Hello,
since I had difficulties in understanding the meaning of the relevant terms
(and still have :-) ) I would like to refer to the book by Hunt & Pointer
(2011): “Measuring Colour”. On page 9ff the terms are defined as follows:
Brightness
Attribute of a visual perception according to which an area appears to exhibit
more or less light. (Adjectives: bright and dim.)
Hue
Attribute of a visual perception according to which an area appears to be
similar to one, or to proportions of two, of the perceived colours red, yellow,
green, and blue.
Colourfulness
Attribute of a visual perception according to which an area appears to exhibit
more or less of its hue.
Lightness
The brightness of an area judged relative to the brightness of a similarly
illuminated area that appears to be white or highly transmitting. (Adjectives:
light and dark.)
Chroma
The colourfulness of an area judged in proportion to the brightness of a
similarly illuminated area that appears to be white or highly transmitting.
(Adjectives: strong and weak.)
Saturation
Colourfulness of an area judged in proportion to its brightness.
In the appendix they define luminance and luminance factor as follows:
Candela per square metre, cd m−2:
Unit of luminance (luminous flux per unit solid angle and per unit projected
area, in a given direction, at a point on a surface). The luminance produced by
a luminous intensity of 1 candela uniformly distributed over a surface area of
1 square metre is 1 candela per square metre. (Obsolete name: nit ).
Other units of luminance are the lambert, the millilambert, the foot-lambert
(sometimes called the equivalent foot-candle), and the apostilb.
1 lambert = 104/π cdm−2
1millilambert = 10/π cdm−2
1 foot-lambert = 10.76/π cd m−2 = 3.426 cd m−2
1 apostilb = 1/π cd m−2 = 0.3183 cd m−2
Luminance factor, β
Ratio of the luminance of an area to that of the perfect diffuser (an ideal
isotropic diffuser with a reflectance equal to unity) identically illuminated.
Hermann-Josef
