Glossary Archives - Page 5 of 16 - book❷net book scanners

Test charts

Posted on 26. July 202223. August 2022 by Karin

Test charts are needed to create device characterization for a camera, scanner or printer when creating a color management system. They are used to objectively measure the accuracy or characteristics of an image processing system to ensure its effective operation and provide long-term assurance.

Test charts can consist of physical templates or be integrated into the image processing system as windows.

In the digitization sector, physical test charts are usually used for quality measurement. It should be noted, however, that these are subject to aging processes and can fade. They should therefore be stored carefully and protected from light.

Test charts contain line, dot or other patterns as well as a defined number of color patches for checking colors, the composition of which is known from the process colors cyan, magenta, yellow and black. A distinction must also be made between ordered (visual) and unordered (random) test charts in which the color patches are arranged randomly.

Depending on the structure and complexity of the test charts, various criteria of the camera or lens used can be tested: among others, sharpness in critical areas such as image center and image edge, chromatic aberration, distortion, vignetting, resolution, color reproduction, dynamic range, white balance, autofocus problems and image noise at different ISO settings.

Various commercially available standardized test charts are mostly used to match the specific requirements. As a universal standard, the Universal Test Target (UTT) has also been developed on the basis of current ISO standards to provide an insight into the overall image quality of the scan results of all types of high-end cameras and scanners. However, it should be noted that the UTT is extremely error-prone in practice due to its simple design with individually affixed test charts and thus has to be handled with extreme care.

Another combination of different targets is also offered by the ISA Golden Thread Device Level Target.

At book2net we prefer to work from a combination of the following test charts:

Applied Image Inc® ISO Resolution Chart (T-10) (determination of resolution)
Imatest^TMScanner SFR & OECF QA-62 (edge sharpness and MTF analysis)
ColorChecker® Digital SG (color management)

Gray chart

Posted on 26. July 202226. July 2022 by Karin

A gray chart is used to measure the dynamic range or tonal value differentiation of a digital camera, scanner or monitor. It is a test chart in which there is a smooth or multi-graded (gray scale chart) transition between dark black and bright white.

Dynamic range

Posted on 26. July 202226. July 2022 by Karin

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.

White balance

Posted on 18. July 202218. July 2022 by Karin

The white balance adjusts the scanner’s camera to the prevailing lighting conditions to ensure a uniform color temperature and thus constant image quality. The color sensitivity of the sensor is thereby adjusted to the respective lighting conditions.

The perception of white is strongly dependent on the environment and the respective light source. In daylight, a pure white appears colder than in fluorescent light, for example, where it appears greener. Even in a controlled environment, this can become a problem.

While the human eye or brain can adjust to the respective light situation and quasi intuitively performs a white balance and compensates for color casts, a digital camera mercilessly reproduces them: If the digital camera is set to daylight, for example, and the picture is taken in artificial light, the image will appear reddish.

A user-defined white balance directly during installation therefore guarantees accurate colors right from the start. Since a change in the lighting environment always necessitates a new white balance, a constant and uniform lighting situation should generally be ensured when using planetary scanners.

White balance should be achieved by means of a full-format scan of a surface that is as white or at least neutral gray as possible. Plain white paper is often used for this purpose, but it often contains optical brighteners and can therefore lead to distorted results with color casts.

At book2net, we therefore use high-precision, spectrally neutral white balance targets to ensure precise user-defined, in-camera white balance under local lighting conditions.

Color temperature

Posted on 18. July 202218. July 2022 by Karin

The color temperature is a measure for the quantitative description of the color impression of light sources; the unit of measurement of the color temperature is the temperature unit kelvin (K).

The spectrum of an ideal thermal radiator (“black body”, “black body radiator” or “Planckian radiator”) serves as the reference model for determining the color temperature. This emits electromagnetic radiation in the visible and invisible range, whose wavelength distribution is determined solely by the temperature. For real thermal light sources (flame, light bulb, sun) this is approximately true.

When a black body is slowly heated, it passes through a color scale from dark red, red, orange, yellow, white to light blue. The temperature of the black body at which there is the best possible color match with the light source to be determined is the color temperature of the illuminant. Each natural or artificial light situation can thus be assigned approximately a temperature, which can then be used to describe a light situation mathematically.

Since reddish colors are perceived as “warm” and bluish colors as “cool,” a higher color temperature corresponds to a “cooler” color. Common light sources have color temperatures in the order of magnitude of less than 3,300 K (warm white), 3,300 to 5,300 K (neutral white) to more than 5,300 K (daylight white).

For the practice of photography and digitizing, this means that depending on the existing lighting conditions of the location, a certain color temperature must be set in order to achieve a correct reproduction of colors. In digital photography, this process is called white balance.

Kelvin

Posted on 18. July 202218. July 2022 by Karin

In science and technology, absolute temperatures and temperature differences are not specified in the generally used unit of degrees Celsius but in kelvin (symbol: K).

The kelvin is also used to indicate the color impression of “white” light. The spectrum of a thermal radiator (e.g. light bulb, gas flame, and sun) is given by its temperature, and accordingly one also assigns a “color temperature” to the light of a non-thermal radiator (e.g. LED, fluorescent tube).

If, for example, the color temperature of an LED lamp is given as 3000 K, this means that it produces the same color impression as a thermal radiator with a temperature of 3000 K. This color would be called “warm white”. This color would be called “warm white”, whereby “warm” in this context is not related to temperature, but to the division of colors into “warm” (rather reddish) and “cool” (rather bluish) colors. Thus, high color temperatures stand for rather cold color impressions. Common light sources have color temperatures ranging from below 3,300 K (warm white), 3,300 to 5,300 K (neutral white) to over 5,300 K (daylight white).

LPI

Posted on 12. July 202212. July 2022 by Karin

LPI is an abbreviation for „lines per inch“.

Similar to DPI or PPI, LPI Lines per inch (LPI) is a measurement of printing resolution. A line consists of halftones built up by physical ink dots made by the printer device to create different tones. Specifically LPI is a measure of how close together the lines in a halftone grid are. The quality of printer device or screen determines how high the LPI will be. High LPI indicates greater detail and sharpness.

Conversion of the LPI to DPI can be done by simple multiplication: z.B. 150 LPI x 16 = 2400 DPI

Stitching

Posted on 12. July 202212. July 2022 by Karin

In photography, stitching refers to the use of special software to create a large photograph from various smaller individual shots, which usually show overlapping sections of the subject, e.g. for panoramic shots, if the individual shot does not capture the desired image angle.

In scanning, stitching is used sporadically to achieve a higher resolution in the large format range than would be possible with a full-format single shot.

Glossary, S

Surface structure

Posted on 30. June 202224. August 2023 by Karin

In addition to a distortion-free and true-color imaging technique, the optimal reproduction of surface structures requires in particular a differentiated lighting technique. Not every original to be digitized has a flat surface or texture that is sufficiently illuminated by a simple, conventional light source to be digitized without shadows or reflections./span>

For example, valuable illuminated old manuscripts with heightened and waved surfaces, special inks and colors and especially gold grounds and gildings require a special and equally gentle, conservational illumination technique.

Therefore, we at book2net have developed special lighting systems for the optimal illumination of a wide variety of objects. Whether you want to digitize stamps or large formats, coins or paintings, sealed letters or glass negatives, loose, bound, flat, raised or corrugated originals, glossy or matte surfaces or a wide variety of material structures (transparent, metallic, wooden, textile, earthen etc.) – the book2net scanning systems meet all requirements.

Gentle illumination from cold-light LEDs and Fresnel lenses ensure uniform, flat illumination with a soft edge and infinitely variable regulation of the light emission angle. Depending on the system, additional lighting or individually controllable and synchronized lighting units provide the greatest possible flexibility in the design of desired lighting scenarios such as incident light, sided light or transmitted light.

Multispectral imaging

Posted on 30. June 202228. September 2022 by Karin

Multispectral imaging is one of the imaging techniques that make it possible to take images of objects in the range of selected, very narrow wavelength ranges of the reflected light in order to obtain information about objects that cannot be perceived by the human eye. It can be used to detect and visualize materials and structures that are invisible to the human eye.

Many scientific fields, such as forensics, geology, meteorology and art technology, use multispectral imaging to document and analyze important data about nature as well as man-made objects.

When multispectral imaging is performed, images are usually first taken in the visual spectrum, which means that an object is imaged as it is seen by the naked eye. Then, specific images are taken in different wavelength ranges (e.g., ultraviolet, infrared, and near-infrared) where specific content becomes visible. Such imaging can also be done in combination: i.e., one constructs a composite image that combines the input of multiple spectra, a so-called false-color image. In this case, data from spectra outside the visible range are represented either with an artificial color such as red or blue, or in grayscale. Composite images can show high-energy regions and other interesting things.

In art technology, multispectral imaging is used especially in painting and graphics analysis to reveal image supports, overpaintings (pentimenti), underdrawings, or watermarks, among other things.

Book2net has developed a novel, filterless method that is particularly suitable for the multispectral analysis of graphics, hand drawings and written material.

The book2net multispectral system works without changing filters (i.e. vibration-free) and without post-correction of sharpness and focus in the spectral ranges (i.e. pixel-scale accurate).

Single or series of scans can be performed in definable nm intervals. The scan results can be superimposed and analyzed with pixel accuracy.

For further information see: https://book2net.net/en/multispectral-imaging/

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