Conditions for taking photographs for face image data

Conditions de prise de vues pour données d'image de la face

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Replaced
Publication Date
12-Dec-2007
Withdrawal Date
12-Dec-2007
Current Stage
6060 - International Standard published
Start Date
04-Dec-2007
Completion Date
13-Dec-2007
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ISO/IEC 19794-5:2005/Amd 1:2007 - Conditions for taking photographs for face image data
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INTERNATIONAL ISO/IEC
STANDARD 19794-5
First edition
2005-06-15
AMENDMENT 1
2007-12-15
Information technology — Biometric data
interchange formats —
Part 5:
Face image data
AMENDMENT 1: Conditions for taking
photographs for face image data
Technologies de l'information — Formats d'échange de données
biométriques —
Partie 5: Données d'image de la face
AMENDEMENT 1: Conditions de prise de vues pour données d'image
de la face
Reference number
ISO/IEC 19794-5:2005/Amd.1:2007(E)
ISO/IEC 2007
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ISO/IEC 19794-5:2005/Amd.1:2007(E)
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© ISO/IEC 2007

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ii © ISO/IEC 2007 – All rights reserved
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ISO/IEC 19794-5:2005/Amd.1:2007(E)
Contents Page

Foreword............................................................................................................................................................ iv

Introduction ........................................................................................................................................................ v

B.1 Scope ......................................................................................................................................................1

B.2 Photography recommendations...........................................................................................................2

B.2.1 Recommendations for a photo studio or store ..................................................................................2

B.2.2 Recommendations for photo booths...................................................................................................6

B.2.3 Recommendations for a registration office environment .................................................................9

B.3 Guidelines for printing ........................................................................................................................10

B.3.1 Spatial and tonal resolution trade-offs..............................................................................................11

B.3.2 Recommended printing quality..........................................................................................................11

B.3.3 Use of a photo template ......................................................................................................................12

B.4 Guidelines for scanning......................................................................................................................12

B.4.1 Sampling frequency and quantization levels....................................................................................13

B.4.2 Spatial resolution.................................................................................................................................13

B.4.3 Output colour space............................................................................................................................13

B.4.4 Saturation .............................................................................................................................................13

B.4.5 Image compression .............................................................................................................................13

B.5 Face image quality assessment software .........................................................................................13

B.6 Tables of the recommendations.........................................................................................................15

B.6.1 Scene setting........................................................................................................................................15

B.6.2 Photographing .....................................................................................................................................17

B.6.3 After photographing ............................................................................................................................18

B.6.4 Photographic quality ...........................................................................................................................19

B.7 Experimental data................................................................................................................................19

B.7.1 Experimental results of face recognition in a photo studio and photo booth ..............................19

B.8 Photographic examples ......................................................................................................................20

B.8.1 Photographic examples at a photo studio ........................................................................................21

B.8.2 Photographic examples at a photo booth.........................................................................................26

© ISO/IEC 2007 – All rights reserved iii
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ISO/IEC 19794-5:2005/Amd.1:2007(E)
Foreword

ISO (the International Organization for Standardization) and IEC (the International Electrotechnical

Commission) form the specialized system for worldwide standardization. National bodies that are members of

ISO or IEC participate in the development of International Standards through technical committees

established by the respective organization to deal with particular fields of technical activity. ISO and IEC

technical committees collaborate in fields of mutual interest. Other international organizations, governmental

and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information

technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of the joint technical committee is to prepare International Standards. Draft International

Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as

an International Standard requires approval by at least 75 % of the national 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 and IEC shall not be held responsible for identifying any or all such patent rights.

Amendment 1 to ISO/IEC 19794-5:2005 was prepared by Joint Technical Committee ISO/IEC JTC 1,

Information technology, Subcommittee SC 37, Biometrics.
iv © ISO/IEC 2007 – All rights reserved
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ISO/IEC 19794-5:2005/Amd.1:2007(E)
Introduction

This part of ISO/IEC 19794 is intended to provide a Face Image Format for face recognition applications

requiring the exchange of face image data. Its typical applications include:
a) Human examination of high resolution facial images;
b) Human verification of identity;
c) Computer automated face identification;
d) Computer automated face verification.

To enable applications on a wide variety of devices, including devices that have limited data storage, and to

improve face recognition accuracy, ISO/IEC 19794-5 specifies not only a data format, but also scene

constraints (lighting, pose, expression, etc.), photographic properties (positioning, camera focus, etc.), and

digital image attributes (image resolution, image size, etc.).

This part of ISO/IEC 19794 includes an informative annex, Annex A, entitled “Best practices for Face Images”.

Although Annex A provides guidance on topics such as subject pose and expression, image compression

ratio, color, geometric distortion, spatial resolution and head size, it does not guide photographers or the

designers and operators of photo booths concerning how, for example, they might arrange lighting and

reflective surfaces relative to the camera and subject. It also doesn’t provide specific advice on the acceptable

amount of variation in illumination across the face, on how to avoid shadows on the face or background, or on

a user interface that would ensure proper head positioning.

This Amendment is Annex B to ISO/IEC 19794-5 and is entitled “Conditions for taking photographs for face

image data”. It provides expert guidance for the design of photographic studios, photo booths and registration

offices and, as such, it supplements the information provided in this Part of ISO/IEC 19794. It also provides

guidance on printing quality and on scanning printed face photographs.
© ISO/IEC 2007 – All rights reserved v
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ISO/IEC 19794-5:2005/Amd.1:2007(E)
Information technology — Biometric data interchange
formats —
Part 5:
Face image data
AMENDMENT 1: Conditions for taking photographs for face image
data
Page 46
Add the following Annex after Annex A.
Annex B
(informative)
Conditions for taking photographs for face image data
B.1 Scope

The purpose of this annex is to provide expert guidance (i.e., best practices) for the photography of faces,

especially when the resulting images are to be used for purposes of identification, either by automated face

recognition systems or by human viewers. This guidance is intended for owners and operators of photography

studios, photo stores and other organizations producing or requiring either conventional printed photographs

or digital images of faces that may be used in applications for passports, visas, or other identification

documents and when those images are required to conform to the frontal image types of this part of

ISO/IEC 19794. This guidance is also intended for the designers and operators of photo booths, if those

booths are required to provide face images conforming to the specifications of this standard. This annex may

also be appropriate source material to application developers, application profile standard developers, or

others making more general use of this standard.

There are many factors that affect face recognition system performance, including the individual’s

appearance, such as his or her facial characteristics, hair style, and accessories, and the acquisition

conditions, such as the camera’s field-of-view, focus, depth-of-field, background, and lighting. The acquisition

conditions have, potentially, a greater influence on face recognition accuracy than the individual’s appearance

and, of course, are controllable by the preparer of the face images.

This annex provides recommendations for acquiring two-dimensional (2D) face images directly with an

analogue, digital, or video camera, as well as for image data acquired through traditional photo printing and

digital scanning. [The acquisition of three-dimensional (3D) images is out of the scope of this annex.]

This annex may also be appropriate source material for application developers, application profile standard

developers, or others making more general use of this standard.
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ISO/IEC 19794-5:2005/Amd.1:2007(E)
B.2 Photography recommendations

This clause provides recommendations for photographing (acquiring) face images in a portrait studio, photo

store, photo booth, registration office, or other facility. Guidance concerning the positioning of the subject and

camera is provided, as well as several examples of alternative lighting arrangements. The intent of this

guidance is to ensure that the subject’s face is properly positioned and uniformly illuminated, thereby

producing images that are compliant with this International Standard and are without shadows or hot spots on

the face or excessive glare in eyeglasses.
B.2.1 Recommendations for a photo studio or store

A photo studio or a photo store is typically a professionally operated facility, equipped with an analogue or

digital camera, multiple adjustable light sources, a suitable background or backdrop cloth, and subject

positioning apparatus designed to obtain high quality portraits. This section provides expert guidance for the

owners and operators of such facilities when they must produce photographs compliant with the requirements

of this standard.
B.2.1.1 Recommended positioning and distance between camera and subject

The following recommendations concern the positioning of the subject and the camera.

⎯ The camera-to-subject distance should be within the range of 1.2 to 2.5 m. Arranging the lighting without

creating shadows will likely be difficult if the camera is placed any closer to the subject.

⎯ Proper focus and depth-of-field will be assured by pre-focusing the lens at the distance of the subject’s

eyes and by selecting an appropriate aperture (F-stop) to ensure a depth-of-field of at least 10

centimetres, or approximately the distance from a subject’s nose to ears. The depth-of-field of a lens is

dependent upon its focal length, its effective aperture, and the focus distance. Point sources which are

closer or farther than the distance at which a lens is well focused will be blurred, with the extent of the blur

described by a “circle of confusion.” If the maximum diameter of the circle of confusion is limited by, for

example, the spacing between adjacent pixels in a CCD image sensor, the front and rear distances from

the plane of optimum focus that produce acceptably focused images can be determined. The sum of

these front and rear distances is the depth-of-field (D ).
DoF
D = D + D
DoF front rear
cFs(s− f )
D =
front
f + cF(s− f )
cFs(s− f )
D =
rear
f − cF(s− f )
where :
D = the front focal distance, the distance from the plane of focus
front
to the plane closest to the lens that is still in acceptable focus,
D = the rear focal distance, the distance from the plane of
rear

focus to the plane farthest from the lens that is still in acceptable focus,

c = the diameter of the circle of confusion,
s= the distance from the lens to the object plane (subject's face), and
F= f/a is the F - stop, the lens focal length f divided by the effective lens
aperture a
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ISO/IEC 19794-5:2005/Amd.1:2007(E)
Figure B.1 illustrates these dimensions.
Object
Image
Plane
Plane
Lens
D D
rear front
DoF
Figure B.1 — Dimensions for depth-of-field calculations

• The optimum height of the camera is at the subject’s eye-level. Height adjustment can be done by

either using a height-adjustable stool or adjusting the tripod’s height.

• The subject should be instructed to look directly at the camera and to keep his or her head erect and

shoulders square to the camera. The rotation of the head should conform to the requirements of 7.2.2.

less than +/- 5º
Camera
1.2 - 2.5m
Side view
Figure B.2 — Preferred distance and alignment of camera and subject
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ISO/IEC 19794-5:2005/Amd.1:2007(E)
B.2.1.2 Example of exposure metering at various spots on a subject

The figure below illustrates exposure value (EV) measurement at four spots on a subject’s face, namely the

left and right cheeks, forehead, and chin. The measurements may be made by placing an incident light meter

at the position of a subject’s face and pointing the meter towards the camera. The four readings should be

within 1 EV of one another. If they are not within 1 EV, the lights should be repositioned more symmetrically

about the subject-to-camera line.
Figure B.3 — Positions of incident light meter for exposure value measurement

EV is the value given to any combination of shutter speed and aperture (F-stop) that results in the same

exposure. By definition, an EV value of 0 corresponds to a shutter speed of 1 second and an aperture of F1.0,

for a film speed or equivalent image sensor sensitivity of ISO 100. EV is defined by the following equation:

⎛ ⎞
⎜ ⎟
EV= Log = 2Log (F)− Log (T) ,
2 2 2
⎜ ⎟
⎝ ⎠

where F is the F-stop setting and T is the exposure time. A change of 1 EV corresponds to a one F-stop

aperture increase or decrease or a halving or doubling of the exposure time.
B.2.1.3 Example configurations for a photo studio or store

Described below are three examples of lighting and subject and camera positioning that are applicable to

photographic studio businesses, as well as for some photofinishers that might offer identification photographs,

in addition to their main business of material sales and film developing and printing. Example 1 is a single-light

arrangement in which the placement of a panel of reflective material is used to provide more balanced lighting.

Example 2 is a two-light arrangement with a lower reflective panel providing illumination to the region under a

subject’s chin. Example 3 is the same as Example 2, but with a third light behind the subject to eliminate

shadows on the background material. Several recommendations for camera and subject positioning are also

provided below.
B.2.1.3.1 Example 1: Proper lighting arrangement with a single light

In this arrangement, illustrated in Figure B.4, a single light and multiple reflector panels are employed to

illuminate the subject’s face uniformly. The light, shown with a lamp reflector, should be placed approximately

35 degrees above the line between the camera and the subject and be directed toward the subject’s face at a

horizontal angle of less than 45 degrees from the line. A reflector panel should be placed on the subject’s

opposite side to prevent shadows on the face. As an option, an additional reflector may be placed below and

in front of the subject’s face to illuminate the area around the chin.
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Grey background
Grey background
Grey background
Grey background
ISO/IEC 19794-5:2005/Amd.1:2007(E)
Lamp Lamp
Light Light
reflector reflector
Side reflector
Less than 45º
panel
Camera
35º
Camera
Plane
reflector
Plane
reflector
Tripod
Side reflector
panel
1.2 - 2.5m
Top view
Side view
Figure B.4 — Lighting arrangement for a photo studio with a single front light
B.2.1.3.2 Example 2: Proper lighting with dual lights

In the second example illustrated in Figure B.5, two lights are employed. The lights, shown with lamp

reflectors, should be placed approximately 35 degrees above the line between the camera lens and the

subject. Both lights should be placed within 45 degrees of the line between the camera lens and the subject.

Such an arrangement softens the edge of shadows and makes the lighting on the subject more even. The

optional plane reflector in front of the subject supplies additional light around and below the subject’s chin.

Main light Main light
Lamp
reflector
Front light
Lamp
less than 45º
reflectors
Camera
35º
Camera
Plane
Plane
reflector
Tripod
reflector
Lamp
reflector
Front light
1.2 - 2.5m
Side view Top view
Figure B.5 — Lighting arrangement for a photo studio with dual front lights
B.2.1.3.3 Example 3: Proper lighting with dual lights and background lighting

The use of a background light added to the arrangement shown previously in Example 2 should eliminate

shadows visible on the background behind the face. As illustrated in Figure B.6, the background light should

be aimed at the background and be placed directly behind and below the subject.
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Grey background
Grey background
ISO/IEC 19794-5:2005/Amd.1:2007(E)
Main light
Lamp
Lamp Main light
reflector
Front light
reflector
30 - 45º
Camera
Camera
Plane
Back-
reflector
Plane
Tripod
ground
reflector
light
Back-
Lamp
ground Front light
1.2 - 2.5m
reflector
light
Side view Top view

Figure B.6 — Lighting arrangement for a photo studio with dual front lights and a background light

B.2.2 Recommendations for photo booths

A photo booth is typically a coin-operated, self-portrait photography unit, mostly used for taking ID pictures

and equipped with such tools as a camera, lighting, stool, plain background, printing device and monitoring

screen, and sometimes including an audio self-guidance application. Optimizing photographic technology

enabled its space-saving size, which has contributed to its widespread use around the world. Following are

some guidelines for the design and operation of such photo booths. Front, side, and top views of the

arrangements described in the guidelines are provided. Also provided in this clause are suggestions for

camera and subject positioning and a description of methods to provide feedback to the subject concerning

his or her pose and expression.
B.2.2.1 Proper lighting

⎯ Position multiple lights behind a diffuser panel and symmetrically above the camera. This will provide

even lighting on the subject’s face and eliminate most glare and shadow problems. Place a background

light low and midway between the background and the subject.

⎯ The placement of the front lights 35 degrees above the line between the camera and the subject's head

prevents direct reflection of the flash from a subject’s glasses.

⎯ The inside walls should be white, except directly behind the subject. The white walls serve as reflectors

and ensure that lighting on the face is uniform horizontally and vertically.

⎯ The interior lights of the booth should be left on during operation. This will usually eliminate red-eye

problems associated with photography in dim light.

⎯ To eliminate unwanted shadows around the chin caused by lights above the subject, direct or indirect

lighting from below and in front of the subject should be used.

⎯ To ensure that the booth is free from the effects of external light, an opaque curtain should be employed.

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Grey background
Grey background
ISO/IEC 19794-5:2005/Amd.1:2007(E)
B.2.2.2 Example configuration for a photo booth
Room light
White inner
walls
Lamp reflectors
Lights
Face positioning frame
Background
Adjustable height light behind
stool subject
Front view
White inner
walls Room light
About
Lamp reflector
35º
Lights
Camera
Face positioning
frame
Background
light
Revolving
Light
stool
Side view
0.7 – 1m
Less than
45º
Light
Camera
Light
Top view
Background
Lamp
light
reflector

Figure B.7 — Recommended placements of subject, camera, and lights in a photo booth

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ISO/IEC 19794-5:2005/Amd.1:2007(E)
B.2.2.3 Camera-subject positioning

Proper positioning of the subject and control of the subject’s pose can be improved through feedback provided

to the subject via a mirror or a live-video monitor.

• A display device should be installed in the booth to provide a live image of the subject on the

wall he or she faces. The device could be a one-way (half-silvered) mirror or a left-right reversed

live-video monitor. The display should contain a frame which the subject can use to ensure that

his/her entire head is fully visible, that his/her eyes are at the correct height, and that his/her face

is centered in the camera’s field-of-view. Such a frame is illustrated in the following diagram.

• A height-adjustable chair or stool should be provided to allow the subject to face the camera and

adjust his eyes to the proper height.
• Camera-to-subject distance is generally within 0.7-1.0 m.
Confirming position Confirming position Confirming position
frame example 1: frame example 2: frame example 3:
Outer indicator lines Inner indicator lines Inner indicator frame
Centre line
Centre line
Frame for
Eye Eye
face size
position position
and
line line
position
Height-
adjust-
able
stool
Mirror or video Mirror or video Mirror or video
image image image
Figure B.8 — Use of a display frame for head positioning
B.2.2.4 Adjustment of size, expression, etc. by monitor-GUI

• An image preview should be provided to allow a subject to recapture the image before it’s

printed or written to a storage medium, in case a subject might deem his/her pose or expression

unacceptable. Illustrations of acceptable poses and expressions should be provided inside the

booth.

• The size of the head in the image should be adjustable before printing or storage by allowing the

subject to identify the positions of his/her crown and chin in a preview image. The system would

then scale and crop the image accordingly. An illustration of such a preview image is provided in

figure B.9.

• Alternatively, face detection software that automatically sizes and centers the head within the

field-of-view can be used to ensure proper head positioning. Given that such software

sometimes does not determine the face position correctly, a preview image should be provided

with provision for manual override of the automatically determined position.
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ISO/IEC 19794-5:2005/Amd.1:2007(E)
A repositionable
horizontal line to indicate
the top of the head
A repositionable
horizontal line to indicate
the bottom of the chin
Figure B.9 — Use of movable horizontal lines to set head size
B.2.3 Recommendations for a registration office environment

One of the major application areas of this standard is the use in the context of identity cards and especially

Machine Readable Travel Documents (MRTDs). In this domain, images of applicants are either supplied by

the applicant or taken in a “live enrolment scenario” in the registration office. For the first case, subclauses

B.2.1 and B.2.2 apply. In contrast, this subclause focuses on the recommendations for live enrolment in a

registration office environment, where lack of space often is a major concern. Nonetheless, image quality

should be as close as possible to that achieved through the recommendations provided previously for the

photo studio or photo booth, particularly for MRTDs.
B.2.3.1 Proper lighting

In the best practice arrangement for the Registration Office Environment illustrated in Figure B.10 the subject

and the background are illuminated by two diffuse light sources that are mounted in a console with a small

footprint, so that it fits into a typical registration office environment. The console can be mounted on the floor

or on the wall. Synchronized flash type illumination should be used for these light sources to enable high

shutter speed and, thereby, avoid blur caused by a subject's motion. Direct lighting from the sun should be

prevented in the office by proper means, e.g., by using curtains or roller blinds.

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ISO/IEC 19794-5:2005/Amd.1:2007(E)
Figure B.10 — Recommended placements of subject, camera, and lights
in a registration office environment
B.2.3.2 Camera-subject positioning

• Proper positioning of the subject and control of the subject’s pose can be improved through feedback

via a second live-video monitor facing to the subject. An image preview should be provided to allow a

subject to be recaptured before the image is submitted for further processing, in case a subject might

deem his/her expression unacceptable.

• A revolving and height-adjustable chair or stool with an additional cushion for little children should be

provided to allow the subject to face the camera and adjust his eyes to the proper height.

• Camera to subject distance is generally within 0.5 to 1.0 meter.
B.2.3.3 Operator support

• Proper positioning of the subject and control of the subject’s pose can be improved through feedback

to the operator via a live-video monitor showing the face of the subject during the acquisition process.

An image preview should be provided to allow the subject to be recaptured before the image is

submitted for further processing, in case the operator might deem the pose or expression

unacceptable.

• To further improve the process and before the image is further processed, the operator should

approve the quality of the image. This can be done with the support of face image quality assessment

software,
...

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