Optical density

The optical density or Absorbance indicates the Decimal logarithm of the Opacité, i.e. the reverse of the Transparence. This term is used in photography to measure the transparency of the negative photographic.

The optical density depends on the decimal logarithm of the Lumination for a film. In a given zone, plus the slope of the representative curve is raised, plus film is contrasted. This slope is called, in an unsuitable way, the Gamma of the film.

Mathematical expressions

In photometry, one defines the following quantities for a medium length L crossed by the light:

When one is interested in reflected light by an object, and not in the light which it transmits, the definitions above always apply by replacing the transmission T by the Réflectivité R or the Albédo ρ.

; Examples

snow: $\ rho=93, D= 0 {,} 03$
of reference: $\ rho=18, D= 0 {,} 744$
black velvet: $\ rho=0 {,} 4, D=2 {,} 40$

Remarks

; In biochemistry The optical density is used in Biochimie: to see Law of Beer-Lambert.

The optical term density can also indicate the filter correspondent with this opacity.

Random links:

_de_Córteno_Golgi