Philips circle pattern


The Philips circle pattern refers to a family of related electronically generated complex television station colour test cards. The content and layout of the original colour circle pattern was designed by Danish engineer in the Philips TV & Test Equipment laboratory in Amager near Copenhagen under supervision of chief engineer Erik Helmer Nielsen in 1966–67, largely building on their previous work with the monochrome PM5540 pattern. The first piece of equipment, the PM5544 colour pattern generator, which generates the pattern, was made by Finn Hendil and his group in 1968–69. The same team would also develop the Spanish TVE colour test card in 1973.
Since the widespread introduction of the original PM5544 from the early-1970s, the Philips Pattern has become one of the most commonly used test cards, with only the SMPTE and EBU colour bars as well as the BBC's Test Card F coming close to its usage.
The Philips circle pattern was later incorporated into other test pattern generators from Philips itself, as well as test pattern generators from various other manufacturers. Equipment from Philips and succeeding companies which generate the circle pattern are the PM5544, PM5534, PM5535, PM5644, PT5210, PT5230 and PT5300. Other related test card generators by Philips are the PM5400 family, PM5515/16/18, PM5519, PM5520, PM5522, PM5540, PM5547, PM5552 and PM5631.

Operation

Rather than previous test card approaches that worked by a live camera or monoscope filming a printed card, the Philips PM5544 generates the test patterns fully using electronic circuits, with separate paths for Y, R-Y and B-Y colour components, allowing engineers to reliably test and adjust transmitters and receivers for signal disturbances and colour separation, for instance for PAL broadcasts.
In simple terms, the displayed pattern provides reference levels of black, white and colour saturation, to which a receiver can be set. Displayed image geometry can also be corrected. More technical adjustments are also possible.
Main technical features of the test card:
  • Circle with b/w and colour information
  • *Square wave – repeating black and white blocks resembling a ;
  • *Colour bar – yellow, cyan, green, magenta, red and blue with 100% saturation and 75% amplitude ;
  • *Crossed lines – at the centre of the circle, they allow to check for proper interlace;
  • *Definition lines – sine wave gratings with TV line frequencies corresponding to:
  • ** 0.8, 1.8, 2.8, 3.8 and 4.8 MHz ;
  • ** 1.5, 2.5, 3.5, 4.0, 4.5 and 5.25 MHz ;
  • ** 0.8, 1.8, 2.8, 3.8, 4.8 and 5.63 MHz ;
  • ** 0.5, 1.0, 2.0, 3.0 and 4.0 MHz ;
  • ** 0.8, 1.8, 2.8, 1.8 and 0.8 MHz ;
  • *Stair case – greyscale with 6 levels ;
  • *White black step with needle pulse;
  • *Colour step – red on yellow background colours, 75% amplitude.
  • To the left of the circle:
  • *Vertical bar – line alternating positive and negative R-Y signal;
  • *Vertical bars – positive and negative R-Y signal;
  • *Two rectangles – G-Y signal.
  • To the right of the circle:
  • *Vertical bar – line alternating positive and negative B-Y signal;
  • *Vertical bars – positive and negative B-Y signal;
  • *Two rectangles – G-Y signal.
  • Background:
  • *Grid – made from 14 horizontal x 19 vertical lines;
  • *Background Level – adjustable between 0 and 80% amplitude;
  • *B/W border castellations.

    Pattern variations

4:3 (original)

While the basic specifications of the pattern normally remain consistent, there are often small variations depending on the brand and type of generator used to produce it, as well as how the broadcaster has chosen to configure it. Some television stations have included a digital clock and/or date, as well as the station logo or ID, inside the circle. This practice was common in Asia and some parts of Europe, as well as in South Africa.

SECAM

The Philips circle pattern is geared towards the PAL colour-coding system, but SECAM versions do exist. The most obvious difference is the absence of PAL specific test features. Less noticeable is the change to the multiburst gratings, instead at 0.8, 1.8, 2.8, 1.8 and 0.8 MHz due to the lower luminance bandwidth in the SECAM system.

NTSC

Likewise, there are 525-lines NTSC versions of the pattern. One of the NTSC variants, used in Philippines, Taiwan, Haiti and Japan, has a modified square wave near the top of the circle at 300 kHz and the multiburst gratings at 0.5, 1.0, 2.0, 3.0 and 4.0 MHz. A second variation, used by CBC Montreal in Quebec, Canada, had different gratings and added extra colour bars.

PAL-M

In addition to the 525-line NTSC pattern, a PAL-M version of the pattern was also offered for the Brazilian market. Although no public transmissions are known to exist as of , the pattern is identical to NTSC but also includes achromatic fields adjacent to the side bars.

PAL-N

Though as of no surviving equipment or captures/recordings are known, a version of the pattern existed for the PAL-N system. It is expected to resemble the PAL-B/G pattern however with the gratings of the NTSC version.

BBC Test Card G

Test card G was a quasi-Philips pattern developed by the BBC. It is realised by the physical modification of standard PM5544 generators and differs from the original as follows:
  • Colour bar saturation - 95%
  • Colour bar contrast - 75%
  • Colour bar set-up - 25%
  • Multiburst gratings
  • Multiburst amplitude - 71.4%
The above specifications were incorporated back into standard Philips generators such as the PM5534I/00 and the PM5644I/00.

16:9 (widescreen)

The widescreen version of the Philips circle pattern was designed in 1991. It was only known to be used in PAL regions and retains the signals present in the original, and features additional signals to test signal and picture quality, including Television lines resolution, corner circles and correct overscan and image centering.
Several different types of hardware are known to generate it, including the PM5644, PT5230 and PT5300 and the PM5420.
There are two major variations of the 16:9 circle pattern. The original 1991 pattern contains high frequency components which were useful for testing widescreen televisions in factories, specifically 450/400 TVL diagonal lines and a sixth 5.8 MHz grating. This however made it sub-optimum for public broadcasts as these exceeded the bandwidth of most PAL transmission systems. All pattern components of the PT5230/PT5300 were within the bandwidth of PAL B/G.
Widescreen circle patterns were used by broadcasters such as RAI, BRT, RTL-TVI, Ned3, TVE and KNR TV.

NTSC

Although no public transmissions are known to exist as of , an NTSC widescreen version of the PM5644 and later models were available.

High definition

An HD version of the Philips circle pattern was developed for the PT5300 via the PT8612 HD Signal Generator add-on. It was never formally integrated into the PT8612 thus was not offered for sale.
A 1250 line HD-MAC version of the Philips circle pattern also exists.

Squared version

A variation of the PM5544/34 pattern has been recorded where the circle generator is bypassed or faulty. This reveals the full contents of the central pattern elements, which are normally cropped. Anecdotally this pattern has been referred to as PM5538 however this was not a Philips pattern generator. It was used in some parts of the Middle East like Dubai 33 in the UAE and Jordan Radio and Television Corporation in Jordan.

Mainland Chinese variants

Starting from the 1980s, China Central Television and some provincial mainland Chinese broadcasters began using a heavily modified version of the PM5544 called the GB2097 inspection chart. Later, another modification, anecdotally called PM5549 began to be used at the headends of some mainland Chinese cable television providers.

Physical equipment

PM5544

The design of the original PM5544 is fairly complicated, with an array of analogue signal generators generating each component of the pattern continuously. Digital circuitry is used to sequence the outputs from each module into the final pattern. The circle is internally generated as a square and cropped according to coordinates defined in a 264x252 grid defining half of the circle.
The original used magnetic core to store data for the circle, essentially a very small core rope memory. Suitable ROM chips were not available at the time. Four-fold symmetry was used to minimise the memory requirements. Later versions replaced the core with ROM.
The original PM5544 was not capable of generating a composite video signal by itself. At the time it was introduced three additional pieces of equipment were required:
  • a PM5554 PAL colour encoder,
  • a PM5555 PAL subcarrier generator,
  • a PM5530 sync generator.
Over the years the physical implementation of this supporting equipment was refined, with later PM5544's only requiring two extra pieces of equipment:
  • a PM5545 colour encoder,
  • a PM5532 sync generator,
Eventually all the supporting equipment could be replaced by a PM5638 which fitted into a single 1RU unit.
The physical configuration of the PM5544 depends upon its purpose. A common application was in TV factories where it was typically used in its most basic configuration with no optional extras. When used for broadcasting it was usually fitted with the PM5543 text generator which allowed broadcasters to display text in the upper and lower black boxes.
It was available in 4 versions and did not have the option of an in-pattern clock.

PM5534

In the late-1970s, Philips introduced the PM5534 which replaced the original PM5544. It was fundamentally a very similar design using a mixture of analogue and digital circuitry to generate the pattern, however it no longer required an external sync generator and colour encoder, reducing the rack footprint from 6RU/12RU to 3RU.
The PM5534 was available as a variant with component video outputs and had two pattern effecting options: PM8503 text generator and the PM8504 clock generator.
The PM5534 was available in 6 different versions: PAL-G, PAL-I, PAL-M, PAL-N, SECAM and NTSC.