ISO/TS 20791-3:2023

Photography - Photographic reflection prints - Part 3: Evaluation of glossiness

This document describes the characterization of glossiness of photographic reflection prints, which consists of specular gloss measurement and image clarity measurement. This document is applicable to any photographic printing technology such as inkjet, thermal dye transfer, electrophotography and silver halide technologies. NOTE The level of preferred glossiness depends on the application.

Photographie — Tirages photographiques par réflexion — Partie 3: Évaluation de la brillance

General Information

• Status: Published
• Publication Date: 08-Jun-2023
• ICS: 37.040.20 - Photographic paper, films and plates. Cartridges
• Technical Committee: ISO/TC 42 - Photography
• Drafting Committee: ISO/TC 42 - Photography
• Current Stage: 6060 - International Standard published
• Start Date: 09-Jun-2023
• Due Date: 12-Oct-2024
• Completion Date: 09-Jun-2023

Overview

ISO/TS 20791-3:2023 - Photography - Photographic reflection prints - Part 3: Evaluation of glossiness - defines standardized methods to characterize the glossiness of photographic reflection prints. The technical specification combines two complementary measurements: specular gloss (intensity of mirror-like reflection) and image clarity (distinctness or sharpness of the reflected image). It applies to all common photographic printing technologies including inkjet, thermal dye transfer, electrophotography, and silver halide processes. The goal is to provide reproducible measurement procedures for product development and comparison rather than routine production QA.

Key Topics and Requirements

• Two primary properties: specular gloss and image clarity (also called distinctness of image, DOI).
• Measurement methods: based on ISO 2813 (specular gloss) and ISO 17221 (image clarity), adapted for photographic prints.
• Instrumentation: use a calibrated glossmeter (per ISO 2813) for specular gloss; image clarity instruments follow ISO 17221 principles.
• Angles: gloss measurements are standardized at 20°, 60° and 85°; 20° is recommended for photographic prints with a wide range from high gloss to matte. 60° and 85° are used for other gloss ranges.
• Directional measurements: measure gloss both perpendicular and parallel to the printing direction and report both values plus their average.
• Sample preparation:
  • Test patches: at minimum white (Dmin) and black; optional C, M, Y, R, G, B, grey patches. sRGB patch values (ISO 18944) may be used.
  • Patch size: ≥ 25 mm × 25 mm; specimen size: ≥ 30 mm × 30 mm.
  • Environmental conditioning: standard printing conditions 23 °C ± 3 °C and 50 % RH ± 10 % RH; inks requiring curing should be conditioned (recommendation: at least two weeks under 23 °C ± 2 °C, 50 % RH ± 5 % RH if cure duration is unknown).
  • Backing: prints are recommended to be backed (black boards preferred) to keep surfaces flat; backing must be reported.
• Reporting: measurement conditions, instrument calibration, specimen backing and directional values must be documented.

Applications and Who Uses It

ISO/TS 20791-3:2023 is useful for:

• Print product designers and material developers comparing surface appearance across print technologies.
• Manufacturers and OEMs evaluating surface treatments, coatings, or paper/film substrates.
• Photographic labs and imaging specialists optimizing finish (gloss/matte) for end-use applications.
• Standards bodies and test laboratories performing objective comparisons of print appearance.

This specification helps ensure consistent, reproducible evaluation of perceived shininess and reflected image sharpness, supporting informed design and product comparisons.

Related Standards

• ISO 2813 - Paints and varnishes - Determination of gloss values (20°, 60°, 85°)
• ISO 17221 - Plastics - Determination of image clarity (degree of sharpness of reflected/transmitted image)
• ISO 18913 - Imaging materials - Permanence - Vocabulary
• ISO/TS 20791 series (other parts) for broader photographic material guidance

Keywords: ISO/TS 20791-3:2023, photographic reflection prints, glossiness, specular gloss, image clarity, glossmeter, photographic print testing.

Standards Content (Sample)

TECHNICAL ISO/TS
SPECIFICATION 20791-3
First edition
2023-06
Photography — Photographic
reflection prints —
Part 3:
Evaluation of glossiness
Photographie — Tirages photographiques par réflexion —
Partie 3: Évaluation de la brillance
Reference number
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Terms. 1
3.2 Abbreviations . 2
4 Overview . 2
5 Sample preparations .2
5.1 Test targets . 2
5.2 Printing . 3
5.3 Specimens . 3
6 Measurement of specular gloss . 4
6.1 General . 4
6.2 Apparatus . 4
6.3 Procedure . 5
7 Measurement of image clarity . .5
7.1 General . 5
7.2 Apparatus . 5
7.3 Procedure . 6
8 Test report . 7
Annex A (informative) Other properties related to glossiness . 9
Bibliography .11
iii
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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 42, Photography.
A list of all parts in the ISO 20791 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Glossiness is an optical property regarding reflected light from print surfaces. Many studies have
been conducted on glossiness of industrial materials, and several studies have been reported on
print materials as well, see References [1] to [6]. It is especially important for photographic prints
with respect to printed image characteristic, because there is a wide variety from very high glossy
to dead matte surfaces. As stated in ISO/TR 20791-1, several properties affect the gloss perception of
photographic prints, see References [7]. Specular gloss and image clarity (distinctness of image) are
the two major properties among them. The former relates to the perceived intensity of reflected light
and the latter relates to the sharpness of reflected image. There is also a study stating that perceived
glossiness of photographic prints is well represented by the combination of these two measurements,
[8]
specular gloss and image sharpness .
Some measurements for properties regarding glossiness have been standardized for industrial
materials such as coatings, plastics and papers, see References [9] to [12] and ISO 17221. Among them,
the measurement methods for coatings are standardized with specular gloss and image clarity as
important properties for the reflection characteristics. Some standards for graphic printing and office
[13]
printing basically refer to them while adding methods and cautions specific to each application
[14]
. But there has been no published standard for measuring both specular gloss and image clarity for
photographic prints.
This document provides the measurement methods of two major properties to evaluate glossiness
of photographic prints: specular gloss and image clarity. The methods are based on the existing
documents for coatings and plastics, and specific requirements for photographic prints are defined
regarding sample preparation, measurement procedure and reporting.
v
TECHNICAL SPECIFICATION ISO/TS 20791-3:2023(E)
Photography — Photographic reflection prints —
Part 3:
Evaluation of glossiness
1 Scope
This document describes the characterization of glossiness of photographic reflection prints, which
consists of specular gloss measurement and image clarity measurement. This document is applicable
to any photographic printing technology such as inkjet, thermal dye transfer, electrophotography and
silver halide technologies.
NOTE The level of preferred glossiness depends on the application.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 2813, Paints and varnishes — Determination of gloss value at 20°, 60° and 85°
ISO 17221, Plastics — Determination of image clarity (degree of sharpness of reflected or transmitted
image)
ISO 18913, Imaging materials — Permanence — Vocabulary
3 Terms and definitions
For the purposes of this document, the following terms and definitions given in ISO 18913 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Terms
3.1.1
glossiness
visual characteristic related to shiny and smooth appearance
Note 1 to entry: Based on this appearance, humans perceive features such as reflection characteristics and
roughness of the surface of an object.
3.1.2
specular gloss
ratio of the luminous flux, reflected by the test surface into a specified aperture at the angle of specular
reflection, to that from a standard specularly reflecting surface under the same conditions
[SOURCE: ISO 4046-5:2016, 5.107, modified — Note 1 to entry was deleted.]
3.1.3
image clarity
distinctness of image
DOI
degree of sharpness of an image reflected by a specimen or transmitted through a specimen
[SOURCE: ISO 17221:2014, 3.1, modified — the synonym "distinctness of image (DOI)" was added and
Note 1 to entry was deleted.]
3.2 Abbreviations
C cyan
M magenta
Y yellow
R red
G green
B blue
4 Overview
This document stipulates evaluation methods of glossiness, based on specular gloss and image clarity.
Each measurement method is based on ISO 2813 and ISO 17221 respectively. Specific requirements for
photographic prints are described in Clause 5 for sample preparation, Clause 6 and 7 for measurement
and Clause 8 for reporting. In addition, other properties which relate to glossiness are described in
Annex A.
The purpose of this document is to characterize the glossiness of photographic prints. Since the level
of preferred glossiness depends on the application, this document does not discuss performance
superiority or inferiority. The methods in this document are intended to be used for product design and
product comparison and are not intended to be used for daily quality assurance in manufacturing.
5 Sample preparations
5.1 Test targets
At least white (D ) and black patches shall be printed for measurement. Additional colours such as
min
cyan (C), magenta (M), yellow (Y), red (R), green (G), blue (B) and grey are recommended to evaluate
the effects of colour or density on measured properties. The sRGB encoded patch values described in
ISO 18944 can be applied to test targets for digital printers. Patch size for measurements shall be not
less than 25 mm × 25 mm. Examples of test targets are shown in Figure 1. Figure 1 a) can be used for
both colour and monochrome prints.
NOTE A larger patch size is sometimes necessary for the measurements of specular gloss especially at a
higher angle such as 85°. The manufacturer of each measuring instrument usually provides information about
the aperture size and/or the minimum patch size.
a)  grey step patches b)  C, M, Y, R, G, B colour patches
Figure 1 — Examples of test targets
5.2 Printing
The standard ambient environmental condition for printing shall be a temperature of 23 °C ± 3 °C,
and a relative humidity of 50 % RH ± 10 % RH unless it has been confirmed that the temperature and
humidity do not affect the properties related to gloss. If it is not possible to conduct the test under the
standard environmental condition, the temperature and humidity shall be reported.
Aqueous and solvent inkjet prints, and prints of any type that require curing/stabilization/dry-down
shall be conditioned until the curing process is finished. If the duration of curing is unknown, prints
should be conditioned for at least two weeks after printing, in an environment with a temperature of
23 °C ± 2 °C, with a relative humidity of 50 % RH ± 5 % RH.
5.3 Specimens
The size of specimen shall not be less than 30 mm × 30 mm to cover the minimum size of 25 mm × 25 mm
for a single test patch.
In the case of large size prints, they are cut to fit the above size before measurement.
NOTE The
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