ISO 15739:2013

INTERNATIONAL ISO
STANDARD 15739
Second edition
2013-06-15
Photography — Electronic still-picture
imaging — Noise measurements
Photographie — Imagerie des prises de vue électroniques —
Mesurages du bruit
Reference number
ISO 15739:2013(E)
©
ISO 2013

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ISO 15739:2013(E)

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© ISO 2013
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Published in Switzerland
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ISO 15739:2013(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
4.3 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
5.2 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) Recommended procedure for determining signal to noise ratio .29
Annex E (informative) Recommended practical viewing conditions for various output media .30
Bibliography .31
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ISO 15739:2013(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. 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. 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.
The committee responsible for this document is ISO/TC 42, Photography.
This second edition cancels and replaces the first edition (ISO 15739:2003), which has been
technically revised.
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ISO 15739:2013(E)

Introduction
Noise is an important attribute of electronic photographic systems. The camera noise measurements
described in this International Standard 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 International Standard 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.
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INTERNATIONAL STANDARD ISO 15739:2013(E)
Photography — Electronic still-picture imaging — Noise
measurements
1 Scope
This International Standard 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, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
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
CIE 15:2004, Colorimetry, 3rd edition
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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
Note 1 to entry: The units of measurement for this function are log candelas per square metre.
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)
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
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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 International Standard 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
3.10
noise spectrum
curve or equation which expresses the image noise as a function of two-dimensional image spatial frequencies
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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 Table 1 of ISO 7589:2002 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 Table 2 of ISO 7589:2002 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.
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
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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 14524:2009.
NOTE In particular, if a transmissive chart is used, light from the chart may 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 = 0,2125 R + 0,7154 G + 0,0721 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 15739:2013(E)

channel standard deviation σ (R-Y) and the blue minus luminance channel standard deviation σ (B-Y).
The following Formula (2), as specified in 6.3.3 of ISO 12232:2006 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 International Standard due to new coefficients being introduced in ISO 12232:2006. The revision
of the coefficients was necessary due to a revised experimental procedure that indicated that the original
[4]
values for the coefficients 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 International Standard 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 may 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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ISO 15739:2013(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.
2
5
1
43
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).
2
3
5
4
8
1
7
6
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.
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5.4.3 For a camera that generates 8-bit per channel sRGB encoded signals, as defined in IEC 61966-2-1,
the light source should be adjusted to give a pixel value equal to 118 from the background of the centre
portion of the OECF test chart defined in ISO 14524:2009. The test chart background shall be rendered to
a pixel value of not less than 110 and not greater than 130.
If the camera is unable to deliver a pixel value in the range specified above, for example due to automatic
exposure control, then the transmittance (or reflectance) of the central portion of the OECF may be
varied. For a transmissive chart, the central portion of the chart may be replaced by a neutral density
(ND) filter. For a reflective chart a ND reflectance patch may be placed over the central portion of
the chart. The transmittance (reflectance) of the filter (patch) is initially selected to approximate the
transmittance (reflectance) of the chart background. If the chart background level exceeds 130 a lower
density ND filter (higher reflectance patch) is selected. The automatic exposure control system of the
camera will select a lower exposure level to compensate for the increase in light from the chart. This
will result in a lower chart background level. Note that the chart background level is measured from
the original background area of the test chart and not from the replacement ND filter. If the camera
is still unable to deliver a pixel value in the specified range, then it shall be reported that the camera
was unable to deliver the required test chart level and the pixel value of the chart background that was
delivered shall be reported.
For a camera that generates signals in other colour encodings the light source should be adjusted to
give an output pixel value equal to the encoding values that correspond to a perceptual midtone for the
background of the OECF test chart. The perceptual midton
...