ISO 15781:2013
(Main)Photography — Digital still cameras — Measuring shooting time lag, shutter release time lag, shooting rate, and start-up time
Photography — Digital still cameras — Measuring shooting time lag, shutter release time lag, shooting rate, and start-up time
ISO 15781:2013 specifies how to measure and report the shooting time lag, shutter release time lag, shooting rate and start-up time for digital still cameras, including camera modules in phones and tablet computers. It includes a method that uses control signals inside the digital still camera and a method that determines the timing values without requiring access to the inside of the digital still camera.
Photographie — Caméras numériques — Déacalage dans le temps du mesurage de la prise, décalage dans le temps de l'ouverture de l'objectif, cadence de prise et temps de démarrage
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 15781
First edition
2013-02-15
Photography — Digital still cameras —
Measuring shooting time lag, shutter
release time lag, shooting rate, and
start-up time
Photographie — Caméras numériques — Déacalage dans le temps
du mesurage de la prise, décalage dans le temps de l’ouverture de
l’objectif, cadence de prise et temps de démarrage
Reference number
ISO 15781:2013(E)
©
ISO 2013
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ISO 15781:2013(E)
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© ISO 2013
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ISO 15781:2013(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test conditions . 2
4.1 Illumination of the test scene . 2
4.2 The chart and positioning of the digital still camera . 3
4.3 Battery status . 4
4.4 Memory card . 4
4.5 Flash . 4
5 Measurements . 4
5.1 Definition of measurement. 4
5.2 Measurement method . 6
6 Reporting the results . 9
Annex A (informative) Test results of methods to start the timing device .10
Annex B (informative) Timing device .12
Annex C (informative) Measurement by internal method .16
Annex D (informative) Examples of reporting the result .23
Bibliography .25
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ISO 15781:2013(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.
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 15781 was prepared by Technical Committee ISO/TC 42, Photography.
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ISO 15781:2013(E)
Introduction
Taking pictures of a moving target was nearly impossible in the early days of digital photography. After
pressing the exposure button it took a significant amount of time to capture the image and the chance to
preserve the desired moment was gone.
Part of the time between pressing the exposure button and the exposed picture is needed to focus,
another part is needed to adjust the exposure, etc. This unwelcome but unavoidable period of time is
called shooting time lag. This is often mixed with the term shutter release time lag, which is also
defined in this International Standard. Optimized systems are nowadays able to decrease these time lags.
Capturing the different stages of a fast moving object is sometimes very important especially in areas like
sports or people photography. This high shooting rate requires a fast image processing within the digital
still camera that can be measured according to the method described in this International Standard.
When a photographer decides to capture an image of a changing scene, if his or her digital still camera
takes a long time to be ready to shoot once it is turned on, the opportunity to capture the image is lost.
This time named start-up time is therefore another important value, which can be determined using
this International Standard.
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INTERNATIONAL STANDARD ISO 15781:2013(E)
Photography — Digital still cameras — Measuring
shooting time lag, shutter release time lag, shooting rate,
and start-up time
1 Scope
This International Standard specifies how to measure and report the shooting time lag, shutter release
time lag, shooting rate and start-up time for digital still cameras, including camera modules in phones
and tablet computers. It includes a method that uses control signals inside the digital still camera and a
method that determines the timing values without requiring access to the inside of the digital still camera.
Depending on the method used to start the timing device, there may be a time lag between the activation
of the timing device and the closure of the exposure switch of the digital still camera.
This International Standard does not address the measurement of auto focus accuracy and speed at low
light conditions.
For digital still cameras that continuously shoot images into the buffer, the exposure button only acts as
a selector of an image that was taken before the exposure button was pressed. The methods to measure
shutter time lag and shooting time lag do not address this case and cannot be used for this type of digital
still camera.
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 7589, Photography — Illuminants for sensitometry — Specifications for daylight, incandescent
tungsten and printer
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
digital still camera
device which incorporates an image sensor and produces a digital signal representing a still picture
Note 1 to entry: A digital still camera is typically a portable, hand-held device. The digital signal is usually recorded
on a removable memory, such as a solid-state memory card or magnetic disk.
Note 2 to entry: This term is also defined in ISO 12231, ISO 12232, ISO 15739 and ISO 17321-1.
3.2
shooting time lag
time between pressing the exposure button (firmly depressing the shutter button to the maximum
extent without introducing a discontinuity) on a digital still camera or a module built into a mobile
device and the beginning of the exposure
Note 1 to entry: This period of time includes all measurements and adjustments (e.g. auto focus and exposure
control) a digital still camera needs to make prior to the beginning of the exposure.
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ISO 15781:2013(E)
Note 2 to entry: When the exposure button of a digital still camera is pressed it performs a number of time-
consuming measurements and adjustments, e.g. determination of the exposure and focus adjustment. The time
needed for these procedures is part of the shooting time lag.
3.3
shutter release time lag
time duration to the time of starting the exposure from the time of fully pressing down the shutter
button after having stabilized the focus operation due to half pressing of the shutter, in case of digital
still cameras that distinguish between the half pressing and the fully pressing
Note 1 to entry: Instead of shutter release time lag, the terms shutter lag and release lag are used in some
publications.
3.4
start-up time
time between switching a digital still camera on and the moment the camera has reached a standby
state ready to shoot
Note 1 to entry: It excludes the initialization of a memory card.
3.5
shooting rate
reciprocal of the time between the beginning of the exposure of an image until the beginning of the
exposure of the next image
3.6
standby state
state achieved following the power-up process, in which a digital still camera is powered on and ready
to capture an image
Note 1 to entry: If the digital still camera uses an electronic viewfinder, a preview image is normally displayed
during the standby state.
3.7
pre-capture point
position of a user control of a digital still camera which activates pre-capture processes, such as auto-
focus and exposure calculation
Note 1 to entry: The pre-capture point is typically reached by pressing an exposure button roughly halfway down.
3.8
capture point
position of a user control of a digital still camera which activates the image capture operation
Note 1 to entry: The capture point is typically reached by fully depressing the exposure button.
4 Test conditions
4.1 Illumination of the test scene
The illumination level of the shooting area including the test chart should be even and above 500 lx
and below 5 000 lx. The test scene shall be illuminated in a way that avoids specular reflection (see
Figure 1). This can be achieved by using a geometry typical for reproduction photography, which means
positioning the light sources in approximately a 45° angle to the surface of the chart. The illumination
level of the area shall be reported together with the measurements.
Timing measurements shall be performed under daylight conditions or a tungsten lamp. Procedures
for determining whether the illumination used for OECF measurements is an acceptable match to the
daylight illuminant shall be conducted in accordance with ISO 7589.
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calibrated spectral photometer
test chart
light source tungsten
of iltered to D55
Figure 1 — Principle for illuminating the target
4.2 The chart and positioning of the digital still camera
The digital still camera shall be mounted on a solid stand (e.g. heavy tripod) perpendicular to and facing
the surface of the chart (see Figure 2).
As for a test chart, the chart shall allow the digital still camera to focus easily and allow an easy
determination whether the captured image is correctly focused. Examples include a black-and-white
checker board or the three-line chart shown in informative Annex B. If the above condition is met, a
typical image assessment chart may be used. Also, the ISO 12233 resolution chart may be placed in the
chart area to determine whether the captured images are in focus.
The height of the chart shall be 80 (±10) cm and the distance to the chart shall be adjusted in a way that
the height of the image is in accord with the chart height.
The surround areas should be filled with a reflective area of 18 % neutral grey. Prior to the measurement,
the digital still camera shall be checked to see if it correctly focuses on the chart. If not, the correct focus
shall be obtained by changing the chart or the illumination condition. If different setup conditions are
required when the focal length of the lens is extremely long or short, these setup conditions shall be
reported together with the measurement results.
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Figure 2 — Chart and positioning
4.3 Battery status
A secondary battery should always be fully charged and a primary battery should always be a new one
prior to performing the measurements in order to avoid inconsistent measurements caused by varying
power supply. For cameras that support an AC power supply, the AC power supply should be used.
4.4 Memory card
For digital still cameras that support connection to an external memory card, a card with a sufficient
capacity that does not interfere with the test shall be used. The card shall be initialized and formatted
in the camera. After formatting the card, it shall remain in the digital still camera.
If the digital still camera only has the internal memory, all images should be deleted by initializing the
memory prior to the measurement.
4.5 Flash
If the flash is used to perform the measurements, it shall be reported together with the results.
5 Measurements
5.1 Definition of measurement
5.1.1 General
This International Standard defines two measurement methods. The first method is the “external
measurement” method, which can be performed without disassembling the digital camera. The
second method is the “internal measurement” method, which requires the camera body to be partially
disassembled, in order to perform measurements using electrical signals inside the camera body. The
first method is the preferred method for measurements made by users of digital cameras. The second
method is the preferred method for measurements made by digital camera manufacturers.
NOTE 1 Figures 3, 4, and 5 show the periods of time to be measured.
NOTE 2 “Procedure related to the pre-capture point” means the procedure by which the digital still camera
measures the light intensity and distance, determines the exposure, and adjusts the focus when the pre-capture
point switch of the digital still camera is pressed.
NOTE 3 “Procedure related to the capture point” means the procedure by which the digital still camera processes
the image captures and preparation of the image storage when the capture point switch of the camera is pressed.
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Figure 3 — Measurement period for start-up time
Figure 4 — Measurement period for shooting time lag and shutter release time lag
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Figure 5 — Measurement period for shooting rate
5.1.2 External measurement
The external method of measurement is performed without disassembling the camera with the
advantage that the measurement can be performed on the product level. Specifically, for instance,
the measurement can be performed shooting a timing device that can determine a time interval from
captured images. An example of this method is shown in informative Annex B.
When using the external measurement the acceptable level of the time lag between pressing the
exposure button and activating the timing device is application dependent and needs to be considered
prior to performing a test and the estimated error caused by this time lag shall be reported together
with the results (see Annex B). A test was performed using different approaches and the results are
shown in informative Annex A.
5.1.3 Internal measurement
Internal measurement is a method which directly measures a time interval between input signals and
device control signals and involves disassembling the camera. This allows the operational timing to be
surely obtained and has the advantage that the measurement can be performed accurately and stably.
However, camera manufacturers usually use this method because it is very difficult for parties other
than camera manufacturers to disassemble the camera and select and measure the device control
signals. An example of this method is shown in informative Annex C.
5.2 Measurement method
5.2.1 Start-up time
The digital still camera shall be switched on and set to record mode. Every setting that requires additional
time when switching the camera on (e.g. playing an intro sound) shall be tuned off, and the camera shall
be focused on the timing device before it is switched off again. Start the measurement when the power
switch is turned on again. The measurement value shall be an average of at least 10 measurements.
The digital still camera shall not be disconnected from the power supply until the test is finished. The
measurement results and conditions shall be reported according to the description in Clause 6.
For camera modules in mobile devices the starting point for turning the camera function on is the phone
mode or regular operation mode of the device. If it is necessary to enter one or multiple menus to start
the camera module, this time shall be integrated in the reported start-up time.
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When using the external measurement, the timing device shall electronically be connected to the power
switch or the power supply of the camera, if possible. The accuracy of the timing device for measuring
the start-up time shall be at least 0,1 s (the sampling shall be 0,01 s). If the timing device is started
manually all measured values < 0,5 s shall be reported as 0,5 s and the fact of the manual activation
shall be reported together with the result. When the power switch is turned on, the timing device shall
be started. A picture of the chart (object) shall be taken immediately after the shutter release becomes
active after turning the camera on.
If the shooting images can only be checked through an optical viewfinder, or if the initial setting of the
product is “image display device off” in a digital still camera that consists of both an optical viewfinder
and an image display unit, the time elapsed from operating the power switch until the beginning of the
exposure of the first image, minus the shooting time lag determined from the second image, shall be
called the start-up time.
TT=−T (1)
SS0 L
where
T is start-up time;
S
T is time elapsed from operating the switch until the beginning of the exposure of the first image;
0
T is shooting time lag.
SL
However, in the case where the shooting image cannot be checked through an optical viewfinder, or if
the initial setting of the product is “image display device on” in the camera with both optical viewfinder
and image display unit, the time between switching the power on and the moment the viewfinder image
(through-image) is displayed shall be measured.
When using the internal measurement, suppliers as shown in informative Annex C shall directly observe
appropriate signals, and the time defined in 5.1.1 shall be measured.
5.2.2 Shooting time lag
Prior to each measurement of the shooting time lag, the digital still camera shall be turned to face a
distant object and shall focus on this object. The elapsed time between turning the camera on the stand
and pressing the exposure button shall be less than 3 s.
The distant object shall be located at a distance of at least 100 times the focal length of the camera lens,
or 5 m, whichever is greater.
For products that allow manually focusing to infinity, this option may be used. The focus point can also
be set to infinity using a collimator.
The shooting time lag, T , shall be measured by turning the digital still camera to face the chart and
SL
by fully pressing the exposure button with continuous auto focus turned off. In the case of the external
measurement, the time between starting the timing device and the first illuminated time indicator in
the correct focused image is the shooting time lag. If the image is clearly out of focus it shall not be
used to measure the shooting time lag because in this case the camera may trade the focus accuracy
for higher speed (shutter priority) and the image of the timing device is blurred and unable to show the
correct timing. For cameras that do not deliver sharp images when pressing the exposure button fully,
the digital still camera shall be allowed to focus by first pressing the exposure button halfway down;
immediately after the camera indicates that it is in focus, the exposure button shall be fully pressed. The
timing device shall be started when the exposure button is pressed halfway down and the fact that the
digital still camera did not focus correctly without this manual adjustment shall be reported together
with the results.
In the case of the internal measurement, appropriate signals shall be directly observed as shown in
informative Annex C, and the time period defined in 5.1.1 shall be measured.
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The reported shooting time lag shall be an average of at least 10 measurements shot in a row right after
the previous image has been stored to the storage media and without switching the camera off.
If the measured time is significantly shorter or longer for the first of the 10 images, the measurement
shall be repeated. If the same results occur, values for the first and the following exposures shall be
reported separately.
The measurement results and conditions shall be reported according to the description in Clause 6.
5.2.3 Shutter release time lag
The shutter release time lag shall be measured using the same requirements for the shooting time lag
except that the timing device shall be started after the digital still camera is facing the chart (object)
and is in focus. The measurement results and conditions shall be reported according to the description
in Clause 6.
5.2.4 Shooting rate
The shooting rate should be measured with the camera set to the highest pixel count available in the
camera and the highest image quality (e.g. lowest JPEG compression) available. However, any other
setting may be used and the setting shall be reported along with the measurement results. The camera
shall be positioned as described in 4.2 and correctly focused on the target. To achieve the highest
frequency possible, the digital still camera shall be set to burst mode (if it exists), and the exposure time
shall be 1/100 of a second or less (if adjustable). If the camera does not allow setting mode and exposure
time, the measurement shall be performed using the default setting.
A set of the images should be taken with the camera by keeping the exposure button pressed until the
shooting rate slows significantly down. The reciprocal of the time elapsed from the beginning of the
exposure for one image and the beginning of the exposure of the next image is the value of the shooting
rate. If the shooting rate changes significantly during the test, the number of exposures possible at the
used mode shall be reported along with the value of the shooting rate.
NOTE Digital still cameras often shoot several images at a constant frequency at the beginning of capturing
a series of images. In case the buffer memory fills up because the camera is not able to process and transfer the
images to the storage medium fast enough, the frequency decreases after the memory is full. This is the point
where the camera noticeably slows down.
The shooting rate shall be reported as the mean value for all images taken until the camera begins
to slow down.
n− 11
f = = (2)
tt− T
()
np1
where
f is image frequency;
n is the number of the last image before the camera begins to slow down;
t is the time from the start until the beginning of the exposure for a specific image;
T is the arithmetic mean of the measured value for n intervals from the beginning of the exposure
p
for one image until the beginning of the exposure for the next image.
The measurement results and conditions shall be reported according to the description in Clause 6.
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6 Reporting the results
The results of the timing values described in this International Standard depend on several camera
settings as well as surrounding conditions. Therefore, these camera settings and surrounding conditions
shall be managed enough during the measurement and they shall be reported with the results. In
some cases, however, simpler presentation without complete description on the camera settings or the
surrounding conditions may be used. An example is specification notes in a catalogue for the end users.
The results of measurements should be reported with at least two significant digits. When the shooting
time lag and start-up time is less than one second, the shutter release time lag is less than 10 ms or the
shooting rate is less than one image per second, the results may be reported with one significant digit.
A complete report of the results shall contain all the necessary information in order to reproduce the
measurement. In particular, the following shall be recorded:
— measurement method used;
— identification of the measured product, e.g. product type, serial number, firmware version,
information on the used lens;
— identification of the used memory card, e.g. card specifications, memory size;
— any special environmental conditions in which the test was performed, e.g. illumination of the test
scene, subject distance, special setup conditions;
— any specific conditions necessary to enable the test to be performed, e.g. power supply;
— any operating states of the camera necessary to enable the test to be performed, e.g. number of
recorded pixels, image quality, capture mode (e.g. portrait, sports), focal length, focus mode (e.g.
high speed), flash usage.
An example of a test report with information to report and associated values are given in informative
Annex D.
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Annex A
(informative)
Test results of methods to start the timing device
To find out about the time lag between the actuation of the timing device and the closure of the exposure
switch (activated by the exposure button) of the digital still camera, an experiment has been performed
using several real cameras (see Figure A.1).
A modified version of the timing device mentioned in B.2 has been used. This version used one input for
the micro switch to start the device and a second input that was connected to the exposure button of
the sample camera as a stop signal. This way the time lag between the two signals could be measured.
A positive value in Table A.1 means that the micro switch was ac
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