Densitometry

Densitometry is the quantitative measurement of the color density ( full tone density ), that is, the amount of ink per unit area. This tonal values ​​, but no colors are determined. Densitometry is used in photography and reproduction technology, including for quality assurance.

The word " densitometry " is also used for bone density measurement, the bone densitometry. This is an investigation to determine whether a patient is suffering from osteoporosis ( brittle bones).

Measuring the color density

Densitometry is based on the linearity between amount of color and optical density. The more color, the less light is reflected or transmitted.

Principle: A measuring instrument is first calibrated on the carrier medium in an untreated plot to zero. Then one radiates light of wavelength precisely defined on the color layer. The light penetrates this layer of paint and is filtered in the process, making certain wavelengths disappear or are reduced in intensity. The residual light from the ( usually white ) substrate either reflected and again passes through the color layer, or, in the case of a transparent support (film, foil, ...) occurs in the rear side again. Now the amount of light and type of light in the instrument can be measured photoelectrically. The reflectance value R and the transmission value T can be determined.

Lambert- Beer law:

Where D is the density.

Typical density values ​​in the pressure range between 0.001 and 2 is the inverse value contained in the bill, resulting in high values ​​of R or T low densities, and vice versa. The reciprocal of the transmission value is also called opacity ( to German: opacity ) respectively. To assess the quality of a color or the printing process itself is still needed additional criteria, such as the contrast, the solid ink density, dot gain.