ANSI-IT2.37-2001.pdf

American National Standard for Photography - Print Grain Index - Assessment of Print Graininess from Color Negative Film ANSI/I3A IT2.37-2001 ANSI/I3A IT2.37-2001 Copyright American National Standards Institute Provided by IHS under license with ANSI Licensee=USN Ship Repair Facility Yokosuka/9961031100 Not for Resale, 05/08/2007 22:49:33 MDTNo reproduction or networking permitted without license from IHS -,-,- Copyright American National Standards Institute Provided by IHS under license with ANSI Licensee=USN Ship Repair Facility Yokosuka/9961031100 Not for Resale, 05/08/2007 22:49:33 MDTNo reproduction or networking permitted without license from IHS -,-,- ANSI/I3A IT2.37-2001 American National Standard for Photography Print Grain Index Assessment of Print Graininess from Color Negative Film Secretariat International Imaging Industry Association, Inc. (I3A) Approved August 31, 2001 American National Standards Institute, Inc. Copyright American National Standards Institute Provided by IHS under license with ANSI Licensee=USN Ship Repair Facility Yokosuka/9961031100 Not for Resale, 05/08/2007 22:49:33 MDTNo reproduction or networking permitted without license from IHS -,-,- Approval of an American National Standard requires review by ANSI that the requirements for due process, consensus, and other criteria for approval have been met by the standards developer. Consensus is established when, in the judgement of the ANSI Board of Standards Review, substantial agreement has been reached by directly and materially affected interests. Substantial agreement means much more than a simple majority, but not necessarily unanimity. Consensus requires that all views and objections be considered, and that a concerted effort be made towards their resolution. The use of American National Standards is completely voluntary; their existence does not in any respect preclude anyone, whether he has approved the standards or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not conforming to the standards. The American National Standards Institute does not develop standards and will in no circumstances give an interpretation of any American National Standard. Moreover, no person shall have the right or authority to issue an interpretation of an American National Standard in the name of the American National Standards Institute. Requests for interpretations should be addressed to the secretariat or sponsor whose name appears on the title page of this standard. CAUTION NOTICE: This American National Standard may be revised or withdrawn at any time. The procedures of the American National Standards Institute require that action be taken periodically to reaffirm, revise, or withdraw this standard. Purchasers of American National Standards may receive current information on all standards by calling or writing the American National Standards Institute. American National Standard Published by American National Standards Institute, Inc. 25 West 43rd Street, New York, NY 10036 Copyright © 2003 by American National Standards Institute, Inc. All rights reserved. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without prior written permission of the publisher. Printed in the United States of America Copyright American National Standards Institute Provided by IHS under license with ANSI Licensee=USN Ship Repair Facility Yokosuka/9961031100 Not for Resale, 05/08/2007 22:49:33 MDTNo reproduction or networking permitted without license from IHS -,-,- i Contents Page Forewordii Introduction .iii 1Scope . 1 2Normative references. 1 3Terms and definitions. 1 4Computational steps. 3 5Summary of procedure to calculate the PGI. 12 6Reporting results 13 Tables 1Channel-dependent numerical factors used in equation (1). 11 2Optical printing magnifications 11 3Visual weighting coefficients used in equation (6) 12 Annexes ADerivation of the relationship of print granularity to film granularity 14 BBibliography 16 Copyright American National Standards Institute Provided by IHS under license with ANSI Licensee=USN Ship Repair Facility Yokosuka/9961031100 Not for Resale, 05/08/2007 22:49:33 MDTNo reproduction or networking permitted without license from IHS -,-,- ii Foreword (This foreword 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 is a need to evaluate and 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 Grain Index,“ or PGI) for comparing the graininess of color photographic prints made from color negative films. The method uses the RMS granularity of the color negative film as the input, and computes the PGI for a specified printing magnification. The PGI allows a photographer to choose a film, format and printing magnification based on an objective assessment of the resulting perceived graininess in the final print. This standard contains two annexes that are informative and are not considered part of the standard. Suggestions for improvement of this standard will be welcome. They should be sent to the International Imaging Industry Association, Inc. (I3A), 550 Mamaroneck Ave- nue, Suite 307, Harrison, NY 10528-1612; e-mail: i3astdsi3a.org. This standard was processed and approved for submittal to ANSI by I3A Technical Committee on Image Evaluation, IT2. Committee approval of the standard does not necessarily imply that all committee members voted for its approval. At the time this standard was approved, the IT2 Committee had the following members: Michael R. Goodwin, Chairman Jack Holm, Vice-Chairman Organization RepresentedName of Representative International Imaging Industry Association, Inc. (I3A) .Sharon Bartels Richard Fisch Michael R. Goodwin Thomas Lumenello Robert A. Uzenoff Robert D. Whittal Paul J. Kane (Alt.) Thomas McKeehan (Alt.) CGATS .Larry Steele Graphic Communication AssociationNorman W. Scharpf Graphic MicrosystemsSteven Headley GTI Graphic Technology, IncCharles G. Saleski Photographic Society of America .Jack Holm Ira Current (Alt.) Professional Photographers of America.Tim Mathiesen Radiological Society of North America .Homer L. Twigg, Jr. Eliot L. Siegel US Department of Commerce - National Institute of Standards and Technology.Edward A. Early Individual Expert Daniel Sinto Copyright American National Standards Institute Provided by IHS under license with ANSI Licensee=USN Ship Repair Facility Yokosuka/9961031100 Not for Resale, 05/08/2007 22:49:33 MDTNo reproduction or networking permitted without license from IHS -,-,- iii Introduction RMS-granularity is a useful measure of the microdensity fluctuations present in an area of uniform exposure on a photographic film. These fluctuations arise from the random 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 graininess of prints made from the film negative 1.1) However, the film negative itself is rarely viewed, and it is the graininess of the final viewed 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) of a color photographic print made from a color negative film. The purpose of the PGI is to provide an objective basis for comparing the graininess of color photographic prints made from color negative films at specified magnifications. The PGI is a complement to, rather than a replacement for, rms-granularity. 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 bracket refers to the reference in the Bibliography (annex C). Copyright American National Standards Institute Provided by IHS under license with ANSI Licensee=USN Ship Repair Facility Yokosuka/9961031100 Not for Resale, 05/08/2007 22:49:33 MDTNo reproduction or networking permitted without license from IHS -,-,- AMERICAN NATIONAL STANDARD ANSI/I3A IT2.37-2001 American 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 Index (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 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 maintain 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 IT2.39-1998, 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. Copyright American National Standards Institute Provided by IHS under license with ANSI Licensee=USN Ship Repair Facility Yokosuka/9961031100 Not for Resale, 05/08/2007 22:49:33 MDTNo reproduction or networking permitted without license from IHS -,-,- ANSI/I3A IT2.37-2001 2 3.1 graininess: 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 difference 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 = -log10 T. 3.3 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- point 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 photographic 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 fluctuation 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 Copyright American National Standards Institute Provided by IHS under license with ANSI Licensee=USN Ship Repair Facility Yokosuka/9961031100 Not for Resale, 05/08/2007 22:49:33 MDTNo reproduction or networking permitted without license from IHS -,-,- ANSI/I3A IT2.37-2001 3 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 graininess 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 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 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 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 the film sample; Copyright American National Standards Institute Provided by IHS under license with ANSI Licensee=USN Ship Repair Facility Yokosuka/9961031100 Not for Resale, 05/08/2007 22:49:33 MDTNo reproduction or networking permitted without license from IHS -,-,- ANSI/I3A IT2.37-2001 4 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 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 Tran