BBC test charts

New test cards needed to be made for the introduction of colour television cameras. The cameras had better performance, so a new greyscale was needed to improve the contrast ratio, grey balance, and gamma correction of BBC colour television cameras. Having the black, white and grey levels correctly calibrated helped to create optimum colour fidelity, giving more accurate colour, in the transmission.

The square in the middle was to create ‘super black’ which had little or no reflectance. It was made by cutting an aperture into the card and fixing a small box lined with black flock paper behind it. This reduced the amount of light reflected, to help with camera flare correction adjustments.

Test chart 58, like test chart 57, is designed to improve the contrast ratio, grey balance and gamma correction of BBC colour television cameras. It includes a small square coated in super-black, which reflects far less light than standard black paint. It is also a registration chart; the patterns were used to ensure the BBC cameras were lined-up and displaying the image correctly.

This card was used in BBC Outside Broadcasts, and was visible in the corner of the court at Wimbledon so that the cameras could line-up quickly and easily.

Groups of colour television cameras needed to be adjusted so that there was not a colour difference between them when filming. After greyscale calibration, flesh-tone balance needed to be corrected to get accurate skin-tones. To maintain uniformity, consistency and naturalness, the BBC Research Department developed a very high quality photograph of a live subject for use on a test card. Lynne Holmes, an administrator for the BBC, was used as the model. This was because she had dark hair, which was needed to adjust the black levels in relation to skin colour. The card was also angled, to reduce the reflections from studio lights interfering with the balancing process.

Test card number 61, nicknamed ‘Cardboard Kate’, was introduced in 1977. The test card was needed to make sure skin tones were accurately filmed, but there was no corresponding card to ensure that colour cameras recorded black and darker skin tones correctly.