Visual appearance

The visual appearance of objects is given by the way in which they reflect and transmit light. The color of objects is determined by the parts of the spectrum of (incident white) light that are reflected or transmitted without being absorbed. Additional appearance attributes are based on the directional distribution of reflected (BDRF) or transmitted light (BTDF) described by attributes like glossy, shiny versus dull, matte, clear, distinct, etc..

Appearance of reflective objects

The appearance of reflecting objects is determined by the way the surface reflects incident light. The reflective properties of the surface can be characterized by a closer look at the (micro)-topography of that surface.

Structures on the surface and the texture of the surface are determined by typical dimensions between some 10 mm and 0,1 mm (the detection limit of the human eye is at ~0,07 mm). Smaller structures and features of the surface cannot be directly detected by the unaided eye, but their effect becomes apparent in objects or images reflected in the surface. Structures at and below 0,1 mm reduce the "distinctness of image" (DOI), structures in the range of 0,01 mm induce "haze" and even smaller structures affect the "gloss" of the surface.


::Definition
diffusion, scattering
: process by which the spatial distribution of a beam of radiation is changed in many directions when it is deviated by a surface or by a medium, without change of frequency of its monochromatic components. [CIE No17.4-1987: International lighting vocabulary, 4th ed. (Joint publication IEC/CIE)]


Appearance of transmissive objects

Terminology

Reflective objects [ASTM Standards on Color & Appearance Measurement]

* "Reflectance Factor, R"
* "Gloss Reflectance Factor, Rs"
* "Gloss" (at least six types of "gloss" may be observed depending upon the character of the surface and the spatial (directional) distribution of the reflected light.)
* "Specular Gloss"
* "Distinctness-of-Image Gloss"
* "Sheen"
* "Reflection Haze, H"


Transmissive objects [ASTM Standards on Color & Appearance Measurement]

* "Transmittance, T"
* "Haze"
* "Clarity"


References


* CIE No38-1977: Radiometric and photometric characteristics of materials and their measurement
* CIE No 44-1979: Absolute methods for reflection measurements

BRDF
* F. E. Nicodemus, et al., Geometric Considerations and Nomenclature for Reflectance, U.S. Dept. of Commerce, NBS Monograph 160 (1977)
* John C. Stover, Optical Scattering, Measurement and Analysis, SPIE Press, 1995

External links

Instrumentation for measurement and evaluation of appearance characteristics is available from:

* [http://www.bykgardner.com/ BYK-Gardner]

* [http://www.hunterlab.com/ HunterLab]
* [http://www.display-messtechnik.de/ DM&S]


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