Densitometry is a quantitative measurement of optical density in light-sensitive materials, such as photographic paper or photographic film, due to exposure to light. The optical density is the result of the darkness of the developed image and can be expressed absolutely as the number of black spots (ie, the silver grains in the developed film) in a particular area, but usually it is a relative value, expressed in scale.
Since density is usually measured by decreasing the amount of light that shines through a transparent film, it is also called absorptiometry , the size of light absorption through the medium. The appropriate measuring device is called a densitometer ( absorptiometer ). The decadic logarithm (base-10) of the inverse of the transmittance is called absorbance or density .
DMax and DMin refers to the maximum and minimum density that the material can produce. The difference between the two is the density range . The density range is related to the exposure range (dynamic range), which is the range of light intensity represented by the recording, via the Hurter-Driffield curve. In the context of photography, the dynamic range is often measured in "stops", which is the binary logarithm of the highest and lowest discriminating exposure ratio; in an engineering context, the dynamic range is usually given by decadent logarithms expressed in decibels.
Video Densitometry
Usage
According to the principle of densitometer operation, one can have:
- place densitometry : the light absorption value is measured at one point
- densitometric lines : consecutive point values ​​along the dimensions represented as a graph
- bidimensional densitometry : light absorption values ​​expressed as 2D synthetic images, usually using false color shadows
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. Specialized devices have been developed and are currently used for clinical diagnosis, called bone densitometer .
Maps Densitometry
See also
- Sensitometry
References
External links
- Densitometric Basics , by Mark Vivino.
Source of the article : Wikipedia
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