The IBA's Electronic Test Pattern, ETP1, is now being transmitted
in some ITV regions when programme schedules permit. Up-to-date
information on these test transmissions can be obtained from
the Engineering Information Service of the IBA. This leaflet
explains the important features of this test pattern.
The need for an electronically generated test pattern has arisen
because the IBA is bringing into service four Regional Operations
Centres (ROCs). Over the next few years, these will replace
the 14 IBA Control Centres originally built to monitor and control
the ITV UHF colour television service.
Trade transmissions from the original control centres currently
consist of a combination of standard European Broadcasting Union
(EBU) colour bars and Test Card F. Test Card F is originated
from a 35mm colour slide ; and the equipment needed to play-out
the slide needs regular adjustment. The advent of the new ROCs
allows us to introduce a test-card system which needs no maintenance.
An electronically generated test pattern, when once installed,
requires no adjustment at all, while affording the further advantages
of consistency and reliability. The electronically generated
test pattern will ultimately replace the use of Test Card F
in all IBA transmissions.
The test pattern provides all the basic features necessary
for receiver alignment, and it can be used for overall assessment
of picture quality as, for example, when installing a TV aerial.
Features of the IBA test pattern include :
1. Crosshatch pattern - for convergence check. This may best
be seen with the colour control turned down to give a monochrome
picture. So far as possible, the white grid should be free from
colour fringing. In practice, most receivers tend to give some
slight fringing, particularly near the edges of the picture.
2. EBU colour bars (75% amplitude, 100% saturation).
3. Grey scale - 0%, 20%,40%,60%,80%, 100% amplitude. The difference
in luminance signal voltage between adjacent rectangles should
be approximately constant.
4. Multiburst - for bandwidth /resolution check. Six sets of
sine-wave gratings corresponding to the following frequencies
It is normal for a colour receiver to exhibit a bluish-yellow
pattern (known as 'cross-colour') on the 4.5 MHz grating ; and
also, to a lesser extent, on the 4.0 MHz and 5.25 MHz gratings.
Because of a special filter incorporated in colour receivers,
which prevents the colour sub-carrier from appearing on the
screen, the 4.5 MHz bars are likely to be indistinct. Also,
they are likely to be indistinct on most 405-line monochrome
5. 150 kHz squarewaves - for transient response check. Just
above the colour bar there is a train of 150 kHz squarewaves
(0 % and 75 % amplitude). This is to facilitate a check on any
ringing, overshoot or preshoot. Ideally, there should be sharp
transitions between the black and white rectangles, without
`smudging'. The transmitted transitions are as fast as the UK
625-line standard permits.
6. Black rectangle within white rectangle - for low frequency
response check. Low frequency response can be assessed by the
appearance of the black rectangle within the white rectangle
near the top of the pattern. Poor low frequency response shows
as streaking at the right-hand edges of these rectangles, and
from the border castellations.
7. White needle pulse - for reflections check. Any reflections
of the television signal, from hills or large buildings, can
result in displaced `ghost' images. The effects of short-term
reflections are revealed by secondary images of the white needle
pulse within the black rectangle.
8. Yellow-red-yellow rectangles-for chrominance/ luminance
delay check. The redness of the rectangle near the top of the
pattern should fit snugly between the yellow rectangles.
9. Line synchronization castellations - the left, right and
bottom borders are formed by a pattern of alternate rectangles
in black and colours with high luminance value and with a white
rectangle in each corner. On monochrome receivers these rectangles
appear either as black or as various lighter tones ranging from
grey to white. The right-hand side border serves as a test signal
for checking the line synchronization of receivers - faulty
line synchronization shows as horizontal displacement of those
parts of the picture on the same lines as the lighter toned
rectangles on this side. These castellations, being yellow and
white, provide a check on sync separator performance in the
presence and absence (in 625-line transmissions) of the colour
sub-carrier. The spacing of the left-hand and right-hand castellations
has been staggered to identify the side from which any disturbance
10. Colour receiver reference oscillator castellations. The
coloured border castellations can be used in checking for correct
decoding; top : cyan, bottom: green, left-hand side : red and
blue, right-hand side : yellow.
11. Picture centring castellations. The width of each border
castellation along the sides of the picture is the same as that
of one of the grey rectangles within the crosshatch grid. Similarly,
the height of the castellations along the top and bottom is
equivalent to the height of the grey rectangles within the crosshatch
grid. The picture size on receivers would normally be set for
some slight overscan at the edges, but castellations should
be clearly visible along all four sides of the picture.
The average picture voltage level has been set (nominally) at
50% of the white level voltage.
Engineering Information Service
EIS 120 9/79