used mainly in North America from 1940 to the 1970s with its elements labelled, describing the use of each element in aligning a black & white analog TV receiver. test card (1953) for the French
819-line TV system. Also used in
French Algeria, with modifications also used by
TMC in
Monaco,
Telesaar in the
Saar Protectorate, and
TVN in
Chile test card. Test cards are as old as TV broadcasts, with documented use by the BBC in the United Kingdom in its early
30-line mechanical Baird transmissions from 1934 and later on as simplified "tuning signals" shown before
startup as well as in
Occupied France during World War II. They evolved to include gratings for resolution testing, grids to assist with picture geometry adjustments, and grayscale for brightness and contrast adjustments. For example, all these elements can be seen in a
Radiodiffusion-Télévision Française 819-line test card introduced in 1953.
Philips PM5544,
Telefunken FuBK, etc.), TV station (ex:
BBC test card) or organization (ex:
SMPTE color bars,
EBU colour bars). In
developed countries such as
Australia,
Canada, the
United Kingdom, and the
United States, the financial imperatives of commercial television broadcasting mean that air-time is now typically filled with programmes and commercials (such as
infomercials) 24 hours a day, and non-commercial broadcasters have to match this. A late test card design, introduced in 2005 and fully adapted for HD, SD, 16:9 and 4:3 broadcasts, is defined on ITU-R Rec. BT.1729. It offers markings specificity design to test format conversions, chroma sampling, etc. Formerly a common sight, test cards are now only rarely seen outside of television studios, post-production, and distribution facilities. In particular, they are no longer intended to assist viewers in calibration of television sets. Several factors have led to their demise for this purpose: • Modern
microcontroller-controlled analogue televisions rarely if ever need adjustment, so test cards are much less important than previously. Likewise, modern cameras and camcorders seldom need adjustment for technical accuracy, though they are often adjusted to compensate for scene light levels, and for various artistic effects. • Use of digital interconnect standards, such as
CCIR 601 and
SMPTE 292M, which operate without the non-linearities and other issues inherent to analog broadcasting, do not introduce color shifts or brightness changes; thus the requirement to detect and compensate for them using this reference signal has been virtually eliminated. (Compare with the obsolescence of
stroboscopes as used to adjust the speed of record players.) On the other hand, digital test signal generators do include test signals which are intended to stress the digital interface, and many sophisticated generators allow the insertion of
jitter, bit errors, and other pathological conditions that can cause a digital interface to fail. • Likewise, use of digital broadcasting standards, such as
DVB and
ATSC, eliminates the issues introduced by modulation and demodulation of analog signals. • Test cards including large circles were used to confirm the linearity of the set's deflection systems. As solid-state components replaced
vacuum tubes in receiver deflection circuits, linearity adjustments were less frequently required (few newer sets have user-adjustable "VERT SIZE" and "VERT LIN" controls, for example). In LCD and other deflectionless displays, the linearity is a function of the display panel's manufacturing quality; for the display to work, the tolerances will already be far tighter than human perception. For custom-designed video installations, such as
LED displays in buildings or at live events, some test images are custom-made to fit the specific size and shape of the setup in question. These custom test images can also be an opportunity for the technicians to hide inside jokes for the crew to see while installing equipment for a show. ==Monoscope==