Test card

Test images used to evaluate the image quality of television sets and monitors, as well as to assist in image adjustment and troubleshooting. Some test images are only useful for older devices with picture tubes, others find only in digital image transmission application.

History

In Germany, the "Universal Test Pattern " was designed for ARD in the 1950s by the Institute of Radio Technology, which was broadcast in until about the first broadcast of ZDF. These were a graphic. After the first, purely electronically generated by test pattern generators monochrome test images were utilized. With the advent of color television, the Dutch manufacturer Philips in 1966 commissioned the Danish engineer Finn Hendil ( 1939-2011 ) to make the color sample picture for TVs Philips PM5544 test pattern. It is the most famous, electronically generated color test image that was used for many years in several countries. Prior to the introduction of 24 -hour television programs were in the no-transmit times to end of program test images to see on public television. Until the late 1980s, the test images were shut down a few minutes after sending circuit and switched again until the late morning. The various test images were backed with either a measurement tone ( ZDF) or sound from a radio program (ARD). Especially after setting this regular test image shows in the years after about 1990 (RTL and Sat.1 1991, ProSieben in 1995, ARD and ZDF 1996) obtained the test image from different transmitters also a certain cult status and has developed in some circles has become a popular collector's item. The last German television program which broadcast a test pattern was regular, the hr television by the end of 1997. Today test images are often seen on cable television when there is a malfunction or the station from further abroad via satellite.

In some countries, such as Sweden or Estonia test images can be up in the early afternoon still common, although now also in Sweden, the test pattern is sent only more briefly. Instead, in the spectator peak times at the public broadcasters, the program of a news channel or an automated program preview is switched to run increasingly in the night hours in private channels repetitions or call-in shows. In Italy there once a month technical samples which last from 2:00 at night until 7:00 in the morning. The transmitter is switched off and it runs a test image. Every 1st Monday of the month, there are samples on the transmitter Rai 1, every 2nd Tuesday of the month on Rai 2 and every 3rd Friday of the month on Rai 3

Today, if needed, test images at any time be produced using special test pattern generators, with a few limitations with a test pattern DVD in the DVD player or computers equipped with TV output.

A measurement of the transmission line during operation is carried out at the today only rare analog transmission systems can be with test images, but with special test lines. In this case, a normally non-visible image line is replaced by a special signal, for example, a 2T pulse in the vertical blanking interval. The visible TV image is not changed.

Molding

The same test image ( FuBK test image )

The "normal" test image - FuBK stands for radio operation Commission - consists of various colored and black and white squares, a large circle and a grid for geometry settings, a gray wedge for contrast and brightness control, multiple fields with increasingly dense lines arranged as a (horizontal ) dissolution test. For PAL should still be seen at the maximum displayable video bandwidth of about 5 MHz in all fields just single lines, if that is not the case ( as with a VHS video with approximately 3 MHz) as they become more and more a gray surface. If PAL is used, there are two separate gray fields, the so-called " Unbuntfelder ". In one of these fields is changed in the modulation area in this field, instead of the carrier for the red color difference signal of the carrier for the blue color difference signal in its phase by 180 degrees. The carrier of the red component is not switched to the other field. Is produced so that in both cases, an artificial phase error of 90 degrees. This phase error, the color in the demodulation removes completely, because the red component is consistently normal performed every other row in the receiver. Should the recipient not be no turning back the 180 degrees or the angle between the red and the blue component exactly 90 degrees, the repeal would not be complete and the two fields would be inked.

This figure shows the behavior of the pointer Unbuntfeld in which instead of the red component, the blue component in the phase position in each second row to 180 degrees is switched.

Color bar test pattern

In this color bar test pattern a number of colored vertical bar is created, starting with white representable over all with two each of the primary colors ( RGB) colors and the primary colors even in descending brightness to black. This image is particularly well suited for debugging with an oscilloscope, as all picture lines (except those in the vertical blanking interval ) carry the same information. The oscilloscope can be operated at line frequency and with appropriate triggering one sees a static image when video signal, color difference signals or other oscilloscope, for as all lines are equal, all lines are exactly one above the other written by the oscilloscope. See also: television signal.

SMPTE test pattern

The SMPTE test pattern is similar in structure to the EBU color bar image and has its origin in North America. It is in the lower area for additional colors that enhance receiver equipment according to the NTSC video standard used to control the color setting. The first analog NTSC color television inclined due to the transmission process step up color distortions.

Digital Test Patterns

Due to the increasing proliferation of digital television special test images used in this field are used. This is less about the adjustment of display devices, but for the simple and mostly automatic control of data transmission or to determine the number of transmission errors. This is especially true of motion reproduction, because due to the MPEG encoding with integrated image storage can also be a brief line interruption is not controlled with a simple still image. At least one picture element should have a uniform motion (for example, migrating from left to right beams and vice versa ) in order to uncover example, conversion error (60 Hz/50 Hz frame rate ).

A used mainly in the studio and worldwide broadcasters, lossless digital video transmission according to the Serial Digital Interface standard ( SDI signal ) used similar test patterns, the SMPTE test pattern, extends this but at the bottom of certain color combinations which in the serial encoding of the image information lead to long logic 0 and logic -1 sequences. This data sequences are to receive heavy due to the then lack of timing information for SDI receivers and provide higher quality demands on the used clock sources such as quartz oscillators. These test images are also colloquially referred to as clock - crackers.

Display pattern

It consists of a white grid on a black background. Thus, the image geometry can be checked and the convergence of the picture tube. Under the convergence is understood that the three electron beams are for red, green and blue just above each other.

Single color test images

In red, green and blue.

So that the color purity can be checked. Especially for liquid crystal displays pixels errors can hereby be recognized.

Pumping test image

A larger area of ​​the image is constantly changing from white to black. However, there should be no change in the image size. This test is only useful for cathode ray picture tubes. Of the electron beam, together with the high voltage a circuit (see: Ohm's law). If the image is brighter, more current flows. If the high voltage insufficiently stabilized, these collapses. The high voltage accelerates the electron beam. The high voltage low, also decreases the velocity of electrons. Thus, they are deflected, and the lighter image appear larger. With light - dark cycles a pump of the image may occur.

Special test patterns and elements

• Lena ( test pattern ) - A test pattern of computer graphics
• Frequency broom - A black and white element to detect the resolution
• Siemens Star - Black and white test pattern for printers and digital cameras

Trivia

• In the series 1000 Masterpieces there was a post about " The test image " of the Munich Institute for Radio Technology by Paul -M. Sedlacek and Peter Neuwirth, the first broadcasts of this episode was on October 2, 1994.
• The band lunch break from Dusseldorf published in 1979 the song test image, Die Toten Hosen 1988 a title of the same name on their album A little bit of horror show.
• In the ZDF Digital Sender ZDFneo runs between the individual programs one EBU color bar, after a few seconds it turns out, however, that the beams of actors are represented in huge color bars. There are at least ten different episodes of it.