|Test Card 'F', in its digital form introduced in 1984.
The useful working life for a Test Card 'F' slide was short…
A test card slide would be in use almost continuously!
This lead to problems with colour fading and shrinkage of the film stock. And then there was the question of how well the slide scanner was set up…
Ideally an all electronic test card was required.
Various electronic test cards were used, but I don't wish to sully my web pages with them. Technology moved on and a PROM based picture store became feasible.
My colleague was given the project of generating the test card image. This was the result.
|The background image (greyscale, frequency gratings and
all the other twiddly bits that we engineers love) was computer generated.
The central image was grabbed electronically from the best available test card slide
and merged with the computer generated background.
There are a number of subtle differences between this image and the original – the greyscale spots are now square, the central image is slightly zoomed in compared to the original, the designation letter uses 'serif' style and there is an extra cycle of the 2.5MHz frequency grating…
There are other differences. Can you spot them?
|The 1990s saw the move toward widescreen (16:9) television. The new aspect ratio required a new test card. Various modified forms of test card 'F' were used but the 1984 version was really due for an overhaul. Test card 'W' was the end result. This card has even more exciting engineering twiddly bits… We now get luminance and chrominance sawteeth at the bottom of the frame, pure colour difference castellations on the left of frame, extra framing arrows which correspond to active picture if the image has been aspect ratio converted to either 14:9 or 4:3. The bottom frequency grating is now 6MHz (this image is not intended for analogue broadcast…) and the green blob in the letterbox is designed to highlight luminance to chrominance delays. The spots in the greyscale flash on and off – this indicates that the video feed is 'live' and not an image that has been grabbed in a framestore/VT machine… The highlight of this card is however, the central image. Newly scanned from the original glass plate slide, Carole Hersee is looking even better than ever. We now get to see more of the picture, the clown does have a piece of chalk! It all makes sense now! The central cross on the blackboard really is in the centre of the picture.|
|The new 4:3 test card. There had been a test card 'G'
|For those of you wondering why the clowns coat is not as green as it used to be, this is because it was re-coloured on the original test card. The clown was of course light blue – the same colour as the hat. The designers were aiming to include the primary colours in the central image – Carol's dress was a nice red and the backing was sky blue. No green though. A green wrap was made for the clown, but at the time it wasn't considered to be quite green enough and so the negative was re-touched to make the rather fluorescent colour that we're familiar with.|