ISO INTERNATIONAL STANDARD 12645 First edition 1998-11-01 Graphic technology Process control - Certified reference material for opaque area calibration of transmission densitometers Technologie graphique Maitrise de procédé Materiel de réference certifié pour la calibration des densitometres transmission en pourcentage de superficie opaque ISO Referencenumber ISO12645:1998(E) py IHS under lic Not for Resale ISO 12645:1998(E) Foreword IsO (the International Organization for Standardization) is a worldwide federation of national standards bodies (IsO member bodies). The work of preparing International Standards is normally carried out through ISO technica committees. Each member body interested in a subject for which a technical committee has been established has Commission(lEC)onallmattersofelectrotechnicalstandardization Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard ISO 12645 was prepared by Technical Committee ISO/TC 130, Graphic technology. Annexes A to E of this International Standard for information only. @ISO1998 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic InternationalOrganizationforStandardization Case postale 56·CH-1211Geneve20·Switzerland Internet [email protected] Printed in Switzerland Copyright International Organization for Standardization Not for Resale @ ISO ISO 12645:1998(E) Introduction In the graphic arts, the modulation of transmittance or reflectance is often achieved by printing half-tones rather than continuous tones, as would be the case in photography. The process control of the generation and transfer of half-tone patterns is essential to the graphic arts industry. For the process control of transmission type material one monitors the percentage of the total area that is virtually opaque. Measurements are carried out on well-defined half-tone control patches which contain regularly-spaced, circular half-tone dots. The measuring instrument is either a densitometer or a colorimeter of the spectrophotometer ortristimulustype.Theopaqueareapercentageisusuallysetequaltotheratioof therelativetransmittancefactors ofthehalf-toneandthatofthesolid.Withdensitometersonecalculatesthetransmittancefactorsfromtheiso standard diffuse (opal) densities, the corresponding expression for the ratio has been given by Murray and Davies, see [E.2] and equations (1) and (2) of clause 3. In principle, the opaque area percentage for positive-polarity films should be identical to the tone value as defined in the graphic arts; for negative-polarity films it should be identical to 10o % minus the tone value. In reality, however, independent check on the determination of the tone value by densitometers and colorimeters. In the graphic arts process chain, particularly important steps are "image setting", "film duplication" and "platemaking". During these steps, there is no highly diffusive medium present which could be compared to the opal-glassdiffuserofdensitometersaccordingtoIsO5-2[E.3l.Itwouldthusappearthattheopal-glassinstrument is not the best solution for graphic arts applications. However, the opal-glass design permits a relatively simple construction; such instruments are widely used in the graphic arts industry. When calibrating a densitometer with a stepped density reference material (at least two steps), usually both the zero point andthe slopefactorareadjusted.Thelatteristheratio of thedensitydifference betweenthestepsas readby the densitometer and the density difference as reported by a national standardizing laboratory. If the ratio deviate's from 1, the base of the logarithm used for converting transmittance factor into transmittance factor density is not 10 asrequiredbydefinition.Asa consequence,the tonevalues calculated