1、1 Scope1.1This practice specifies the luminance(measured brightness) of the projection screensfor drive-in theaters intended for the projectionof motion-picture film at 24 frames/sec.1.2The practice defines luminance ratiosamong portions of the total screen area, anddefines the acceptable variations
2、 as viewed frompositions within the audience area.1.3The practice applies to both diffusing anddirectional screens.1.4 Recognizing the complexities and difficultiesof drive-in projection, the practice describescriteria for evaluation of performance that is lessthan optimum, based upon a minimum lumi
3、 -nance level and a maximum luminance variation.2 Normative referenceThe following standard contains provisions which,through reference in this text, constitute provisions ofthis practice. At the time of publication, the editionindicated was valid. All standards are subject torevision, and parties t
4、o agreements based on thispractice are encouraged to investigate the possibilityof applying the most recent edition of the standardindicated below.ANSI/IESNA RP-16-1996, Nomenclature and Defini -tions for Illuminating Engineering3 Measurement3.1 Measurement of screen luminance and colorof projection
5、 light is made with the projector incomplete operation with its lens set at focusposition, but with no film in the aperture, andunder ambient light conditions similar to thoseexisting during show time.3.2Screen luminance shall be measured witha photometer having the spectral luminousefficiency of th
6、e standard observer (photopicvision) as defined in ANSI/IESNA RP-16.3.3The acceptance angle of the photometershall be 2 or less. When in use within a theater,the instrument shall be so located along the lineof sight to the screen area being measured as toaccept light from a screen area no larger tha
7、n acircle whose diameter is 10% of the screenwidth.4 Luminance level4.1In an ideal situation, when permitted by thetechnology of motion-picture projection, and whenthe viewing environment is sufficiently close tothat of the indoor theater, the screen luminanceand distribution shall be that specified
8、 inANSI/SMPTE 196M, 16 fL 2 fL (55 cd/m 2 7cd/m 2), as measured from a position on thelongitudinal centerline of the ramp area and mid -way between the foremost and rearmost ramps.4.2The recommended minimum luminance atthe center of the screen shall be 7 fL (24 cd/m 2 ),as measured from the central
9、position defined in4.1.4.3 When maximum compromise must be made,as discussed in annexes A.1 and A.2, the lumi -nance at the center of the screen, measuredfrom any car position, shall in no case be lessthan 4.5 fL (15 cd/m 2 ).Screen Luminance for Drive-In TheatersRevision of RP 12-1992RP 12-1997SMPT
10、E RECOMMENDED PRACTICEPage 1 of 3 pagesApproved January 8, 1997Copyright 1997 by theSOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS595 W. Hartsdale Ave., White Plains, NY 10607(914) 761-11005 Luminance distribution5.1The luminance at a distance of 10% of thescreen width from the side edges of the
11、 screen,and on its horizontal axis, as measured fromthe central position defined in 4.1, shall becompared with the center luminance readingobtained, and shall fall within the range of 55%to 100% of that reading. The distribution of pro -jection illumination shall be symmetrical aboutthe geometric ce
12、nter of the screen.5.2The minimum luminance measured fromany car position to any point on the horizontalcenterline of the screen within the 10% pointsdefined in 5.1 shall be no less than 33% of themaximum luminance on the horizontal centerlinemeasured from that same position.6 Spectral distributionT
13、he light reflected from the screen shall have a spec -tral distribution approximating that of a blackbody ata color temperature of 5400 K 400 K, the use o f ashort-arc xenon or carbon-arc light source beingassumed.7 Multiple projector adjustment7.1When the presentation involves change -overs among t
14、wo or more projectors operating tothe same screen format, their luminances asmeasured in 4.1 shall agree within a maximumrange of 10%.7.2When the presentation involves change -overs among two or more projectors operating todifferent screen formats or areas, their lumi -nances as measured in 4.1 shal
15、l agree within amaximum range of 15%.7.3The apparent color of the projection lightfrom projectors intended for interchangeablysequential operation shall be consistent with oneanother within a range of no more than 400 K.Annex A (informative)Additional dataA.1 Standard luminanceAs a minimum goal for
16、theater maintenance and adjustment,it is a consensus that there is a working threshold forluminance below which picture quality is noticeablydegraded. Under this condition, the operation becomes verysensitive to sky light, neighboring luminances interfere,adjustment of projection equipment becomes m
17、ore critical,and mood or key variations in the prints become distractingand the presentation begins to lose its artistic purpose.Permissible luminance range is limited by the criterion thata good release print must provide acceptable quality whenprojected at any luminance within the range.A.2 Operat
18、ing luminancePicture quality is most desirable in drive-in theaters whereit is possible to achieve the luminance levels of indoortheaters. This practice recognizes, however, that there aremany drive-in theaters wherein screen sizes, viewing condi -tions, and other factors dictate limitations not enc
19、ounteredin conventional indoor theaters. When a very large screenarea, long projection throw distance, extended viewingdistance, and high ambient light level are involved, it isnecessary to achieve maximum efficiency in all elements ofthe system to ensure acceptable projection results.The values in
20、4.2 and 5.2 represent an operating compro -mise that may be useful. They also describe the minimumcondition for an acceptable projected image where stray andambient light can be considered negligible.A.3 Directional screensA maximum permissible luminance distribution range on agiven screen is specif
21、ied in 5.1 and 5.2. This condition canbe achieved by several procedures, including one or moreof the following: choice of a screen with a suitable reflectionpattern, limitation of the seating area so that no patron viewsthe picture from an angle at which the luminance is outsidethe tolerance of the
22、standard, and screen curvature.Present directional screens show a large variation in gainwith changes in the projection and viewing angles, necessi -tating the 3:1 luminance range in 5.2 when gain screens arefitted into existing theaters. Even this range effectively limitsthe maximum luminance gain
23、of the screen; and the widerthe theater becomes, the lower the maximum luminancegain must be to meet luminance specifications with mostexisting directional screens.A.4 Luminance photometerThe measurement of luminance with uncertainty of less than10% requires a good photometer. Since there are no tru
24、eLambertian surfaces, and even the theatrical matte screensmay depart by more than 10%, the brightness will vary withthe angle of observation. A photometer having a large fieldangle will indicate the average luminance within its field, andif this includes a large area of the screen (or of the screen
25、and surround), this average may be substantially differentfrom the observed brightness. It has been found that withinthe geometric restrictions under which photometers areused in theaters, their luminance indication correlates wellRP 12-1997Page 2 of 3 pageswith the observed brightness if the field
26、angle of thephotometer is about 2 or smaller.A photometer having a small field angle may receive lightfrom such a small screen area as to detect luminance differ -ences due to defects in the screen, imaging of the projectionsource, etc. When measuring the luminances required inclauses 4 and 5, the l
27、uminances of immediately adjacentareas should be observed to be sure the reading is relevant.A.5 Ambient lightRecognizing the limitations in an outdoor environment,every effort should be made to keep ambient light on thescreen to a minimum. This may be done by careful place -ment of the screen and c
28、ontrolling light sources in andaround the theater. Distracting light sources (signs, streetlights, etc.) should be shielded, or kept out of the field ofview of the audience.Annex B (informative)BibliographyANSI/SMPTE 196M-1995, Motion-Picture Film - IndoorTheater Projection - Screen Luminance and ViewingConditions RP 12-1997Page 3 of 3 pages
