SIST EN 61146-1:1999
(Main)Video cameras (PAL/SECAM/NTSC) - Methods of measurement -- Part 1: Non-broadcast single-sensor cameras
Video cameras (PAL/SECAM/NTSC) - Methods of measurement -- Part 1: Non-broadcast single-sensor cameras
Applicable to the assessment of performance of non-broadcast colour video cameras equipped with a single-tube or solid-state imager.
Meßverfahren für Videokameras (PAL/SECAM/NTSC) -- Teil 1: Kameras mit einem Aufnahmesensor für den Gebrauch außerhalb des Rundfunks
Caméras vidéo (PAL/SECAM/NTSC) - Méthodes de mesure -- Partie 1: Caméras monocapteurs hors de la radiodiffusion
Concerne l'évaluation des performances des caméras couleur vidéo hors de la radiodiffusion, ce type de caméra étant équipé d'un seul tube analyseur ou d'un capteur solide.
Video cameras (PAL/SECAM/NTSC) - Methods of measurement -- Part 1: Non-broadcast single-sensor cameras (IEC 61146-1:1994)
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 61146-1:1999
01-april-1999
Video cameras (PAL/SECAM/NTSC) - Methods of measurement -- Part 1: Non-
broadcast single-sensor cameras (IEC 61146-1:1994)
Video cameras (PAL/SECAM/NTSC) - Methods of measurement -- Part 1: Non-
broadcast single-sensor cameras
Meßverfahren für Videokameras (PAL/SECAM/NTSC) -- Teil 1: Kameras mit einem
Aufnahmesensor für den Gebrauch außerhalb des Rundfunks
Caméras vidéo (PAL/SECAM/NTSC) - Méthodes de mesure -- Partie 1: Caméras
monocapteurs hors de la radiodiffusion
Ta slovenski standard je istoveten z: EN 61146-1:1996
ICS:
33.160.40 Video sistemi Video systems
SIST EN 61146-1:1999 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
NORME
CEI
INTERNATIONALE
IEC
61146-1
INTERNATIONAL
Première édition
STANDARD
First edition
1994-05
Caméras vidéo (PAL/SECAM/NTSC) –
Méthodes de mesure –
Partie 1:
Caméras monocapteurs hors de la radiodiffusion
Video cameras (PAL
/SECAM/NTSC) –
Methods of measurement –
Part 1:
Non-broadcast single-sensor cameras
© IEC 1994
Droits de reproduction réservés —
Copyright - all rights reserved
Aucune partie de cette
publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in
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quelque forme que ce soit et par aucun any form or by any means, electronic or mechanical,
procédé, électronique ou mécanique,
y compris la photo- including photocopying and microfilm, without permission in
copie et les
microfilms, sans l'accord écrit de l'éditeur. writing from the publisher.
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Telefax: +41 22 919 0300 e-mail: inmail@iec.ch IEC web site http: //www.iec.ch
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XD
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Me1HnyHapogHaR 311014TPOTeXHM413Cliall HOMMCCHR
Pour prix, voir catalogue en vigueur
•
• For price, see current catalogue
---------------------- Page: 2 ----------------------
1146-1 ©IEC:1994 – 3 –
CONTENTS
Page
FOREWORD 5
SECTION 1: GENERAL
Clause
1 Scope 7
2 Normative references 7
3 Conditions 9
SECTION 2: LUMINANCE VIDEO CHARACTERISTICS
4 Luminance sensitivity 11
5 Luminance resolution 17
6 Luminance signal-to-noise ratio 21
7 Luminance amplitude/frequency response 27
8 Luminance waveform distortion and pulse response 31
9 Luminance gamma characteristics 39
10 Luminance white clipping and compression rate 47
11 Luminance dynamic range and contrast range 51
12 Luminance white non-uniformity 51
CHROMINANCE
SECTION 3: VIDEO CHARACTERISTICS
13 Chrominance signal-to-noise ratio 59
14 Chrominance amplitude/frequency response 67
15 White and black balance 71
16 Colour and white reproduction non-uniformity 83
17 Grey-scale non-purity (white tracking error) 87
18 Colour reproduction 95
SECTION 4: OTHER CHARACTERISTICS
19 Luminance and chrominance moirés 109
20 Lag 121
21 Sticking (image retention) 131
22 Blooming 135
23 Smearing 139
24 Geometric distortions 147
Annexes
A Reference list of test charts 153
B
Arrangement of the CIE colour chips of the colour reproduction test chart 173
C Trap filter characteristics for PAL, NTSC, and SECAM systems 177
D
Letter symbols 183
E
Bibliography 187
---------------------- Page: 3 ----------------------
1146-1 ©IEC:1994 — 5 —
INTERNATIONAL ELECTROTECHNICAL COMMISSION
VIDEO CAMERAS (PAL/SECAM/NTSC) —
METHODS OF MEASUREMENT —
Part 1: Non-broadcast single-sensor cameras
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization
comprising all national electrotechnical committees (IEC National Committees). The object of the IEC is to
promote international cooperation on all questions concerning standardization in the electrical and
electronic fields. To this end and in addition to other activities, the IEC publishes International Standards.
Their preparation is entrusted to technical committees; any IEC National Committee interested in
the subject dealt with may participate in this preparatory work. International, governmental and
non-governmental organizations liaising with the IEC also participate in this preparation. The IEC
collaborates closely with the International Organization for Standardization (ISO) in accordance with
conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of the IEC on technical matters, prepared by technical committees on
which all the National Committees having a special interest therein are represented, express, as nearly as
possible, an international consensus of opinion on the subjects dealt with.
3) They have the form of recommendations for international use published in the form of standards, technical
reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
International Standard IEC 1146-1 has been prepared by IEC technical committee 84:
Equipment and systems in the field of audio, video, and audiovisual engineering.
The text of this standard is based on the following documents:
DIS Report on voting AMDIS Report on voting
84/60B(CO)146 84/60B(CO)156
84(CO)103 84/60B(CO)135/138
Full information on the voting for the approval of this part of the standard can be found in
the reports on voting indicated in the above table.
IEC 1146-1 forms part 1 of a series of publications under the general title: Video cameras
(PAL/SECAM/NTSC) — Methods of measurement.
Annexes A, B, C and D form an integral part of this standard.
Annex E is for information only.
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1146-1 © I EC:1994 — 7 —
VIDEO CAMERAS (PAL /SECAM/NTSC) –
METHODS OF MEASUREMENT –
Part 1: Non-broadcast single-sensor cameras
Section 1: General
1 Scope
This part of IEC 1146 is applicable to the assessment of performance of non-broadcast
colour video cameras equipped with a single-tube or solid-state imager.
This part of IEC 1146 defines test patterns and measurement conditions, so as to make
possible the comparison of the results of measurements. The methods of measurement
are designed to make possible the assessment of the performance of the camera by using
the lens input and any electrical output terminals of the device (e.g. Y/C and composite).
This part of IEC 1146 does not specify limiting values for various characteristics.
2 Normative references
The following normative documents contain provisions which, through reference in this
text, constitute provisions of this part of IEC 1146. At the time of publication, the editions
indicated were valid. All normative documents are subject to revision, and parties to
agreements based on this part of IEC 1146 are encouraged to investigate the possibility of
applying the most recent editions of the normative documents listed below. Members of
IEC and ISO maintain registers of currently valid International Standards.
chrominance signal-to-random noise ratio for video
IEC 883: 1987, Measuring method for
tape recorders
Transmission performance of television circuits designed
CCIR Recommendation 567-3:
for use in international connections (1978-1982-1986-1990)
Characteristics of television systems
CCIR Report 624-4: 1974-1978-1982-1986-1990,
CIE 15: 1971, Colorimetry: Official Recommendation of the International Commission on
Illuminants
Supplement 2: 1987, Recommendation on uniform colour space. Colour difference
equation — psychometric colour terms
CIE 13-2: 1988, Method of measuring and specifying colour rendering of light sources
CIE 01: 1986, Colorimetric illuminants
---------------------- Page: 5 ----------------------
1146-1 ©IEC:1994 — 9 —
CIE 02: 1986,
Colorimetric observers
IEC 27:
Letter symbols to be used in electrical technology
IEC 50(845): 1987, International Electrotechnical Vocabulary (1EV) — Chapter 845:
Lighting
3 Conditions
3.1 Environmental conditions
All measurements shall be carried out within the environmental conditions as specified by
the manufacturer.
The environmental conditions during measurement, at least the temperature and the
relative humidity, shall be reported together with the presentation of the results of
measurements.
An adequate warm-up time shall be allowed.
3.2 Conditions of measurements
Except when otherwise indicated, the measurements shall be carried out by measuring the
output signal of the camera when it is shooting different test charts, depending on the
characteristic to be measured.
Each test pattern shall be specified, together with the lighting conditions (illumination
intensity, correlated colour temperature of the light source, etc.).
The use of transparent test charts instead of the reflection types may be allowed;
however, the reflection types should be used in questionable cases.
Unless otherwise stated, all measurements shall be made in automatic mode.
3.3 Conditions of shooting
Unless otherwise stated, the conditions of shooting shall be as follows.
—
The subject illumination of a reflective test chart shall be 2 000 lx ± 5 % (see note).
— ±
The luminance of a transparent test chart, at peak white, shall be 636 cd/m 2 5 %.
— The non-uniformity of the subject illumination shall be less than 5 %.
— The correlated colour temperature of the light source shall be 3 100 K ± 100 K.
—
The white balance shall be set manually or automatically to 3 100 K ± 100 K.
---------------------- Page: 6 ----------------------
Oo
1146-1
IEC:1994 — 11 —
— The test chart shall be shot by the camera so that the frame limited by the arrows
coincides exactly with the edges of the picture displayed on the video monitor in
underscan mode.
— The focus control shall be in auto or manual mode, and shall be in optimum focus.
— The iris control shall be in auto or manual mode.
— In order to obtain the desired exposure level, it may be advantageous to add an
illuminated white card or a black area, and also to adjust the lens zoom so that the
measurement does not depend on exactly filling the screen to the arrows of the test
chart.
— The gain control, if any, shall be set to "0 dB" gain.
— The optical filter, if any, shall be set to "open position".
NOTE – Measured by a luxmeter at the centre of the test chart, the receptor pointing in the direction of
the camera.
3.4 Reference conditions
Unless otherwise specified, the reference luminance output signal level is assumed to
be 700 mV peak-to-peak (p.-p.) for PAL and SECAM systems and 714 mV peak-to-peak
for NTSC systems (from the blanking level to the peak white level).
NOTE – In the following clauses, it is also assumed, for the purpose of giving examples of output voltage
obtained under certain conditions, that the rated output voltage is also 700 mV p.-p. or 714 mV p.-p.
Section 2: Luminance video characteristics
4 Luminance sensitivity
4.1 Characteristic to be specified
The minimum subject illumination for which the video camera produces a luminance output
level of one-half the rated level.
4.2 Method of measurement
The equipment arrangement and the grey-scale test chart shall be as shown in
a)
figure 1.
b) The conditions of shooting shall be those mentioned in 3.3.
c) Either the screen size or the zoom condition may be changed, or a black or white
subject may be added, to give the rated output level, if this level is not obtained due to
the automatic light control.
d) In order to simulate a decrease of the subject illumination without changing the
correlated colour temperature of the observed light, a neutral density filter such as the
---------------------- Page: 7 ----------------------
1146-1 ©IEC:1994 — 13 —
Kodak Wratten* density filter No. 96 or equivalent shall be placed in front of the camera
lens.
The density of the filter shall be increased until the video output level E decreases to
half the rated output level corresponding to the level of the white area i n
the centre of
the grey scale test pattern (see figure 1).
The density (D) of the filter is read, and the sensitivity is then calculated by means of
the following formula:
illumination 2 000
Sensitivity =
attenuation of filter
4.3 Presentation of results
The value of the sensitivity shall be reported in lux.
* The Kodak Wratten density filter is an example of a suitable product available commercially. This
information is given for the convenience of users of this International Standard and does not constitute an
endorsement by the IEC of this product.
---------------------- Page: 8 ----------------------
1146-1 ©IEC:1994
— 15 —
Test chart No. 1
Underscan
colour TV monitor
OM
M
Grey-scale pattern (reflective type)
Gamma: 2,2
iiiiiiuiii9J —
—Reflectance (white area) : 89,9 %
in
Figure 1 — Luminance sensitivity
---------------------- Page: 9 ----------------------
1146-1 © I EC:1994 - 17 -
5 Luminance resolution
5.1 Characteristic to be specified
The resolution power of the luminance channel is:
- for the horizontal resolution, the number of vertical black and white bars within a
horizontal dimension equal to the picture height (TV lines);
- for the vertical resolution, the number of horizontal black and white bars within the
picture height.
5.2 Method of measurement
a) The equipment arrangement and the test chart shall be as shown in figure 2.
The test chart is either a radial resolution chart with circles corresponding to the num-
ber of TV lines or the conventional EIAJ-A chart or equivalent. This allows the measure-
ment of both the horizontal and the vertical resolution.
b) The conditions of shooting shall be those mentioned in 3.3.
c)
The resolution shall be evaluated on a monochrome TV monitor whose frequency
response shall exceed the bandwidth of the camera under test.
d)
The horizontal resolution is defined by the number of TV lines corresponding to the
limit of visibility of the vertical bars. The number of vertical bars may be measured as
the depth of modulation measured by an oscilloscope. It is estimated that a depth of
modulation of 5 % corresponds to the limit of visibility of the human eye (note).
e)
The vertical resolution is defined by the number of TV lines corresponding to the
limit of visibility of the horizontal bars.
NOTE — In case it is difficult to read the depth of modulation of 5 % on an oscilloscope, the number of
black and white lines at a modulation depth of 10 % may be reported, together with the value of the
modulation depth.
5.3
Presentation of results
The results shall be reported as follows:
-
horizontal resolution: TV lines;
- vertical resolution: TV lines.
Horizontal resolution in lines per picture width, is the number of TV lines per picture height
multiplied by the aspect ratio.
In cases of cameras equipped with exchangeable lens, the type shall be reported. If
possible, the characteristics of the lens used in the test should be reported.
---------------------- Page: 10 ----------------------
1146-1 ©
IEC:1994 19 -
-
Light
CT = 3100 K
Test chart
Light M
CT = 3100 K
Input not
terminated
4
•
•
Oscilloscope
^
Input terminated
by 75 0
Underscan monochrome
TV monitor
Test chart (reflective type) No. 3
Radial resolution chart
Figure 2 - Luminance resolution
---------------------- Page: 11 ----------------------
1146-1 ©IEC:1994
– 21 –
6 Luminance signal-to-noise ratio
6.1
Characteristics to be specified
The noise behaviour of the luminance channel, expressed as the signal-to-noise ratio.
6.2 Method of measurement
a) The equipment arrangement and the test chart shall be as shown in figures 3a
and 3b, respectively.
b) The conditions of shooting shall be those mentioned in 3.3, except for the following:
1)
subject illumination: Measurement shall be made at 2 000 lx and at the minimum
Ilumination level defined in clause 4, luminance sensitivity (see note).
NOTE – A neutral density filter may be placed in front of the lens in order to obtain the same illumi-
nation condition as in the measurement of the luminance sensitivity in clause 4. If required, an
additional measurement may be made at an intermediate luminance value.
2)
focusing shall be adjusted to infinity to be out of focus.
c) The noise superimposed on the output signal shall be measured by a noise meter
having the following characteristics:
1)
the noise meter shall have a gating function in order to perform noise
measurement in the steady flat portion of the signal only;
2) the measuring instrument shall be preceded by the following band-limiting filters:
–
low-pass filter according to CCIR Recommendation 567, annex Il with:
fc
= 5 MHz for the 625 line/50 field system (PAL/SECAM);
= 4,2 MHz for the 525 line/60 field system (NTSC);
c
–
high-pass filter according to CCIR Recommendation 567, annex Ill, with
c = 200 kHz;
– the chrominance subcarrier trap filter shall be switched on (see figures C.1
and C.2). In the case of SECAM, the chrominance subcarrier trap filter shall
have an attenuation of more than 46 dB for 4,25000 MHz and 4,40625 MHz (see
figure C.3);
– the weighting network, according to CCIR Recommendation 567, annex II,
shall be switchable ON and OFF,
3) the meter shall read the r.m.s. value of the noise V
Nrms
d) The reference level
V shall be the amplitude of the 100 % white output picture
ref
signal level, i.e from the blanking level to the white level.
e) The signal-to-noise ratio, S/N, shall be calculated as follows:
S/N = 20 Ig (
(dB)
V
ref
/ VNrms)
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1146-1 ©IEC:1994 — 23 —
6.3
Presentation of results
The results, i.e the unweighted and weighted values of S/N (dB) shall be stated for the two
conditions of illumination defined in 6.2, that is:
a) at 2 000 lx;
b) at the minimum sensitivity illumination (clause 4).
The luminance signal level shall be reported in this measurement.
6.4
Alternative method
6.4.1 Method of measurement
a)
The equipment arrangement of figure 3a shall be used, except that a neutral density
filter shall be put in the middle of the white chart, as in figure 3c, or alternatively, the
vertical grey-scale test chart can be used to measure the S/N ratio at different
luminance levels (see note 1).
b)
The conditions of shooting mentioned in 6.2b) are applicable.
c) The lens zoom may be adjusted in order to obtain a grey level of 50 % in the middle
of the active line, as shown in figure 3e.
d) The noise superimposed on the output signal shall be measured by a noise meter
having the same characteristics as that mentioned in 6.2c), but having a gate function
in order to permit noise measurement in the middle of the active field period, as shown
in figures 3d and 3e.
e)
In order to measure the signal-to-noise ratio, 6.2d) and 6.2e) shall be applied.
NOTES
1 The vertical grey-scale chart may be a conventional grey-scale chart vertically placed (see figure 3f).
2 The visual effects of correlated noise may not be represented adequately by this measurement.
6.4.2 Presentation of results
The presentation of the results shall be as mentioned in 6.3.
---------------------- Page: 13 ----------------------
1146-1 ©IEC:1994 - 25 -
Light
CT=3100K
41
Out of focus
^^ _Video
camera
Neutral density filter
used at low light
only
conditions
Light
CT=3100K
Test chart Inputs not
\ terminated
Input terminated
by 75 Q
Oscilloscope
Figure 3a - Equipment arrangement
^ 4
a
t
M
4
4
White pattern
•
Neutral density
4
filter
4 I ♦
•
I * Figure 3c - White test pattern
ir
Reflectance: > 0,7
Figure 3b - Test chart No. 2
(reflective type)
Test chart No. 1
Window gating
I
N
I
I Figure 3d - Output picture
I^ I
__^
t I
I
ilfl•^^
Noise to be
measured Gamma: 2,2
-
50 %
- Reflectance
(white area) : 89,9 %
Figure 3e - Output signal
Figure 3f - Grey scale pattern
(reflective type)
Figure 3 - Luminance signal-to-noise ratio
---------------------- Page: 14 ----------------------
1146-1 ©IEC:1994 - 27 -
7 Luminance
amplitude/frequency response
7.1 Characteristic to be specified
The amplitude/frequency response of the luminance channel, i.e., the amplitude of the
output signal relative to a reference level as a function of frequency.
7.2 Method of measurement
a)
The equipment arrangement and the test chart shall be as shown in figure 4.
The test chart shall be the multiburst chart having sinusoidal patterns of different pitch,
as given in figure 4.
The multiburst frequencies are:
0,5 - 1,0 - 1,5 - 2,0 - 2,5 - 3,0 - 4,0 - 5,0 - 6,0 MHz.
b) The conditions of shooting shall be those mentioned in 3.3. A black or white subject
may be added in order to obtain a luminance signal level of half of the rated level for
the background of the chart.
c) For SECAM, a trap filter shall be inserted after the camera output (see figure 4)
in order to suppress the chrominance subcarriers. The attenuation shall be greater than
46 dB for 4,25000 MHz and 4,40625 MHz (see annex C and note 1).
d) The output signal shall be measured on an oscilloscope (note 2). The reference
level V
shall be the level corresponding to the burst 0,5 MHz. The peak-to-peak
ref
amplitude Vn(p_p) of each frequency burst of the output signal shall be related to the
reference level V
to obtain the amplitude frequency response A, as indicated by the
ref
following expression:
p)
A = 20 Ig Vn(p (dB)
Vref
NOTES
1 In the case of separated Y/C signals, the trap filter is not used.
2 In some cases, it may be necessary to separate the amplitude of the wanted signals and alias
frequencies by measuring the output signal in the frequency domain by a spectrum analyser (aliases
caused by undersampling and optical low-pass filter characteristics).
3 If sinusoidal patterns are not available, rectangular shaped black and white patterns (bars) can also be
used.
7.3 Presentation of results
The results shall be reported in a table or a graph with the X axis representing the frequen-
cies, the Y axis representing the amplitude in dB and the measured amplitudes indicated
by dots.
---------------------- Page: 15 ----------------------
- 29 -
1146-1 © I EC:1994
Out of focus
Video
camera
For
SECAM measurement
Trap
only (see 7.2c) -'►
filter
Light
CT = 3100 K
Input not
Input terminated
terminated --^
Ay
by 7511
4
•
Oscilloscope
Test chart No. 6
Underscancolour
TV monitor
Sinusoidal multiburst chart
(reflective type) :
- The frequency burst is sinusoidal pattern
- The reflectance of grey area is 40
- The reflectance of the peak white pa rt is 60,3 %
05 1.0 1.5 20 2.5 3 4 5 5
- The reflectance of the blackest part is 23,4 %
Grey area
In MHz
Figure 4 – Luminance amplitude/frequency response
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1146-1 ©I EC:1994 — 31 —
8 Luminance waveform distortion and pulse response
8.1 Characteristics to be specified
The distortions of a bar signal and of a 2T pulse caused in the luminance channel.
8.2
Method of measurement
a) The equipment arrangement and the test chart shall be as shown in figure 5a.
b). The conditions of shooting shall be those mentioned in 3.3.
c) The output signal shall be measured by an oscilloscope on two selected lines L
and M. The following distortions shall be calculated by means of the formulae given
with the respective figures:
1) Selected line L
— overshoot Amplitude figure 5b
Duration figure 5c
— undershoot Amplitude figure 5b
Duration figure 5d
— smear Amplitude figure 5e
Duration figure 5e
— streaking Amplitude figure 5f
Duration figure 5f
2) Selected line M
— 2T pulse Amplitude figure 5g
8.3 Presentation of results
The results of measurement shall be reported in a table showing distortions and values in
percentage or in microseconds.
NOTE – To improve the apparent sharpness of the visible picture, some cameras may produce an over-
shoot at the edges of a bar signal. Taking this into account, it should be noticed that a smaller amplitude of
overshoots and undershoots does not necessarily indicate better picture quality.
---------------------- Page: 17 ----------------------
- 33 -
1146-1 ©IEC:1994
For SECAM measurement
Trap
only (see 7.2c)
filter
Input not
Input terminated
terminated
by 75 S2
Oscilloscope
Underscan
colour TV monitor
Test chart No.9
(reflective or
transparent ty
pe)
Line M
Line L
Figure 5a - Equipment arrangement and test chart
Figure 5 — Luminance waveform distortion and pulse response
---------------------- Page: 18 ----------------------
1146-1 ©IEC:1994
- 35 -
Figure 5b - Overshoot and undershoot
amplitude
Figure 5c - Overshoot duration
Figure 5d - Undershoot duration
Figure 5c - Overshoot: Amplitude = x 100
Duration = do in }us
Figure 5d - Undershoot: Amplitude = a x 100
Duration = du in µs
Figure 5 - Luminance waveform distortion and pulse response
(continued)
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1146-
1 ©IEC:1994 — 37 —
10 b
r
100
1
Amplitude: â x 100
Duration ds in }is
a
Figure 5e — Smear
b
1
Amplitude: x 100
â
10 b Duration dt in
µs
I 100 a
dt
Figure 5f — Streaking
Amplitude: x 100
b
a = amplitude specified in figure 5f
Figure 5g — 2T pulse amplitude
Figure 5 — Luminance waveform distortion and pulse response
(concluded)
---------------------- Page: 20 ----------------------
1146-1 ©IEC:1994 – 39 –
9 Luminance gamma characteristics
9.1 Characteristics to be specified
The behaviour of the gamma correction applied to the luminance signal in order to
compensate the non-linear characteristics of the cathode ray tube used for television dis-
play (see note).
NOTE – The characteristic of the cathode ray tube used for television display is an exponential function
is in the order of 2,2. This non-linearity is compensated by a gamma correc-
Lo = AV', where the exponent
T
tion in the analyser (video camera) whose characteristic is given by the formula:
V= K (La)117
where
V is the output signal of the camera;
Lo is the luminance of the TV display screen;
K is the constant (gain of the camera amplifier);
La is the luminance signal at the output of the imager.
The overall characteristics of the analyser plus the electro-optic converter will be:
= A(K (La) )7 = mLa
Lo 1/7
where
A is the constant (gain of the TV set amplifier);
m is the phosphor dot brightness efficiency.
shows that the proportionality condition is satisfactory to obtain a correct colour reproduc-
The result mLa
tion (see figures 6b, 6c and 6d).
9.2 Method of measurement
The equipment arrangement shall be as shown in figure 6a.
a)
b) The test chart shall be a grey-scale chart. The reflectance of each area from black
to white shall vary according to a curve having a gamma of 2,2 (see figure 6c).
c) The conditions of shooting shall be those mentioned in 3.3.
For SECAM, see 7.2, item c).
d)
e) The output signal shall be measured by an oscilloscope.
If the camera has a gamma of 0,45 (that is the inverse of the grey scale 2,2), the video
output signal represents a grey scale having a gamma of 1; this means that the
amplitude of the steps related to the black level are in equal increments (see figures 6d
and 6e).
n of the output signal, that is from the level at the
f) The amplitude Vo(n) of each step
step n=3 to the level at the step n=10, shall be measured (see figure 6e).
g) shall be the amplitude from blanking level to white level
The reference level V
ref
(see figure 6e). However, step V0(0) may be taken as reference; this should be
reported with the results of measurement.
---------------------- Page: 21 ----------------------
1146-1 ©IEC:1994 — 41 —
NL (n)
h) The gamma error shall be calculated as the percentage of the deviation
of the level at each Vo (n), from the theoretical level Vt(n) of the corresponding step.
as shown in the following
The errors shall be calculated from step n=3 to step n=10,
formula:
t(n)) l Vt(n) x 100 (%)
NL(n) = (Vo(n) - V
where
Vt /10 for n=10
(n) = n=3 to
Vrefn
9.3 Presentation of results
n of each step, and the
The results shall be reported in a table showing the number
gamma error in percentage for the two references, as follows:
blanking level;
a)
b) step Vo(0).
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1146-1 © I EC:1994
- 43 -
Video
camera
SECAM
Test chart For measurement
- –
only (see 7.2c)
Input not
Input terminated
terminated
by 75 i2
Oscilloscope
Test chart No. 1
Underscan colour
■TV monitor
Grey-scale pattern (reflective type)
– Gamma: 2,2
– Reflectance (white area): 89,9 %
Figure 6a – Equipment arrangement and test chart
Figure 6 - Luminance gamma characteristics
---------------------- Page: 23 ----------------------
1146-1 © I
EC:1994 - 45 -
Luminance
cd/m 2
L
Figure 6b - Camera
Output signal
A
Illuminationy
0
1
lx
Figure 6d - Camera output signal
Vef.
l
Vo(0)
Figure 6e - Video output signal
Figure 6 - Luminance gamma characteristics (concluded)
---------------------- Page: 24 ----------------------
1146-1 ©IEC:1994 – 47 –
10 Luminance white clipping and compression rate
10.1 Characteristics to be specified
The white clipping level of the luminance signal is the level at which the white saturation
appears. This level is compared to the rated reference luminance signal, and expressed in
per cent.
The compression rate is defined as the maximum subject illumination for which details can
be distinguished from the next lower illumination level below the white saturation level.
10.2 Method of measurement
a) The equipment arrangement and the grey-scale test chart shall be as shown in
figure 7.
b) The conditions of shooting shall be those mentioned in 3.3.
c) The output signal from the black level shall be measured by an oscilloscope.
d) Adjust the fens zoom ratio in order to increase the angle of view, and thus the
output signal amplitu
...
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