have got a new color. Take away a bit more red, and you have just created yet another color. What most people do not know is that they can choose the level of color detail their camera records. A bigger color space captures more colors than a smaller one.

Color spaces differ in the number of colors that can be visualized within a color space. When it comes to working with digital devices, sRGB, AdobeRGB and ECI-RGB are among the most important and well-known color spaces:

The smallest of these color spaces, is sRGB. The sRGB color space was originally developed as a color space for CRT monitors in order to display images created in sRGB as similarly as possible on all monitors.

AdobeRGB is able to represent about 35% more color ranges than sRGB is able to. The color gamut was primarily improved in the green tones, including the blue-green area, i.e. the so-called cyan tones.

The ECI-RGB V2 color space is one of the standardised RGB colour spaces. It is the recommended color space in the Metamorfoze Preservation Imaging Guidelines and the only one allowed at the highest level of these imaging standards. As a working colour space for professional image processing ECI-RGB V2 covers practically all printing processes as well as all widespread display technologies. ECI-RGB thus particularly fulfils the requirements for true colour reproduction. A corresponding ICC profile for integration in image processing programs can be downloaded free of charge from the ECI website and allows constant colour reproduction on all output devices.

Camera slider

The majority of our scanners are designed with a fixed geometry. This minimizes mechanical movements and allows the systems to work without wear for several years. One disadvantage, however, is that formats and resolutions are fixed. If, for example, you scan an A4 sheet with an A1+ scanner, you “give away” a large part of the recording area with the background, which is detected and removed by the software when automatic scanning is activated.

For institutions with different originals and especially changing format sizes in their collections, which always want to get the best possible resolution, we therefore offer flexible reprographic systems. These are equipped with adjustable camera sliders to which our capturing unit is attached. This allows the user to easily adjust the height of the camera, either manually or motorized, depending on the model. For large originals, the camera unit is moved upwards, i.e. away from the original; for small photos or slides, downwards, thus increasing the resolution of the scans.

Our software allows defining individual camera positions and calibration settings, so that the user can conveniently vary between the different options with just one mouse click.

The perfect solution for archives and institutions with changing and heterogeneous holdings.

Cultural property protection

In 2016, Germany modernized its cultural property protection law with a comprehensive reform, thereby adapting German law to EU and international standards, above all to the UNESCO Convention of 1970. The Act on the Protection of Cultural Property came into force on August 6, 2016. It protects cultural property that bears witness of the German cultural history, but also such cultural property which is classified as national cultural property by other countries. Key points include the prevention of illegal trade, the improvement of mechanism for restitution, the modernization of the regulations on nationally valuable cultural assets and the protection of museum collections. (

In this context, digitization is a fundamental contribution to the preservation of cultural heritage and is therefore promoted through state initiatives.

In addition to the documentation for information assurance and scientific research, disaster recovery is a particular challenge in digitizing cultural assets. It calls for special damage-specific or cause-specific measures, as in the case of the destruction of the valuable holdings of the Anna Amalia Library in Weimar in devastating fire in 2004. The serious damages caused by fire and fire extinguishing water not only require highly complex restoration measures, but also pose complex challenges for the digitization process:

Such damaged and fragile books and documents require tailor-made scan systems that meet the highest conservation requirements in terms of handling and lighting, but also offer the appropriate technology to restore text and image information that can no longer be seen with the naked eye. In such cases innovative systems such as the book2net multispectral system can make a decisive contribution to securing and restoring information in a gentle and contact-free manner.

German Federal Document Safeguarding Project

According to The Hague Convention for the Protection of Cultural Property, the German Federal and State Archives have been scanning and microfilming their most valuable collections since 1961. The microfilming is carried out on behalf of the Federation under the leadership of the Federal Office of Civil Protection and Disaster Assistance (BBK). The archive material is security-filmed on microfilm in accordance with selection criteria defined by the Federal Government and in compliance with specified technical standards.
Here, too, book2net makes an active contribution to securing cultural assets with its scanning systems. As part of the conversion of the microfilming devices to digital technology, which was agreed between the Federal Office for Civil Protection and Disaster Assistance (BBK) and the Conference of Heads of the Federal and State Archives Administrations (KLA), four of the German state archives involved have already decided to purchase a total of 12 book2net high-performance archive scanners. The state archives of Hesse, Baden-Württemberg, North Rhine Westphalia and the Secret State Archives Prussian Cultural Heritage Foundation are the first institutions to have opted for our newly developed high-performance scanner book2net Archive Pro.

Accordance to international digitization guidelines

The digitization of valuable cultural objects should be carried out both as gently and extensive as possible in order to ensure permanent access even for future generations. 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 on the objects. The development of and compliance with guidelines should therefore be a mandatory prerequisite for every digitization project 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). 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.

Continuous light

Continuous light is understood in artistic photography as an artificial light source that illuminates a motif over a longer period of time. One of the advantages is that, in contrast to natural light, there can be no light fluctuations. The distance between the subject and the lamp as well as the output of the continuous light lamp have an influence on the brightness of the object to be exposed. Another advantage of artificial permanent lighting is that the quality of the photo can be recognized before the actual picture is taken, since shadows and brightness can be regulated by adjusting the height. This is particularly important in analog photography. The disadvantage, however, is that the continuous light can produce color distortions, especially if a little daylight is also involved.

Our systems use sustainable and gentle LED lighting: by default, it is only switched on during the scan and slowly raised and lowered within a second to protect the operator’s eyes. This mode of operation extends the service life of the LEDs, which are generally very long-lived, even further.

Image sensor / CMOS versus CCD

There are two types of image sensors for industrial cameras on the market: CCD and CMOS sensors.

Both, CCD sensors (Charge Coupled Device) and CMOS sensors (Complementary Metal Oxide Semiconductor) convert light (photons) into electrical signals (electrons).In terms of performance, CMOS sensors have now not only caught up with CCD sensors, but also outperformed them. The main difference between the two types of sensors lies in their technical design.

Let’s first compare how the two sensor types work:

Camera sensors use picture elements called “pixels” to detect light. A common analogy when it comes to pixels is to imagine a series of buckets collecting rainwater.

The big difference happens when you read out the sensor!

Area sensor bucket analogy

CCD image sensors read out each pixelsequentially.

In our bucket analogy water is poured from one bucket to the next like an old-fashioned fire brigade.

CCD sensor bucket analogy

CMOS image sensors read out each pixel in parallel. This means that CMOS cameras can read 100 times faster than a comparable CCD camera..

CMOS sensor bucket analogy

As a result of the integrated evaluation electronics, CMOS sensors offer the following advantages compared to CCD:

  • Very high frame rates compared to a CCD of the same size
  • Significantly lower power consumption
  • No artifacts, i.e. unintentionally created differences to the image source, such as blooming and smearing typical for CCD do not occur.
  • Lower need for light: Sensitive historical documents and books can be digitized particularly gently, as the light intensity can be significantly reduced during capture.
  • Due to the flexible read out through direct addressing of the individual pixels, CMOS sensors offer more options for binning & partial scan/ ROI.
  • Smaller size of the camera, as the evaluation logic can be integrated on the same chip (system on a chip).


In the area of cultural property protection, conservation or preservation refers to all measures that serve to examine, document and preserve the authenticity of works that are important in terms of art and cultural history and that are worthy of protection, without undertaking irreversible interventions that damage the object or change it massively. In 2000 the guidelines for preventive conservation were laid down in the Vantaa document.

Conservation is a preventive measure to secure the property and protect it from destruction, be it through catastrophes, wars or climatic influences, and to avoid restoration. However, a professional restoration can also be necessary for the permanent preservation of an object.

In the museum and archiving area, the conservation measures for exhibited and stored objects primarily include ensuring and controlling a stable room climate with regard to temperature and humidity as well as reducing light and pollutant emissions.

In a broader sense, the digitization of cultural assets is also a conservation measure. It enables objects to be seen, examined and researched without being subject to physical stress from transport, exposure or use. At the same time, however, the digitization process itself must meet preservation requirements and must not lead to any damage to the objects.

book2net - preservation approved book cradle

Modern scanning systems for the digitization of valuable cultural objects must therefore have the appropriate preservative components. These include, among other things, an adjustable, gentle lighting system, wear-preventing contact surfaces, book cradles with book spine release and adjustable opening angle and special glass, controllable pressure processses as well as special supplements for careful handling.