Category Archives: Glossary

Chromatic abberation

In optics, chromatatic aberration (also abbreviated to CA) is a failure of a lens that occurs when light of different wavelengths or colors is refracted to different extents. This can lead to lateral chromatic aberration, which manifests itself primarily at image edges in green and red or blue and yellow color fringes at light-dark transitions. Longitudinal color errors can also occur in the form of different discolorations in front of and behind the focal plane.

apochromatic image of a building

Comparison of an image without and with chromatic aberration, in this case a lateral chromatic aberration.

Source: Wikimedia Commons (unchanged)
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Since such color errors should be avoided when digitizing, our systems work with a chromatic-corrected lens that compensates for this phenomenon. Otherwise, colored fragments would show around the edges of black letters, for example, and the scan would not be identical with the original.

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?

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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 eciRGB 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 eciRGB 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 eciRGB v2 covers practically all printing processes as well as all widespread display technologies. eciRGB 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.

Exposure time

When scanning, the exposure time determines the length of time light falls on the sensor. If all other parameters remain constant, the picture becomes brighter with increasing exposure time. In inexpensive cameras, the exposure time is regulated by a mechanical shutter and it is set how long the shutter stays open to let the light through when taking the picture. The shutter then closes and no further information reaches the sensor.

In contrast, in our systems, we are using our X71 camera, which works with an electronic shutter. The 71 megapixel camera was especially designed for demanding continuous use in the digitization sector, providing a long service life. Therefore, the camera does not work with a mechanical fastener that is susceptible to wear. In order to regulate the time in which the sensor receives information, the sensor is electronically darkened and hence completely motion-free. This guarantees constant and reproducible exposure times even with high-volume digitization projects. The use of highly sensitive area sensors also reduces the duration of the necessary exposure time and, as a result, the scan time, thus supporting the most gentle and productive scanning.

The exposure time can also be individually regulated using our Easy Scan scanning software, which is very helpful, for example, when digitizing transparencies. Due to the changing film and transparency templates, it may be necessary to adjust the exposure time individually in order to obtain optimal results, regardless of the film density, material or pigment type.


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.


In photographic technology, optical vignetting (edge decoration) is an effect that may be wanted in artistic photography, but is not desired when digitizing documents, which require a true-to-original capturing. Vignetting is essentially a decrease in brightness towards the edge area of the image, which is caused by the light guidance through the objective and the axially arranged openings connected to it.

The resulting images are significantly darker due to the drop in light from the edge and mostly the “lighter” center of the image is shown in a circle.

In order to avoid this effect with our scanners, we work with special lenses in which this effect has already been corrected, unlike conventional camera lenses. Subsequent image manipulation or correction using software is therefore not necessary.


When taking a picture with a microscope through the eyepiece. This photo was taken “freehand” with a compact camera above the microscope eyepiece.
Due to lack of optical adjustment, the edge of the camera sensor cannot be exposed.

Source: Wikipedia Commons (unchanged)  Copyright: Creative Commons Attribution-Share Alike 3.0 Unported

Related Topics

Processing time

The processing time (processing speed) is an important factor in high-volume digitization projects, especially in the service sector. It not only includes the pure scanning time, but also the time required to transfer, save and, if necessary, to display data. Generally, the processing time is the time that is required between turning individual pages. Depending on the system, there are also other parameters that influence the process time. For example, when scanning with a glass plate or a motorized book cradle, the process time increases, as additional time is required for opening and closing the glass plate or lowering and repositioning the book cradle.

It is therefore advisable for extensive projects not only to consider the pure scanning time of a system specified by the manufacturer, which is always the same regardless of the glass plate, book cradle or other configurations, but also to consider the processing time of the desired system with all the necessary components. Only then is it possible to precisely calculate the time required relative to the amount of documents.

Furthermore, the processing time should always be considered in relation to the area of application of a scanner. Book scanners with incident light work much more slowly than high-speed document feeder scanners, which can easily scan 200 pages per minute. However, the requirements are also different: Book scanners offer a significantly higher quality and are suitable for sensitive, fragile, fragmented as well as stapled and bound originals. Document feeder scanners, on the other hand, usually require their originals to be in good condition and can score particularly well with throughput and the processing of large stacks of paper. Document scanners in the high-end area such as the book2net SCAMIG series also have an adjustable feed control and a unique slow-down mode, with which even sensitive originals and documents of different sizes can be scanned efficiently and gently. However, bound originals cannot be digitized with this type of scanner. High-end document scanners such as the book2net SCAMIG series also have an adjustable feed control and a unique slow-down mode, with which even sensitive originals and documents of different sizes can be scanned efficiently and gently. However, bound originals cannot be digitized with this type of scanner.

But also planetary book scanners used in the production area of service providers or in the public customer area of libraries and archives should provide a scanning time of less than one second and a processing time less than 3 seconds to ensure smooth and efficient workflow.

Flatbed scanner

In contrast to planetary scanners, which are operating contactless with incident light, flatbed scanners work on the same principle as a copier: The original is placed on a pane of glass and light-sensitive sensors are guided under the pane of glass during scanning.

This method makes it possible to scan not only single pages and photos but also bulky documents such as books. However, in order to achieve a sharp image, the original usually has to lie flat on the glass plate. This can lead to irreparable damage to the book spine due to the high pressure load. In addition, the handling is very cumbersome as the flap has to be opened each time for the next scan; the book has to be taken out, the page turned again, etc. Likewise, this type of scanning does not allow a distortion-free and reproducible capturing of the original.

Some flatbed scanners also have a document feeder for single pages. Inexpensive flatbed scanners are therefore mainly used in office operations, where documents are mostly scanned in A4 up to A3 format.

High-priced flatbed scanners, especially in the large format area, also work with conservative LED lighting and high-resolution line sensor technology, which also enables digitization without pressure to a certain extent, but is clearly inferior to planetary scanners in terms of protection of the originals, handling and productivity.

Document scanner

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.

Hybrid scanning systems

Extensive digitization projects, in which a large number of different documents are to be scanned gently and efficiently at the same time, are often faced with the problem of finding the optimal scanning systems in terms of quality, workflow and cost efficiency. 

Therefore, at book2net, we have developed versatile hybrid scanning solutions for our customers. These are particularly suitable for the demanding requirements of retro-digitization projects in archives, libraries and digitization centers and enable the document-friendly, user-friendly and productive digitization of both bound and stapled templates as well as loose sheets.

Depending on the project requirements, we will put together a tailor-made package consisting of a book2net planetary book scanner (A1 / A2) for fragile, bound or stapled originals and an A3 SCAMIG document scanner for single sheets or loose stacks of sheets. In this way, the advantages of two scanning worlds are ideally combined: contactless, gentle incident-light digitization with the speed and high throughput of feeder scanners.

The scanning software of the book scanner serves as an interface for both scanners. This means that within the scan software you always receive all scans from both devices in the correct order and can export them together and feed them into further workflows. This eliminates time-consuming work steps such as merging individual scans from different devices and increases productivity significantly without compromising the quality and care in handling your documents.

Benefit from our hybrid scanning systems!


Line sensor

Line sensors are light or radiation sensitive detectors (mostly semiconductor detectors), which consists of one or sometimes several rows of pixels (lines) to capture information. The counterpart to the line sensor is the area sensor, which has a rectangular arrangement (matrix) of pixels.

Line sensors are based on the original development for data storage from 1969 and have not changed significantly to this day. The light-sensitive sensors are very suitable for scanning documents in order to capture an image. The detector runs close to the original, scans the document line by line and combines the information from the individual scan lines to form an overall image. Sometimes only one line is used; sometimes a separate line is used for each color channel (red, green, blue).
This technology is still employed today in scanners, fax machines and copiers because it is very cheap and available in large quantities.

A major disadvantage of using this type of sensor in scanners is that the image capturing takes a comparatively long time due to the sequential scanning and that mechanical wear always takes place due to the movement of the components. This can lead to premature wear, especially with production scanners that have to digitize large quantities of documents in continuous operation.

In addition, the depth of field of line sensors is very small and covers only a few millimeters. Particularly in the case of books with a deep book fold or wavy pages that are not completely flat, this leads to blurring or even loss of information in the digitized material.

At book2net, we therefore only use image area sensors in our scanning systems.