Deciphering the Language of TV Test Patterns
What came first, television or television test patterns? By all accounts the static bull’s-eye that appeared on early TVs from the 1940s through the 1970s, before stations aired 24 hour programming or when transmission malfunctions occurred, did not precede the actual invention of television, which surprisingly was being tested as early at the 1880s, but it was the first transmission on a TV screen.
The TV test pattern was broadcast in the 1920s. Aesthetics were not important. It was technically drafted to allow electrical engineers a guide from which to calibrate and produce a viable image. It ultimately became a nostalgic icon of the black and white TV era.
Originally a circular bulls-eye was patterned on the original oscilloscope format that preceded the common rectangular, curved tube. It showed an image in the form of a wave. These were called “test charts” and included designs that checked transmitter performance from studio to antenna and, of course, the picture resolution. When the circle looked egg-shaped, for example, that meant the TV scans were not uniform.
The interior of the pattern was divided into sections. The innermost, shaded circles consisted of three concentric circular areas of varied density. The central area was black. The next circle showed an intermediate gray tone and the outer ring was white. These were used to test the contrast and shading. Four bars shot out as rays in four directions from the bulls-eye. These were “definition wedges” and consisted of vertical and horizontal black and white lines, arranged to increase in width as they moved out from the center. The horizontal lines measured vertical resolution and the vertical measured the horizontal.
This image served specific purposes. Regular adjustments on cameras and studio monitors were made throughout the day. “An experienced broadcast engineer could glance at the drawing of the Indian Chief and quickly know if everything was OK or if more careful adjustment was needed,” notes Wikipedia. The chart provided all the elements needed to adjust perspective, framing, linearity, frequency response, differential gain, contrast and brightness. When color TV was introduced the chart was colorized but by the 70s it was no longer useful. And yet another design icon and cultural artifact became obsolete.