SIST ISO 15739:2018
Photography - Electronic still-picture imaging - Noise measurements
Photography - Electronic still-picture imaging - Noise measurements
This document specifies methods for measuring and reporting the noise versus signal level and dynamic
range of digital still cameras. It applies to both monochrome and colour electronic digital still cameras.
Photographie - Imagerie des prises de vue électroniques - Mesurages du bruit
Fotografija - Digitalno upodabljanje mirujočih slik - Meritve slikovnega šuma
Ta dokument določa metode za merjenje in poročanje o ravni hrupa glede na signal ter dinamični razpon digitalnih fotoaparatov. Uporablja se za enobarvne in barvne elektronske digitalne fotoaparate.
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SLOVENSKI STANDARD
SIST ISO 15739:2018
01-februar-2018
1DGRPHãþD
SIST ISO 15739:2014
)RWRJUDILMD'LJLWDOQRXSRGDEOMDQMHPLUXMRþLKVOLN0HULWYHVOLNRYQHJDãXPD
Photography - Electronic still-picture imaging - Noise measurements
Photographie - Imagerie des prises de vue électroniques - Mesurages du bruit
Ta slovenski standard je istoveten z: ISO 15739:2017
ICS:
37.040.99 Drugi standardi v zvezi s Other standards related to
fotografijo photography
SIST ISO 15739:2018 en,fr
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST ISO 15739:2018
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SIST ISO 15739:2018
INTERNATIONAL ISO
STANDARD 15739
Third edition
2017-05
Photography — Electronic still-picture
imaging — Noise measurements
Photographie — Imagerie des prises de vue électroniques —
Mesurages du bruit
Reference number
ISO 15739:2017(E)
©
ISO 2017
---------------------- Page: 3 ----------------------
SIST ISO 15739:2018
ISO 15739:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved
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SIST ISO 15739:2018
ISO 15739:2017(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test conditions . 3
4.1 General . 3
4.2 Illumination . 3
4.2.1 Characteristics . 3
4.2.2 Daylight illumination. 3
4.2.3 Tungsten illumination . 3
4.2.4 Uniformity of illumination and reflection test chart illumination geometry . 4
4.2.5 Light source amplitude variations . 4
4.3 Temperature and relative humidity . 4
4.4 White balance. 4
4.5 Infrared (IR) blocking filter. 4
4.6 Photosite integration time . 4
4.7 Colour noise weighting . 4
4.8 Compression . 5
5 Noise measurement procedures . 5
5.1 General . 5
5.1.1 Uniform field noise measurement methods . . 5
5.1.2 Test densities . 5
5.1.3 Adjustment of illumination, test density placement and camera lens focus. 6
5.2 Measurement of a DSC having a removable lens . 6
5.3 Measurement of a DSC having manual exposure control . 7
5.4 Measurement of a DSC using a test chart . 7
6 Calculation and reporting of results . 9
6.1 General . 9
6.2 Signal-to-noise ratios — large area . 9
6.3 DSC dynamic range .12
Annex A (normative) Noise component analysis .14
Annex B (normative) Visual noise measurements .18
Annex C (informative) Removing low frequency variations from the image data .27
Annex D (informative) Procedure for determining signal-to-noise ratio .29
Annex E (informative) Practical viewing conditions for various output media .30
Bibliography .31
© ISO 2017 – All rights reserved iii
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SIST ISO 15739:2018
ISO 15739:2017(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.
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 on 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 the following
URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 42, Photography.
This third edition cancels and replaces the second edition (ISO 15739:2013), of which it constitutes a
minor revision with the addition of IEC 61966-2–1:1999 to Clause 2 and changes in Annex B.
iv © ISO 2017 – All rights reserved
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SIST ISO 15739:2018
ISO 15739:2017(E)
Introduction
Noise is an important attribute of electronic photographic systems. Camera noise measurements
described in this document are performed in the digital domain, using digital analysis techniques.
Since the noise performance of an image sensor may vary significantly with exposure time and
operating temperature, these operating conditions are specified. The visibility of noise to human
observers depends on the magnitude of the noise, the apparent tone of the area containing the noise
and the spatial frequency of the noise. The magnitude of the noise present in an output representation
depends on the noise present in the stored image data and the contrast amplification or gain applied to
the data in producing the output. The noise visibility is different for the luminance (or monochrome)
channel and the colour (or colour difference) channels. Therefore, this document accounts for these
factors in measuring and reporting the camera noise measurements. Annex A specifies the method for
determining the components of the digital camera noise from a number of samples. The perceptibility
of noise in an image can vary depending on the viewing distance, spatial frequency, density, colour
and viewing conditions. Annex B describes a procedure for measuring the visual noise level using a
human visual model as a method for weighting the spectral components of the noise. A method for
removing low frequency variations in the patch data resulting, for example, from luminance shading is
given in Annex C. A recommended step-by-step procedure for determining the signal-to-noise ratio and
incremental gain is provided in Annex D. In Annex E, recommendations for practical viewing conditions
for various output media are given.
© ISO 2017 – All rights reserved v
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SIST ISO 15739:2018
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SIST ISO 15739:2018
INTERNATIONAL STANDARD ISO 15739:2017(E)
Photography — Electronic still-picture imaging — Noise
measurements
1 Scope
This document specifies methods for measuring and reporting the noise versus signal level and dynamic
range of digital still cameras. It applies to both monochrome and colour electronic digital still cameras.
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 554, Standard atmospheres for conditioning and/or testing — Specifications
ISO 7589:2002, Photography — Illuminants for sensitometry — Specifications for daylight, incandescent
tungsten and printer
ISO 12232:2006, Photography — Digital still cameras — Determination of exposure index, ISO speed
ratings, standard output sensitivity, and recommended exposure index
ISO 14524:2009, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic
conversion functions (OECFs)
ITU-R BT.709-5, Parameter values for the HDTV Standards for production and International programme
exchange
IEC 61966-2–1:1999, Multimedia systems and equipment — Colour measurement and management – Part
2-1: Colour management — Default RGB colour space — sRGB
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1
camera opto-electronic conversion function
camera OECF
relationship between the input scene log luminances and the pixel values for an opto-electronic digital
capture system
2.
Note 1 to entry: The unit of measurement for this function are log cd/m
10
3.2
clipping value
pixel value that remains constant for further increases in exposure (highlight clipping value) or for
further decreases in exposure (dark clipping value)
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ISO 15739:2017(E)
3.3
digital still camera
DSC
camera that produces a digital still image from the digitized output of a solid-state photo sensor and
records the digital still image using a digital memory, such as a removable memory card
3.4
image sensor
electronic device which converts incident electromagnetic radiation into an electronic signal
Note 1 to entry: A charge coupled device (CCD) array is an example of an image sensor.
3.5
incremental gain function
incremental gain
change in the pixel values of the DSC divided by the change in the exposure values
Note 1 to entry: For the determination of incremental gain values, log input values are not used.
Note 2 to entry: If the input exposure points are very finely spaced and the output noise is small compared to
the quantization interval, the incremental gain function can have a jagged shape. Such behaviour is an artefact
of the quantization process and is 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.
3.6
incremental output signal
exposure level multiplied by the incremental gain at that particular exposure level
3.7
incremental signal-to-noise ratio
ratio of the incremental output signal to the root mean square (rms) noise level, at a particular signal level
Note 1 to entry: This is typically expressed as a graph or table showing the incremental signal-to-noise ratio
versus input signal level for the full range of input signal levels.
3.8
DSC dynamic range
ratio of the maximum exposure level that provides a pixel value below the highlight clipping value to
the minimum exposure level that can be captured with an incremental signal-to-temporal-noise ratio
of at least 1, as determined in accordance with ISO 15739
3.9
noise
unwanted variations in the response of an imaging system
3.9.1
total noise
all the unwanted variations, consisting of pattern noise and temporal noise, of the values in the digitized
output captured by a single exposure
Note 1 to entry: The procedure in this document for calculating the total noise requires multiple frames.
3.9.2
fixed pattern noise
unwanted variations of the values in the digitized output which remain constant between exposures
3.9.3
temporally varying noise
unwanted variation in the values of the digitized output that changes from one exposure to the next
due to sensor dark current, photon shot noise, analogue processing and quantization
2 © ISO 2017 – All rights reserved
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3.10
noise spectrum
curve or equation which expresses the image noise as a function of two-dimensional image spatial
frequencies
3.11
focal plane opto-electronic conversion function
focal plane OECF
relationship between the input focal plane log exposures and the output pixel values for an opto-
electronic digital image capture system
Note 1 to entry: The units of measurement for this function are log lux seconds.
10
3.12
exposure time
total time period during which the photo sensor is able to integrate the light from the scene to form
an image
3.13
test density
spectrally non-selective transmittance filter used to reduce an input luminance to a predefined ratio of
the unfiltered luminance
4 Test conditions
4.1 General
The following measurement conditions should be used as nominal conditions when measuring the
noise of a DSC. If it is not possible or appropriate to achieve these nominal operating conditions, the
actual operating conditions shall be listed along with the reported results.
4.2 Illumination
4.2.1 Characteristics
The noise measurements shall indicate whether illumination conforming to the standard photographic
daylight or tungsten illuminant was used. ISO 7589 describes the procedures for determining if the
characteristics of the illumination used in a specific noise determination test are an acceptable match
to the standard photographic daylight and tungsten illuminants.
4.2.2 Daylight illumination
For daylight measurements without the camera lens, illumination conforming to the ISO sensitometric
daylight illuminant specified in ISO 7589:2002, Table 1 shall be used. This illuminant is defined as the
product of the spectral power distribution of CIE Illuminant D55 and the spectral transmittance of the
ISO standard camera lens. For measurements with the camera lens in place, the spectral characteristics
of the illumination shall conform to CIE illuminant D55.
4.2.3 Tungsten illumination
For tungsten measurements without the camera lens, illumination conforming to the ISO sensitometric
tungsten illuminant specified in ISO 7589:2002, Table 2 shall be used. This illuminant is defined as the
product of the average spectral power distribution of experimentally measured sources having a colour
temperature of approximately 3 050 K and the spectral transmittance of the ISO standard camera
lens. For measurements with the camera lens in place, the spectral characteristics of the illumination
shall conform to the average spectral power distribution of experimentally measured sources having a
colour temperature of approximately 3 050 K.
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SIST ISO 15739:2018
ISO 15739:2017(E)
4.2.4 Uniformity of illumination and reflection test chart illumination geometry
The illumination should meet the uniformity requirements of the measurement procedures described
in Clause 5. For reflection test charts, the sources are positioned so that the angular distribution of
influx radiation is at its maximum at 45° to the test chart normal, and is negligible at angles of less than
40° or more than 50° to the normal, at any point on the test chart.
Additional shielding of the camera may be necessary to prevent stray illumination from the light
sources, or from other reflections, entering the camera lens. The illuminance incident on reflection
charts, or the luminance used to illuminate transmission charts, shall not vary by more than 2 % from
the mean value over the surface area of the chart as defined in ISO 14524.
NOTE In particular, if a transmissive chart is used, light from the chart can reflect off the camera or camera
operator back to the surface of the chart and be imaged by the camera. Such reflections need to be avoided. This
can be accomplished by shrouding the camera with black cloth and having the operator stand in a position that
avoids such reflections.
4.2.5 Light source amplitude variations
The light source shall be fixed-level with combined short-term and supply amplitude variations of less
than ± 2 %.
4.3 Temperature and relative humidity
The ambient room temperature during the acquisition of the test data shall be 23 °C ± 2 °C, as specified
in ISO 554, and the relative humidity shall be 50 % ± 20 %. Additional measurements at 0 °C and 40 °C
are recommended. The normal camera operating temperature (internal rise above ambient) shall
be achieved before beginning the tests. If the ambient temperature varies throughout the room, for
example as a result of heat generated by light sources, the ambient room temperature shall be measured
at a distance of between 0,1 m and 0,2 m from the camera under test at the same height.
4.4 White balance
For a colour camera, the camera white balance shall be adjusted, if possible, to provide proper white
balance (equal RGB signal levels) for the illumination light source, as specified in ISO 14524.
4.5 Infrared (IR) blocking filter
If required, an infrared blocking filter shall be used, as specified in ISO 14524.
4.6 Photosite integration time
The photosite integration time should not be longer than 1/30 s.
4.7 Colour noise weighting
For colour cameras using a single exposure process, the camera noise may be determined using a
weighted sum of the colour outputs to derive the luminance. If the proper luminance weighting values for
the RGB channel spectral sensitivities are known, they shall be used to calculate the luminance channel
data. If these values are not known, the following weighting, given in ITU-R BT.709, shall be used:
Y = 0,212 5 R + 0,715 4 G + 0,072 1 B (1)
For colour cameras with luminance and colour-difference outputs, the standard deviation of the camera
noise may be computed from the luminance channel standard deviation σ (Y), the red minus luminance
4 © ISO 2017 – All rights reserved
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ISO 15739:2017(E)
channel standard deviation σ (R-Y) and the blue minus luminance channel standard deviation σ (B-Y).
Formula (2), as specified in ISO 12232:2006, 6.3.3, shall be used:
2 2 2 1/2
σ (D) = [σ (Y) + 0,279 σ (R-Y) + 0,088 σ (B-Y) ] (2)
NOTE The coefficients of the chrominance variances, σ (R-Y) and σ (B-Y), in Formula (2) were updated
in this document due to new coefficients being introduced in ISO 12232. The revision of the coefficients was
necessary due to a revised experimental procedure that indicated that the original values for the coefficients
[4]
overemphasized the contribution of chrominance noise to perception .
4.8 Compression
If the DSC includes any form of lossy compression, the compression shall be disabled, if possible, during
the noise measurements. If the compression cannot be turned off, then measurements should be taken
and the compression level reported with the noise measurement result, for example, the actual camera
switch setting (fine, standard, etc.) and the approximate average number of bits per pixel.
5 Noise measurement procedures
5.1 General
These measurement procedures shall be used to determine the noise, the midtone signal-to-noise ratio
and the dynamic range. The minimum requirement is to specify the midtone signal-to-total-noise ratio
and the dynamic range of the digital camera under test. In addition, the fixed pattern and temporal
noise components can be expressed individually. The measurement of visual noise defined in Annex B
shall not be performed and reported in place of the midtone signal-to-total noise ratio. It may, however,
be performed and reported together with the midtone signal-to-total-noise ratio.
NOTE The noise measurement procedures described in this document are intended to measure the temporal
and fixed pattern noise standard deviations spatially over the image. They do not take into account the variation
in the mean pixel value between individual frames captured by a DSC. This type of frame to frame variation in
mean pixel value can be introduced due to changes in ambient temperature, camera power supply or lighting
flicker. The illumination and temperature requirements specified in the standard will minimize these variations.
If it is required to include the effects of frame to frame variations in the calculation of temporal noise standard
deviation then the standard deviation of individual pixel values needs to be calculated across multiple frames.
5.1.1 Uniform field noise measurement methods
The method of measuring the uniform field noise will be dependent on the type of camera and its
level of exposure automation. If the camera lens can be removed, then the sensor noise level can be
measured without any shading effects from the lens. The noise measurement procedures for DSCs
having removable lenses or manual exposure control are described in 5.2 and 5.3, respectively.
On automatic exposure cameras having through-the-lens (TTL) exposure control and no manual exposure
control override capability, the test chart and measurement methods described in 5.4 shall be used.
5.1.2 Test densities
For the noise measurement procedures described in 5.2 and 5.3, a set of test densities shall be used to
provide signal levels to determine the camera OECF. The densities should correspond to the densities
of the patches from a test chart specified in ISO 14524. The density of the lightest patch shall provide
a signal level that is at or above the maximum unclipped level from the camera. The density of the
darkest patch should be greater than or equal to 2,0. If the density of the darkest patch is less than 2,0,
then a test density of 2,0 (1 % transmittance) shall be used to provide a “black reference” signal level to
determine the camera dynamic range.
© ISO 2017 – All rights reserved 5
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SIST ISO 15739:2018
ISO 15739:2017(E)
5.1.3 Adjustment of illumination, test density placement and camera lens focus
The light source and diffuser (where applicable) shall be adjusted to give the maximum unclipped level
from the camera. If necessary, an appropriate neutral density filter should be used to cover the camera
exposure control sensor in order to adjust the signal level to provide the maximum unclipped level
from the camera. In some circumstances, it may not be possible to reach the maximum unclipped level
due to the limitations in the resolution of the exposure adjustment or in the light source used. In this
case, expose the uniform field in such a way that the exposure is increased by the smallest possible step
from the exposure leading to the maximum unclipped level so that the output signal is “just clipped”.
Test densities (when used) shall completely cover the area exposed, when the camera lens is removed.
If the camera lens focus is adjustable, it shall be set to infinity.
5.2 Measurement of a DSC having a removable lens
5.2.1 General
This method involves the exposure of the DSC sensor directly to specific quantities of uniform
illumination with the lens removed. The illumination shall have the spectral characteristics specified
in 4.2 and shall be produced by a small source at a distance, such that the largest dimensions of the
source and the sensor are no greater than one twentieth of the distance between them, as shown in
Figure 1. Reflective surfaces shall not be placed where they could cause additional illumination to be
incident on the sensor.
Key
1 light source
2 test density
3 camera under test
4 lens removed
5 digital image sensor
Figure 1 — Illumination for cameras with removable lenses
5.2.2 The focal plane OECF shall be measured according to ISO 14524.
6 © ISO 2017 – All rights reserved
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SIST ISO 15739:2018
ISO 15739:2017(E)
5.3 Measurement of a DSC hav
...
INTERNATIONAL ISO
STANDARD 15739
Third edition
2017-05
Photography — Electronic still-picture
imaging — Noise measurements
Photographie — Imagerie des prises de vue électroniques —
Mesurages du bruit
Reference number
ISO 15739:2017(E)
©
ISO 2017
---------------------- Page: 1 ----------------------
ISO 15739:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 15739:2017(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test conditions . 3
4.1 General . 3
4.2 Illumination . 3
4.2.1 Characteristics . 3
4.2.2 Daylight illumination. 3
4.2.3 Tungsten illumination . 3
4.2.4 Uniformity of illumination and reflection test chart illumination geometry . 4
4.2.5 Light source amplitude variations . 4
4.3 Temperature and relative humidity . 4
4.4 White balance. 4
4.5 Infrared (IR) blocking filter. 4
4.6 Photosite integration time . 4
4.7 Colour noise weighting . 4
4.8 Compression . 5
5 Noise measurement procedures . 5
5.1 General . 5
5.1.1 Uniform field noise measurement methods . . 5
5.1.2 Test densities . 5
5.1.3 Adjustment of illumination, test density placement and camera lens focus. 6
5.2 Measurement of a DSC having a removable lens . 6
5.3 Measurement of a DSC having manual exposure control . 7
5.4 Measurement of a DSC using a test chart . 7
6 Calculation and reporting of results . 9
6.1 General . 9
6.2 Signal-to-noise ratios — large area . 9
6.3 DSC dynamic range .12
Annex A (normative) Noise component analysis .14
Annex B (normative) Visual noise measurements .18
Annex C (informative) Removing low frequency variations from the image data .27
Annex D (informative) Procedure for determining signal-to-noise ratio .29
Annex E (informative) Practical viewing conditions for various output media .30
Bibliography .31
© ISO 2017 – All rights reserved iii
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ISO 15739:2017(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.
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 on 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 the following
URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 42, Photography.
This third edition cancels and replaces the second edition (ISO 15739:2013), of which it constitutes a
minor revision with the addition of IEC 61966-2–1:1999 to Clause 2 and changes in Annex B.
iv © ISO 2017 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 15739:2017(E)
Introduction
Noise is an important attribute of electronic photographic systems. Camera noise measurements
described in this document are performed in the digital domain, using digital analysis techniques.
Since the noise performance of an image sensor may vary significantly with exposure time and
operating temperature, these operating conditions are specified. The visibility of noise to human
observers depends on the magnitude of the noise, the apparent tone of the area containing the noise
and the spatial frequency of the noise. The magnitude of the noise present in an output representation
depends on the noise present in the stored image data and the contrast amplification or gain applied to
the data in producing the output. The noise visibility is different for the luminance (or monochrome)
channel and the colour (or colour difference) channels. Therefore, this document accounts for these
factors in measuring and reporting the camera noise measurements. Annex A specifies the method for
determining the components of the digital camera noise from a number of samples. The perceptibility
of noise in an image can vary depending on the viewing distance, spatial frequency, density, colour
and viewing conditions. Annex B describes a procedure for measuring the visual noise level using a
human visual model as a method for weighting the spectral components of the noise. A method for
removing low frequency variations in the patch data resulting, for example, from luminance shading is
given in Annex C. A recommended step-by-step procedure for determining the signal-to-noise ratio and
incremental gain is provided in Annex D. In Annex E, recommendations for practical viewing conditions
for various output media are given.
© ISO 2017 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 15739:2017(E)
Photography — Electronic still-picture imaging — Noise
measurements
1 Scope
This document specifies methods for measuring and reporting the noise versus signal level and dynamic
range of digital still cameras. It applies to both monochrome and colour electronic digital still cameras.
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 554, Standard atmospheres for conditioning and/or testing — Specifications
ISO 7589:2002, Photography — Illuminants for sensitometry — Specifications for daylight, incandescent
tungsten and printer
ISO 12232:2006, Photography — Digital still cameras — Determination of exposure index, ISO speed
ratings, standard output sensitivity, and recommended exposure index
ISO 14524:2009, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic
conversion functions (OECFs)
ITU-R BT.709-5, Parameter values for the HDTV Standards for production and International programme
exchange
IEC 61966-2–1:1999, Multimedia systems and equipment — Colour measurement and management – Part
2-1: Colour management — Default RGB colour space — sRGB
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1
camera opto-electronic conversion function
camera OECF
relationship between the input scene log luminances and the pixel values for an opto-electronic digital
capture system
2.
Note 1 to entry: The unit of measurement for this function are log cd/m
10
3.2
clipping value
pixel value that remains constant for further increases in exposure (highlight clipping value) or for
further decreases in exposure (dark clipping value)
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ISO 15739:2017(E)
3.3
digital still camera
DSC
camera that produces a digital still image from the digitized output of a solid-state photo sensor and
records the digital still image using a digital memory, such as a removable memory card
3.4
image sensor
electronic device which converts incident electromagnetic radiation into an electronic signal
Note 1 to entry: A charge coupled device (CCD) array is an example of an image sensor.
3.5
incremental gain function
incremental gain
change in the pixel values of the DSC divided by the change in the exposure values
Note 1 to entry: For the determination of incremental gain values, log input values are not used.
Note 2 to entry: If the input exposure points are very finely spaced and the output noise is small compared to
the quantization interval, the incremental gain function can have a jagged shape. Such behaviour is an artefact
of the quantization process and is 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.
3.6
incremental output signal
exposure level multiplied by the incremental gain at that particular exposure level
3.7
incremental signal-to-noise ratio
ratio of the incremental output signal to the root mean square (rms) noise level, at a particular signal level
Note 1 to entry: This is typically expressed as a graph or table showing the incremental signal-to-noise ratio
versus input signal level for the full range of input signal levels.
3.8
DSC dynamic range
ratio of the maximum exposure level that provides a pixel value below the highlight clipping value to
the minimum exposure level that can be captured with an incremental signal-to-temporal-noise ratio
of at least 1, as determined in accordance with ISO 15739
3.9
noise
unwanted variations in the response of an imaging system
3.9.1
total noise
all the unwanted variations, consisting of pattern noise and temporal noise, of the values in the digitized
output captured by a single exposure
Note 1 to entry: The procedure in this document for calculating the total noise requires multiple frames.
3.9.2
fixed pattern noise
unwanted variations of the values in the digitized output which remain constant between exposures
3.9.3
temporally varying noise
unwanted variation in the values of the digitized output that changes from one exposure to the next
due to sensor dark current, photon shot noise, analogue processing and quantization
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3.10
noise spectrum
curve or equation which expresses the image noise as a function of two-dimensional image spatial
frequencies
3.11
focal plane opto-electronic conversion function
focal plane OECF
relationship between the input focal plane log exposures and the output pixel values for an opto-
electronic digital image capture system
Note 1 to entry: The units of measurement for this function are log lux seconds.
10
3.12
exposure time
total time period during which the photo sensor is able to integrate the light from the scene to form
an image
3.13
test density
spectrally non-selective transmittance filter used to reduce an input luminance to a predefined ratio of
the unfiltered luminance
4 Test conditions
4.1 General
The following measurement conditions should be used as nominal conditions when measuring the
noise of a DSC. If it is not possible or appropriate to achieve these nominal operating conditions, the
actual operating conditions shall be listed along with the reported results.
4.2 Illumination
4.2.1 Characteristics
The noise measurements shall indicate whether illumination conforming to the standard photographic
daylight or tungsten illuminant was used. ISO 7589 describes the procedures for determining if the
characteristics of the illumination used in a specific noise determination test are an acceptable match
to the standard photographic daylight and tungsten illuminants.
4.2.2 Daylight illumination
For daylight measurements without the camera lens, illumination conforming to the ISO sensitometric
daylight illuminant specified in ISO 7589:2002, Table 1 shall be used. This illuminant is defined as the
product of the spectral power distribution of CIE Illuminant D55 and the spectral transmittance of the
ISO standard camera lens. For measurements with the camera lens in place, the spectral characteristics
of the illumination shall conform to CIE illuminant D55.
4.2.3 Tungsten illumination
For tungsten measurements without the camera lens, illumination conforming to the ISO sensitometric
tungsten illuminant specified in ISO 7589:2002, Table 2 shall be used. This illuminant is defined as the
product of the average spectral power distribution of experimentally measured sources having a colour
temperature of approximately 3 050 K and the spectral transmittance of the ISO standard camera
lens. For measurements with the camera lens in place, the spectral characteristics of the illumination
shall conform to the average spectral power distribution of experimentally measured sources having a
colour temperature of approximately 3 050 K.
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4.2.4 Uniformity of illumination and reflection test chart illumination geometry
The illumination should meet the uniformity requirements of the measurement procedures described
in Clause 5. For reflection test charts, the sources are positioned so that the angular distribution of
influx radiation is at its maximum at 45° to the test chart normal, and is negligible at angles of less than
40° or more than 50° to the normal, at any point on the test chart.
Additional shielding of the camera may be necessary to prevent stray illumination from the light
sources, or from other reflections, entering the camera lens. The illuminance incident on reflection
charts, or the luminance used to illuminate transmission charts, shall not vary by more than 2 % from
the mean value over the surface area of the chart as defined in ISO 14524.
NOTE In particular, if a transmissive chart is used, light from the chart can reflect off the camera or camera
operator back to the surface of the chart and be imaged by the camera. Such reflections need to be avoided. This
can be accomplished by shrouding the camera with black cloth and having the operator stand in a position that
avoids such reflections.
4.2.5 Light source amplitude variations
The light source shall be fixed-level with combined short-term and supply amplitude variations of less
than ± 2 %.
4.3 Temperature and relative humidity
The ambient room temperature during the acquisition of the test data shall be 23 °C ± 2 °C, as specified
in ISO 554, and the relative humidity shall be 50 % ± 20 %. Additional measurements at 0 °C and 40 °C
are recommended. The normal camera operating temperature (internal rise above ambient) shall
be achieved before beginning the tests. If the ambient temperature varies throughout the room, for
example as a result of heat generated by light sources, the ambient room temperature shall be measured
at a distance of between 0,1 m and 0,2 m from the camera under test at the same height.
4.4 White balance
For a colour camera, the camera white balance shall be adjusted, if possible, to provide proper white
balance (equal RGB signal levels) for the illumination light source, as specified in ISO 14524.
4.5 Infrared (IR) blocking filter
If required, an infrared blocking filter shall be used, as specified in ISO 14524.
4.6 Photosite integration time
The photosite integration time should not be longer than 1/30 s.
4.7 Colour noise weighting
For colour cameras using a single exposure process, the camera noise may be determined using a
weighted sum of the colour outputs to derive the luminance. If the proper luminance weighting values for
the RGB channel spectral sensitivities are known, they shall be used to calculate the luminance channel
data. If these values are not known, the following weighting, given in ITU-R BT.709, shall be used:
Y = 0,212 5 R + 0,715 4 G + 0,072 1 B (1)
For colour cameras with luminance and colour-difference outputs, the standard deviation of the camera
noise may be computed from the luminance channel standard deviation σ (Y), the red minus luminance
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ISO 15739:2017(E)
channel standard deviation σ (R-Y) and the blue minus luminance channel standard deviation σ (B-Y).
Formula (2), as specified in ISO 12232:2006, 6.3.3, shall be used:
2 2 2 1/2
σ (D) = [σ (Y) + 0,279 σ (R-Y) + 0,088 σ (B-Y) ] (2)
NOTE The coefficients of the chrominance variances, σ (R-Y) and σ (B-Y), in Formula (2) were updated
in this document due to new coefficients being introduced in ISO 12232. The revision of the coefficients was
necessary due to a revised experimental procedure that indicated that the original values for the coefficients
[4]
overemphasized the contribution of chrominance noise to perception .
4.8 Compression
If the DSC includes any form of lossy compression, the compression shall be disabled, if possible, during
the noise measurements. If the compression cannot be turned off, then measurements should be taken
and the compression level reported with the noise measurement result, for example, the actual camera
switch setting (fine, standard, etc.) and the approximate average number of bits per pixel.
5 Noise measurement procedures
5.1 General
These measurement procedures shall be used to determine the noise, the midtone signal-to-noise ratio
and the dynamic range. The minimum requirement is to specify the midtone signal-to-total-noise ratio
and the dynamic range of the digital camera under test. In addition, the fixed pattern and temporal
noise components can be expressed individually. The measurement of visual noise defined in Annex B
shall not be performed and reported in place of the midtone signal-to-total noise ratio. It may, however,
be performed and reported together with the midtone signal-to-total-noise ratio.
NOTE The noise measurement procedures described in this document are intended to measure the temporal
and fixed pattern noise standard deviations spatially over the image. They do not take into account the variation
in the mean pixel value between individual frames captured by a DSC. This type of frame to frame variation in
mean pixel value can be introduced due to changes in ambient temperature, camera power supply or lighting
flicker. The illumination and temperature requirements specified in the standard will minimize these variations.
If it is required to include the effects of frame to frame variations in the calculation of temporal noise standard
deviation then the standard deviation of individual pixel values needs to be calculated across multiple frames.
5.1.1 Uniform field noise measurement methods
The method of measuring the uniform field noise will be dependent on the type of camera and its
level of exposure automation. If the camera lens can be removed, then the sensor noise level can be
measured without any shading effects from the lens. The noise measurement procedures for DSCs
having removable lenses or manual exposure control are described in 5.2 and 5.3, respectively.
On automatic exposure cameras having through-the-lens (TTL) exposure control and no manual exposure
control override capability, the test chart and measurement methods described in 5.4 shall be used.
5.1.2 Test densities
For the noise measurement procedures described in 5.2 and 5.3, a set of test densities shall be used to
provide signal levels to determine the camera OECF. The densities should correspond to the densities
of the patches from a test chart specified in ISO 14524. The density of the lightest patch shall provide
a signal level that is at or above the maximum unclipped level from the camera. The density of the
darkest patch should be greater than or equal to 2,0. If the density of the darkest patch is less than 2,0,
then a test density of 2,0 (1 % transmittance) shall be used to provide a “black reference” signal level to
determine the camera dynamic range.
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5.1.3 Adjustment of illumination, test density placement and camera lens focus
The light source and diffuser (where applicable) shall be adjusted to give the maximum unclipped level
from the camera. If necessary, an appropriate neutral density filter should be used to cover the camera
exposure control sensor in order to adjust the signal level to provide the maximum unclipped level
from the camera. In some circumstances, it may not be possible to reach the maximum unclipped level
due to the limitations in the resolution of the exposure adjustment or in the light source used. In this
case, expose the uniform field in such a way that the exposure is increased by the smallest possible step
from the exposure leading to the maximum unclipped level so that the output signal is “just clipped”.
Test densities (when used) shall completely cover the area exposed, when the camera lens is removed.
If the camera lens focus is adjustable, it shall be set to infinity.
5.2 Measurement of a DSC having a removable lens
5.2.1 General
This method involves the exposure of the DSC sensor directly to specific quantities of uniform
illumination with the lens removed. The illumination shall have the spectral characteristics specified
in 4.2 and shall be produced by a small source at a distance, such that the largest dimensions of the
source and the sensor are no greater than one twentieth of the distance between them, as shown in
Figure 1. Reflective surfaces shall not be placed where they could cause additional illumination to be
incident on the sensor.
Key
1 light source
2 test density
3 camera under test
4 lens removed
5 digital image sensor
Figure 1 — Illumination for cameras with removable lenses
5.2.2 The focal plane OECF shall be measured according to ISO 14524.
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5.3 Measurement of a DSC having manual exposure control
5.3.1 General
These measurements shall be used for all cameras that use manual exposure control, or exposure
control based on a separate exposure control sensor.
5.3.2 The camera OECF shall be measured according to ISO 14524.
5.3.3 The diffuser shall be uniform and close to the camera, preferably less than one tenth of the
minimum focus distance of the camera under test, to prevent diffuser blemishes from influencing
the noise measurements. The diffuser may be illuminated by either transmissive or reflective light
(see Figure 2).
Key
1 transmissive uniform fixed level light source
2 reflective uniform fixed level light source
3 diffuser
4 test density
5 camera lens
6 camera under test
7 camera exposure control sensor
8 digital image sensor
Figure 2 — Uniform field noise measurements
5.4 Measurement of a DSC using a test chart
5.4.1 General
These measurements shall be used for TTL automatic exposure cameras having no manual exposure
control override.
5.4.2 The camera OECF shall first be measured in accordance with ISO 14524.
5
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