Category Archives: I

Imaging techniques

In the field of art technology, imaging techniques belong to the non-invasive analysis procedures, i.e. they enable a non-destructive examination of artworks in contrast to analysis procedures in which material samples have to be removed.

These imaging methods make use of radiation of different wavelengths (from X-rays to the NIR range) and their very specific penetration and interaction with the materials of a work of art. This makes it possible to visualize material structures or differences that are invisible to the human eye.

Standard techniques include special photographic techniques such as sided light or multispectral photography. Other classic techniques, especially in the field of painting examination, include radiography, infrared reflectography  (IRR), and macro X-ray fluorescence scanning (RFA imaging), which combines imaging and material analysis.

Spectroscopy is another non-destructive analysis method.


Book cradle

Mechanical book cradles that are designed for a support angle of up to 180° usually also have a so-called book cradle lock. This works like a brake that prevents the book cradle from making compensating movements during the scan and thus prevents blurring. In addition, there is often also the option of locking the book cradle as a whole by hand or foot switch and using it only as a flat support table.

Glass plate

Professional scanning systems that work with glass plates also have the option of locking the open glass plate to enable scanning without pressure for particularly sensitive originals.

ICC profile

What is an ICC color profile?

Your photo looks different on the monitor than on your smartphone or printout? Does this sound familiar? Just as every person perceives colors differently, every imaging device (monitor, scanner, digital camera) reproduces colors individually. This is called color space. Each color space has a defined range of colors that it can represent. This means that each input or output device speaks a different “language”, so to speak, when it comes to the colors it can display. In order for them to “speak the same language”, they must be calibrated and a color profile must be created.

To enable consistent color management between input and output devices in the digital workflow, the International Color Consortium (ICC) has developed an international standard format for color profiles. With the ICC color profile, a color image created with an input device (digital camera, scanner) can be reproduced in true color on a monitor or by a printer.

The first link in the process chain is the camera or scanner. Especially in digital preservation, it is particularly important to calibrate the camera or scanner using standardized color templates (e.g. X-Rite ColorChecker) and to create a corresponding color profile to ensure color-accurate reproduction.

True color straight from the camera

The book2net scanners and repro-systems are the only systems on the market equipped with a so-called true-color color management. Directly from the camera, it is possible to generate true-color images according to the color spaces sRGB, Adobe 1998 RGB, ECI RGB V1 and ECI RGB V2 and an ICC color profile. The corresponding ICC profile can be embedded in the image file. There is no need to use additional software such as Photoshop or Lightroom.

This makes it possible to meet all requirements of the digitization guidelines and standards without any problems.

The big advantage of book2net True Color Management: Unlike the creation of an ICC profile, which is calculated e.g. by means of a 24-bit color scan of an X-Rite Color Checker by a “calibration software”, the book2net True Color Management takes advantage of performing all calculations and adjustments in the internal imaging area of the camera with a color and analysis depth of 48 bits. Colors are hit even more precisely and noise is minimized.

The result: METAMORFOZE, FADGI and ISO/TS 19264-1:2017 compliant scan results!

Image sensor / area sensor

In contrast to line sensors, image area sensors have a matrix with pixels, i.e. an x- and a y-axis. The area sensor offers a high dynamic range and a fill factor of almost 100%. These sensors are very suitable for high-resolution camera systems in industry and science, where a special focus is placed on maintenance-free and wear-free systems. In addition, due to their high quality, surface sensors are used in the areas of document digitization and capture, measurements and inspections, medicine and research as well as for 3D vision.

A considerable advantage of area sensors compared to line sensors is that the image sensor area can be exposed simultaneously and without delay, without the need to add up individual segments. The overall result is output immediately. This enables very quick and gentle digitization, as the templates are only exposed to external environmental influences, such as incidence of light, for a short time. The scanning time for high-quality area sensors is approx. 0.3 seconds, which leads to enormous productivity, especially for large digitization projects.

At book2net, we only use area sensors for all of our scanning systems, as they combine all the advantages for our customers and the areas of application required: high depth of field, short scanning and processing times, high image quality and the option of live video preview. The latter is particularly helpful when positioning the originals on the scanning surface. With the help of the preview image and our Live Control Professional software module, users receive a finished result proposal before the scan is actually triggered. If needed, frames can be set within the live image, the quality can be checked and the orientation selected. This avoids incorrect scans and further optimizes productivity.

Image circle

The image circle is the mental circle that touches on all four corners of a sensor. It is important to know that an image that hits the sensor through the optics, i.e. the lens, has a round shape. The sensor, however, is rectangular. Thus, the image circle should always be larger than the area of the sensor in order not to “give up” any sensor area and to avoid dark spots at the edges of the image.
Depending on the size and geometric format of the sensor and optics, the image circle can be very different. However, especially when selecting suitable lenses, this size serves as a guide. For optimal image quality, the image circle and sensor area should match well.

The sensor of the X71 camera used in our systems has an image circle of 43 mm.

ISO/TS 19264-1:2017

In 2012, the ISO (International Organization for Standardization) began to define uniform standards in the field of digitization and long-term archiving in order to specify both the necessary processes and the required image quality and make them comparable.

This led to the publication of three basic documents:

ISO 19262 essentially defines the terms used in the field of image capturing in order to achieve a standardization of the language,

ISO 19263 describes the workflow problems and provides detailed information on how analytical measurements should be performed,

Finally, ISO 19264 describes these measurements in detail and provides targets and tolerance values for the various aspects. It specifies exactly which properties are to be measured, how they are to be measured and how the results of the analysis are to be presented.

In the revised version, ISO / TS 19264-1: 2017 has meanwhile become the international standard for the quality analysis of digital imaging systems (cameras and scanners) in the field of cultural heritage. In addition to METAMORFOZE, it is the main quality assessment standard in Europe in particular.

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).