Optical density (extinction [1] ) is a measure of the attenuation of light by transparent objects (such as crystals, glass, photographic film) or light reflections by opaque objects (such as photography, metals, etc.).
Calculated as the decimal logarithm of the ratio of the radiation flux incident on an object, to the radiation flux passing through it (reflected from it), that is, it is the logarithm of the reciprocal of the transmittance ( reflection ) [2] :
For example, D = 4 means that the light was weakened 10 4 = 10 000 times, that is, for a person this is a completely black object, and D = 0 means that the light has passed (reflected) completely.
In terms of optical density, the requirements for the exposure of negatives are specified.
A device for measuring the optical density is called a densitometer . In X-ray methods of non-destructive testing, the optical density of an X-ray image is a parameter for evaluating the image's suitability for further decoding. Allowable values ββof optical density in X-ray methods of non-destructive testing are regulated in accordance with the requirements of GOST.
Notes
- β Simon A.D., Colloid Chemistry, 2003 , p. 128
- β Kaporsky L. N. Optical density // Physical encyclopedia / Ch. ed. A. M. Prokhorov . - M .: Great Russian Encyclopedia , 1992. - T. 3. Magnetoplasma compressor - Poynting theorem. - p. 441. - 672 p. - 48 000 copies - ISBN 5-85270-019-3 .
Literature
- Simon A.D. Colloid chemistry. - 3rd ed., Ext. and rev. - M .: Agar, 2003. - 320 p. - ISBN 5-89218-151-0 .