Equidensitometry is the technique of measuring ''equidensities'' in a photographic deposit or photographic layer, such as
photographic films
Photography is the visual art, art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It i ...
and
photographic plates
Photographic plates preceded photographic film as a capture medium in photography, and were still used in some communities up until the late 20th century. The light-sensitive emulsion of silver salts was coated on a glass plate, typically thinn ...
.
*Equidensities are points, lines and areas having equal
densities
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek language, Greek letter Rho (letter), rho), although the Latin letter ''D'' ca ...
also called isodensities.
* First order equidensities are points, lines and areas having isodensities obtained by applying one of the listed below techniques once, thus they exhibit one particular Density in the original
*Second order equidentities are points and lines having isodensities obtained by applying one of the listed below techniques twice, thus they exhibit two particular Densities in the original. Second order equidensities do not normally show areas.
* Equidensity series is a sandwich (in register) of a number of different equidensities. Usually each equidensity is coded by color or raster.
Photographic and computerized image processing techniques
Four techniques of obtaining equidensities are:
*
Tone separation process
*
Sabattier effect
The Sabatier effect, also known as pseudo-solarization (or pseudo-solarisation) and erroneously referred to as the Sabattier effect, is a phenomenon in photography in which the image recorded on a negative or on a photographic print is wholly o ...
, also called pseudo-solarization
*
Agfacontour Professional film (discontinued)
* Computerized
LUTs Manipulating custom curves (U-curves) in photo-editing programs such as
PhotoShop
Adobe Photoshop is a raster graphics editor developed and published by Adobe Inc. for Windows and macOS. It was originally created in 1988 by Thomas and John Knoll. Since then, the software has become the industry standard not only in raster ...
provide tools to obtain equidensities in digital image processing.
Applications
Interpretation or measurement of an image is sometimes aided by simplification of the density pattern.
[Applied Photography, Arnold et al, Focal Press, pages 422-426] This results in data reduction and enables
keying (areas or lines with iso-densities to unique patterns, grey values or colours). This keying to singular grey- or colour values is known in modern image processing as
using L.U.T.s.
The fact that a certain density of a photographic layer has been caused by a specific amount of
actinic radiation (visual light, UV-light, X-Rays, autoradiography, etc.) can be used to qualify and perform spatial measurements of a physical phenomenon. A calibrated photographic process is used to obtain quantitative measurements as well.
Equidensitometry with Agfacontour made it possible to obtain reproducible equidensities similar to pseudosolarized photographic films and prints. The Agfacontour film contained two special emulsions with each different spectral sensitivity. Using color filters (yellow or magenta) during the exposure on Agfacontour one could control the width of the equidensity. By varying the exposure one could change the density in the image that showed on Agfacontour as equidensity. Although the material exhibited very low sensitivity (long exposures were necessary) the results were very reproducible and second order equidensities were sharp and clear, something that with pseudosolarization was almost impossible to achieve without special procedures.
[ Agfacontour Professional in Wissenschaft und Technik, C. Sauer, Agfa-Gevaert AG Druckschrift nr. 152, 1. Auflage 1974 (in German)]
In the following fields equidensitometry is used extensively:
* Photoelastic Stress Analysis, using polarized light and birefringent models of the object under test.
*
Interferometry
Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...
*
Astronomy
Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
(f.i.
Nebula
A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regio ...
and
Corona
Corona (from the Latin for 'crown') most commonly refers to:
* Stellar corona, the outer atmosphere of the Sun or another star
* Corona (beer), a Mexican beer
* Corona, informal term for the coronavirus SARS-CoV-2, which causes the COVID-19 di ...
images)
*
Thermography
Infrared thermography (IRT), thermal video and/or thermal imaging, is a process where a Thermographic camera, thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are ...
(today easily achieved electronically with
thermographic cameras)
*
Autoradiography
An autoradiograph is an image on an X-ray film or nuclear emulsion produced by the pattern of decay emissions (e.g., beta particles or gamma rays) from a distribution of a radioactive substance. Alternatively, the autoradiograph is also available ...
*
Radiology
Radiology ( ) is the medical discipline that uses medical imaging to diagnose diseases and guide their treatment, within the bodies of humans and other animals. It began with radiography (which is why its name has a root referring to radiat ...
(
Mammography
Mammography (also called mastography) is the process of using low-energy X-rays (usually around 30 kVp) to examine the human breast for diagnosis and screening. The goal of mammography is the early detection of breast cancer, typically through d ...
and other low contrast images of organs and bones
*
Nondestructive testing
Nondestructive testing (NDT) is any of a wide group of analysis techniques used in science and technology industry to evaluate the properties of a material, component or system without causing damage.
The terms nondestructive examination (NDE), n ...
in industrial manufacturing)
*
Electron microscopy
An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...
*
Plasma photography
*
(Vertical) aerial photography interpretation
*
Photogrammetry
Photogrammetry is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant ima ...
1st. order equidensities after pseudo-solarization of original
File:X-Ray_image_of_right_hand;_colored_equidensity-series_using_pseudo-solarization.jpg, Original: X-Ray image of right hand;
colored 1st. order equidensity-series using pseudo-solarization, B&W copies chromogenic developed
See also
*
Densitometry
Densitometry is the quantitative measurement of optical density in light-sensitive materials, such as photographic paper or photographic film, due to exposure to light.
Overview
Optical density is a result of the darkness of a developed picture ...
References
{{Photography
Science of photography
Photographic techniques