ISO 12233:2000

Photography - Electronic still-picture cameras - Resolution measurements

Specifies methods for measuring the resolution of electronic still picture cameras. Is applicable to the measurement of both monochrome and colour cameras which output digital data or analog video signals.

Photographie — Appareils de prises de vue électroniques — Mesurages de la résolution

Fotografija - Digitalne kamere za mirujoče slike - Merjenje ločljivosti

Določa metode za merjenje ločljivosti digitalnih kamer za mirujoče slike. Velja za merjenje pri črno-belih in barvnih kamerah, ki proizvajajo digitalne podatke ali analogne videosignale.

General Information

• Status: Withdrawn
• Publication Date: 30-Aug-2000
• Withdrawal Date: 30-Aug-2000
• ICS: 37.040.10 - Photographic equipment. Projectors
• Technical Committee: ISO/TC 42 - Photography
• Drafting Committee: ISO/TC 42/WG 18 - Electronic still picture imaging
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 11-Feb-2014
• Completion Date: 13-Dec-2025
• Ref Project: SIST ISO 12233:2011 - Photography - Electronic still-picture cameras - Resolution measurements

Relations

• Consolidated By: ISO 3175-2:2010 - Textiles - Professional care, drycleaning and wetcleaning of fabrics and garments - Part 2: Procedure for testing performance when cleaning and finishing using tetrachloroethene
• Effective Date: 06-Jun-2022
• Revised: ISO 12233:2014 - Photography - Electronic still picture imaging - Resolution and spatial frequency responses
• Effective Date: 26-Feb-2011

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 12233
First edition
2000-09-01
Photography — Electronic still-picture
cameras — Resolution measurements
Photographie — Appareils de prises de vue électroniques — Mesurages
de la résolution
Reference number
©
ISO 2000
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ii © ISO 2000 – All rights reserved

Contents Page
Foreword.iv
0 Introduction.v
0.1 Purpose.v
0.2 Technical background.v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Test chart.5
4.1 Introduction.5
4.2 Material .6
4.3 Size.6
4.4 Test patterns .6
4.5 Test-pattern modulation.6
4.6 Units .6
4.7 Features .6
4.8 Positional tolerance.6
5 Test conditions .10
5.1 Test-chart illumination .10
5.2 Camera framing and lens focal-length setting .10
5.3 Camera focusing.10
5.4 Camera settings.10
5.5 White balance.11
5.6 Luminance and colour measurements.11
5.7 Gamma correction .11
6 Test measurements .11
6.1 Visual resolution.11
6.2 Limiting resolution.12
6.3 Spatial frequency response.12
6.4 Aliasing ratio .15
7 Presentation of results.15
7.1 Introduction.15
7.2 Visual resolution.15
7.3 Limiting resolution.15
7.4 Spatial frequency response (SFR) .15
7.5 Aliasing ratio .16
Annex A (informative) SFR measurement algorithm C-code.17
Annex B (informative) Test-chart dimensions.28
Annex C (normative) Spatial frequency response (SFR) algorithm.29
Annex D (informative) Relationships between resolution metrics.31
Bibliography.32
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 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 12233 was prepared by Technical Committee ISO/TC 42, Photography.
Annex C forms a normative part of this International Standard. Annexes A, B and D are for information only.
iv © ISO 2000 – All rights reserved

0 Introduction
0.1 Purpose
The spatial resolution capability is an important attribute of an electronic still-picture camera. Resolution
measurement standards allow users to compare and verify spatial resolution measurements. This International
Standard defines terminology, test charts and test methods for performing resolution measurements for analog and
digital electronic still-picture cameras.
0.2 Technical background
One of the most important characteristics of an electronic still-picture camera is the ability of the camera to capture
fine detail found in the original scene. This ability to resolve detail is determined by a number of factors, including
the performance of the camera lens, the number of addressable photoelements in the optical imaging device, and
the electrical circuits in the camera, which may include image compression and gamma correction functions.
Different measurement methods can provide different metrics to quantify the resolution of an imaging system, or a
component of an imaging system, such as a lens. Resolution measurement metrics include resolving power,
limiting resolution (at some specified contrast), spatial frequency response, MTF and OTF.
The first step in measuring resolution is to capture an image of a suitable test-chart with the camera under test. The
test chart should include patterns with sufficiently fine detail, such as edges, lines, square waves, or sine wave
patterns. The test chart defined in this International Standard has been designed specifically to evaluate electronic
still-picture cameras. It has not been designed to evaluate other electronic imaging equipment such as input
scanners, CRT displays, hard-copy printers, or electrophotographic copiers, nor individual components of an
electronic still-picture camera, such as the lens.
The resolution measurements described in this International Standard are performed in the digital domain, using
digital analysis techniques. For electronic still-picture cameras that include only analog outputs, the analog signal
needs to be digitized, so that the digital measurement can be performed. The digitizing equipment is characterized,
so that the effects of the digitization process can be removed from the measurement results. When this is not
possible, the type of digitizing equipment used shall be reported along with the measurement results.
The spatial frequency response (SFR) measurement method described in this International Standard uses a
computer algorithm to analyse digital image data from the electronic still-picture camera. Digitized image values
near slanted vertical and horizontal black to white edges are digitized and used to compute the SFR values. The
use of a slanted edge allows the edge gradient to be measured at many phases relative to the image sensor
photoelements, in order to eliminate the effects of aliasing. This technique is mathematically equivalent to
performing a moving knife edge measurement.
INTERNATIONAL STANDARD ISO 12233:2000(E)
Photography — Electronic still-picture cameras — Resolution
measurements
1 Scope
This International Standard specifies methods for measuring the resolution of electronic still-picture cameras. It is
applicable to the measurement of both monochrome and colour cameras which output digital data or analog video
signals.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 7589:1984, Photography — Illuminants for sensitometry — Specifications for daylight and incandescent
tungsten.
ISO 14524:1999, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic
conversion functions (OECFs).
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
3.1
addressable photoelements
number of active photoelements in an image, which is equal to the number of active lines of photoelements
multiplied by the number of active photoelements per line
NOTE It is possible that the number of addressable photoelements may be different for the different colour records of an
image. When the signal values of the photoelements are digitized, the digitized code values may be referred to as picture
elements, or pixels.
3.2
aliasing
output image artifacts that occur in a sampled imaging system for input images having significant energy at
frequencies higher than the Nyquist frequency of the system
3.3
cycles per millimetre
cy/mm
unit used for specifying resolution characteristics in terms of the response of an imaging system to a linear radiance
sine wave input, as a function of the frequency of the sine wave
NOTE 1 A range of input sine wave frequencies is obtained in this International Standard through the use of a sharp edged
target.
NOTE 2 Most pictorial imaging systems exhibit non-linear behaviour, which may result in the nature of the target affecting the
measured resolution characteristics. Distance units other than millimetres may also be used.
3.4
aliasing ratio
value equal to the "maximum minus minimum" modulation divided by the "average" modulation of an electronic still-
picture camera when imaging a frequency burst of constant spatial frequency
NOTE The aliasing ratio is described in 6.4.
3.5
edge spread function
ESF
normalized spatial signal distribution in the linearized output of an imaging system resulting from imaging a
theoretical infinitely sharp edge
3.6
effectively spectrally neutral
having spectral characteristics which result in a specific imaging system producing the same output as for a
spectrally neutral object
3.7
electronic still-picture camera
camera incorporating an image sensor that outputs an analog or digital signal representing a still-picture, or records
an analog or digital signal representing a still-picture on a removable media, such as a memory card or magnetic
disc
3.8
gamma correction
process that alters the image data in order to modify the tone reproduction
3.9
horizontal resolution
resolution value measured in the longer image dimension, corresponding to the horizontal direction for a
"landscape" image orientation, typically using a vertically oriented test-chart feature
3.10
image aspect ratio
ratio of the image width to the image height
3.11
image compression
process that alters the way digital image data is encoded in order to reduce the size of an image file
3.12
image sensor
electronic device that converts an optical image into an electronic signal; for example a charge coupled device
(CCD) array
3.13
limiting resolution
value of that portion of a specified resolution test pattern, measured in line widths per picture height, that
corresponds to an average modulation value equal to some specified percentage of the modulation value at a
specified reference frequency
EXAMPLE The limiting resolution may be the test pattern value, in line widths per picture height (LW/PH), corresponding
to a camera output modulation level of 5 % of the camera output modulation level at a reference frequency of 10 LW/PH.
2 © ISO 2000 – All rights reserved

3.14
line pairs per millimetre
lp/mm
metric for specifying resolution in terms of the number of equal width black and white line pairs per millimetre that
can be resolved according to some criterion, such as visual resolution or limiting resolution
NOTE distance units other than millimetres may also be used.
3.15
lines per millimetre
lines/mm
metric for specifying resolution in terms of the number of equal-width black and white lines per millimetre that can
be resolved according to some criterion, such as visual resolution or limiting resolution
NOTE Distance units other than millimetres may also be used.
3.16
line spread function
LSF
normalized spatial signal distribution in the linearized output of an imaging system resulting from imaging a
theoretical infinitely thin line
NOTE If the imaging system is operating in an isoplanatic region and in its linear range, the LSF is equal to the first
derivative of the ESF.
3.17
line widths per picture height
LW/PH
metric for specifying the width of a solid line on a test chart, relative to the height of the active area of the chart,
which is equal to the height of the active area of the test chart divided by the width of a black line, that is equal to
the total number of lines of the same width which can be placed edge to edge within the height of a test target, or
within the vertical field of view of a camera
NOTE If the height of the active area of the chart equals 20 cm, a black line of 1 000 LW/PH has a width equal to
20/1 000 cm.
3.18
linearized
digital signal conversion performed to invert the camera opto-electronic conversion function (OECF) so that the
resulting signal is approximately linearly proportional to the scene luminance
3.19
modulation
difference between the minimum and maximum signal levels divided by the sum of these levels
3.20
modulation transfer function
MTF
modulus of the optical transfer function
3.21
normalized spatial frequency
unit used for expressing spatial frequency response, where the distance dimension has been removed by
multiplying the spatial frequency in cycles per millimetre by the sampling period in millimetres
NOTE Normalized spatial frequency is particularly appropriate for comparing the spatial frequency response of imaging
systems where the rendering magnification is unknown, and the total number of samples is equal.
3.22
Nyquist limit
spatial frequency equal to 1/2 times the inverse of the sampling period
NOTE Energy at an input spatial frequency above the Nyquist limit will alias to a spatial frequency below the Nyquist limit in
the output image. The Nyquist limit may be different in the two orthogonal directions.
3.23
optical transfer function
OTF
two-dimensional Fourier transform of the imaging system's point spread function
NOTE 1 For the OTF to have significance, it is necessary that the imaging system be operating in an isoplanatic region and
in its linear range.
NOTE 2 The OTF is a complex function whose modulus has unity value at zero spatial frequency.
3.24
point spread function
PSF
normalized spatial signal distribution in the linearized output of an imaging system resulting from imaging a
theoretical infinitely small point source
3.25
resolution
measure of the ability of a camera system, or a component of a camera system, to depict picture detail
NOTE Resolution measurement metrics include resolving power, limiting resolution, spatial frequency response (SFR),
MTF and OTF.
3.26
sampling aspect ratio
ratio of the sample spacing in the two orthogonal sampling directions
NOTE If the sample spacing is equal, the aspect ratio of the sampling grid is 1:1 or "square", so that the sampling aspect
ratio provides "square pixels".
3.27
sampled imaging system
imaging system or device which generates an image signal by sampling an image at an array of discrete points, or
along a set of discrete lines, rather than a continuum of points
NOTE The sampling at each point is done using a finite size sampling aperture or area.
3.28
sample spacing
physical distance between sampling points or sampling lines
NOTE The sample spacing may be different in the two orthogonal sampling directions.
3.29
spatial frequency response
SFR
measured amplitude response of an imaging system as a function of relative input spatial frequency
NOTE 1 The SFR is normally represented by a curve of the output response to an input signal of unit amplitude, over a
range of spatial frequencies.
NOTE 2 The SFR is normalized to yield a value of unity at a spatial frequency of 0.
3.30
spectrally neutral
test chart is spectrally neutral if the relative spectral power distributions of the incident and reflected (or transmitted)
light are equal
3.31
test chart
arrangement of test patterns designed to test particular aspects of an imaging system
4 © ISO 2000 – All rights reserved

3.32
test pattern
specified arrangement of spectral reflectance or transmittance characteristics used in measuring an image quality
attribute
The test pattern spectral characteristics include the following types:
3.32.1
bi-tonal pattern
pattern that is spectrally neutral or effectively spectrally neutral, and consists exclusively of two reflectance or
transmittance values in a prescribed spatial arrangement
NOTE Bi-tonal patterns are typically used to measure resolving power, limiting resolution and SFR.
3.32.2
grey scale pattern
pattern that is spectrally neutral or effectively spectrally neutral, and consists of a large number of different
reflectance or transmittance values in a prescribed spatial arrangement
NOTE Grey scale patterns are typically used to measure opto-electronic conversion functions.
3.32.3
spectral pattern
pattern that is specified by the spatial arrangement of features with differing spectral reflectance or transmittance
values
NOTE Spectral patterns are typically used to measure colour reproduction.
3.33
vertical resolution
resolution value measured in the shorter image dimension, corresponding to the vertical direction for a "landscape"
image orientation, typically using a horizontally oriented test-chart feature
3.34
visual resolution
spatial frequency at which the individual black and white lines of a test pattern reproduced on a display or print can
no longer be distinguished by human observers, or are reproduced at a spatial frequency lower than the spatial
frequency of the corresponding area of the test chart, as a result of aliasing
4 Test chart
4.1 Introduction
A reproduction of a test chart for measuring the resolution of an electronic still-picture camera is shown in Figure 1.
Figure 2 is a diagram showing the locations of particular features of the test chart, which may be either a reflective
or transmissive chart. The purpose of each test pattern element is listed in Table 1. A complete spreadsheet
specification of the test chart is given for information in annex A.
The measurements described in clause 6 can be performed using test charts other than the chart shown in
Figure 1. For example, the test patterns present in the test chart can be separated and rearranged, if required, for
specific test objectives. The framing and the reproduction scale of the patterns can also be varied, if required, for
specific test objectives.
The chart shown in Figure 1 is designed to measure cameras having a limiting resolution of less than
2 000 LW/PH. Nevertheless, it is possible to use the chart to measure the visual resolution or limiting resolution of
an electronic still camera having a limiting resolution greater than 2 000 LW/PH. This is accomplished by adjusting
the camera to target distance, or the focal length of the camera lens, so that the test-chart active area fills only a
fraction of the vertical image height of the camera. This fraction is then measured in the digital image, by dividing
the number of image lines in the camera image by the number of lines in the active chart area. The values of all
test-chart features, in LW/PH, printed on the chart or specified in this International Standard, are multiplied by this
fraction, to obtain their correct values. For example, if the chart fills 1/4 of the vertical image height of the camera, a
feature labelled as 1 000 LW/PH on the chart corresponds to 4 000 LW/PH using this chart framing.
4.2 Material
The test chart may be either a transparency that is rear illuminated, or a reflection test card that is front illuminated.
A reflection chart shall have an approximately Lambertian base material. A transparency chart shall be rear
illuminated by a diffuse source.
4.3 Size
The active height of reflection test charts should be not less than 20 cm. The active height of transparencies shall
be not less than 10 cm. The chart should have a 16:9 image aspect ratio, with indicators for 1:1, 4:3 and 3:2 image
aspect ratios.
4.4 Test patterns
The test chart shall have bi-tonal patterns and should be spectrally neutral.
NOTE Use of bi-tonal test charts provides the sharpest possible features and minimizes the cost of producing the chart.
4.5 Test-pattern modulation
For reflectance charts, the ratio of the maximum chart reflectance R to the minimum chart reflectance R for
max min
large test-pattern areas should be not less than 40:1 and not greater than 80:1, and shall be reported if it is outside
this range. For transmissive charts, the ratio of the maximum chart transmittance T to the minimum chart
max
transmittance T for a large test pattern should be not less than 40:1 and not greater than 80:1, and shall be
min
reported if it is outside this range. Modulation ratios for the finer test-chart features, relative to the ratio for large
test-pattern areas, should preferably be reported by the chart manufacturer as described in annex B, so that these
values may be used to correct the SFR values measured using the chart.
4.6 Units
All test-chart features are specified in units of line widths per picture height (LW/PH), where the height is the active
image distance in the shorter test-chart dimension.
NOTE This allows measurements to be reported using units that are independent of the sample spacing and the image
aspect ratio.
4.7 Features
The test chart should include horizontal, vertical and diagonally oriented hyperbolic wedges, sweeps and tilted
bursts. It may also include a circle and long, slightly slanted lines to measure geometric linearity (distortion).
NOTE The finest features are 2 000 LW/PH, which is equivalent to 1 000 line pairs per picture height.
4.8 Positional tolerance
The position of any test-chart feature shall be proportional to the values given in normative annex C and shall be
reproduced with a tolerance of � 1/1 000 picture heights (equivalent to � 1/10 % of the active test-chart height). In
addition, the width and duty cycle ratio of each feature (white or black line) of J, JS, K, KS, O and P in Figure 2
shall be reproduced with a tolerance of � 5 % of the feature width.
This tolerance requires all test-chart features to be accurately located to with � 2/10 mm for a test-chart height of
20 cm. In addition, the width of the white or black lines comprising the 2 000 LW/PH portion of K1 are required to
fall within the range of 1/2 000 � 5 % of the actual test-chart height, equal to 95/1 000 mm to 105/1 000 mm for a
test-chart height of 20 cm.
6 © ISO 2000 – All rights reserved

Figure 1 — Resolution test chart
Figure 2 — Test-chart features
8 © ISO 2000 – All rights reserved

Table 1 — Test-chart elements
Element Purpose
A Black border with inner edge which defines active target area
a
Black and white framing arrows used to frame target vertically
B
Used for horizontal framing only for 16:9 aspect ratio image formats
B1 White framing arrows used to assist in framing target
a
Centre dual-frequency zone plate inside black square used to set focus
C
a
Framing lines and arrows that define 1:1, 4:3 and 3:2 aspect ratios
D
a
Slightly slanted lines used to check scan linearity and "stair stepping"
E
a
100 LW/PH to 1 000 LW/PH black bars to measure horizontal pulse response
G1
a
100 LW/PH to 1 000 LW/PH black bars to measure vertical pulse response
G2
J1 100 LW/PH to 600 LW/PH hyperbolic zone plate used to measure centre horizontal visual resolution
J2 100 LW/PH to 600 LW/PH hyperbolic zone plate used to measure centre vertical visual resolution
a
100 LW/PH to 600 line width hyperbolic zone plate used to measure corner horizontal visual
JS1
resolution
a
100 LW/PH to 600 line width hyperbolic zone plate used to measure corner vertical visual resolution
JS2
K1 500 LW/PH to 2 000 LW/PH hyperbolic zone plate used to measure centre horizontal visual
resolution
K2 500 LW/PH to 2 000 LW/PH hyperbolic zone plate used to measure centre vertical visual resolution
a
500 LW/PH to 1 000 line width hyperbolic zone plate used to measure corner horizontal visual
KS1
resolution
a
500 LW/PH to 1 000 line width hyperbolic zone plate used to measure corner vertical visual
KS2
resolution
a
L1 Slightly slanted (approx. 5�) small black squares used to measure vertical and horizontal SFR at
extreme corners of image
a
L2 45� diagonal black square used to measure diagonal SFR
L3
Slightly slanted (approx. 5�) black bar used to measure centre horizontal SFR
L4 Slightly slanted (approx. 5�) black bar used to measure centre vertical SFR
a
Circle with cross and � used to observe scanning nonlinearities
M
a
Checkerboard patterns used to observe image compression artifacts
N
O1 Tilted (approx. 5�) square wave bursts used to measure horizontal aliasing ratio
O2
Tilted (approx. 5�) square wave bursts used to measure vertical aliasing ratio
a
100 to 1 000 line square wave sweep
P1
a
100 to 1 000 line square wave sweep
P2
a
Indicators that can be used for automatic target alignment
R
a
T1, T2 Slanted (approx. 5�) H-shaped bars used to measure SFR at far sides of image
a
Indicates optional element.
5 Test conditions
5.1 Test-chart illumination
The luminance of the test chart shall be sufficient to provide an acceptable camera output signal level. The test
chart shall be uniformly illuminated as shown in Figure 3, so that the luminance of any white area of the chart is
within � 10 % of the average luminance near the centre of the chart. The illumination sources should be baffled to
prevent direct illumination of the camera lens by the illumination sources. The area surrounding the test chart
should be of low reflectance, to minimize flare light. The chart should be shielded from any reflected light. The
illuminated test chart shall be effectively spectrally neutral with respect to either the daylight or tungsten illuminants
given in ISO 7589.
Figure 3 — Test-chart illumination method
5.2 Camera framing and lens focal-length setting
The camera shall be positioned to properly frame the test target. The vertical framing arrows are used to adjust the
magnification and the horizontal arrows are used to centre the target horizontally. The tips of the centre vertical
black framing arrows should be fully visible and the tips of the centre white framing arrows should not be visible.
The target shall be oriented so that the horizontal edge of the chart is approximately parallel to the horizontal
camera frame line. The approximate distance between the camera and the test chart should be reported along with
the measurement results.
5.3 Camera focusing
The camera focus should be set by performing a series of image captures at varying focus settings, and selecting
the focus setting that provides the highest average modulation level at a spatial frequency of about 1/4 the camera
Nyquist frequency. Alternately, the camera focus may be set so that the zone plate in the centre of the chart
exhibits the maximum aliasing possible.
5.4 Camera settings
The camera lens aperture (if adjustable) and the exposure time should be adjusted to provide a near maximum
signal level from the white test target areas. The settings shall not result in signal clipping in either the white or
black areas of the test chart, or regions of edge transitions.
10 © ISO 2000 – All rights reserved

Electronic still-picture cameras may include image compression, to reduce the size of the image files and allow
more images to be stored. The use of image compression can significantly affect resolution measurements. Some
cameras have switches that allow the camera to operate in various compression or resolution modes. The values
of all camera settings that may affect the results of the measurement, including lens focal length, aperture and
resolution or compression mode (if adjustable), shall be reported along with the measurement results.
Multiple SFR measurements may be reported for different camera settings, including a setting that uses the
maximum lens aperture size (minimum f-number) and maximum camera gain.
5.5 White balance
For a colour camera, the camera white balance should be adjusted, if possible, to provide proper white balance
[equal red, green and blue (RGB) signal levels] for the illumination light source, as specified in ISO 14524.
5.6 Luminance and colour measurements
Resolution measurements are normally performed on the camera luminance signal. For colour cameras that do not
provide a luminance output signal, a luminance signal should be formed from an appropriate combination of the
colour records, rather than from a single channel such as green.
5.7 Gamma correction
The signal representing the image from an electronic still-picture camera will probably be a non-linear function of
the scene luminance values. Since the SFR measurement is defined on a linearized output signal, and such a non-
linear response will affect SFR values, the signal shall be linearized before the data analysis is performed.
Linearization is accomplished by applying the inverse of the camera OECF to the output signal via a lookup table or
appropriate equation. The measurement of the OECF shall be as specified in ISO 14524, using the standard
reflection camera OECF test chart.
6 Test measurements
6.1 Visual resolution
The visual resolution is the lowest value of the test pattern, in LW/PH, where the individual black and white lines
can no longer be distinguished, or are reproduced at a spatial frequency lower than the spatial frequency of the
corresponding area of the test chart, as a result of aliasing. The test chart includes vertical, horizontal, and diagonal
hyperbolic wedges near the centre and corners of the target, labelled as K1, K2, KS1, KS2, KD, J1, J2, JS1, JS2
and JD in Figure 2, which are used to perform this test.
The centre horizontal visual resolution is determined by observing the vertically oriented hyperbolic wedges
labelled J1 and K1 in Figure 2, and the centre vertical visual resolution is determined by observing the horizontally
oriented hyperbolic wedges labelled J2 and K2. The 45� diagonal visual resolution is determined using the
diagonally oriented hyperbolic wedges labelled KD and JD. The four corner horizontal and vertical visual-resolution
values may be determined using the appropriate corner wedges, labelled JS1, JS2, KS1 and KS2.
To determine the visual resolution, the image of the test target is reproduced on a monitor or hard-copy print, and
the visual resolution is subjectively judged. Observers should be well acquainted with the appearance of aliasing,
so that they do not seriously misjudge the visual resolution of the camera. The visual-resolution value shall not
exceed the Nyquist limit.
To perform the test properly, the monitor or hard-copy print shall have sufficient resolution so as not to affect the
camera visual-resolution measurement. A preferred method for reducing the effect of the output device is to
digitally magnify the portions of the image representing the hyperbolic wedges by replicating lines and pixels, so
that the number of addressable pixels used to display this portion of the image is an integer multiple of the number
of addressable pixels of digital data provided from the electronic still-picture camera.
6.2 Limiting resolution
The limiting resolution is the value, in LW/PH, of that portion of a black and white resolution wedge where the
resolution response (average depth of modulation value) equals 5 % of the reference response. The test chart
includes vertical and horizontal square wave sweeps, labelled as P1 and P2 in Figure 2, which are used to perform
this measurement. For P1, the reference response is defined as the difference between the signal values from the
slanted black bar L4 and the white region just below the L4 bar. For P2, the reference response is defined as the
difference between the signal values from the right vertical slanted black bar of T1 and the white region just to the
right of this bar. The sweeps include fiducial marks labelled a1 to 10, which correspond to 100 LW/PH to
1 000 LW/PH. Care should be taken in determining the 5 % level to avoid the influence of noise. If necessary,
multiple images should be averaged to reduce the noise level.
6.3 Spatial frequency response
6.3.1 Introduction
The spatial frequency response (SFR) of an electronic still-picture camera is measured by analysing the camera
data near a slanted black to white edge. For the target shown in Figure 2, the black L3 bar shall be used to
measure the horizontal SFR and the black L4 bar shall be used to measure the vertical SFR, in the centre of the
image. The diagonal black square L2 shall be used to measure the diagonal SFR near the centre of the image. The
L1 and L4 test patterns may be used to measure the SFR at other locations in the image.
The SFR measurement can be performed automatically by image-processing software, as part of an easy to use
1)
image processing or analysis software package . To perform the measurement, the digital camera output data in
the region of specified black to white and white to black edges on the test chart are analysed by a defined
numerical algorithm. If the camera provides only analog output signals, the signals shall be digitized by a suitable
analog to digital converter and stored in a suitable memory to allow the data to be analysed by the algorithm.
6.3.2 SFR algorithm
The SFR algorithm is given in normative annex C and shown in flow-chart form in Figure 4. A diagram depicting the
key steps of the SFR algorithm is shown in Figure 5. A sample C-code is given for information in annex D.
The algorithm can automatically compute the SFR, using image data from a user-defined rectangular region of the
image which represents a vertically oriented black to white or white to black slightly slanted edge, depicting a
"horizontal" transition. To measure the vertical SFR, a horizontally oriented edge is used, and the digital image data
is rotated 90� before performing the calculation. The user then selects the region containing the slightly slanted
edge. If the image is coloured, a luminance record is created before the SFR calculation is performed. The image
code values shall then be linearized by inverting the opto-electronic conversion function (OECF) of the camera. The
opto-electronic conversion function shall be measured as specified in ISO 14524.
Next, for each line of pixels perpendicular to the edge, the derivative of the linearized image data is computed
using a "1/2, + 1/2" finite impulse response (FIR) filter, meaning that the derivative value for pixel "X" is equal to
�1/2 times the value of the pixel immediately to the left, plus 1/2 times the value of the pixel to the right. The
centroid of this derivative is calculated to determine the position of the edge on each line. A best-line fit to the
centroid locations is then calculated. Error messages shall be reported if any centroid is within 2 pixels of either
side of the input image edges, or if the edge does not contain at least 20 % modulation. The number of lines used
in the analysis shall be truncated to provide an equal number of lines at each phase of the edge position relative to
the horizontal centre of the pixel. This may be done by keeping the largest integer number of phase rotations within
the block, and deleting any remaining rows at the bottom of the block. A one-dimensional supersampled line spread
function shall be formed using the derivatives of the truncated two-dimensional image data. Using the first line as
reference points, the data points from all the other lines shall be placed into one of four "bins" between these
1) For example, as part of the development of this standard, the SFR algorithm, written in the C programming language, has
been incorporated in a plug-in for Adobe Photoshop. Photoshop is the trade-name of a product supplied by Adobe Systems
Incorporated. This information is given for the convenience of users of this International Standard and does not constitute an
endorsement by ISO of the product named. Equivalent products may be used if they can be shown to lead to the same results.
12 © ISO 2000 – All rights reserved

reference points, according to the distance from the edge for that particular line. This creates a single
supersampled "composite" line spread function, having four times as many points along the line as the original
image data. The line spread function shall be multiplied by a Hamming window, to reduce the effects of noise by
reducing the influence of pixels at the extremes of the window, which have response due to noise but little
response due to the image edge located at the centre of the window. The discrete Fourier transform (DFT) of the
windowed line spread function shall be calculated. The SFR is the normalized modulus of the DFT of the line
spread function. The SFR shall be reported as defined in 7.1.
Figure 4 — Flow-chart of SFR measurement algorithm
Figure 5 — Key steps of SFR measurement algorithm
14 © ISO 2000 – All rights reserved

6.4 Aliasing ratio
The aliasing level is measured using the horizontal and vertical 100 LW/PH to 1 000 LW/PH slanted burst patterns
labelled O1 and O2 (see Figure 2).
In the absence of aliasing, the signal level from each black bar, or each white bar, should be identical for each bar
in the burst. Because of aliasing, however, the signal responses of the camera to the white bars of a particular
burst may not be ident
...

SLOVENSKI STANDARD
01-julij-2011
)RWRJUDILMD'LJLWDOQHNDPHUH]DPLUXMRþHVOLNH0HUMHQMHORþOMLYRVWL
Photography - Electronic still-picture cameras - Resolution measurements
Photographie - Appareils de prises de vue électroniques - Mesurages de la résolution
Ta slovenski standard je istoveten z: ISO 12233:2000
ICS:
37.040.10 Fotografska oprema. Photographic equipment.
Projektorji Projectors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL ISO
STANDARD 12233
First edition
2000-09-01
Photography — Electronic still-picture
cameras — Resolution measurements
Photographie — Appareils de prises de vue électroniques — Mesurages
de la résolution
Reference number
©
ISO 2000
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ii © ISO 2000 – All rights reserved

Contents Page
Foreword.iv
0 Introduction.v
0.1 Purpose.v
0.2 Technical background.v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Test chart.5
4.1 Introduction.5
4.2 Material .6
4.3 Size.6
4.4 Test patterns .6
4.5 Test-pattern modulation.6
4.6 Units .6
4.7 Features .6
4.8 Positional tolerance.6
5 Test conditions .10
5.1 Test-chart illumination .10
5.2 Camera framing and lens focal-length setting .10
5.3 Camera focusing.10
5.4 Camera settings.10
5.5 White balance.11
5.6 Luminance and colour measurements.11
5.7 Gamma correction .11
6 Test measurements .11
6.1 Visual resolution.11
6.2 Limiting resolution.12
6.3 Spatial frequency response.12
6.4 Aliasing ratio .15
7 Presentation of results.15
7.1 Introduction.15
7.2 Visual resolution.15
7.3 Limiting resolution.15
7.4 Spatial frequency response (SFR) .15
7.5 Aliasing ratio .16
Annex A (informative) SFR measurement algorithm C-code.17
Annex B (informative) Test-chart dimensions.28
Annex C (normative) Spatial frequency response (SFR) algorithm.29
Annex D (informative) Relationships between resolution metrics.31
Bibliography.32
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 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 12233 was prepared by Technical Committee ISO/TC 42, Photography.
Annex C forms a normative part of this International Standard. Annexes A, B and D are for information only.
iv © ISO 2000 – All rights reserved

0 Introduction
0.1 Purpose
The spatial resolution capability is an important attribute of an electronic still-picture camera. Resolution
measurement standards allow users to compare and verify spatial resolution measurements. This International
Standard defines terminology, test charts and test methods for performing resolution measurements for analog and
digital electronic still-picture cameras.
0.2 Technical background
One of the most important characteristics of an electronic still-picture camera is the ability of the camera to capture
fine detail found in the original scene. This ability to resolve detail is determined by a number of factors, including
the performance of the camera lens, the number of addressable photoelements in the optical imaging device, and
the electrical circuits in the camera, which may include image compression and gamma correction functions.
Different measurement methods can provide different metrics to quantify the resolution of an imaging system, or a
component of an imaging system, such as a lens. Resolution measurement metrics include resolving power,
limiting resolution (at some specified contrast), spatial frequency response, MTF and OTF.
The first step in measuring resolution is to capture an image of a suitable test-chart with the camera under test. The
test chart should include patterns with sufficiently fine detail, such as edges, lines, square waves, or sine wave
patterns. The test chart defined in this International Standard has been designed specifically to evaluate electronic
still-picture cameras. It has not been designed to evaluate other electronic imaging equipment such as input
scanners, CRT displays, hard-copy printers, or electrophotographic copiers, nor individual components of an
electronic still-picture camera, such as the lens.
The resolution measurements described in this International Standard are performed in the digital domain, using
digital analysis techniques. For electronic still-picture cameras that include only analog outputs, the analog signal
needs to be digitized, so that the digital measurement can be performed. The digitizing equipment is characterized,
so that the effects of the digitization process can be removed from the measurement results. When this is not
possible, the type of digitizing equipment used shall be reported along with the measurement results.
The spatial frequency response (SFR) measurement method described in this International Standard uses a
computer algorithm to analyse digital image data from the electronic still-picture camera. Digitized image values
near slanted vertical and horizontal black to white edges are digitized and used to compute the SFR values. The
use of a slanted edge allows the edge gradient to be measured at many phases relative to the image sensor
photoelements, in order to eliminate the effects of aliasing. This technique is mathematically equivalent to
performing a moving knife edge measurement.
INTERNATIONAL STANDARD ISO 12233:2000(E)
Photography — Electronic still-picture cameras — Resolution
measurements
1 Scope
This International Standard specifies methods for measuring the resolution of electronic still-picture cameras. It is
applicable to the measurement of both monochrome and colour cameras which output digital data or analog video
signals.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 7589:1984, Photography — Illuminants for sensitometry — Specifications for daylight and incandescent
tungsten.
ISO 14524:1999, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic
conversion functions (OECFs).
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
3.1
addressable photoelements
number of active photoelements in an image, which is equal to the number of active lines of photoelements
multiplied by the number of active photoelements per line
NOTE It is possible that the number of addressable photoelements may be different for the different colour records of an
image. When the signal values of the photoelements are digitized, the digitized code values may be referred to as picture
elements, or pixels.
3.2
aliasing
output image artifacts that occur in a sampled imaging system for input images having significant energy at
frequencies higher than the Nyquist frequency of the system
3.3
cycles per millimetre
cy/mm
unit used for specifying resolution characteristics in terms of the response of an imaging system to a linear radiance
sine wave input, as a function of the frequency of the sine wave
NOTE 1 A range of input sine wave frequencies is obtained in this International Standard through the use of a sharp edged
target.
NOTE 2 Most pictorial imaging systems exhibit non-linear behaviour, which may result in the nature of the target affecting the
measured resolution characteristics. Distance units other than millimetres may also be used.
3.4
aliasing ratio
value equal to the "maximum minus minimum" modulation divided by the "average" modulation of an electronic still-
picture camera when imaging a frequency burst of constant spatial frequency
NOTE The aliasing ratio is described in 6.4.
3.5
edge spread function
ESF
normalized spatial signal distribution in the linearized output of an imaging system resulting from imaging a
theoretical infinitely sharp edge
3.6
effectively spectrally neutral
having spectral characteristics which result in a specific imaging system producing the same output as for a
spectrally neutral object
3.7
electronic still-picture camera
camera incorporating an image sensor that outputs an analog or digital signal representing a still-picture, or records
an analog or digital signal representing a still-picture on a removable media, such as a memory card or magnetic
disc
3.8
gamma correction
process that alters the image data in order to modify the tone reproduction
3.9
horizontal resolution
resolution value measured in the longer image dimension, corresponding to the horizontal direction for a
"landscape" image orientation, typically using a vertically oriented test-chart feature
3.10
image aspect ratio
ratio of the image width to the image height
3.11
image compression
process that alters the way digital image data is encoded in order to reduce the size of an image file
3.12
image sensor
electronic device that converts an optical image into an electronic signal; for example a charge coupled device
(CCD) array
3.13
limiting resolution
value of that portion of a specified resolution test pattern, measured in line widths per picture height, that
corresponds to an average modulation value equal to some specified percentage of the modulation value at a
specified reference frequency
EXAMPLE The limiting resolution may be the test pattern value, in line widths per picture height (LW/PH), corresponding
to a camera output modulation level of 5 % of the camera output modulation level at a reference frequency of 10 LW/PH.
2 © ISO 2000 – All rights reserved

3.14
line pairs per millimetre
lp/mm
metric for specifying resolution in terms of the number of equal width black and white line pairs per millimetre that
can be resolved according to some criterion, such as visual resolution or limiting resolution
NOTE distance units other than millimetres may also be used.
3.15
lines per millimetre
lines/mm
metric for specifying resolution in terms of the number of equal-width black and white lines per millimetre that can
be resolved according to some criterion, such as visual resolution or limiting resolution
NOTE Distance units other than millimetres may also be used.
3.16
line spread function
LSF
normalized spatial signal distribution in the linearized output of an imaging system resulting from imaging a
theoretical infinitely thin line
NOTE If the imaging system is operating in an isoplanatic region and in its linear range, the LSF is equal to the first
derivative of the ESF.
3.17
line widths per picture height
LW/PH
metric for specifying the width of a solid line on a test chart, relative to the height of the active area of the chart,
which is equal to the height of the active area of the test chart divided by the width of a black line, that is equal to
the total number of lines of the same width which can be placed edge to edge within the height of a test target, or
within the vertical field of view of a camera
NOTE If the height of the active area of the chart equals 20 cm, a black line of 1 000 LW/PH has a width equal to
20/1 000 cm.
3.18
linearized
digital signal conversion performed to invert the camera opto-electronic conversion function (OECF) so that the
resulting signal is approximately linearly proportional to the scene luminance
3.19
modulation
difference between the minimum and maximum signal levels divided by the sum of these levels
3.20
modulation transfer function
MTF
modulus of the optical transfer function
3.21
normalized spatial frequency
unit used for expressing spatial frequency response, where the distance dimension has been removed by
multiplying the spatial frequency in cycles per millimetre by the sampling period in millimetres
NOTE Normalized spatial frequency is particularly appropriate for comparing the spatial frequency response of imaging
systems where the rendering magnification is unknown, and the total number of samples is equal.
3.22
Nyquist limit
spatial frequency equal to 1/2 times the inverse of the sampling period
NOTE Energy at an input spatial frequency above the Nyquist limit will alias to a spatial frequency below the Nyquist limit in
the output image. The Nyquist limit may be different in the two orthogonal directions.
3.23
optical transfer function
OTF
two-dimensional Fourier transform of the imaging system's point spread function
NOTE 1 For the OTF to have significance, it is necessary that the imaging system be operating in an isoplanatic region and
in its linear range.
NOTE 2 The OTF is a complex function whose modulus has unity value at zero spatial frequency.
3.24
point spread function
PSF
normalized spatial signal distribution in the linearized output of an imaging system resulting from imaging a
theoretical infinitely small point source
3.25
resolution
measure of the ability of a camera system, or a component of a camera system, to depict picture detail
NOTE Resolution measurement metrics include resolving power, limiting resolution, spatial frequency response (SFR),
MTF and OTF.
3.26
sampling aspect ratio
ratio of the sample spacing in the two orthogonal sampling directions
NOTE If the sample spacing is equal, the aspect ratio of the sampling grid is 1:1 or "square", so that the sampling aspect
ratio provides "square pixels".
3.27
sampled imaging system
imaging system or device which generates an image signal by sampling an image at an array of discrete points, or
along a set of discrete lines, rather than a continuum of points
NOTE The sampling at each point is done using a finite size sampling aperture or area.
3.28
sample spacing
physical distance between sampling points or sampling lines
NOTE The sample spacing may be different in the two orthogonal sampling directions.
3.29
spatial frequency response
SFR
measured amplitude response of an imaging system as a function of relative input spatial frequency
NOTE 1 The SFR is normally represented by a curve of the output response to an input signal of unit amplitude, over a
range of spatial frequencies.
NOTE 2 The SFR is normalized to yield a value of unity at a spatial frequency of 0.
3.30
spectrally neutral
test chart is spectrally neutral if the relative spectral power distributions of the incident and reflected (or transmitted)
light are equal
3.31
test chart
arrangement of test patterns designed to test particular aspects of an imaging system
4 © ISO 2000 – All rights reserved

3.32
test pattern
specified arrangement of spectral reflectance or transmittance characteristics used in measuring an image quality
attribute
The test pattern spectral characteristics include the following types:
3.32.1
bi-tonal pattern
pattern that is spectrally neutral or effectively spectrally neutral, and consists exclusively of two reflectance or
transmittance values in a prescribed spatial arrangement
NOTE Bi-tonal patterns are typically used to measure resolving power, limiting resolution and SFR.
3.32.2
grey scale pattern
pattern that is spectrally neutral or effectively spectrally neutral, and consists of a large number of different
reflectance or transmittance values in a prescribed spatial arrangement
NOTE Grey scale patterns are typically used to measure opto-electronic conversion functions.
3.32.3
spectral pattern
pattern that is specified by the spatial arrangement of features with differing spectral reflectance or transmittance
values
NOTE Spectral patterns are typically used to measure colour reproduction.
3.33
vertical resolution
resolution value measured in the shorter image dimension, corresponding to the vertical direction for a "landscape"
image orientation, typically using a horizontally oriented test-chart feature
3.34
visual resolution
spatial frequency at which the individual black and white lines of a test pattern reproduced on a display or print can
no longer be distinguished by human observers, or are reproduced at a spatial frequency lower than the spatial
frequency of the corresponding area of the test chart, as a result of aliasing
4 Test chart
4.1 Introduction
A reproduction of a test chart for measuring the resolution of an electronic still-picture camera is shown in Figure 1.
Figure 2 is a diagram showing the locations of particular features of the test chart, which may be either a reflective
or transmissive chart. The purpose of each test pattern element is listed in Table 1. A complete spreadsheet
specification of the test chart is given for information in annex A.
The measurements described in clause 6 can be performed using test charts other than the chart shown in
Figure 1. For example, the test patterns present in the test chart can be separated and rearranged, if required, for
specific test objectives. The framing and the reproduction scale of the patterns can also be varied, if required, for
specific test objectives.
The chart shown in Figure 1 is designed to measure cameras having a limiting resolution of less than
2 000 LW/PH. Nevertheless, it is possible to use the chart to measure the visual resolution or limiting resolution of
an electronic still camera having a limiting resolution greater than 2 000 LW/PH. This is accomplished by adjusting
the camera to target distance, or the focal length of the camera lens, so that the test-chart active area fills only a
fraction of the vertical image height of the camera. This fraction is then measured in the digital image, by dividing
the number of image lines in the camera image by the number of lines in the active chart area. The values of all
test-chart features, in LW/PH, printed on the chart or specified in this International Standard, are multiplied by this
fraction, to obtain their correct values. For example, if the chart fills 1/4 of the vertical image height of the camera, a
feature labelled as 1 000 LW/PH on the chart corresponds to 4 000 LW/PH using this chart framing.
4.2 Material
The test chart may be either a transparency that is rear illuminated, or a reflection test card that is front illuminated.
A reflection chart shall have an approximately Lambertian base material. A transparency chart shall be rear
illuminated by a diffuse source.
4.3 Size
The active height of reflection test charts should be not less than 20 cm. The active height of transparencies shall
be not less than 10 cm. The chart should have a 16:9 image aspect ratio, with indicators for 1:1, 4:3 and 3:2 image
aspect ratios.
4.4 Test patterns
The test chart shall have bi-tonal patterns and should be spectrally neutral.
NOTE Use of bi-tonal test charts provides the sharpest possible features and minimizes the cost of producing the chart.
4.5 Test-pattern modulation
For reflectance charts, the ratio of the maximum chart reflectance R to the minimum chart reflectance R for
max min
large test-pattern areas should be not less than 40:1 and not greater than 80:1, and shall be reported if it is outside
this range. For transmissive charts, the ratio of the maximum chart transmittance T to the minimum chart
max
transmittance T for a large test pattern should be not less than 40:1 and not greater than 80:1, and shall be
min
reported if it is outside this range. Modulation ratios for the finer test-chart features, relative to the ratio for large
test-pattern areas, should preferably be reported by the chart manufacturer as described in annex B, so that these
values may be used to correct the SFR values measured using the chart.
4.6 Units
All test-chart features are specified in units of line widths per picture height (LW/PH), where the height is the active
image distance in the shorter test-chart dimension.
NOTE This allows measurements to be reported using units that are independent of the sample spacing and the image
aspect ratio.
4.7 Features
The test chart should include horizontal, vertical and diagonally oriented hyperbolic wedges, sweeps and tilted
bursts. It may also include a circle and long, slightly slanted lines to measure geometric linearity (distortion).
NOTE The finest features are 2 000 LW/PH, which is equivalent to 1 000 line pairs per picture height.
4.8 Positional tolerance
The position of any test-chart feature shall be proportional to the values given in normative annex C and shall be
reproduced with a tolerance of � 1/1 000 picture heights (equivalent to � 1/10 % of the active test-chart height). In
addition, the width and duty cycle ratio of each feature (white or black line) of J, JS, K, KS, O and P in Figure 2
shall be reproduced with a tolerance of � 5 % of the feature width.
This tolerance requires all test-chart features to be accurately located to with � 2/10 mm for a test-chart height of
20 cm. In addition, the width of the white or black lines comprising the 2 000 LW/PH portion of K1 are required to
fall within the range of 1/2 000 � 5 % of the actual test-chart height, equal to 95/1 000 mm to 105/1 000 mm for a
test-chart height of 20 cm.
6 © ISO 2000 – All rights reserved

Figure 1 — Resolution test chart
Figure 2 — Test-chart features
8 © ISO 2000 – All rights reserved

Table 1 — Test-chart elements
Element Purpose
A Black border with inner edge which defines active target area
a
Black and white framing arrows used to frame target vertically
B
Used for horizontal framing only for 16:9 aspect ratio image formats
B1 White framing arrows used to assist in framing target
a
Centre dual-frequency zone plate inside black square used to set focus
C
a
Framing lines and arrows that define 1:1, 4:3 and 3:2 aspect ratios
D
a
Slightly slanted lines used to check scan linearity and "stair stepping"
E
a
100 LW/PH to 1 000 LW/PH black bars to measure horizontal pulse response
G1
a
100 LW/PH to 1 000 LW/PH black bars to measure vertical pulse response
G2
J1 100 LW/PH to 600 LW/PH hyperbolic zone plate used to measure centre horizontal visual resolution
J2 100 LW/PH to 600 LW/PH hyperbolic zone plate used to measure centre vertical visual resolution
a
100 LW/PH to 600 line width hyperbolic zone plate used to measure corner horizontal visual
JS1
resolution
a
100 LW/PH to 600 line width hyperbolic zone plate used to measure corner vertical visual resolution
JS2
K1 500 LW/PH to 2 000 LW/PH hyperbolic zone plate used to measure centre horizontal visual
resolution
K2 500 LW/PH to 2 000 LW/PH hyperbolic zone plate used to measure centre vertical visual resolution
a
500 LW/PH to 1 000 line width hyperbolic zone plate used to measure corner horizontal visual
KS1
resolution
a
500 LW/PH to 1 000 line width hyperbolic zone plate used to measure corner vertical visual
KS2
resolution
a
L1 Slightly slanted (approx. 5�) small black squares used to measure vertical and horizontal SFR at
extreme corners of image
a
L2 45� diagonal black square used to measure diagonal SFR
L3
Slightly slanted (approx. 5�) black bar used to measure centre horizontal SFR
L4 Slightly slanted (approx. 5�) black bar used to measure centre vertical SFR
a
Circle with cross and � used to observe scanning nonlinearities
M
a
Checkerboard patterns used to observe image compression artifacts
N
O1 Tilted (approx. 5�) square wave bursts used to measure horizontal aliasing ratio
O2
Tilted (approx. 5�) square wave bursts used to measure vertical aliasing ratio
a
100 to 1 000 line square wave sweep
P1
a
100 to 1 000 line square wave sweep
P2
a
Indicators that can be used for automatic target alignment
R
a
T1, T2 Slanted (approx. 5�) H-shaped bars used to measure SFR at far sides of image
a
Indicates optional element.
5 Test conditions
5.1 Test-chart illumination
The luminance of the test chart shall be sufficient to provide an acceptable camera output signal level. The test
chart shall be uniformly illuminated as shown in Figure 3, so that the luminance of any white area of the chart is
within � 10 % of the average luminance near the centre of the chart. The illumination sources should be baffled to
prevent direct illumination of the camera lens by the illumination sources. The area surrounding the test chart
should be of low reflectance, to minimize flare light. The chart should be shielded from any reflected light. The
illuminated test chart shall be effectively spectrally neutral with respect to either the daylight or tungsten illuminants
given in ISO 7589.
Figure 3 — Test-chart illumination method
5.2 Camera framing and lens focal-length setting
The camera shall be positioned to properly frame the test target. The vertical framing arrows are used to adjust the
magnification and the horizontal arrows are used to centre the target horizontally. The tips of the centre vertical
black framing arrows should be fully visible and the tips of the centre white framing arrows should not be visible.
The target shall be oriented so that the horizontal edge of the chart is approximately parallel to the horizontal
camera frame line. The approximate distance between the camera and the test chart should be reported along with
the measurement results.
5.3 Camera focusing
The camera focus should be set by performing a series of image captures at varying focus settings, and selecting
the focus setting that provides the highest average modulation level at a spatial frequency of about 1/4 the camera
Nyquist frequency. Alternately, the camera focus may be set so that the zone plate in the centre of the chart
exhibits the maximum aliasing possible.
5.4 Camera settings
The camera lens aperture (if adjustable) and the exposure time should be adjusted to provide a near maximum
signal level from the white test target areas. The settings shall not result in signal clipping in either the white or
black areas of the test chart, or regions of edge transitions.
10 © ISO 2000 – All rights reserved

Electronic still-picture cameras may include image compression, to reduce the size of the image files and allow
more images to be stored. The use of image compression can significantly affect resolution measurements. Some
cameras have switches that allow the camera to operate in various compression or resolution modes. The values
of all camera settings that may affect the results of the measurement, including lens focal length, aperture and
resolution or compression mode (if adjustable), shall be reported along with the measurement results.
Multiple SFR measurements may be reported for different camera settings, including a setting that uses the
maximum lens aperture size (minimum f-number) and maximum camera gain.
5.5 White balance
For a colour camera, the camera white balance should be adjusted, if possible, to provide proper white balance
[equal red, green and blue (RGB) signal levels] for the illumination light source, as specified in ISO 14524.
5.6 Luminance and colour measurements
Resolution measurements are normally performed on the camera luminance signal. For colour cameras that do not
provide a luminance output signal, a luminance signal should be formed from an appropriate combination of the
colour records, rather than from a single channel such as green.
5.7 Gamma correction
The signal representing the image from an electronic still-picture camera will probably be a non-linear function of
the scene luminance values. Since the SFR measurement is defined on a linearized output signal, and such a non-
linear response will affect SFR values, the signal shall be linearized before the data analysis is performed.
Linearization is accomplished by applying the inverse of the camera OECF to the output signal via a lookup table or
appropriate equation. The measurement of the OECF shall be as specified in ISO 14524, using the standard
reflection camera OECF test chart.
6 Test measurements
6.1 Visual resolution
The visual resolution is the lowest value of the test pattern, in LW/PH, where the individual black and white lines
can no longer be distinguished, or are reproduced at a spatial frequency lower than the spatial frequency of the
corresponding area of the test chart, as a result of aliasing. The test chart includes vertical, horizontal, and diagonal
hyperbolic wedges near the centre and corners of the target, labelled as K1, K2, KS1, KS2, KD, J1, J2, JS1, JS2
and JD in Figure 2, which are used to perform this test.
The centre horizontal visual resolution is determined by observing the vertically oriented hyperbolic wedges
labelled J1 and K1 in Figure 2, and the centre vertical visual resolution is determined by observing the horizontally
oriented hyperbolic wedges labelled J2 and K2. The 45� diagonal visual resolution is determined using the
diagonally oriented hyperbolic wedges labelled KD and JD. The four corner horizontal and vertical visual-resolution
values may be determined using the appropriate corner wedges, labelled JS1, JS2, KS1 and KS2.
To determine the visual resolution, the image of the test target is reproduced on a monitor or hard-copy print, and
the visual resolution is subjectively judged. Observers should be well acquainted with the appearance of aliasing,
so that they do not seriously misjudge the visual resolution of the camera. The visual-resolution value shall not
exceed the Nyquist limit.
To perform the test properly, the monitor or hard-copy print shall have sufficient resolution so as not to affect the
camera visual-resolution measurement. A preferred method for reducing the effect of the output device is to
digitally magnify the portions of the image representing the hyperbolic wedges by replicating lines and pixels, so
that the number of addressable pixels used to display this portion of the image is an integer multiple of the number
of addressable pixels of digital data provided from the electronic still-picture camera.
6.2 Limiting resolution
The limiting resolution is the value, in LW/PH, of that portion of a black and white resolution wedge where the
resolution response (average depth of modulation value) equals 5 % of the reference response. The test chart
includes vertical and horizontal square wave sweeps, labelled as P1 and P2 in Figure 2, which are used to perform
this measurement. For P1, the reference response is defined as the difference between the signal values from the
slanted black bar L4 and the white region just below the L4 bar. For P2, the reference response is defined as the
difference between the signal values from the right vertical slanted black bar of T1 and the white region just to the
right of this bar. The sweeps include fiducial marks labelled a1 to 10, which correspond to 100 LW/PH to
1 000 LW/PH. Care should be taken in determining the 5 % level to avoid the influence of noise. If necessary,
multiple images should be averaged to reduce the noise level.
6.3 Spatial frequency response
6.3.1 Introduction
The spatial frequency response (SFR) of an electronic still-picture camera is measured by analysing the camera
data near a slanted black to white edge. For the target shown in Figure 2, the black L3 bar shall be used to
measure the horizontal SFR and the black L4 bar shall be used to measure the vertical SFR, in the centre of the
image. The diagonal black square L2 shall be used to measure the diagonal SFR near the centre of the image. The
L1 and L4 test patterns may be used to measure the SFR at other locations in the image.
The SFR measurement can be performed automatically by image-processing software, as part of an easy to use
1)
image processing or analysis software package . To perform the measurement, the digital camera output data in
the region of specified black to white and white to black edges on the test chart are analysed by a defined
numerical algorithm. If the camera provides only analog output signals, the signals shall be digitized by a suitable
analog to digital converter and stored in a suitable memory to allow the data to be analysed by the algorithm.
6.3.2 SFR algorithm
The SFR algorithm is given in normative annex C and shown in flow-chart form in Figure 4. A diagram depicting the
key steps of the SFR algorithm is shown in Figure 5. A sample C-code is given for information in annex D.
The algorithm can automatically compute the SFR, using image data from a user-defined rectangular region of the
image which represents a vertically oriented black to white or white to black slightly slanted edge, depicting a
"horizontal" transition. To measure the vertical SFR, a horizontally oriented edge is used, and the digital image data
is rotated 90� before performing the calculation. The user then selects the region containing the slightly slanted
edge. If the image is coloured, a luminance record is created before the SFR calculation is performed. The image
code values shall then be linearized by inverting the opto-electronic conversion function (OECF) of the camera. The
opto-electronic conversion function shall be measured as specified in ISO 14524.
Next, for each line of pixels perpendicular to the edge, the derivative of the linearized image data is computed
using a "1/2, + 1/2" finite impulse response (FIR) filter, meaning that the derivative value for pixel "X" is equal to
�1/2 times the value of the pixel immediately to the left, plus 1/2 times the value of the pixel to the right. The
centroid of this derivative is calculated to determine the position of the edge on each line. A best-line fit to the
centroid locations is then calculated. Error messages shall be reported if any centroid is within 2 pixels of either
side of the input image edges, or if the edge does not contain at least 20 % modulation. The number of lines used
in the analysis shall be truncated to provide an equal number of lines at each phase of the edge position relative to
the horizontal centre of the pixel. This may be done by keeping the largest integer number of phase rotations within
the block, and deleting any remaining rows at the bottom of the block. A one-dimensional supersampled line spread
function shall be formed using the derivatives of the truncated two-dimensional image data. Using the first line as
reference points, the data points from all the other lines shall be placed into one of four "bins" between these
1) For example, as part of the development of this standard, the SFR algorithm, written in the C programming language, has
been incorporated in a plug-in for Adobe Photoshop. Photoshop is the trade-name of a product supplied by Adobe Systems
Incorporated. This information is given for the convenience of users of this International Standard and does not constitute an
endorsement by ISO of the product named. Equivalent products may be used if they can be shown to lead to the same results.
12 © ISO 2000 – All rights reserved

reference points, according to the distance from the edge for that particular line. This creates a single
supersampled "composite" line spread function, having four times as many points along the line as the original
image data. The line spread function shall be multiplied by a Hamming window, to r
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