SMPTE EG 28-1993 Annotated Glossary of Essential Terms for Electronic Production.pdf

1、SMPTE EG*28 93 I 8357403 0000080 835 I -_ - SM PTE ENG IN EE RI NG GU I DELI N E EG 28-1993 Annotated Glossary of Essential Terms for Electronic Production Pegelof45pagas 1 scope Program production, as a skill and an applied art, historicaiiy began when photographic anematogra- phy fdlowed the Greek

2、 theater, and from there, expanded to embrace television and video. Now essential further contributions and modulations are recognized from computer graphics, data processing, graphic arts, telecommunications, psydiophycics, etc., and their affiliates. Each of these technologies not only contributes

3、 associated hardware and software resources, but - since each has had an independent development - brings unfamiliar terms and uniquely specific definitions to a nominaiiy common vocabu- w. Program production, which is defined in overview in figure 1 and in detail within the text of this glossary, i

4、s increasingly reliant upon this full spectrum of resources to be effective and efficient in its subsets of origination, pt-production, and distribution. Program origination is provided with a multiplicity of potentiai sources for capturing, generating, and eval- uating images. Post-production offer

5、s an increasingiy evolving pallet of tools for merging, integrating, and evaluating source material to achieve maximum artistic impact. Distribution channels and facilities are multiplying both in number and in diversity, suggesting that program creative formats may need to be trans- fonrred eventua

6、lly into a multiplicity of distribution formats in order to meet definitive needs. Specific technical glossaries have developed within each technology. In the broadly electronic environ- ment - embracing electronic imaging, computer graphics, data processing, and telecommunications -the primary refe

7、rence directing unambiguous com- munication is ANSI/IEEE 100, Dictionary of Electrical and Electronics Terms, with 24,793 entries in the fourth edition. Within the photographic environment there have been several more informai glossaries. IS0 4246, Cinematography - Vocabulary, is taking leadership i

8、n coordination with a multilingual vocab- ulary responding to international concerns for precise communication. Graphic arts is another present focus for integrating technologies. And psychophysics iden- tifying and quantifying the transfer function to human perception is defining the validity of as

9、sumptions on what is acceptable and improving methods of evalu- ation. Each of these technologies meets at the interface with program production as an essential partner. This glossary beings together many of the terms that are essential in the production process. h draws upon the existing data bases

10、 when appropriate, noting the specific definitions and interpretations that apply to program production. its intent is to include only those terms which impact upon productions basic needs and procedures, and whose clear interpretation in this environment is therefore essential. Nevertheless, it is

11、important to recognize prevaient alternate definitions, perhaps relating to other applications of the participat- ing technologies and thus to caution and to identify that one specific definition which may be most appro- priate to program production. Annotations are an essential component of this gl

12、os- sary since translations often must be accompanied by explanations. It is thus the objective of this limited scope glossary to help darify and promote both com- munication and understanding among the formerly distinct technologies invoived. 01993byttie SocIfTY OF MOTION PICTURE AND TELEVISION ENG

13、INEERS 595 W. Wale Ave., white Plains, NY 10607 (914) 761-1100 Approved May 1,1993 SMPTE EG*F28 93 EA 8357402 O000082 771 EG 2-1993 I- Page 2 of 45 pages SMPTE EG*28 93 8357401 O000082 bo8 2 Definitions adaptation: Visual process whereby approxi- mate compensation is made for changes in the luminanc

14、es and colors of stimuli, especially in the case of changes in illuminants“ Hunt. AES: Audio Engineering Society, New York. Of potential interest in electronic production are the following: SC-2, Subcommittee on Digital Audio; SC-3, Subcommittee on the Preservation and Restoration of Audio Recording

15、; and SC-4. Subcommittee on Acoustics. alias: An artifact in the reproduced image. 1. Most commonly, artifacts result from sam- pling frequencies or bandwidth limits too low for faithful reproduction of image detail, and thereby violating the Nyquist limit. Video images are sampled in two or three d

16、imensions and com- puter graphics are sampled in three. (Time = T related to field or frame rate; image height = Y related to scanning lines; and for pixel-type sensors, image width = X. Upon presentation in the display, the signal is customarily reformatted to appear continuous in X.) Sampling theo

17、ry establishes that the resulting frequency spectrum consists of an infinite number of copies of the baseband signal. These copies overlap if the sampling frequency is less than 2max, where Fmax is the maximum frequency expected to be recoverable from the image without alias. The spectrum copies are

18、 separated if the sampling frequency is greater than 2Fmax. With overlapped spectra, aliasing has been introduced and cannot be removed. Thus the ratio of imaging bandwidth to sampling frequency is a critical design feature. With the desired sequence of separated spectra, aliasing can be avoided in

19、the display by the choice of a bandpass reconstruction filter that passes only one copy of the spectrum. 2. Appear- ance of multiple copies of the baseband spectra may also result from FM modulation of an analog video spectrum with its inevitable sidebands and harmonics; if the sidebands of a harmon

20、ic over- lap the baseband sidebands, visible aliasing is observed. A sufficiently low modulation index (the FM equivalent of the ratio of video bandwidth to sampling frequency) becomes critical for these systems. 3. In a composite (complex) spectral channel, any crosstalk of the information cannot b

21、e eliminated by filtering, EG 2-1993 and will produce aliasing, for example as cross- color and/or cross-luminance. 4. Moir from color subcarrier decoded as luminance pro- duces aliasing. 5. In a rectilinearly sampled system, lines not parallel to a sampling axis will appear stepped unless antialias

22、ing processing algorithms have been applied. cf. artifact; com- posite color; cross-color; cross-luminance; Nyquist limit. alpha channel: (production) In electronic pro- duction and post-production, there is increas- ing application of 4:4:4:4 encoding - which provides full-bandwidth R, G, and B plu

23、s the additional alpha channel to carry processing information. An adaptation from computer graph- ics, the alpha channel may contain information for linear key, for luminance and/or chroma transparency, for variable edge enhancement, and similar image-processing information. The term alpha derives

24、from a processing coefficient designed to provide a degree of transparency in the foreground. The parameter a carries trans- parency information, used in the formula that computes the composite (of a foreground image and a background image) = (1-a)(fore- ground)+(a)(background). cf. chroma key; comp

25、osite image; linear key; matte channel; post-production. aperture, camera: The available maximum dimensions of the optical image on the active surface of the photo-sensor, within which good quality image information is being recorded. The camera aperture determines the maximum usable scene informati

26、on captured and intro- duced into the system, and available for subse- quent processing and display. These dimensions are usually defined by standards. (Note - Not to be confused with lens aperture, which defines the luminous flux transmission of the optical path.) cf. aperture, clean; aperture, dis

27、play; aperture, production; aperture, safe action; display; post-production. aperture,c(ean: (video) The concept of a clean aperture in a digital system defines an inner picture area (within the production aperture) within which the picture information is subjec- tively uncontaminated by all edge tr

28、ansient distortions (SMPTE 260M). Filtrations for bandwidth limitation, multiple digital blanking, cascaded spatial filtering, etc., introduce tran- PSge 3 Of 45 SMPTE EG*Z8 93 I 8357403 0000083 544 EG 2-1993 sient disturbances at the picture boundaries, both horizontally and vertically. It is not p

29、ossible to impose any bounds on the number of cascaded digital processes which might be encountered in the practical post-production system. Hence, the clean aperture is defined to represent an acceptable (and practical) worst- case level of protection. cf. aperture, camera; aperture, display; apert

30、ure, production; aperture, safe action; production, electronic, digital. aperturecorrection: In a scanned image system: I. Electrical compensation for the distortion introduced by the limiting size of a scanning aperture” IEEE 1001. 2. (video): The properties of the camera lens, optical beam-splitti

31、ng instal- lation, and camera tube all contribute to a re- duced signal at higher spatial frequencies - generally falling off as an approximate (sin X)B 0.008 856 * = oo(Y/Y,)/ - (z/Zn)“3 an y/v, 1 L* = 116(Y/Yn)/3 - 16 X,Y,Z describe the color stimulus considered, and Xn, Yn, Zn describe a specifie

32、d white ach- romatic stimulus .e., white reference CIE 845-0346. Equal distances in the color space represent approximately equal color differ- ences“ Hunt. cf. color space, reference; Image file architecture; video index. CIELUV color space: “Three-dimensional, approx- imately uniform color space p

33、roduced by plotting in rectangular coordinated L*,u*,v* quantities defined by the equations: L* = 1 1 6(Y/Yn)“3 - 16 U*= 13L*(u-un) b* = 13 L* (Y - Y n) Y/Yn 0.008856 Y,u ,v describe aie color stimulus considered, and Yn, u n, v n describe a specified white achromatic stimulus white referenoel CIE 8

34、45-03-541. “The EG 2-1993 coordinates of the associated chromaticity diagram are u and v . L* is the approximate correlation of lightness, u * and v are used to calculate an approx- imte correlate of chroma“ Ref. CIE Pub 15.2.1. “Equal distances in the color space represent approximately equal color

35、 differences“ Hunt. cf. color space, reference; image nie architecture; video index. CMYK color space: “A subtractive color space with cyan, magenta, and yellow as primary color set with an optional addition of black (K). For such a color set subtractive color mixture applies. The CMYK values used r

36、epresent the amount of colorant placed onto the background medium. They include the effects of dot gain“ CIE; also IS0 86131. cf. color space, reference; image file architecture; video index. code: “A plan for representing each of a finite number of values or symbols as a particular arrangement or s

37、equence of discrete conditions or events. To encode (cf.) is to express given information by means of a code“ IEEE IOO. “A system of rules defining a one-to-one correspon- dence between information and its representa- tion by characters, symbols, or signal elements“ CCIR. coior,additive: I. “Over a

38、wide range of condi- tions of observation, many colors can be matched completely by additive mixtures in suit- able amounts of three fixed primary colors The choice of three primary colors, though very wide, is not entirely arbitrary. Any set which is such that none of the primaries can be matched b

39、y a mixture of the other two can be used“ Wyszecki and Stiles. 2. It follows that the primary color vectors so defined are linearly independent. Therefore, transformations of a metameric match from one color space to another can be predicted via a matrix calcula- tion. The limitations of color gamut

40、 apply to each space. 3. The additive color generaliza- tion forms the basis of most image capture, and of most self-luminous displays (.e., CRTs, etc.). cf. CiELab color space; CIELuv color space; color space, reference; color, subtractive; display; Image capture; metameric match; R,G,B color space

41、; spectrophotometric match. color ooordinate transfonnation: “Com putat ion of the tristimulus values of colors in terms of SMPTE EG*E!8 93 O 835740L 0000089 Tb2 EG 2-1993 one set of primaries from the tristimulus values of the same colors in another set of primaries. Note: This computation may be p

42、erformed elec- trically in a color television system“ IEEE IOO. cf. tristimulus values. color correction: “The adjustment of a color re- production process to improve the perceived- color conformity of the reproduction to the original“ IEEE 1001. colordifierence signal: The chrominance vectors carry

43、ing the color information in a composite format. The color-difference signals have been defined by the CCIR for existing television systems Report 624-41 as follows: NTSC E/= -(0.27)( B-Ey) + (0.74)(-) EQ=+ (O.42)(s-Efy) + (0.48)(- y) PAL u = (0.493)(E B - E y) E V = (0.877)(E R - E y) SECAM D R = -

44、 (1.902)( R - y) D 6 = + (1.505)( 8 - E y) The subscripts Y, RI and B refer to luminance and to color-difference points on the chromaticity plane, de- rived from the relationship of the primary colors red and blue to the luminance. AI1 of the primed values are gamma pre-corrected signals. Convention

45、ally, all color-difference vectors are bandwidth limited. cf. CCIR; chrominance; Y, CR, CB, or Y, PR, PB; R,G,B color space. colorgamut: I. In a system employing three color primaries to encode image color, each primary can be located on a CIE chromaticity diagram and these points connected as a pla

46、ne figure. If the apexes are then connected with an appropriate value on the white point axis, a solid figure is produced enclosing the color gamut for that system. (On the CIE chromaticity diagrams, the points in x,y,z space approximate an inverted tetrahedron. In u,v,w space, they become a somewha

47、t irregular four-cornered solid.) 2. Colors within the color gamut solid volume can be reproduced by the system as metameric matches. Colors outside the color gamut solid volume cannot be matched. Note that the area of the cross-section from the color gamut solid is a function of the lumi- nance. 3.

48、 Although it is advantageous to have the widest possible color gamut for the ability to provide metameric matches for the largest number of colors, the required transformations from origination colorimetry to colorimetry matched to available display primaries, for ex- ample, may require large matrix

49、 coefficients and, therefore, a signal-to-noise penalty. The choice of color gamut is a compromise between color rendition and signal-to-noise. cf. color- difference signal; color match, corresponding; color match, metameric; colors, primary; color space, reference; luminance; luminance range; white point. colorimetry: 1. “Measurement of colors based on a set of conventions“ CIE 845-05-101.2. “The techniques for the measurement of color and for the interpretation of th