Dictionary Definition
grating adj : unpleasantly harsh or grating in
sound; "a gravelly voice" [syn: gravel, gravelly, rasping, raspy, rough]
Noun
1 a barrier that has parallel or crossed bars
blocking a passage but admitting air [syn: grate]
2 a frame of iron bars to hold a fire [syn:
grate]
3 optical device consisting of a surface with
many parallel grooves in it; disperses a beam of light (or other
electromagnetic radiation) into its wavelengths to produce its
spectrum [syn: diffraction
grating]
User Contributed Dictionary
Adjective
grating- (typically of a voice) harsh and unpleasant
Noun
Synonyms
Related terms
Verb
grating- present participle of grate
Extensive Definition
A grating is any regularly spaced collection of
essentially identical, parallel, elongated elements.
Gratings usually consist of a single set of elongated elements, but
can consist of two sets, in which case the second set is usually
perpendicular to
the first (as illustrated). When the two sets are perpendicular,
this is also known as a grid.
Gratings as filters
A grating covering a drain (as illustrated) can be a
collection of iron bars (the identical, elongated elements) held
together (to ensure the bars are parallel and regularly spaced) by
a lighter iron frame. Gratings over drains and air vents are
used as filters,
to block movement of large particles (such as leaves) and to allow
movement of small particles (such as water or air).
Diffraction gratings
Grating can also be a diffraction
grating: a reflecting
or transparent
sheet on which there are many, fine, parallel,
equally spaced grooves.
Gratings as pictures
A grating can also be a picture having the
characteristics of a grating. For example, a picture might be of a
collection of parallel black bars separated by equal-sized white
bars. These sorts of gratings are described by a graph
(illustrated). On the y-axis of the graph
is the luminance
obtained by moving a light meter
over the grating perpendicular to the orientation of the grating.
On the x-axis of the graph
is the distance the light meter moved. The example is a square-wave
grating (see second panel of the illustration); the graph consists
of flat, low lines (corresponding to the black bars), with abrupt
corners leading to flat high lines (corresponding to the white
bars). One period
(or cycle) of
such a grating consists of one black bar and one adjacent white
bar. Gratings where the black bars have a different width from the
white bars are rectangular and are
described by the duty cycle.
The duty
cycle is the ratio of width of the black bar to period (or
pitch, i.e. the sum of the
widths of one black and one white bar).
Gratings are usually specified by four parameters. Spatial
frequency is the number of cycles occupying a particular
distance (e.g., 10 lines [or cycles] per millimeter). Contrast
is a measure of the difference in luminance between the light parts
of the grating and the dark parts. It is usually expressed as
Michelson contrast: the maximum luminance minus the minimum
luminance divided by the maximum luminance plus the minimum
luminance. Phase is
the position of the graph relative to some standard position. It is
usually measured in degrees
(from 0 to 360 for one complete cycle) or in radians (2π for one complete
cycle). Orientation is
the angle the grating
makes with some standard orientation (such as the y-axis in a
picture). It is also usually measured in degree or in
radians.
Grating elements can have luminances other than
that of sharp-edged bars. If the graph of a grating is sinusoidal (see top panel in
the illustration), the grating looks like a set of blurry light and
dark bars and it is called a sine-wave
grating.
Sine-wave gratings are used extensively in
optics to determine the
transfer
functions of lenses. A
lens will form an image of a sine-wave grating that is still
sinusoidal, but with some reduction in its contrast depending on
the spatial frequency and possibly some change in phase. The branch
of mathematics dealing with this part of optics is Fourier
analysis.
Gratings are also used extensively in research
into visual
perception. Campbell and Robson promoted using sine-wave
gratings by arguing that the human visual performs a Fourier
analysis on retinal images.
See also
References
grating in German: Gitterrost
grating in Japanese: グレーチング
Synonyms, Antonyms and Related Words
abrasion, absonant, ajar, andiron, annoying, antagonistic, antipathetic, arabesque, at cross-purposes,
at loggerheads, at odds, at variance, at war, atomization, atonal, attrition, basketry, basketwork, beating, bolter, brecciation, cacophonous, cancellation, chafing, chain, clashing, coal tongs, colander, comminution, conflicting, confused, contradictory, contrary, cracked, crane, cranky, creaking, croaking, crook, cross, cross-hatching,
crossing-out, crumbling, crushing, damper, detrition, diaphonic, differing, disaccordant, disagreeable, disagreeing, disconsonant, discordant, discrepant, disharmonic, disharmonious, disintegration, disproportionate,
dissident, dissonant, divergent, dry, filigree, fire hook, fire
tongs, firedog, flat, fragmentation, fret, fretting, fretwork, galling, granulation, granulization, grate, grid, griddle, gridiron, grill, grille, griller, grillwork, grinding, gritty, hachure, harsh, hatching, hoarse, hostile, immelodious, immiscible, inaccordant, incompatible, inharmonic, inharmonious, interlacement, intertexture, intertwinement, irksome, irritant, irritating, irritative, jangling, jangly, jarring, jostling, lace, lacery, lacework, lacing, lattice, latticework, levigation, lifter, mashing, mesh, meshes, meshwork, musicless, negative, nerve-jangling,
nerve-racking, nerve-rending, nerve-shaking, nerve-trying, net, netting, network, nonmelodious, off, off-key, off-tone, offensive, out of accord, out
of pitch, out of tone, out of tune, out of whack, piercing, plexure, plexus, poker, pothook, pounding, powdering, raddle, rasping, raspy, raucous, repugnant, reticle, reticulation, reticule, reticulum, riddle, rough, salamander, scraping, scrapy, scratching, scratchy, screeching, screen, screening, sharp, shredding, shrill, sieve, sifter, smashing, sorter, sour, spit, squawking, squeaky, stinging, strident, stridulous, texture, tissue, tongs, tracery, trellis, trelliswork, tripod, trituration, trivet, tuneless, turnspit, uncongenial, unharmonious, unmelodious, unmusical, untunable, untuned, untuneful, variant, vexatious, warring, wattle, weave, weaving, web, webbing, webwork, weft, wicker, wickerwork