1、American National Standardfor Photography - Print Grain Index -Assessment of Print Graininess from Color Negative FilmANSI/I3A IT2.37-2001ANSI/I3AIT2.37-2001ANSI/I3A IT2.37-2001American National Standardfor Photography Print Grain Index Assessment of Print Graininessfrom Color Negative FilmSecretari
2、atInternational Imaging Industry Association, Inc. (I3A)Approved August 31, 2001American National Standards Institute, Inc.Approval of an American National Standard requires review by ANSI that therequirements for due process, consensus, and other criteria for approval havebeen met by the standards
3、developer.Consensus is established when, in the judgement of the ANSI Board ofStandards Review, substantial agreement has been reached by directly andmaterially affected interests. Substantial agreement means much more thana simple majority, but not necessarily unanimity. Consensus requires that all
4、views and objections be considered, and that a concerted effort be madetowards their resolution.The use of American National Standards is completely voluntary; theirexistence does not in any respect preclude anyone, whether he has approvedthe standards or not, from manufacturing, marketing, purchasi
5、ng, or usingproducts, processes, or 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 anin
6、terpretation of an American National 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 orw
7、ithdrawn at any time. The procedures 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 AmericanNation
8、al Standards Institute.American National StandardPublished byAmerican National Standards Institute, Inc.25 West 43rd Street, New York, NY 10036Copyright 2003 by American National Standards Institute, Inc.All rights reserved.No part of this publication may be reproduced in anyform, in an electronic r
9、etrieval system or otherwise,without prior written permission of the publisher.Printed in the United States of AmericaiContentsPageForeword iiIntroduction . iii1 Scope . 12 Normative references . 13 Terms and definitions . 14 Computational steps. 35 Summary of procedure to calculate the PGI. 126 Rep
10、orting results 13Tables1 Channel-dependent numerical factors used in equation (1). 112 Optical printing magnifications 113 Visual weighting coefficients used in equation (6) 12AnnexesA Derivation of the relationship of print granularity to film granularity 14B Bibliography 16iiForeword (This forewor
11、d is not part of American National Standard ANSI/I3A IT2.37-2001.)The grainy appearance of directly viewed photographic prints, (as opposed to, e.g.,the granularity of film negatives, which are not often directly viewed) is often of prima-ry interest in the evaluation of image quality. Because there
12、 is a need to evaluateand compare this graininess, there has been a need to specify a standardized meth-od for its assessment.This standard defines “graininess“ and provides an objective basis (the “Print GrainIndex,“ or PGI) for comparing the graininess of color photographic prints made fromcolor n
13、egative films. The method uses the RMS granularity of the color negative filmas the input, and computes the PGI for a specified printing magnification. The PGIallows a photographer to choose a film, format and printing magnification based onan objective assessment of the resulting perceived grainine
14、ss in the final print.This standard contains two 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 International Imaging Industry Association, Inc. (I3A), 550 Mamaroneck Ave-nue, Suite 307,
15、Harrison, NY 10528-1612; e-mail: i3astdsi3a.org.This standard was processed and approved for submittal to ANSI by I3A TechnicalCommittee on Image Evaluation, IT2. Committee approval of the standard does notnecessarily imply that all committee members voted for its approval. At the time thisstandard
16、was approved, the IT2 Committee had the following members:Michael R. Goodwin, ChairmanJack Holm, Vice-ChairmanOrganization Represented Name of RepresentativeInternational Imaging Industry Association, Inc. (I3A) . Sharon BartelsRichard FischMichael R. GoodwinThomas LumenelloRobert A. UzenoffRobert D
17、. WhittalPaul J. Kane (Alt.)Thomas McKeehan (Alt.)CGATS . Larry SteeleGraphic Communication Association Norman W. ScharpfGraphic Microsystems Steven HeadleyGTI Graphic Technology, Inc Charles G. SaleskiPhotographic Society of America . Jack HolmIra Current (Alt.)Professional Photographers of America
18、 . Tim MathiesenRadiological Society of North America . Homer L. Twigg, Jr.Eliot L. SiegelUS Department of Commerce - National Instituteof Standards and Technology. Edward A. EarlyIndividual ExpertDaniel SintoiiiIntroductionRMS-granularity is a useful measure of the microdensity fluctuations present
19、 in anarea of uniform exposure on a photographic film. These fluctuations arise from therandom distribution of silver halide grains present in the original photographic layers.It has been shown that relative changes in the measured film rms-granularity corre-late with relative changes in the grainin
20、ess of prints made from the film negative 1.1)However, the film negative itself is rarely viewed, and it is the graininess of the finalviewed image or print that is of primary interest in the evaluation of image quality.This standard specifies procedures for computing the “Print Grain Index“ (PGI) o
21、f acolor photographic print made from a color negative film. The purpose of the PGI is toprovide an objective basis for comparing the graininess of color photographic printsmade from color negative films at specified magnifications.The PGI is a complement to, rather than a replacement for, rms-granu
22、larity. In fact,rms-granularity is part of the data required to compute the PGI.The PGI scale defined in this standard is intended for prints made by optically enlarg-ing color negative films coated on transparent support onto color reflecting materials(photographic papers).1)The number in the brack
23、et refers to the reference in the Bibliography (annex C).AMERICAN NATIONAL STANDARD ANSI/I3A IT2.37-2001American National Standard for Photography Print Grain Index Assessment of Print Graininess from Color Negative Film 1 1 Scope This standard describes a method for determining the Print Grain Inde
24、x (PGI) of a uniform neutral color photographic print made from an unmodulated neutral exposure of a color negative film. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this American National Standard. At the time of
25、publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this American National Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO mainta
26、in registers of currently valid International Standards. ANSI/I3A IT2.40-2003, Root Mean Square (rms) Granularity of Film (Images on One Side Only) Method for Measuring ANSI/ISO 2721:1982 (R1997), ANSI/PIMA IT3.301-1990 (R1997), Photography Cameras Automatic controls of exposure ANSI/PIMA IT2.39-199
27、8, Photography Black-and-white, continuous-tone films Photographic modulation transfer function ISO 5-3:1995, Photography Density measurements Part 3: Spectral conditions 3 Terms and definitions For the purposes of this standard, the following terms and definitions apply. ANSI/I3A IT2.37-20012 3.1 g
28、raininess: Sensation produced, in the mind of an observer viewing a photographic image, by random inhomogeneity in what should be structureless areas. NOTE 1: Graininess is, therefore, a subjective quantity that is measured by psychophysical methods. NOTE 2: Above threshold, the just-noticeable diff
29、erence in graininess detectable by observers viewing uniform areas having an ISO visual density of about 1.0 corresponds to a difference in rms-granularity of 6% in monochrome materials 2. 3.2 microdensity: Transform of the microtransmittance factor in accordance with the relation: D = -log10T. 3.3
30、microtransmittance factor: Transmittance factor of a small area of the film or paper measured on a suitable instrument such as a microdensitometer or microphotometer. NOTE 1: In general, the microtransmittance factor of a uniformly exposed and developed film or paper sample varies from point-to-poin
31、t on the sample. NOTE 2: The measured microtransmittance factor of a given sample may depend on the optical geometry of the instrument with which it is measured. 3.4 print grain index (PGI): A perceptually uniform scale (above threshold) that correlates with the graininess of a uniform color photogr
32、aphic print as perceived by an observer. NOTE: PGI is calculated for a specified film printed at a specified magnification. 3.5 rms-granularity: Objective characterization of the spatial microdensity fluctuations in a uniformly exposed and developed photographic layer 3. NOTE: The spatial fluctuatio
33、n is observed when the microdensity of the layer is measured at various points over the surface and is the result of the random distribution of the absorbent species in the layer. The fluctuation in the microdensity over an area of the specimen is characterized by its standard deviation (D), and is
34、ANSI/I3A IT2.37-20013 generally a function of the specimen macrodensity. This quantity is termed “rms-granularity.“ 4 Computational steps A number of physical and perceptual factors affect the perceived graininess of the final viewed print. The process of printing a negative film and the resulting g
35、raininess of the print can be modeled as a series of transformations, each of which encompasses several physical and/or perceptual factors. 4.1 Conversion of color negative film rms-granularity to color print rms-granularity This transformation models the physically measurable print rms-granularity
36、in terms of the physically measurable film rms-granularity and the parameters of the optical printing system, print material, and measurement instrumentation. 4.1.1 Relationship of print granularity to film granularity The first, and most complex, transformation models the printing of the film grain
37、 pattern from the color negative onto the photographic paper. An approximate relationship between the granularity of the print and the granularity of the film negative is derived in annex A. Based on this derivation, the following equation gives the relationship between the film rms-granularity and
38、the print rms-granularity, ( ) ( ) ( ) ( ) ( ) ( ) ( )m MTF MTF m d d SCF pr pm i pr neg i i n i p ; 1 1 int , , = (1) where: i is an index pertaining to the channel of interest (i = R, G, B); p,i is the rms-granularity of the print; in, is the matte-adjusted, exposure-averaged rms-granularity of th
39、e film sample; ANSI/I3A IT2.37-20014 SCFi is the spectral correction factor for the ith channel; dneg is the diameter of the circular aperture used to measure the rms-granularity of the film negative; dprint is the diameter of the circular aperture used to measure the rms-granularity of the print; i
40、is the average gradient of the print material D-LogE curve at the print densities of interest; m is the optical printing magnification; MTFpm (1)is the value of the Modulation Transfer Function (MTF) of the print material at a spatial frequency of 1 cycle/mm on the print; MTFpr(1;m)is the lens MTF f
41、actor at a spatial frequency of 1 cycle/mm on the print and magnification m. All of these factors are discussed sequentially, and values for each are subsequently specified. 4.1.2 Matte-adjusted, exposure-averaged film rms-granularity For the calculation of the PGI, the rms-granularity shall be meas
42、ured. All recommended procedures for sample preparation and measurement given in ANSI/I3A IT2.40 shall be followed. Two adjustments shall be made to these measurements before they are used to compute the PGI. The first adjustment pertains to the effect of matte particles on the measured film rms-gra
43、nularity. Color negative photographic films commonly incorporate matte particles in the film overcoat to protect against ferrotyping. These particles are transparent, but they protrude from the surface and cause light scattering. This light scattering causes a microdensity variation when the rms-gra
44、nularity is measured with a microdensitometer. Tests have shown that while the diffuse illumination of most photographic printers lessens the contribution of this component to the resulting print granularity, it is not completely negligible 1. To estimate the rms-granularity due to this component, t
45、he following procedure is used: ANSI/I3A IT2.37-20015 1) A sample of the color negative film, the PGI of which is to be determined, is bleached and fixed. This treatment removes all of the noise from the imaging components, leaving only the effects of the surface behind. This is referred to as the m
46、atte sample. 2) A sample of the color negative film, the PGI of which is to be determined, is prepared for rms-granularity measurement and placed in the microdensitometer. This will be referred to as the “film sample.“ The microdensitometer is focused on the film sample, following the procedure reco
47、mmended in ANSI/I3A IT2.40. The rms-granularity of the film sample may be measured at this time. 3) The film sample is removed from the microdensitometer and replaced with the matte sample. Without readjusting the focus of the instrument, the rms-granularity of the matte sample is measured, followin
48、g the same procedure used to measure the film sample. Once the rms-granularity of the matte sample has been measured, the film rms-granularity is adjusted for the matte rms-granularity as follows: ( ) ( ) ( ) 2 2 , 5 . 0 M, n a n D D = (2) where: n,a(D)is the matte-adjusted rms-granularity of the fi
49、lm sample at average density D; n(D)is the rms-granularity of the film sample at average density D; mis the rms-granularity of the matte sample. The 0.5 weighting of the matte rms-granularity in this adjustment has been determined experimentally 1. This adjustment shall be made to each of the red, green, and blue film rms-granularity measurements. The second adjustment pertains to the density dependence of the film rms-granularity. As stated in 3.5, the rms-granularity of the film is usually dependent on the film macro density
