MULTI BURST TEST CHAR
A line raster is arranged in the center of the test chart which
produces frequencies of 0.5 to 10
MHz in the output of the TV camera. 0.5 MHz line pairs are also
arranged at the center of the
line raster immediately adjacent to the 5 MHz line pairs. Bar
rasters are located in the corners
of the test charts and produce frequencies of 0.5 and 5 MHz.
The frequencies response of modulation depth and the uniformity of
modulation depth can be
established with the aid of the line rasters. The signal amplitude
of the 0.5 MHz rasters is the
Measuring equipment: Video oscilloscope or preferably video oscilloscope with memory.
Measurements conditions: The camera settings must be as follows
Shading correction: ON
Aperture correction: OFF
Gamma correction: OFF
Contour correction: OFF
Color correction: OFF
Iris: F/5.6 for 2/3 “CCD, F/4 1/2” CCD
The test chart is evenly illuminated so that for the low frequency
burst at 0.5 MHz the amplitude
of the video signal at the output of the correctly positioned and
focused camera is 0% (0V) for
the black bars and 100% (700mV/ 75 Ohms) for the white bars.
Care must be taken to avoid clipping of the signal to be measured
at the black and white level.
Measurements can be made on the various camera output signals, but
preferably on the Y
luminance signal (or coded Y with perfect B and W balance). This
measurement is made
at the center of the image and at the corners so that account is
taken of the lateral chromatic
aberration of the lens. In addition to determining camera response
to the particular value of
5 MHz, measurement of the response at the other frequencies serves
to plot a curve giving
contrast loss according to the spatial frequency of the test chart.
Frequency bursts of 0.5
MHz and 1 to 7 MHz are recommended for this measurement. The
measurements give the
contrast loss of the camera response at the value of 1 to 7 MHz.
The obtained response is
a contrast transfer function (CTF).
Mathematical relations can be used to calculate the MTF according
to the CTF values:
MTF(N)= π/4[CTF(N) + 1/3 CTF(3N) - 1/5 CTF(5N) + 1/7 CTF(7N) - 1/9
CTF(9N) + 1/11 CTF(11N) ...]
where N is the spatial frequency of the test chart analysed; N in
In the - probable - case of a beat affecting camera response for a
given spatial frequency,
and under certain conditions only, the measured signal reassembles
amplitude-modulated carrier signal, as shown in the following
The percentage of modulation is then defined by the relation:
% mod = M / X
The interference ripple at this frequency is given by:
p % = m / M
x = Amplitude of the 0.5 MHz signal
The results of the measurement can be shown in a table representing
the various areas of
the image measured.
CTF values at 5 MHz
xxx % xxx %
xxx % xxx %