1、 American National Standards Institute11 West 42nd StreetNew York, New York10036ANSI/I3A IT2.39-1998 (R2004) for Photography Black-and-White, Continuous-Tone Films Photographic Modulation Transfer FunctionANSI/PIMA IT2.39-1998Revision and redesignation ofANSI PH2.39-1977 (R1990)American National Sta
2、ndardfor Photography Black-and-White, Continuous-Tone Films Photographic Modulation Transfer FunctionSecretariatPhotographic theirexistence does not in any respect preclude anyone, whether he has approvedthe standards or not, from manufacturing, marketing, purchasing, or usingproducts, processes, or
3、 procedures not conforming to the standards.The American National Standards Institute does not develop standards andwill in no circumstances give an interpretation of any American NationalStandard. Moreover, no person shall have the right or authority to issue aninterpretation of an American Nationa
4、l Standard in the name of the AmericanNational Standards Institute. Requests for interpretations should beaddressed to the secretariat or sponsor whose name appears on the titlepage of this standard.CAUTION NOTICE:This American National Standard may be revised orwithdrawn at any time. The procedures
5、 of the American National StandardsInstitute require that action be taken periodically to reaffirm, revise, orwithdraw this standard. Purchasers of American National Standards mayreceive current information on all standards by calling or writing the AmericanNational Standards Institute.American Nati
6、onal StandardPublished byAmerican National Standards Institute, Inc.11 West 42nd Street, New York, NY 10036Copyright 1998 by American National Standards InstituteAll rights reserved.No part of this publication may be reproduced in anyform, in an electronic retrieval system or otherwise,without prior
7、 written permission of the publisher.Printed in the United States of AmericaiContentsPageForewordii1Scope . 12Normative references . 13Definitions. 14Sampling and storage. 25Test method 26Test patterns. 27Camera. 58Camera and test pattern system calibration. 69Exposure 710Processing 811Evaluation 8F
8、igures1Variable area test pattern . 32Variable area calibration patch. 43System calibration 64Analysis of measurements . 105Data presentation example. 11AnnexesATest method considerations . 12BAdjustment of test pattern modulation 13CSuggested optics 14DMicrodensitometry considerations 15EInterlabor
9、atory tests 16FBibliography 17iiForeword(This foreword is not part of American National Standard ANSI/PIMA IT2.39-1998.)Modulation transfer curves have become an accepted means of describing certaincharacteristics relating to the sharpness of sensitized photographic materials. Thisstandard describes
10、 a method for measuring the photographic modulation transferfunction of black-and-white, continuous-tone films that have an emulsion coated onone side of a transparent support. Color photographic materials have been specifi-cally excluded from the scope of this standard due to the complexity of spec
11、ifying theinput modulation of the actinic exposure and the associated readout of the resultingimages.When certain conditions are fulfilled, the modulation transfer curve for one compo-nent of a system can be cascaded with the modulation transfer curves representingother components of the system. Alt
12、hough such cascading is useful and desirable insystems that include photographic components, this standard does not claim that themodulation transfer function will necessarily give a representative system responsewhen it is cascaded with other components of the system.Factors beyond the scope of thi
13、s standard have to be included when precise predic-tions of the density of fine detail in photographic reproductions are to be derived bycascading the modulations transfer curves of system components. A method for pre-dicting the densities of fine detail in photographic images has been proposed by C
14、. N.Nelson 3.1)It is important to note that the photographic modulation transfer function, as it is de-fined in this standard, is a measure of the apparent scattering of light within an un-processedemulsion: it is nota measure of the transmittance of the processedphotographic image. The gradient of
15、the density log exposure curve provides a veryapproximate factor relating the modulation associated with the light scattered withinthe unprocessedemulsion with the modulation associated with the light transmittedby the processedemulsion. A more exact relationship can be obtained by means ofthe more
16、detailed procedures given in Nelsons paper.This standard has been written in such a way as to allow the use of the basic camerasystem, except for optics, that meets the requirements of ANSI/PIMA IT2.38-1998,Photography Photographic materials Determination of ISO resolving power.This standard contain
17、s six annexes that are informative and are not considered partof the standard.Suggestions for improvement of this standard will be welcome. They should be sentto the Photographic e-mail: .This standard was processed and approved for submittal to ANSI by PIMA TechnicalCommittee on Image Evaluation, I
18、T2. Committee approval of the standard does notnecessarily imply that all committee members voted for its approval. At the time thisstandard was approved, the IT2 Committee had the following members:Michael R. Goodwin, ChairmanJack Holm, Vice-ChairmanJames E. Harvey, Secretary_1)Numbers in brackets
19、correspond to references listed in annex F.iiiOrganization Represented Name of RepresentativePhotographic Elis the minimum irradiance measured in the sinusoidal pattern.3.2 photographic modulation transfer factor (PMTF): For a given spatial frequency, it is the ratio ofthe apparent modulation of the
20、 exposure pattern in the emulsion, as measured by photographic radiometryusing the emulsion as its own radiometer, to the actual modulation of the sinusoidal pattern incident on theemulsion surface (see annex A).ANSI/PIMA IT2.39-199823.3 photographic modulation transfer function: The functional rela
21、tionship between modulationtransfer factors and spatial frequency when the modulation transfer factors are derived by the method de-scribed in this standard.4 Sampling and storage4.1 Product samplingIn determining the photographic modulation transfer function of a product, it is important that the s
22、amplesevaluated are representative of those used by the consumer. No fewer than three samples shall be ob-tained from the plant of the manufacturer or from an accredited distributor if they cannot be obtained di-rectly from the manufacturer. In any case, the samples should be taken from products sto
23、red in accor-dance with the manufacturers recommendations and available in the market. Each sample shall repre-sent a different batch of product.4.2 Storage of samplesAfter procurement from the manufacturer or distributor, all samples of a product shall be stored in the un-opened package for 2 to 4
24、months under conditions recommended by the manufacturer. When no specificrecommendation is made, storage shall be at 23oC + 5oC and a relative humidity of 50% + 20%. At theend of this storage period, samples should be tested. The basic objective in selecting and storing samplesas described above is
25、to ensure the film characteristics obtained are representative of those obtained by aconsumer at the time of use.5 Test methodPatterns with spatially varying sinusoidal irradiances and calibration areas are projected onto the film by ahigh-quality lens system. The processed exposures are subsequentl
26、y evaluated with a suitable microden-sitometer.6 Test patterns6.1 Types of test patternsSinusoidal test patterns may be either the variable area type or the variable transmittance type. In eithercase, the size of the images in the film plane shall be the same for all frequencies and shall be 2.0 mm
27、+0.5 mm in width and 1.6 mm + 0.4 mm in height. The harmonic content of the sinusoidal test patterns atany frequency, as measured in the film plane, shall not exceed 10%.6.1.1 Variable area test patternThe variable area test pattern requires the use of a cylindrical lens at the imaging lens to smear
28、 the patternimage into a variable irradiance distribution in the film plane. A variable area test pattern, such as isshown in figure 1, may consist of the upper portion, where the vertical height of the opening is propor-tional to a sinusoidal function of the horizontal distance, and the lower porti
29、on which is of constant heightand serves to reduce the modulation of the sinusoidal portion of the test pattern.ANSI/PIMA IT2.39-19983Figure 1 Variable area test pattern6.1.2 Variable transmittance test patternIn this case, the transmittance of the pattern varies with distance in a sinusoidal manner
30、 between themaximum and minimum limits that define the modulation of the test pattern. The maximum transmittanceof any portion of the pattern shall not exceed 50%.6.2 Aerial image modulationThe modulation of the aerial image of the test pattern shall be 35% + 5%. The exact modulation of theaerial im
31、age shall be measured by the method described in 8.1. To produce this modulation level, it will benecessary to have the modulation of the test patterns increase with increasing spatial frequency to com-pensate for the modulation transfer function characteristics of the camera lens.All test-pattern a
32、erial images shall have the same average irradiance + 12% (see annex B).6.3 Test pattern frequenciesThe lowest spatial frequency in the film plane shall be 1.2 cycles/mm + 5%. The highest frequency shallbe 200 cycles/mm + 5%. There shall be at least thirteen frequencies, and the increments between f
33、re-quencies shall be no more than a factor of 1.6.A typical set of frequencies is 1.25, 1.6, 2.5, 4.0, 6.3, 10, 16, 25, 40, 63, 100, 160, and 200 cycles per mil-limeter.6.4 Illumination of the test patternsThe test patterns shall be transilluminated with a light source having a correlated color temp
34、erature of3000 K + 250 K or 5500 K as specified in ANSI/ISO 7589, ANSI/NAPM IT2.29. A color filter may be usedwith these illuminants. If used, the color filter should be stated with any results determined by this method.ANSI/PIMA IT2.39-199846.4.1 UniformityThe irradiance across the test pattern are
35、a, as measured in the film plane, shall be uniform within + 4%over the central 1.2 mm x 1.2 mm area and within + 8% over the remaining area. A measurement methodis described in clause 8.6.4.2 SpecularityEither diffuse or specular illumination of the test patterns may be used. In the case of the vari
36、able trans-mittance test patterns, the same type of illumination shall be used for the test pattern calibration to ensurethat the evaluation of their harmonic content is valid. In the case of specular illumination of the test pat-terns, care shall be taken to ensure that the full aperture of the cam
37、era lens is filled with light from the testpatterns.6.5 Calibration patches6.5.1 Variable area calibration patchesIn addition to the sinusoidal test patterns, the film shall be exposed to a series of calibration patches hav-ing known exposure increments. One such test object patch is shown in figure
38、 2.There shall be at least eleven such patterns having log exposure increments no larger than 0.10 frompatch to patch. The openings of these test objects shall range from at least twice the maximum total verti-cal opening of the lowest frequency sinusoidal pattern to one-half the minimum total verti
39、cal opening. Onepatch (the sixth, if there are eleven patches) should have an opening such that its effective irradiance, asmeasured in the exposure plane by the radiometric technique outlined in clause 8, is equal to the averageeffective irradiance, measured in the film plan, of the lowest frequenc
40、y sinusoidal test pattern. The cali-bration patch images in the film exposure plane shall be the same size as the sinusoidal test pattern im-ages.Figure 2 Variable area calibration patchANSI/PIMA IT2.39-199856.5.2 Variable transmittance calibration patchesThe calibration patches for use with the var
41、iable transmittance test patterns shall be the same size as thetest patterns. The transmittance of the lightest calibration patch shall be at least twice the maximumtransmittance in the lowest frequency sinusoidal test pattern. The transmittance of the most dense cali-bration patch shall be approxim
42、ately one-half the minimum transmittance in the lowest frequency sinusoi-dal test pattern.There shall be at least eleven calibration patches. The density increments between patches shall be nomore than 0.10. One patch (the sixth, if there are eleven patches) should have a transmittance equal tothe a
43、verage transmittance of the lowest frequency sinusoidal test pattern.7 Camera 17.1 Imaging lensThe imaging lens shall be a high-quality lens operating at a numerical aperture of 0.16 + 0.01 or /3.2 to/3.0 (see annex C). The focal length of the lens system, operating conjugates, and test pattern dime
44、n-sions shall be selected to produce the specified frequencies and image size in the exposure plane.7.2 Smearing lensTo convert the sinusoidally varying height of the test pattern to a sinusoidally varying irradiance in the im-age, and to convert the calibrated test object patches to image areas hav
45、ing uniform irradiances propor-tional to the height of the calibration patch openings, it is necessary to use a cylindrical lens element at theimaging lens on the side toward the test patterns. The cylindrical lens shall be of high quality, and shallhave no power in the horizontal direction and a po
46、wer in the vertical direction that depends on other sys-tem parameters.7.3 Film exposure planeThe camera shall contain a flat reference surface against which the emulsion side of the photographic filmis pressed during exposure. A central hole in the reference surface shall be as small as is practica
47、l, butshall not block any of the relevant light and shall not interfere mechanically with the imaging lens. The ef-fective area of the reference surface shall be held to a minimum to minimize the probability of foreign parti-cles affecting the focus.Measurements of all films shall be made with the e
48、mulsion surface placed against the reference surface.Provision shall be made to hold films flat; for this purpose, a blackened flat vacuum back has been foundto be satisfactory. The amount of stray light reaching the film exposure plane should be minimized, andcare must be taken to keep the referenc
49、e surface and the vacuum back clean and free from imperfections.7.4 Focus settingThe best focus position shall be determined by a photographic test that uses the sensitized material to beevaluated, the illuminant that is to be used to determine the modulation transfer function, and a test patternfrequency that will give a modulation transfer value of approximately 0.5. A series of exposures shall bemade at focus positions that are separated by no more than 5 m. After processing, the test patterns shallbe read on a microdensitometer.The best focus p
