Information technology -- Automatic identification and data capture techniques -- Optical Character Recognition (OCR) quality testing

ISO/IEC 30116:2016 - specifies the methodology for the measurement of specific attributes of OCR-B character strings, - defines a method for evaluating these measurements and deriving an overall assessment of character string quality, - defines a reference decode algorithm for OCR-B, and - gives information on possible causes of deviation from optimum grades to assist users in taking appropriate corrective action. ISO/IEC 30116:2016 applies to OCR-B as defined in ISO 1073‑2, but its methodology can be applied partially or wholly to other OCR fonts.

Technologies de l'information -- Techniques automatiques d'identification et de capture des données -- Essais de qualité des caractères pour reconnaissance optique

General Information

Status
Published
Publication Date
04-Oct-2016
Current Stage
9020 - International Standard under periodical review
Start Date
15-Oct-2021
Ref Project

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INTERNATIONAL ISO/IEC
STANDARD 30116
First edition
2016-10-01
Information technology — Automatic
identification and data capture
techniques — Optical Character
Recognition (OCR) quality testing
Technologies de l’information — Techniques automatiques
d’identification et de capture des données — Essais de qualité des
caractères pour reconnaissance optique
Reference number
ISO/IEC 30116:2016(E)
ISO/IEC 2016
---------------------- Page: 1 ----------------------
ISO/IEC 30116:2016(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2016, 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/IEC 2016 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/IEC 30116:2016(E)
Contents Page

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

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

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Abbreviated terms .............................................................................................................................................................................................. 3

5 Quality grading ....................................................................................................................................................................................................... 3

6 Measurement methodology for OCR-B .......................................................................................................................................... 3

6.1 Overview of methodology ............................................................................................................................................................. 3

6.2 Obtaining the test image ................................................................................................................................................................. 3

6.2.1 Measurement conditions .......................................................................................................................................... 3

6.2.2 Raw image ............................................................................................................................................................................. 3

6.2.3 Reference grey-scale image .................................................................................................................................... 3

6.2.4 Binarized image ................................................................................................................................................................ 4

6.3 Reference reflectivity measurements .................................................................................................................................. 4

6.3.1 General requirements .................................................................................................................................................. 4

6.3.2 Light sources ....................................................................................................................................................................... 4

6.3.3 Effective resolution ........................................................................................................................................................ 4

6.3.4 Optical geometry ............................................................................................................................................................. 4

6.3.5 Inspection area .................................................................................................................................................................. 8

6.4 Basis of symbol grading .................................................................................................................................................................. 8

6.5 Capture the raw image ..................................................................................................................................................................... 9

6.6 Image assessment parameters and grading .................................................................................................................. 9

6.6.1 Determining the document horizontal axis .............................................................................................. 9

6.6.2 Character best-fit algorithm .................. ................................................................................................................. 9

6.6.3 Position of a character .............................................................................................................................................11

6.6.4 Character evaluation value (CEV) in the best-fit location .........................................................11

6.6.5 Background noise ...................................................................... ...................................................................................12

6.6.6 Contrast PCS of the characters ..........................................................................................................................12

7 Reporting the grade .......................................................................................................................................................................................12

Annex A (normative) OCR-B character centreline coordinates .............................................................................................14

Annex B (normative) Threshold determination method .............................................................................................................20

Annex C (normative) OCR reference decode algorithm .................................................................................................................24

Annex D (informative) Example calculation of character evaluation value (CEV) .............................................25

Bibliography .............................................................................................................................................................................................................................29

© ISO/IEC 2016 – All rights reserved iii
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ISO/IEC 30116:2016(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.

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 document 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 and IEC 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 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: www.iso.org/iso/foreword.html.

The committee responsible for this document is ISO/JTC 1, Information technology, Subcommittee SC 31,

Automatic identification and data capture techniques.
iv © ISO/IEC 2016 – All rights reserved
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ISO/IEC 30116:2016(E)
Introduction

For the inspection of ID documents, i.e. MRTDs (Machine Readable Travel Documents) according to

ISO/IEC 7501 (all parts)/ICAO Doc 9303 (all parts) and driving licences according to ISO/IEC 18013

(all parts), a reliable and ergonomic document inspection technology is essential. Considering RFID

interoperability, strong improvement has been reached introducing mechanisms for interoperability

evaluation and testing of MRTDs and reader devices. Similar standards for optical reading would

improve the reliability of OCR. This is especially important because OCR of the document’s MRZ (Machine

Readable Zone) is essential for accessing BAC (Basic Access Control) and/or SAC (Supplementary Access

Control) protected passports.

Thus, reliable OCR makes the performance of automated border control systems, as well as of many

other applications, more predictable. Furthermore, the evaluation of document reader products can be

done much easier. This standardization project defines test methods to evaluate OCR document quality.

Furthermore, it defines requirements ensuring the compliance to the applicable OCR standards. The

project applies experiences from other domains such as bar code reading and possibly other test

methods for OCR. Where conflicts in the specification work between MRTDs and driving licenses may

arise, satisfying the definitions for MRTDs is given preference.
© ISO/IEC 2016 – All rights reserved v
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INTERNATIONAL STANDARD ISO/IEC 30116:2016(E)
Information technology — Automatic identification and
data capture techniques — Optical Character Recognition
(OCR) quality testing
1 Scope
This document

— specifies the methodology for the measurement of specific attributes of OCR-B character strings,

— defines a method for evaluating these measurements and deriving an overall assessment of character

string quality,
— defines a reference decode algorithm for OCR-B, and

— gives information on possible causes of deviation from optimum grades to assist users in taking

appropriate corrective action.

This document applies to OCR-B as defined in ISO 1073-2, but its methodology can be applied partially

or wholly to other OCR fonts.
2 Normative references
There are no normative references in this document.
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
binarized image

binary (black/white) image created by applying the global threshold to the pixel (3.5) values in the

reference grey-scale image
3.2
document reference edge

physical (i.e. mechanical) end of the surface with the MRZ whose position is determined by putting a

black background under the surface with the MRZ and sliding the document up against a physical stop

3.3
inspection area

rectangular area which contains the entire symbol (3.11) to be tested inclusive of its quiet zones

3.4
character outline limits
outlines of an ideal printed image of a character

Note 1 to entry: This is a qualitative evaluation utilized in ISO 1831 that is replaced in this document with SWT.

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ISO/IEC 30116:2016(E)
3.5
pixel
individual light-sensitive element in a light-sensitive array

Note 1 to entry: Examples of light-sensitive array are CCD (charge coupled device) or CMOS (complementary

metal oxide semiconductor) device.
3.6
raw image

matrix of the reflectance values in x and y coordinates across a two-dimensional image, derived from

the discrete reflectance values of each pixel (3.5) of the light-sensitive array
3.7
reference grey-scale image
raw image (3.6) convolved with a synthesized circular aperture
3.8
scan grade

result of the assessment of a single scan of an OCR symbol, derived by taking the lowest grade achieved

for any measured parameter of the reference grey-scale and binarized images (3.1)

3.9
stroke width

nominal dimension perpendicular to the direction of the line making up an OCR character

3.10
stroke width template

inner and outer character boundaries defined by circles whose centres follow the line created by the

character centreline coordinates defined in Annex A
3.11
symbol

group of OCR characters comprising the entire machine-readable entity (e.g. Machine Readable Zone

(MRZ) as specified in ICAO 9303, sizes ID-1, ID-2 and ID-3) including quiet zones and the document

reference edge (3.2)

Note 1 to entry: Document sizes are defined in ISO/IEC 7501 (all parts) (ICAO 9303) as TD1, TD2 and TD2,

whereas the same sizes are defined in ISO/IEC 7810 as ID-1, ID-1 and ID-3. In this document, we use the terms

ID-1, ID-2 and ID-3.
3.12
X-tolerance
0,08 mm for Size I with a nominal stroke width (3.9) of 0,35 mm

Note 1 to entry: 0,08 mm for Size I with a nominal stroke width of 0,35 mm was originally defined in

ISO 1831:1980, Table 2.
3.13
Y-tolerance
0,15 mm for Size I with a nominal stroke width (3.9) of 0,35 mm

Note 1 to entry: 0,15 mm for Size I with a nominal stroke width of 0,35 mm was originally defined in

ISO 1831:1980, Table 2.
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ISO/IEC 30116:2016(E)
4 Abbreviated terms
COL character outline limits
CEV character evaluation value
MRZ machine readable zone
SWT stroke width template
5 Quality grading

Quality grades for best-fit, PCS, position and background noise are determined as one of three levels:

recommended, needs attention and not recommended. The parameter with the lowest grade is the

grade of the symbol.
6 Measurement methodology for OCR-B
6.1 Overview of methodology

The basis of the measurement methodology is the evaluation of reflectance from the symbol. This

methodology is also intended to correlate with conditions encountered in OCR scanning systems. The

method starts by obtaining the raw image, which is a high-resolution grey-scale image of the symbol

captured under controlled illumination and viewing conditions.
6.2 Obtaining the test image
6.2.1 Measurement conditions

A test image of the symbol shall be obtained in a configuration that mimics the typical scanning

situation for that symbol, but with substantially higher resolution (see 6.3.3), uniform illumination and

at best focus. The reference optical arrangement is defined in 6.3.4. Alternative optical arrangements

may be used provided that the measurements obtained with them can be correlated with the use of the

reference optical arrangement.

Ambient light levels shall be controlled in order not to influence the measurement results. Whenever

possible, measurements shall be made on the symbol in its final configuration, i.e. the configuration

in which it is intended to be scanned. For MRTD evaluation, optically personalized samples shall be

used. This includes that all layers available at a document including laminations, security features and

protective layers shall be present.

Two principles govern the design of the optical set-up. First, the test image’s grey-scale shall be

nominally linear and not be enhanced in any way. Second, the image resolution shall be adequate to

produce consistent readings, which generally requires that the character stroke-widths span at least

10 image pixels.
6.2.2 Raw image

The raw image is a matrix of the actual reflectance values for each pixel of the light-sensitive array,

from which are derived the reference grey-scale image and the binarized image which are evaluated for

the assessment of symbol quality.
6.2.3 Reference grey-scale image

The reference grey-scale image is obtained from the raw image by processing the individual pixel

reflectance values through a synthetic circular aperture equal to 0,2 mm.
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ISO/IEC 30116:2016(E)
6.2.4 Binarized image

The binarized image is obtained from the reference grey-scale image by applying the algorithm defined

in Annex B.
6.3 Reference reflectivity measurements
6.3.1 General requirements

Equipment for assessing the quality of symbols in accordance with this subclause shall comprise a

means of measuring and analysing the variations in the reflectivity of a symbol on its substrate over an

inspection area which shall cover the full height and width of the symbol.

The measured reflectance values shall be expressed in percentage terms by means of calibration and

reference to recognized national standards laboratories, where 100 per cent should correspond to the

reflectance of a barium sulphate or magnesium oxide reference sample.

It should be ensured that all materials visible to the camera or close to the optical path are reflection-

free, at least in IR illumination. In particular, the background the symbol is attached to shall be IR

absorbing. The environment temperature shall be between 20°C and 25°C.
6.3.2 Light sources

Measurements shall be made using light emitting diode (LED) light sources at 890 nm and 940 nm

wavelengths.

All illumination elements shall have a diameter of 25 mm or less and may be shaped as circles, squares

or similar.
6.3.3 Effective resolution

The effective resolution of an instrument that implements this document shall be sufficient to ensure

that the parameter grading results are consistent irrespective of the rotation of the symbol. The effective

resolution is the product of the resolution of the light-sensitive array and of the magnification of the

associated optical system and effected by distortions introduced by the optical system. The reference

optical arrangement requires an effective resolution of not less than 10 pixels per stroke width.

6.3.4 Optical geometry

A reference optical geometry is defined for reflectivity measurements and consists of

— flood incident illumination, uniform across the inspection area, from a set of four light sources

arranged at 90-degree intervals around a circle concentric with the inspection area and in a plane

parallel to that of the inspection area, at a height which will allow incident light to fall on the centre

of the inspection area at an angle of 45° to its plane, and

— a light collection device, the optical axis of which is perpendicular to the inspection area and passes

through its centre, and which focuses an image of the test symbol on a light-sensitive array.

The light reflected from the inspection area shall be collected and focused on the light-sensitive array.

Implementations may use alternative optical geometries and components, provided that their

performance can be correlated with that of the reference optical arrangement defined in this subclause.

Figure 1 and Figure 2 illustrate the principle of the optical arrangement, but are not intended to

represent actual devices; in particular, the magnification of the device is likely to differ from 1:1. For

example, it is possible to use a 10 MP industrial camera without IR cut filter with a sensor size of ½”. The

image could be captured from a distance of approximately 350 mm and the lens chosen appropriately.

The resulting magnification then would be 1:21.
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ISO/IEC 30116:2016(E)
Key
1 light-sensing element
2 lens providing 1:1 magnification (measurement A = measurement B)
3 inspection area
4 light sources
ϑ angle of incidence of light relative to plane of symbol = 45°
Figure 1 — Reference optical arrangement — Side view
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ISO/IEC 30116:2016(E)
Key
1 light source
2 symbol
Figure 2 — Reference optical arrangement — Top view
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ISO/IEC 30116:2016(E)
Figure 3 — Reference optical arrangement — Angles and tolerances

When setting up a reference optical arrangement, the following considerations shall be made. The

symbol (e.g. the MRZ of an ID-3 MRTD) has a size of approximately 24 mm × 125 mm (marked as a

bar in the bottom of Figure 3). For other document sizes (ID-1, ID-2), the same size of the object to be

captured shall be used. All areas not covered by the travel document but visible to the camera shall be

made of IR-absorbing material. The small rectangles at the left and right border of Figure 3 represent

the illumination elements.

The nominal illumination angle shall be 45° as given in Figure 1. This angle is measured in the middle

axis of the MRZ zone. An angle of 45° directly determines that the horizontal and vertical distance of

the illumination from the centre of the symbol is identical. This distance should be 200 mm as depicted

in Figure 3.
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ISO/IEC 30116:2016(E)

For the small side of the symbol (24 mm), the minimal and maximal illumination angles at the symbol

borders are 43,3° and 46,8°, as shown in Table 1.

The difference between the nominal angle (in the centre) and the angles at the borders is much higher

for the long side of the symbol; 37,3° and 55,5°.
Table 1 — Dark pixel portion for threshold of 4.5
Angle Short side (24 mm) Long side (125 mm)
α 45° 45°
α′ 46,8° 55,5°
α″ 43,3° 37,3°
Figure 4 — Reference optical arrangement — Reflection considerations

Figure 4 shows the position where the direct reflection of the illumination at the symbol (i.e. caused by

plain lamination) will not be visible to the camera. The distance between the camera and the symbol

should be approximately 350 mm.
6.3.5 Inspection area

The inspection area within which all measurements shall be a rectangular area framing the complete

symbol. The centre of the inspection area shall be as close as practicable to the centre of the field of

view. For example, the MRZ in a passport shall be placed accordingly.
6.4 Basis of symbol grading

OCR symbol quality assessment shall be based on the measurement and grading of parameters of the

reference grey-scale image, the binarized image derived from it and the application of the reference

decode algorithm to these. Quality grading of these parameters shall be used to provide a relative

measure of symbol quality under the measurement conditions used.
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ISO/IEC 30116:2016(E)
6.5 Capture the raw image

Centre the symbol in the field of view and align the average bottom edge of the characters with the

sensor as precisely as possible, but always with less than +/−5° deviation.

Find and replace the brightest and darkest 0,005 % pixels in the overall image with the median of the

9 pixels consisting of itself and its 8 immediate neighbours.

Apply the aperture defined in 6.2.3 to the raw image to create a reference grey-scale image.

6.6 Image assessment parameters and grading
6.6.1 Determining the document horizontal axis

The application shall define the MRZ region in relation to the document reference edge.

6.6.2 Character best-fit algorithm

These steps should be followed in order to find the best-fit position of the character outline limit (SWT)

gauges on a character image captured from a machine-readable character string in order to find the

location of the characters.

Using the binarized image, determine four corner positions that bound the character image. From these

points, establish four more points that are further away from the character by the nominal stroke

width. These four points define the range over which the SWT gauges will be moved in order to find the

best-fit position. An example is shown in Figure 5.
Key
1 vertical range
2 horizontal range
Figure 5 — Sample corner positions

Create the SWT for each defined character in Annex A by moving a circle of radius of the appropriate

tolerance value around the centreline of the character and saving the outermost points (note that this is

equivalent to finding the points perpendicular to the centre line at a distance equal to the radius of the

circle). An example of this process is in Figure 6. Figure 7 illustrates the tolerances of the SWT boxes as

derived from ISO 1831.
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ISO/IEC 30116:2016(E)
Figure 6 — SWT creation example

a) X-tolerance. Radius 6,75 “sq” inside 10,75 b) Y-tolerance. Radius 5 “sq” inside 12,5 “sq”

“sq” outside outside
NOTE 1 These are the tolerances from ISO 1831:1980, Table 2.

NOTE 2 “Sq” is the count of squares from the original drawings (see Annex A) where each square equals

1/50 mm.
Figure 7 — SWT tolerance gauges
10 © ISO/IEC 2016 – All rights reserved
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ISO/IEC 30116:2016(E)

Overlay the original captured image with the SWT Y-tolerance gauges such that the horizontal axis of

the gauges is parallel with the document reference edge. Starting with the four extreme positions, move

the SWT Y-tolerance gauges right and left and up and down relative to the document reference edge to

each test position.

At each test position, sum up the reflectance values of each SWT Y-tolerance gauge resolution pixel

within the region defined by the minimum gauge. The test position with the lowest sum is used to

determine the position of the character. If there is more than one test position with the same lowest

sum (e.g. the inside of the minimum gauge is all black), then for each equivalent test position, sum up

the reflectance values of each gauge resolution pixel outside the maximum gauge. The equivalent test

position with the highest sum is used to determine the position of the character. If there is more than

one test position with the same highest sum, then compute the average of these positions and use it to

determine the position of the character.
6.6.3 Position of a character

Using the test position determined in 6.6.2, the location of a character is the origin of the SWT, where

the origin is defined as (0,0) for every character in Annex A.

The position of every character is determined and graded according to an application specific profile.

The character with the lowest grade determines the position grade.
6.6.4 Character evaluation value (CEV) in the best-fit location

A pixel is outside or inside a border if more than 50 % of the pixel area is outside or inside the border,

respectively.

For each tolerance template on every character, use the optimal position of the template placed over the

binarized character in the image. The following lists the variables to be used to calculate the CEV grades:

a) CEV_X_Inside — number of white pixels inside the X-tolerance inner boundary;

b) CEV_X_Outside — number of black pixels outside the X-tolerance outer boundary;

c) CEV_Y_Inside — number of white pixels inside the Y-tolerance inner boundary;
d) CEV_Y_Outside — umber of black pixels outside the Y-tolerance outer boundary;

e) Y_Boundary_Area — total number of image pixels of any color inside the Y-tolerance outer

boundary;

f) Y_Inside_Total — total number of image pixels of any color inside the Y-tolerance inner boundary;

g) Character_Region_Total — total number of image pixels in the rectangular area defined by

the Y-tolerance outer template of the chosen character plus a one-stroke width boundary. The

Character Region Total is computed as the product of the width of the Y-tolerance outer boundary

plus two times the nominal stroke width rounded to the nearest number of pixels and the height of

the Y-tolerance outer boundary plus the two times
...

DRAFT INTERNATIONAL STANDARD
ISO/IEC DIS 30116
ISO/IEC JTC 1/SC 31 Secretariat: ANSI
Voting begins on: Voting terminates on:
2015-09-30 2015-12-30
Information technology — Automatic identification and
data capture techniques — Optical Character Recognition
(OCR) quality testing
Titre manque
ICS: 35.040
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/IEC DIS 30116:2015(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. ISO/IEC 2015
---------------------- Page: 1 ----------------------
ISO/IEC DIS 30116:2015(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2015, 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/IEC 2015 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/IEC WD 30116
Contents Page

Foreword .......................................................................................................................................................v

Introduction ..................................................................................................................................................vi

1 Scope ................................................................................................................................................1

2 Normative references .......................................................................................................................1

3 Terms and definitions ......................................................................................................................1

3.1 binarized image ................................................................................................................................1

3.2 document reference edge ................................................................................................................1

3.3 inspection area .................................................................................................................................2

3.4 COL ...................................................................................................................................................2

3.5 pixel...................................................................................................................................................2

3.6 raw image .........................................................................................................................................2

3.7 reference grey-scale image ..............................................................................................................2

3.8 scan grade ........................................................................................................................................2

3.9 stroke width ......................................................................................................................................2

3.10 SWT ...................................................................................................................................................2

3.11 symbol ..............................................................................................................................................3

3.12 X-Tolerance.......................................................................................................................................3

3.13 Y-Tolerance.......................................................................................................................................3

4 Abbreviated terms ............................................................................................................................3

5 Quality grading .................................................................................................................................3

6 Measurement methodology for OCR-B ...........................................................................................3

6.1 Overview of methodology ................................................................................................................3

6.2 Obtaining the test image ..................................................................................................................3

6.2.1 Measurement conditions..................................................................................................................3

6.2.2 Raw image ........................................................................................................................................4

6.2.3 Reference grey-scale image.............................................................................................................4

6.2.4 Binarized image ................................................................................................................................4

6.3 Reference reflectivity measurements ..............................................................................................4

6.3.1 General requirements.......................................................................................................................4

6.3.2 Light sources ....................................................................................................................................4

6.3.3 Effective resolution ..........................................................................................................................4

6.3.4 Optical geometry ..............................................................................................................................4

6.3.5 Inspection area .................................................................................................................................7

6.4 Basis of symbol grading ..................................................................................................................8

6.5 Capture the raw image .....................................................................................................................8

6.6 Image assessment parameters and grading ...................................................................................8

6.6.1 Determining the document horizontal axis .....................................................................................8

6.6.2 Character best-fit algorithm .............................................................................................................8

6.6.3 Position of a character ...................................................................................................................10

6.6.4 Character Evaluation Value (CEV) in the best-fit location ............................................................10

6.6.5 Background noise ..........................................................................................................................11

6.6.6 Contrast PCS of the characters .....................................................................................................11

7 Reporting the Grade .......................................................................................................................11

Annex A OCR-B Character Centreline Coordinates (Normative) ..............................................................13

Annex B Threshold Determination Method (Normative) ...........................................................................21

B.1 Algorithm description ....................................................................................................................21

B.2 Example ..........................................................................................................................................21

Annex C OCR Reference Decode Algorithm (Normative) .........................................................................25

Annex D Example calculation of Character Evaluation Value (CEV)
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ISO/IEC WD 30116
Bibliography
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ISO/IEC WD 30116
Foreword

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(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

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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/IEC 30116 was prepared by Technical Committee ISO/TC , , Subcommittee SC 31, Automatic identification

and data capture techniques.

This second/third/... edition cancels and replaces the first/second/... edition (), [clause(s) / subclause(s) / table(s)

/ figure(s) / annex(es)] of which [has / have] been technically revised.
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ISO/IEC WD 30116
Introduction

For the inspection of ID documents, i.e. MRTDs (Machine Readable Travel Documents) according to ISO/IEC

7501 and driving licences according to ISO/IEC 18013, a reliable and ergonomic document inspection

technology is essential. Considering RFID interoperability, strong improvement has been reached introducing

mechanisms for interoperability evaluation and testing of MRTDs and reader devices. Similar standards for

optical reading would improve the reliability of OCR. This is especially important because OCR of the

document’s MRZ (Machine Readable Zone) is essential for accessing BAC (Basic Access Control) and/or SAC

(Supplementary Access Control) protected passports.

Thus, reliable OCR makes the performance of Automated Border Control systems as well as of many other

applications more predictable. Furthermore, the evaluation of document reader products can be done much

easier. This standardization project defines test methods to evaluate OCR document quality. Furthermore, it

defines requirements ensuring the compliance to the applicable OCR standards. The project applies

experiences from other domains such as bar code reading and possibly other test methods for OCR. Where

conflicts in the specification work between MRTDs and driving licenses may arise, satisfying the definitions for

MRTDs shall be given preference.
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DIS ISO/IEC WD 30116
Information technology — Automatic identification and data
capture techniques — Optical Character Recognition (OCR)
quality testing
1 Scope
This International Standard

-specifies the methodology for the measurement of specific attributes of OCR-B character strings;

-defines a method for evaluating these measurements and deriving an overall assessment of character string

quality;
-defines a reference decode algorithm for OCR-B;

-gives information on possible causes of deviation from optimum grades to assist users in taking appropriate

corrective action.

This International Standard applies to OCR-B as defined in ISO 1073-2, but its methodology can be applied

partially or wholly to other OCR fonts.
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/IEC 19762 Information technology -- Automatic identification and data capture (AIDC) techniques --

Harmonized vocabulary
3 Terms and definitions
3.1
binarized image

binary (black/white) image created by applying the Global Threshold to the pixel values in the reference grey-

scale image
3.2
document reference edge

physical (i.e. mechanical) end of the surface with the MRZ whose position is determined by putting a black

background under the surface with the MRZ and sliding the document up against a physical stop

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ISO/IEC WD 30116
3.3
inspection area

rectangular area which contains the entire symbol to be tested inclusive of its quiet zones

3.4
character outline limits
outlines of an ideal printed image of a character

Note: this is a qualitative evaluation utilized in ISO 1836 that is replaced in this standard with SWT

3.5
pixel

individual light-sensitive element in a light-sensitive array (e.g. CCD (charge coupled device) or CMOS

(complementary metal oxide semiconductor) device)
3.6
raw image

matrix of the reflectance values in x and y coordinates across a two-dimensional image, derived from the

discrete reflectance values of each pixel of the light-sensitive array
3.7
reference grey-scale image
raw image convolved with a synthesised circular aperture
3.8
scan grade

result of the assessment of a single scan of an OCR symbol, derived by taking the lowest grade achieved for

any measured parameter of the reference grey-scale and binarized images
3.9
stroke width

nominal dimension perpendicular to the direction of the line making up an OCR character

3.10
stroke width template

the inner and outer character boundaries defined by circles whose centres follow the line created by the

character centreline coordinates defined in Annex A
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ISO/IEC WD 30116
3.11
symbol

group of OCR characters comprising the entire machine-readable entity (e.g. Machine Readable Zone (MRZ)

as specified in ICAO Doc 9303, sizes ID-1, ID-2, and ID-3) including quiet zones and the document reference

edge
3.12
X-Tolerance
0,08 mm for Size I with a nominal stroke width of 0,35 mm

Note: 0,08 mm for Size I with a nominal stroke width of 0,35 mm was originally defined in ISO 1831 Table 2

3.13
Y-Tolerance
0,15 mm for Size I with a nominal stroke width of 0,35 mm

Note: 0,15 mm for Size I with a nominal stroke width of 0,35 mm was originally defined in ISO 1831 Table 2

4 Abbreviated terms
COL = character outline limits
CEV = character evaluation value
MRZ = Machine Readable Zone
SWT = Stroke width template
5 Quality grading

Quality grades for Best-Fit, PCS, Position and Background Noise are determined as one of three levels,

Recommended, Needs attention and Not recommended. The parameter with the lowest grade is the grade of

the symbol.
6 Measurement methodology for OCR-B
6.1 Overview of methodology

The basis of the measurement methodology is the evaluation of reflectance from the symbol. This methodology

is also intended to correlate with conditions encountered in OCR scanning systems. The method starts by

obtaining the raw image, which is a high-resolution grey-scale image of the symbol captured under controlled

illumination and viewing conditions.
6.2 Obtaining the test image
6.2.1 Measurement conditions

A test image of the symbol shall be obtained in a configuration that mimics the typical scanning situation for that

symbol, but with substantially higher resolution (see 6.3.3), uniform illumination, and at best focus. The

reference optical arrangement is defined in 6.3.4. Alternative optical arrangements may be used provided that

the measurements obtained with them can be correlated with the use of the reference optical arrangement.

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ISO/IEC WD 30116

Ambient light levels shall be controlled in order not to influence the measurement results. Whenever possible,

measurements shall be made on the symbol in its final configuration, i.e. the configuration in which it is intended

to be scanned. For MRTD evaluation, optically personalized samples shall be used. This includes that all layers

available at a document including laminations, security features and protective layers shall be present.

Two principles govern the design of the optical set-up. First, the test image’s grey-scale shall be nominally linear

and not be enhanced in any way. Second, the image resolution shall be adequate to produce consistent

readings, which generally requires that the character stroke-widths span at least ten image pixels.

6.2.2 Raw image

The raw image is a matrix of the actual reflectance values for each pixel of the light-sensitive array, from which

are derived the reference grey-scale image and the binarized image which are evaluated for the assessment of

symbol quality.
6.2.3 Reference grey-scale image

The reference grey-scale image is obtained from the raw image by processing the individual pixel reflectance

values through a synthetic circular aperture equal to 0,2 mm.
6.2.4 Binarized image

The binarized image is obtained from the reference grey-scale image by applying the algorithm defined in Annex

6.3 Reference reflectivity measurements
6.3.1 General requirements

Equipment for assessing the quality of symbols in accordance with this clause shall comprise a means of

measuring and analysing the variations in the reflectivity of a symbol on its substrate over an inspection area

which shall cover the full height and width of the symbol.

The measured reflectance values shall be expressed in percentage terms by means of calibration and reference

to recognised national standards laboratories, where 100 per cent should correspond to the reflectance of a

barium sulphate or magnesium oxide reference sample.

It should be ensured that all materials visible to the camera or close to the optical path are reflection free, at

least in IR illumination. In particular, the background the symbol is attached to shall be IR absorbing. The

environment temperature shall be between 20 and 25°C.
6.3.2 Light sources

Measurements shall be made using LED light sources at 890 and 940 nm wavelengths.

All illumination elements shall have a diameter of 25 mm or less and may be shaped as circles, squares or

similar.
6.3.3 Effective resolution

The effective resolution of an instrument that implements this international standard shall be sufficient to ensure

that the parameter grading results are consistent irrespective of the rotation of the symbol. The effective

resolution is the product of the resolution of the light-sensitive array and of the magnification of the associated

optical system and effected by distortions introduced by the optical system. The reference optical arrangement

requires an effective resolution of not less than ten pixels per stroke width.
6.3.4 Optical geometry

A reference optical geometry is defined for reflectivity measurements and consists of:

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ISO/IEC WD 30116

 flood incident illumination, uniform across the inspection area, from a set of four light sources arranged at

90 degree intervals around a circle concentric with the inspection area and in a plane parallel to that of the

inspection area, at a height which will allow incident light to fall on the centre of the inspection area at an

angle of 45° to its plane, and

 a light collection device, the optical axis of which is perpendicular to the inspection area and passes through

its centre, and which focuses an image of the test symbol on a light-sensitive array.

The light reflected from the inspection area shall be collected and focussed on the light-sensitive array.

Implementations may use alternative optical geometries and components, provided that their performance can

be correlated with that of the reference optical arrangement defined in this section. Figures 1 and 2 illustrate

the principle of the optical arrangement, but are not intended to represent actual devices; in particular the

magnification of the device is likely to differ from 1:1. For example, it is possible to use a 10MP industrial camera

without IR cut filter with a sensor size of ½”. The image could be captured from a distance of approx. 350 mm

and the lens chosen appropriately. The resulting magnification then would be 1:21.

4 4
1 – Light sensing element
2 – Lens providing 1:1 magnification (measurement A = measurement B)
3 – Inspection area
4 – Light sources
 - Angle of incidence of light relative to plane of symbol = 45°
Figure 1 — Reference optical arrangement – side view
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ISO/IEC WD 30116
Figure 2 — Reference optical arrangement – top view
Figure 3 — Reference optical arrangement – angles and tolerances
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ISO/IEC WD 30116

When setting up a reference optical arrangement, the following considerations shall be made. The Symbol (e.g.,

the MRZ of an ID-3 MRTD) has a size of approx. 24 mm x 125 mm (marked as a bar in the bottom of Figure 3).

For other document sizes (ID-1, ID-2) the same size of the object to be captured shall be used. All areas not

covered by the travel document but visible to the camera shall be made of IR absorbing material. The small

rectangles at the left and right border of Figure 3 represent the illumination elements.

The nominal illumination angle shall be 45° as given in Figure 1. This angle is measured in the middle axis of

the MRZ zone. An angle of 45° directly determines that the horizontal and vertical distance of the illumination

from the centre of the symbol is identical. This distance should be 200 mm as depicted in Figure 3.

For the small side of the Symbol (24 mm) the minimal and maximal illumination angles at the symbol borders

are 43,3° and 46,8°, as shown in Table 1.

The difference between the nominal angle (in the centre) and the angles at the borders is much higher for the

long side of the symbol; 37,3° and 55,5°.
Table 1 — Dark pixel portion for threshold of 4.5
Angle Short side (24 mm) Long side (125 mm)
α 45° 45°
α’ 46,8° 55,5°
α’’ 43,3° 37,3°
Figure 4 — Reference optical arrangement – reflection considerations

Figure 4 shows the position where the direct reflection of the illumination at the symbol (i.e. caused by plain

lamination) will not visible to the camera. The distance between the camera and the symbol should be

approximately 350 mm.
6.3.5 Inspection area

The inspection area within which all measurements shall be a rectangular area framing the complete symbol.

The centre of the inspection area shall be as close as practicable to the centre of the field of view. For

example, the MRZ in a passport shall be placed accordingly.
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ISO/IEC WD 30116
6.4 Basis of symbol grading

OCR symbol quality assessment shall be based on the measurement and grading of parameters of the

reference grey-scale image, the binarized image derived from it, and the application of the reference decode

algorithm to these. Quality grading of these parameters shall be used to provide a relative measure of symbol

quality under the measurement conditions used.
6.5 Capture the raw image

Centre the symbol in the field of view and align the average bottom edge of the characters with the sensor as

precisely as possible, but always with less than +/- 5 degrees deviation.

Find and replace the brightest and darkest 0,005% pixels in the overall image with the median of the nine pixels

consisting of itself and its eight immediate neighbours.

Apply the aperture defined in 6.2.3 to the raw image to create a reference grey-scale image.

6.6 Image assessment parameters and grading
6.6.1 Determining the document horizontal axis

The application shall define the MRZ region in relation to the Document Reference Edge.

6.6.2 Character best-fit algorithm

These steps should be followed in order to find the best-fit position of the character outline limit (SWT) gauges

on a character image captured from a machine readable character string in order to find the location of the

characters.

Using the binarized image, determine four corner positions that bound the character image. From these points,

establish four more points that are further away from the character by the nominal stroke width. These four

points define the range over which the SWT gauges will be moved in order to find the best-fit position.

Horizontal range
Vertical range
Figure 5 — Sample corner positions

Create the SWT for each defined character in Annex A by moving a circle of radius of the appropriate tolerance

value around the centreline of the character and saving the outermost points (note that this is equivalent to

finding the points perpendicular to the centre line at a distance equal to the radius of the circle). An example of

this process is in Figure 6 below.
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ISO/IEC WD 30116
140
140 140
120 120 120
100 100 100
80 80 80
60 60
40 40
20 20
0 0

-50 -40 -30 -20 -10 0 10 20 30 40 -50 -40 -30 -20 -10 0 10 20 30 40 -50 -40 -30 -20 -10 0 10 20 30 40 50

Figure 6 — SWT creation example
140
140
120
120
100
100
40 40
20 20
0 0
-60 -40 -20 0 20 40 60
-60 -40 -20 0 20 40 60
-20 -20
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ISO/IEC WD 30116

Figure 7 — Left: Radius 6,75 “sq” inside 10,75 “sq” outside (Note: this is the X-tolerance from ISO

1831 Table 2). Right: Radius 5 “sq” inside 12,5 “sq” outside (Note: this is the Y-tolerance from ISO

1831 Table 2). “Sq” is the count of squares from the original drawings (See Annex A) where each

square equals 1/50 mm.

Overlay the original captured image with the SWT Y-tolerance gauges such that the horizontal axis of the

gauges is parallel with the Document Reference Edge. Starting with the four extreme positions, move the SWT

Y-tolerance gauges right and left, and up and down relative to the Document Reference Edge to each test

position.

At each test position, sum up the reflectance values of each SWT Y-tolerance gauge resolution pixel within the

region defined by the minimum gauge. The test position with the lowest sum is used to determine the position

of the character. If there is more than one test position with the same lowest sum (e.g. the inside of the minimum

gauge is all black), then for each equivalent test position, sum up the reflectance values of each gauge resolution

pixel outside the maximum gauge. The equivalent test position with the highest sum is used to determine the

position of the character. If there is more than one test position with the same highest sum, then compute the

average of these positions and use it to determine the position of the character.

6.6.3 Position of a character

Using the test position determined in 6.6.2, the location of a character is the origin of the SWT, where the

origin is defined as (0,0) for every character in Annex A.

The position of every character is determined and graded according to ???. The character with the lowest grade

determines the Position Grade.
6.6.4 Character Evaluation Value (CEV) in the best-fit location

A pixel is outside or inside a border if more than 50% of the pixel area is outside or inside the border respectively.

For each tolerance template on every character, use the optimal position of the template placed over the

binarized character in the image. The following lists the variables to be used to calculate the CEV grades.

CEV_X_Inside – Number of white pixels inside the X-tolerance inner boundary.
CEV_X_Outside – Number of black pixels outside the X-tolerance outer boundary.
CEV_Y_Inside – Number of white pixels inside the Y-tolerance inner boundary.
CEV_Y_Outside – Number of black p
...

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