Widescreen Test Card Development
Snell & Wilcox's first attempt at a widescreen version of Test Card F
With the forthcoming digital television services using a 16 x 9 aspect ratio, a widescreen
version of the test card was required. Although it may not be transmitted very much (if at
all) we would certainly need it internally to check the alignment of Aspect Ratio Converters
(ARCs) and the alignment of widescreen monitors.
In 1997, when PMS were installing the SDV (Serial Digital Video) matrix in CAR, they also
installed a Snell & Wilcox rack with five Frame Pattern Generator cards. These can
generate a large number of line-repetitive test signals, as well as one complete frame of any
picture. The obvious candidate for the picture was the Test Card, although ideally we
needed two versions - the normal 4 x 3 Test Card F, and also a widescreen version. The 4 x
3 test card has been generated digitally since 1984, and so Research Department were able to
provide S&W with the data file for storing in the FPG's EPROMs. S&W then
quickly hacked that data to provide a 16 x 9 variant. As some of you may have seen, they
did this by taking the two edge squares from the grid, including the corner diagonals, and
inserted these on opposite sides. When re-sampled this gave the correct aspect ratio, but
aesthetically was not particularly pleasing, as can be seen from the above picture. As each
generator card can only store one or the other, some of the cards have the 4x3 version, and
other the 16x9 version.
The original test card data had a number of minor errors in it which had been barely
noticeable in the analogue version, but which were now much more apparent without the PAL
footprint all over them:
- The top and bottom lines (23 and 623) were blank, instead of having half a line of
video. (And in the digital domain, there are no half lines - they are all full,
resulting in a 576 line picture, not 574 and two halves!)
- The data was pre-blanked to nominal (analogue) active line width. Digital lines have
nine pixels outside of the nominal analogue blanking position (about two/thirds of a
microsecond). Even if it was only required in the analogue domain, assuming the DAC
re-blanked the signal (in exactly the same place!) double blanking a signal increases the
overall blanking width by about 120ns due to the rise-time of the blanking
- The second step down on the greyscale actually comprised two levels 10mV
- There was a grey spot on the top line of the colour bars in the magenta section.
- The arrow heads at the sides drooped down slightly.
- The anti-aliasing of the black/white/black vertical lines under the centre circle left
something to be desired.
- The centre picture had originally been grabbed on a Quantel which did not co-time the
chrominance samples, but this had not been compensated for in the SDV data, resulting in
noticeable chrome/lum delay.
- The centre picture was generally 'orrible, being soft, noisy, ringy, and sat up.
- S&W's widescreen card still had the ident letter F under the centre circle.
Richard Russell in Research Department (Kingswood Warren, near Tadworth, in Surrey)
created a rather more aesthetically pleasing widescreen test card, correcting most of these
Richard Russell's interim widescreen test card
Original picture obtained and re-scanned
George Hersee, the SCPD ("Studio
Department") engineer involved in the creation of the original
Test Card F, and whose daughter, Carole, it is in the centre picture, died of a heart attack on
Wednesday the 11th April 2001, aged 76. Back in 1998 I contacted him, and luckily he still
had the original 6cm square transparency from which the centre picture was taken. He
kindly lent me the slide, and I arranged for an external professional scanning firm (Masterlith,
of Mitcham in Surrey) to provide a high quality scan. They were able to provide an image
just over 5000 pixels square, with a colour depth of 48 bits (16 each from Red, Green, and
Blue). Arranging that was a saga in itself. They have one of the few Agfa Selectscan
2000 scanners in the country, but had to get special software over from the manufacturers in
America to provide the 48-bit data! The results justified the effort involved,
however. On the left below is a reduction of the scan showing the whole area of the slide,
while on the right is the detail obtained from around her right eye.
And so a new Test Card is born
With this vastly improved source picture, to which Richard Russell has applied appropriate
colour- and gamma-correction, a clean new test card has been born. It has been created
with the full 10-bit accuracy available on serial digital video, and a number of new features
- The cross on the blackboard in the picture was always stated as being NEAR the centre
of the picture. It was indeed near, but not precise. Having obtained the rescan, we
have taken the opportunity of making it PRECISELY the centre of the picture. This
necessitated zooming out and panning right a little, which also resulted in a rather better
composed picture than the original, giving Carole some headroom, showing her elbow, and the
whole of the doll. The colour of the doll's dress is noticeably duller, but is more
realistic. The original looked fluorescent, and George admits that the lab tinkered with
it for Test Card F. The new picture is also not so sat up or
- Probably the most obvious addition is the green block in the top black streak-box.
This is to show chrome/lum delay. It was supposedly possible on the doll's yellow
button, but that was notoriously difficult. This green block will quickly show, by means
of a grey edge, if there is any delay, either horizontally or vertically. (The white
arrow-head on the Magenta bar at the top of the screen is a rather more sensitive indicator to
horizontal delay errors, but will often be out of sight on over-scanned domestic
- The coloured blocks at the edges of the old test card were to show sync-separation and
burst-gating problems - both irrelevant to digitally transmitted signals. The blocks on
the right have been replaced by horizontal colour bars, with a fast, non-anti-aliased transition
between each bar. Any line-averaging chrominance processing will thus readily be
seen. The blocks on the left individually have only R-Y and B-Y components, decoding to
minimum and maximum legal values of Red (top), and Blue (bottom).
- The colour bars at the top of the picture (and those on the right) are 100%
saturation. The old test card used so-called 95% bars, where no subcarrier goes below
black level. This was only relevant to analogue transmission on negatively modulated UHF
carriers, and again is meaningless to digital transmission. 100% bars have thus been
substituted to test the full legal range.
- Along the bottom are various ramp waveforms:
- Bottom left is a slightly over-range luminance ramp which goes from 240.0 down to 12.0
(235.0 and 16.0 being nominal White and Black respectively.)
- Just above that is a shallow luminance ramp, rising at one 10-bit level per pixel, and
centred about the 3/8ths level. It thus goes through both the 1/4 and 1/2 full range
points, and will show any DAC non-monotonicity and/or quantisation depth truncation (8-bit
processing, for example).
- On the right are shallow R-Y and B-Y ramps, changing at two 10-bit steps per (chrominance)
pixel in order to cover a reasonable range, while still indicating quantisation depth
- Extra arrow-heads have been added on the centre-line at the sides to show where the edge of
4 x 3 and 14 x 9 centre cut-out pictures should be. This is to aid in
setting up aspect ratio converters and monitors.
- The frequency gratings have different frequencies, having been increased in proportion to
the aspect ratio so that they are spatially similar to those on the 4 x 3 test
card. The frequencies (when in the analogue domain) are, from the top down: 2 Mhz, 3.33
Mhz, 4.0 MHz, 4.67 MHz, 5.33 MHz, & 6.0 MHz. That the last is outside the usual
analogue pass-band of 5.5 MHz is irrelevant, as this signal will be distributed digitally where
it is only limited by the Shannon/Nyquist rule of half sampling frequency
(= 6.75 MHz). (Where it is available internally as an analogue PAL signal, the
bandwidth limit doesn't apply.)
- Signals are increasingly being passed through synchronisers and other frame-stores, and we
have seen in the analogue world how they can be shifted up or down by one line to effectively
swap fields. This results in the loss of the top or bottom line though, which is often not
immediately apparent. The top and bottom lines of the new test card are therefore
distinctive, and not anti-aliased with the adjoining lines. As such they appear to
flicker, but this makes their presence more obvious, and hence also their absence. The top
line (23) has the Wide Screen Signalling data on the left, and continues with castellations to
the end of the line at a similar frequency to the basic WSS data (833KHz). The bottom line
is castellated all the way across at this same frequency.
- The dot in the bottom step of the greyscale was intended to assist setting the brightness of
a monitor, ensuring it wasn't too sat down. But it was quite a bright dot, so setting
was inaccurate. Also, there was no way of telling if the monitor was too sat up. For
many years we have used the special PLUGE signal (Picture monitor Line-Up Generator Equipment)
which has super-black and slightly sat-up stripes at ±3%. This principle has been
introduced onto the test card, which now has two dots on the black step of the greyscale.
Unlike genuine PLUGE however, they are at ±7%, as 3% dots weren't easily visible with
such a bright overall picture.
The top step of the greyscale was previously at 91%, with the centre dot at 100%. This has been
changed so that the top step is now 100%, and there are two dots, again at ±7%, thus
showing if any premature clipping has occurred.
The dots on the original Test Card F slide were circular, but they were made square (presumably
for simplicity) on the electronic test card. With the state of current computer
technology, it was easy to make them circular again.
- Finally, some form of movement was required. This was difficult, as it had to be
aesthetically acceptable. A digital clock was considered, but the only one available (by
Miles, as used in the DTA) was £12,000, the keyer only passed 8-bit data, and it didn't
re-calculate the EDH! However, the current Snell & Wilcox Frame Pattern Generator has
the ability to switch cleanly at the rate of one a second, to and fro between any two
patterns. The (lossless) compression used in the storage of the signals in this generator
meant that two test cards could be stored if there were only minor differences. A second
version of the test card was thus created without the dots in the greyscale, and the generator
set to switch continuously between the two. Because the dots are relatively faint, this is
very unobtrusive, and so far no-one has noticed until it has been pointed out to them.
Once you know it is there, however, it is quite easy to see, and thus determine whether you have
a "live" signal, or a frozen frame-store. (SCAR also have a pair of Test Card
generators, but theirs are manufactured by Crystal Vision, and regrettably don't have this
Test Card 'M'
Snell & Wilcox are running the Test Card 'M' Development Group. Seeing the
need for a test signal to check MPEG decoders, they are developing a suite of test signals,
carefully pre-encoded as MPEG data streams. The main signal is their new test card, M (see
above), which has lots of movement on it:
- The yellow arrows rotate within the centre circle.
- The coloured cube (directly above the centre circle in this picture) moves across the screen
rotating and changing colour as it goes.
- A "clock-hand" rotates once per second on the small clock face
at the bottom centre.
- The chrominance and luminance zone plates bottom left and bottom right respectively) are
- On the latest version (not shown here) there are pointers moving against graduated scales at
both sides, and simultaneously there is a click on both left and right sound channels. The
intention being to check for lip-sync errors.
- The rainbow coloured column to the left of the centre circle is also slowly moving.
This is to check for accurate gamma and colour-balance correction, as the luminance is intended
to be constant. Any inaccuracies show as apparent coggles in the width of the
S&W are keen for the industry to standardise on this test signal. It does, however,
present a number of operational difficulties for broadcasters on a day-to-day basis:
- The signal is only available as a pre-encoded MPEG data stream. This would be
difficult to transmit, as DTA works at 270Mb SDV. It would need switching in the Coding
& Multiplex room in the same fashion as the spare MPEG coder is switched to
- A separate higher bit-rate version would be required for the sustaining feeds to the Regions
(which would thus suffer decoding and recoding before transmission), and to be simultaneously
switched when the "normal" signal was fed to the London transmitters.
- The bit-rate is pre-set, so is unlikely to be easily operationally changeable (especially
dynamically) to suit our Network requirements.
- Sound is also pre-encoded, and is thus limited to what can be stored - a few seconds worth
at most. This is fine for internal lip-sync type tests, but the public are not likely to
be too impressed by clicks, or tone.
- Teletext is also pre-encoded, and again limited to perhaps one or two pages. There
could be no header clock showing the correct time. ("PDC"
The above would seem to preclude the use of this test card for the usual public "trade
test transmissions". If we had a spare channel (???) or prior to the start of a
service, then perhaps this could be used, but it doesn't seem very likely.
Further, it is no use internally for general widescreen use, as there isn't directly a
270Mb signal available, and an MPEG decoder would need to be tied up.
Being only available in the MPEG data domain, this test signal is thus limited to specific
in-house applications, and production line testing for receiver manufacturers, but Joe Public
ain't gonna get to see it.
Views and opinions expressed on this page are entirely those of the
author, and not of the BBC or BBC Technology Ltd.
Page updated 1st March 2004