SIST ISO 21550:2011

SLOVENSKI STANDARD
01-julij-2011
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Photography - Electronic scanners for photographic images - Dynamic range
measurements
Photographie - Scanners électroniques pour images photographiques - Mesurages
d'intervalles dynamiques
Ta slovenski standard je istoveten z: ISO 21550:2004
ICS:
37.040.10 Fotografska oprema. Photographic equipment.
Projektorji Projectors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL ISO
STANDARD 21550
First edition
2004-10-01
Photography — Electronic scanners for
photographic images — Dynamic range
measurements
Photographie — Scanners électroniques pour images
photographiques — Mesurages d'intervalles dynamiques

Reference number
©
ISO 2004
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©  ISO 2004
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ii © ISO 2004 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Test chart . 4
4.1 Representation and recommended size .4
4.2 The reflective test chart. 5
4.3 The transparent test chart. 6
5 Test conditions. 6
5.1 General. 6
5.2 Temperature and relative humidity . 6
5.3 Luminance and colour measurements .7
5.4 Scanner settings . 7
6 Measuring the Scanner OECF . 7
6.1 General. 7
6.2 Scanner settings . 7
7 Calculation of the scanner dynamic range. 8
7.1 Luminance OECF . 8
7.2 Scanner dynamic range. 8
7.3 Determination of the signal to noise ratio. 8
8 Presentation of results . 9
8.1 General. 9
8.2 Scanner OECF . 10
8.3 Scanner dynamic range measurements. 11
Annex A (normative) Scanner OECF Test Patches. 12
Annex B (normative) Density shift to measure ISO scanner d . 13
max
Bibliography . 14

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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. 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.
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.
ISO 21550 was prepared by Technical Committee ISO/TC 42, Photography.
iv © ISO 2004 – All rights reserved

Introduction
The use of scanners to provide digital image files is rapidly growing. A standard is needed in order to measure
the ability of scanners to capture tones especially in the dark areas of the original. At the present time most
manufacturers calculate the dynamic range from the bit depth of the implemented A/D conversion which is
usually higher than the actual capabilities of the scanner. This International Standard can be used for
photofinishing, professional, graphic arts and consumer scanners.
This International Standard specifies methods for measuring the ability of scanners to capture tones especially
in the dark areas of the original. The scanner measurements described in this International Standard are
performed in the digital domain, using digital analysis techniques. A test chart of appropriate size and
characteristics is scanned and the resulting data is analysed. The test chart described in this International
Standard is designed specifically to evaluate continuous tone film and reflection scanners. It is not designed
for evaluating electronic still-picture cameras, video cameras, or bi-tonal document scanners.

INTERNATIONAL STANDARD ISO 21550:2004(E)

Photography — Electronic scanners for photographic
images — Dynamic range measurements
1 Scope
This International Standard specifies methods for measuring and reporting the dynamic range of electronic
scanners for continuous tone photographic media. It applies to scanners for reflective and to scanners for
transmissive media.
2 Normative references
The following referenced documents are indispensable for the application 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 5-2, Photography — Density measurements — Part 2: Geometric conditions for transmission density
ISO 5-4, Photography — Density measurements — Part 4: Geometric conditions for reflection density
ISO 554, Standard atmospheres for conditioning and/or testing — Specifications
ISO 12231, Photography — Electronic still-picture cameras — Terminology
ISO 12232:1998, Photography — Electronic still-picture cameras — Determination of ISO speed
ISO 14524, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic
conversion functions (OECFs)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12231 and the following apply.
3.1
addressable photoelements
number of active photoelements in an image sensor
NOTE This is equal to the number of active lines of photoelements, multiplied by the number of active photoelements
per line.
3.2
aliasing
output image artefacts that occur in a sampled imaging system for input images having significant energy at
frequencies higher than the Nyquist frequency of the system
3.3
digital output level
numerical value assigned to a particular output level, also known as the digital code value
3.4
edge spread function
ESF
normalized spatial signal distribution in the linearized output of an imaging system resulting from imaging a
theoretical infinitely sharp edge
3.5
effectively spectrally neutral
characteristic of an imaging system whereby the output is the same as that produced from a spectrally neutral
object
3.6
electronic scanners for photographic film
scanner that incorporates an image sensor whose output is a digital signal that represents a still film image
3.7
fast scan direction
scan direction corresponding to the direction of the alignment of the addressable photoelements in a linear
array image sensor
3.8
gamma correction
process that alters the image data in order to modify the tone reproduction
3.9
image sensor
electronic device that converts incident electromagnetic radiation into an electronic signal; e.g. a charge
coupled device (CCD) array
3.10
incremental gain function
change in output level (digital code value) divided by the change in input level (luminance or exposure) as a
function of input level
NOTE 1 For the determination of incremental gain values, log input values are not used.
NOTE 2 If the input exposure points are very finely spaced and the output noise is small compared to the quantization
interval, the incremental gain function may have a jagged shape. Such behaviour is an artefact of the quantization process
and should be removed by using an appropriate smoothing algorithm, or by fitting a smooth curve to the data. In some
cases it may be desirable to fit a curve to the input-output data and then determine the incremental gain function by taking
the first derivative of the function used for the curve fit.
3.11
incremental output signal
input level multiplied by the system incremental gain at that level
3.12
incremental signal to noise ratio
ratio of the incremental output signal to the root-mean-squared (rms) noise level, at a particular signal level
NOTE This is typically expressed as a graph or table showing the rms noise level versus output signal level for the
full range of output signal levels.
3.13
ISO scanner dynamic range
difference of the maximum density where the incremental gain is higher than 0,5, as determined according to
ISO 21550 to the minimum density that appears unclipped
2 © ISO 2004 – All rights reserved

3.14
noise
unwanted variations in the response of an imaging system
3.15
resolution
measure of the ability of a digital image capture system, or a component of a digital image capture system, to
capture fine spatial detail
NOTE Resolution measurement metrics include resolving power, limiting visual resolution, SFR, Modulation Transfer
Function (MTF) and Contrast Transfer Function (CTF).
3.16
sampled imaging system
imaging system or device which generates an image signal by sampling an image at an array of discrete
points, or along a set of discrete lines, rather than a continuum of points
NOTE The sampling at each point is done using a finite size sampling aperture or area.
3.17
sample spacing
physical distance between sampling points or sampling lines
NOTE 1 The sample spacing may be different in the two orthogonal sampling directions.
NOTE 2 Measured in units of distance (e.g. microns, mm).
3.18
sampling frequency
reciprocal of sample spacing
NOTE This is expressed in samples per unit distance [e.g. dots per inch (dpi)].
3.19
scanner
electronic device that converts a fixed image, such as a film or film transparency, into an electronic signal
3.20
scanner opto-electronic conversion function
Scanner OECF
relationship between the input density and the digital output levels for a scanner
3.21
slow scan direction
direction in which the scanner moves the photoelements (perpendicular to the lines of active photoelements in
a linear array image sensor)
3.22
spatial frequency response
SFR
measured amplitude response of an imaging system as a function of relative input spatial frequency
NOTE The SFR is normally represented by a curve of the output response to an input sinusoidal spatial luminance
distribution of unit amplitude, over a range of spatial frequencies. The SFR is normalized to yield a value of 1,0 at a spatial
frequency of 0.
3.23
spectrally neutral
test chart equality of the relative spectral power distributions of the incident and reflected (or transmitted) light
3.24
test chart
arrangement of test patterns designed to test particular characteristics
3.25
test pattern
specified arrangement of spectral reflectance or transmittance characteristics used in measuring an image
quality attribute
3.26
test pattern types
3.26.1
bi-tonal patterns
patterns that are spectrally neutral or effectively spectrally neutral, and consist exclusively of two reflectance
or transmittance values in a prescribed spatial arrangement
NOTE Bi-tonal patterns are typically used to measure resolving power, limiting resolution and SFR.
3.26.2
grey scale patterns
patterns that are spectrally neutral or effectively spectrally neutral, and consist of a large number of different
reflectance or transmittance values in a prescribed spatial arrangement
NOTE Grey scale patterns are typically used to measure opto-electronic conversion functions.
3.26.3
spectral patterns
patterns that are specified by the spatial arrangement of features with differing spectral reflectance or
transmittance values
NOTE Spectral patterns are typically used to measure colour reproduction.
4 Test chart
4.1 Representation and recommended size
This section defines the type and specifications of the test chart depicted in Figure 1. This test chart can be
made at various sizes to correspond to popular film sizes. The recommended size for the reflective version is
100 × 150 mm and for the transparent version it is 24 × 36 m
...