ISO INTERNATIONAL STANDARD 6846 Second edition 1992-12-15 Photography Black-and-white continuous-tone papers Determination of ISO speed and ISO range for printing Photographie -- Papiers noir et blanc pour images a tons continus Détermination de la sensibilite ISO et de I'étendue ISo pour le tirage Reference number ISO 6846:1992(E) No reproduction or networking permitted without license from IHS Not for Resale ISO 6846:1992(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 technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISo collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. 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 6846 was prepared by Technical Committee ISO/TC 42, Photography. Thissecond edition cancelsandreplacesthefirst edition (ISO 6846:1983), of which it constitutes a technical revision. Annexes A, B, C and D of this International Standard are for information only. ISO1992 by any means, electronic or mechanical, including photocopying and microfilm, without per- mission in writingfromthe publisher. International Organization for Standardization Case Postale 56 . CH-1211 Geneve 20 · Switzerland Printed in Switzerland CopyrightiemationaOrganizationfoStandardization Not for Resale ISO 6846:1992(E) Introduction This International Standard establishes a method for measuring those photographiccharacteristicsofpapers usedforprintingfromnegativeim- ageswhichwill aid usersto selecttheappropriateproductsfortheirap- plications. IsO speed and IsO range are two measurements considered important for this purpose. Studies have shown that highly acceptable prints are generally obtained if the log exposure range (LER) of a photographic paper is equal to the ef- fective density range of the negative.1) Therefore, isO range, which is di- rectly related to LER provides a useful criterion for grading papers. Some diversion from this criterion canbe required to obtain optimum prints be cause of subject matter, individual preferences, and paper characteristics such as Dmax, surface and curve shape. and designations which makes it extremely difficult for users to identify products which are comparable for printing characteristics. The IsO range number is introduced to reduce this source of confusion. IsO range is not a measure of image contrast, but a useful guide for sel- a given effective negative density range, and for comparing products from ferent types of objective measurements in relation to two specified points on the paper characteristic curve a) difference in density between the two points (density range); b) the slope of a straight line connecting the points (average gradient); and c) the difference in log exposure for the two points (log exposure range). Of the three, log exposure range is most closely associated with the concept of paper contrast grades (see annexes B and C). illuminance range at the printing plane when printers are employed that diffuse density criteria normally exist only in contact printing, the term "effective density range" has been introduced (see annex A). It is the effective density range of the negative which should be matched with the log exposure range of the printing material in the usual projection printing mode for optimum tone reproduction. 1) JONES, L.A. and NELSON, C.N. Control of Photographic Printing: Improve- ments inTechnologyandfurtherAnalysisof Results.JournaloftheOptical