Category Archives: Glossary

Candela (cd) is an internationally standardized physical unit of measurement for the luminous intensity of a light source in a certain direction.

Candela is used to describe more precisely the luminous flux emitted by a light source in a certain direction. Candela is the Latin word for candle; 1 candela therefore corresponds approximately to the amount of light emitted by a candle. Since a light source does not emit its light uniformly in all directions, another unit of measurement to lumens is necessary. While the unit of measurement lumen generally indicates the luminous flux of a light source, this value still says nothing about how focused or wide the emitted light beam is.

The candela value, which measures the intensity of light at a specific beam or solid angle, helps in this determination. An analysis of the light intensity in relation to all directions can be modeled into a so-called luminous intensity distribution curve. Depending on the design of a light source, the luminous intensity is distributed uniformly or irregularly over a given solid angle.

The higher the candela number given, the more focused the light beam. 1 candela of a light source is when its illuminance with a distance of one meter is 1 lux; i.e. lux and candela are interdependent in consequence.

The color depth indicates how many different color levels are available for each individual pixel of a graphic. Since the “fineness” of the gradations depends on how much memory is used per pixel, the color depth is specified in bits.

With 8 bits, for example, 256 color shades can be distinguished for one color channel. A color is created by mixing several color channels of a color space. For computer graphics, the RGB color space is usually used, in which colors are composed by additive mixing of the three primary colors red, green and blue. Even most common computer monitors can only distinguish 8 bits per channel.

One speaks of a true-color representation if the current color depth has at least 24 bits, i.e. 8 bits per color channel (red, green, blue). A color depth of 24 bits corresponds to approx. 16 million colors; this means that practically every conceivable color can be reproduced true to life.

In the field of color management, the terms calibration and profiling are often used interchangeably, although they are actually two different processes.

In digital imaging, all input devices (e.g. digital camera, scanner) as well as output devices (e.g. monitor, printer) should be calibrated and profiled to avoid color errors due to faulty devices.

During calibration, devices are trimmed to technical boundary conditions (on the screen, for example, compliance with a specific color temperature); during profiling, on the other hand, the devices are measured and an associated ICC profile is created. Strictly speaking, calibration takes place before profiling, but is often performed in a single pass using special tools.

The difference between calibration and profiling can be clearly understood using the example of a digital bathroom scale: When the scale is turned on, it is usually calibrated automatically so that when it is completely unloaded, the display shows 0 kg. Profiling, on the other hand, would mean that reference measurements are created for a certain number of reference weights (10 kg, 20 kg, 30 kg, etc.) and that a correction value is in turn stored in a profile for each reference weight (e.g. that the scale displays 5% too much when loaded with a weight of 10 kg, only 3% too much when loaded with 50 kg, and only 1% too much when loaded with 100 kg).

A professionally performed color calibration serves to optimize and measurably compare the image quality of a scanner.

The perception of colors by the human eye is extremely subjective and also dependent on the surrounding lighting conditions. In addition, every imaging device, whether digital camera, scanner, monitor or color printer, has device-specific color interpretations that are reflected in different color models, color spaces or color tones.

Therefore, a professional color calibration, individually adapted to the respective camera sensor, when installing a scanner guarantees accurate colors right from the start.

Color calibration is usually performed using a color target that contains standardized color patches. This is scanned and then the calibration software compares the colors determined by the scanner with the target colors (the actual colors of the individual color patches on the calibration slide are standardized). From the comparison of the actual colors with the target colors, a device-specific color profile (ICC profile) is created, which is now used for each subsequent scan. In this way, individual color errors of a scanner can be corrected. Such an ICC profile is always created for a specific scanner only and cannot be transferred to another device of the same construction.

The color calibration should always be done using professional color targets with color reference standards that correspond to the common digitizing standards.

In the professional digitizing sector, the creation of a color profile is part of the standard scope of delivery.

Unlike the human eye, which can perceive almost any number of different colors, each image-processing input and output device has its own finite color space, called a device-specific color space. For example, a normal RGB screen represents colors from a combination of 256 red, green and blue tones each; this corresponds to a maximum number of 16,777,216 displayable color tones. But even with this enormous number, not every color that the human eye perceives can be represented. Moreover, even devices that work in the same color space reproduce colors differently.

Therefore, in order to ensure uniform color reproduction across different devices – for example within the process chain of scanner, image-processing PC, desktop publishing viewer and printer – the image data must be digitally matched or offset against each other. This is done by special color management modules. They create color profiles for the respective devices, which describe the colors in relation to a reference color space. The conversion is done on the basis of ICC profiles with so-called rendering intents.

Every imaging device, whether a digital camera, scanner, monitor or color printer, has device-specific color interpretations that translate into different color models, color spaces or hues. Input devices such as digital cameras and scanners as well as many output devices such as monitors and displays use the RGB color model, while printers use the CMY or CMYK color model.

A color profile is used to translate colors from one color space to another without distorting the color fidelity of the original. A color profile stores how a particular device represents colors against a device-independent color space. The color profiles are created device-specifically by color management systems, and the conversion is usually based on ICC profiles with so-called rendering intents.

The aim of a color profile is thus to achieve unchanged color reproduction on all devices connected in an imaging process chain (e.g. scanner, image-processing PC, desktop publishing viewer and printer).

In the professional digitizing sector, such color profiles are part of the standard scope of delivery.