Densitometry


Densitometry
Principle of spot light densitometry

Densitometry is the quantitative measurement of optical density in light-sensitive materials, such as photographic paper or film, due to exposure to light. Optical density is a result of the darkness of a developed picture and can be expressed absolutely as the number of dark spots (i.e., silver grains in developed films) in a given area, but usually it is a relative value, expressed in a scale.

Since density is usually measured by the decrease in the amount of light which shines through a transparent film, it is also called absorptiometry, the measure of light absorption through the medium. The corresponding measuring device is called a densitometer (absorptiometer). The logarithm of the reciprocal of the transmittance is called the absorbance or density.[1]

DMax and DMin refer to the maximum and minimum density that can be recorded on the material. The difference between the two is the density range.[1] The density range is related to the exposure range (dynamic range), which is the range of light intensity that is represented by the recording, via the Hurter–Driffield curve. The dynamic range can be measured in "stops", which is the binary logarithm of the ratio of highest and lowest distinguishable exposures.

Contents

Uses

According to the principle of operation of the densitometer, one can have:

  • spot densitometry: the value of light absorption is measured at a single spot
  • line densitometry: the values of successive spots along a dimension are expressed as a graph
  • bidimensional densitometry: the values of light absorption are expressed as a 2D synthetic image, usually using false-color shading

Dual energy X-ray absorptiometry is used in medicine to evaluate calcium bone density, which is altered in several diseases such as osteopenia and osteoporosis. Special devices have been developed and are in current use for clinical diagnosis, called bone densitometers.

See also

References

  1. ^ a b Davies, Adrian (2005). The Focal Digital Imaging A-Z. Focal Press. ISBN 0240519809. http://books.google.com/books?id=j7l0CxBUwGwC&pg=PT44&dq=density+dmax+dmin+logarithm&ei=2j23R7OwKJbWzAT4gpXGBQ&sig=DqqcRgdi1GeJs_J5GnzBIS3ZB44. 

External links


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Look at other dictionaries:

  • densitometry — n. measuring the optical density of a substance by shining light through it and measuring the intensity of the transmitted light. [WordNet 1.5] …   The Collaborative International Dictionary of English

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  • densitometry — densitometrija statusas T sritis fizika atitikmenys: angl. densitometry vok. Densitometrie, f; Schwärzungsmessung, f rus. денситометрия, f pranc. densitométrie, f; mesurage de densités optiques, m …   Fizikos terminų žodynas

  • densitometry — noun see densitometer …   New Collegiate Dictionary

  • densitometry — See densitometer. * * * …   Universalium

  • densitometry — noun a) The measurement of optical density by use of a densitometer b) The measurement of body density …   Wiktionary

  • densitometry — A procedure utilizing a densitometer. * * * den·si·tom·e·try (den″sĭ tomґə tre) determination of variations in density by comparison with that of another material, or with a certain standard …   Medical dictionary

  • Densitometry — Денситометрия …   Краткий толковый словарь по полиграфии

  • densitometry — n. measurement of density, measurement of crowdedness …   English contemporary dictionary