Test Cards and Ceefax

Test Cards and Ceefax

An interview with Edwin Parsons a BBC preservation expert

Edwin Parsons, a preservation expert from the BBC's Archives, explains why the test cards and Ceefax matter more than you might think.


Test Card F

The most famous test card is known as test card F, and this was the very first colour test card, and most people remark on it because it has the photograph of the little girl and the clown. I'm told that the test card actually looks like a baffling array of lines and squiggles and things like that, but of course as an engineer it's always looked quite different to me. Every detail on the test card has a purpose.

Well the circle in the middle should, in fact, look a circle and not either egg shaped or like a rugby ball. And this is for checking the width, the height and also the vertical linearity of the picture. It is said that the X from the noughts and crosses game is actually the middle of the picture and therefore that should be in the middle of your screen. A young girl was chosen to feature in the picture because she wouldn't be old enough to wear make-up or have fancy hairdos, so we get natural flesh tones without make-up and it wouldn't be subject to changing fashions.

A colour television picture is made of the three primary colours: red, green and blue images, three images which you see as one. The clown's colours aren't chosen by accident. They are the primary and complementary colours and are actually there for a test purpose. On an old fashioned television set like this, which has a glass tube, it actually makes a colour picture by putting the red, green and blue picture on top of each other. Now so that all those three pictures can be accurately aligned on top of each other, engineers would use this grid or grille and they would align the three pictures perfectly on top of each other.

The lines in the corner show how good the focus is in the corner of the television tube. It's never as good there as it is in the centre. This is known as a letterbox, for obvious reasons, and it was put there for an engineering purpose but it will show up another problem that you could receive at home when your aerial picks up a reflected signal with the main signal and you'll see a second image to the right. Most people call this ghosting.

The lines down this side are known as frequency gratings and show how accurate the television set was tuned, how good the set was focused, and if you could only see the thickest ones your television set either wasn't very good or there was a tuning error. Of course, if you could see the finest ones, which is the highest frequency, you had a very good television set.

On this side this is a greyscale, which goes from more or less black to more or less white. The little dot in the middle is actually slightly above black and the idea was that you adjusted it so that it just disappeared. The arrowheads, there are four of them altogether. One of them is under the colour bars now. These show the limit of the pictures. Now on your TV at home this would actually be adjusted to be just outside the actual physical screen. As you see on professional monitors we've got it adjusted so you actually see the full picture.

The mysterious girl in the picture is Carol Hersee and she's the daughter of BBC engineer George Hersee, who was developing the colour test card. In fact, George Hersee photographed both his daughters, Carol's younger sister as well, but it was Carol who won the day. Carol Hersee is the person who's been on television the most. It's reckoned she's been on screen for 70,000 hours. That's on screen continuously for eight years.

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