Test Card F - Technical Information

Technical Information

Virtually all the designs and patterns on the card have some significance. Along the top (see above) are 95% colour-bars in descending order of luminance - white, yellow, cyan, green, magenta, red, blue and black. There are triangles on each of the four sides of the card to check for correct overscanning of the picture. Standard greyscale and frequency response tests are found on the left and right respectively of the central picture. On the updated Test Card J, the X on the noughts-and-crosses board is an indicator for aligning the centre of the screen.

The blocks of colour on the sides would cause the picture to tear horizontally if the sync circuits were not adjusted properly. The closely spaced lines in various parts of the screen allowed focus to be checked from centre to edge; mistuning would also blur the lines. All parts of the greyscale would not be distinct if contrast and brightness (both internal preset settings and user adjustments) were not set correctly. The black bar on a white background revealed ringing and signal reflections. The castellations along the top and bottom also revealed possible setup problems.

A child was depicted so that wrong skin colour would be obvious and not subject to changing make-up fashions. The juxtaposed garish colours of the clown were such that a common transmission error called chrominance/luminance delay inequality would make the clown's yellow buttons turn white.

Modern circuitry using large-scale integration is much less susceptible to most of these problems. Some of them are also associated with cathode ray tubes; liquid crystal displays (LCDs), that are not scanned at high speed, also help. The test card was a vital tool in its day, but has become far less important.

The name of the broadcasting channel usually appeared in the space underneath the letter F — a sans-serif F denoting an original optical version of the test card.

Originally a photographic slide made up of two transparencies in perfect registration—one containing the colour information and the other the monochrome background. The card was converted to electronic form in 1984 when electronic storage became possible.