The visual appearance of objects is given by the way in which they reflect and transmit

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

. The

color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are assoc ...

of objects is determined by the parts of the

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of color ...

of (incident white) light that are reflected or transmitted without being absorbed. Additional appearance attributes are based on the directional distribution of reflected ( BRDF) or transmitted light (BTDF) described by attributes like glossy, shiny versus dull, matte, clear, turbid, distinct, etc.

Appearance of reflective objects

The appearance of reflecting objects is determined by the way the surface reflects incident

. The reflective properties of the surface can be characterized by a closer look at the (micro)-

topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary s ...

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 Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including ...

: 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.

Basic types of light reflection

Appearance of transmissive objects

{, class="wikitable" , - ! colspan="2", Appearance of a Transmissive Object , - , , align="right", Figure 6: graduation of a ruler as seen through a translucent scattering layer (frosted glass). The original distinctness of image can be seen in the center of the lower graduation (around 0). On the left side the frosted glass is in contact with the ruler surface and it is 4 cm above the ruler surface at the right side of the image. With increasing distance between ruler graduation and scattering layer the blur (''haze'', also see

turbidity Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Fluids ...

) increases and the '' distinctness of image'' (''clarity'') decreases. , -

Terminology

Reflective objects * ''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'' (for a specified specular angle), the ratio of (

)

flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ...

reflected at a specified angle (or angles) from the specular direction to the flux similarly reflected at the specular angle by a specified gloss standard. Transmissive objects ASTM Standards on Color & Appearance Measurement * ''

Transmittance Transmittance of the surface of a material is its effectiveness in transmitting radiant energy. It is the fraction of incident electromagnetic power that is transmitted through a sample, in contrast to the transmission coefficient, which is th ...

, T'' * ''Haze'' (

) * ''Clarity''

References

* R. S. Hunter, R. W. Harold: The Measurement of Appearance, 2nd Edition, Wiley-IEEE (1987) * CIE No 38-1977: 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) Optics

Appearance of reflective objects

Basic types of light reflection

Appearance of transmissive objects

Terminology

See also

References