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Densitometry

 
Densitometry

 
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Densitometry
 
 
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Densitometry is the quantitative measurement
Measurement

Measurement is the process of assigning a number to an attribute according to a rule or set of rules. The term can also be used to refer to the result obtained after performing the process....
 of optical density
Optical density

In optics, density is a unitless measure of the transmittance of an optical element for a given length at a given wavelength ?:|||= the per-unit opacity ...
 in light-sensitive materials, such as photographic paper
Photographic paper

This article is about light-sensitive photographic media; for digital printing media please see Photo printer, photo paper and inkjet paper.Photographic paper is paper coated with light-sensitive chemicals, used for making photographic prints....
 or film
Photographic film

Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and of the film....
, due to exposure to light
Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
. 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 nitrate
Silver nitrate

Silver nitrate, also known as lunar caustic, is a soluble chemical compound with chemical formula silverNitrogenOxygen3. This compound is a versatile precursor to many other silver compounds, such as those used in photography....
 grains in developed films) in a given area, but usually it is a relative value, expressed in a scale
Scale (ratio)

The concept of scale is applicable if a system is represented Proportionality ly by another system. For example, for a scale model of an object, the ratio of corresponding lengths is a Dimensionless number scale, e.g....
.

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
Absorption (electromagnetic radiation)

In physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom....
 through the medium.






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Densitometry
Densitometry is the quantitative measurement
Measurement

Measurement is the process of assigning a number to an attribute according to a rule or set of rules. The term can also be used to refer to the result obtained after performing the process....
 of optical density
Optical density

In optics, density is a unitless measure of the transmittance of an optical element for a given length at a given wavelength ?:|||= the per-unit opacity ...
 in light-sensitive materials, such as photographic paper
Photographic paper

This article is about light-sensitive photographic media; for digital printing media please see Photo printer, photo paper and inkjet paper.Photographic paper is paper coated with light-sensitive chemicals, used for making photographic prints....
 or film
Photographic film

Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and of the film....
, due to exposure to light
Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
. 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 nitrate
Silver nitrate

Silver nitrate, also known as lunar caustic, is a soluble chemical compound with chemical formula silverNitrogenOxygen3. This compound is a versatile precursor to many other silver compounds, such as those used in photography....
 grains in developed films) in a given area, but usually it is a relative value, expressed in a scale
Scale (ratio)

The concept of scale is applicable if a system is represented Proportionality ly by another system. For example, for a scale model of an object, the ratio of corresponding lengths is a Dimensionless number scale, e.g....
.

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
Absorption (electromagnetic radiation)

In physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom....
 through the medium. The corresponding measuring device is called a densitometer
Densitometer

A densitometer is a Measuring instrument that measures the degree of darkness of a photographic or semitransparent material or of a reflecting surface....
 (absorptiometer). The logarithm
Logarithm

In mathematics, the logarithm of a number to a given base is the Power or exponent to which the base must be raised in order to produce the number....
 of the reciprocal of the transmittance
Transmittance

In optics and spectroscopy, transmittance is the fraction of incident light at a specified wavelength that passes through a sample. Specifically, visible transmittance is this fraction for visible light....
 is called the absorbance
Absorbance

In spectroscopy, the absorbance A is defined as,where is the intensity of light at a specified wavelength ? that has passed through a sample and is the intensity of the light before it enters the sample or incident light intensity....
 or density.

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. The density range is related to the exposure range (dynamic range
Dynamic range

Dynamic range is a term used frequently in numerous fields to describe the ratio between the smallest and largest possible values of a changeable quantity, such as in sound and light....
), 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
Binary logarithm

In mathematics, the binary logarithm is the logarithm for base 2. It is the inverse function of ....
 of the ratio of highest and lowest distinguishable exposures.

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
    False-color

    A false-color image is an image that depicts a subject in colors that differ from those a faithful full-color photograph would show.A true-color image of a subject is an image that appears to the human eye just like the original subject would: a green tree appears green in the image, a red apple red, a blue sky blue, etc....
     shading


Dual energy X-ray absorptiometry
Dual energy X-ray absorptiometry

Dual energy X-ray absorptiometry is a means of measuring bone mineral density . Two X-ray beams with differing energy levels are aimed at the patient's bones....
 is used in medicine
Medicine

Medicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
 to evaluate calcium
Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the earth's Crust ....
 bone
Bone

Bones are rigid organ that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red blood cell and white blood cells and store minerals....
 density, which is altered in several diseases such as osteopenia
Osteopenia

Osteopenia is a condition where bone mineral density is lower than normal. It is considered by many doctors to be a precursor to osteoporosis. However, not every person diagnosed with osteopenia will develop osteoporosis....
 and osteoporosis
Osteoporosis

Osteoporosis is a disease of bone that leads to an increased risk of bone fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is disrupted, and the amount and variety of collagen proteins in bone is altered....
. Special devices have been developed and are in current use for clinical diagnosis
Diagnosis

Diagnosis is the identification of the nature of anything, either by process of elimination or other analytical methods. Diagnosis is used in many different disciplines, with slightly different implementations on the application of logic and experience to determine the cause and effect relationships....
, called bone densitometers.

See also


  • Sensitometry
    Sensitometry

    Sensitometry is the scientific study of light-sensitive materials, especially photographic film. The study has its origins in the work by Ferdinand Hurter and Vero Charles Driffield with early black-and-white emulsions....


External links


  • , by Mark Vivino.