U.S. Philips Corporation

Bts Broadcast Television Systems Gmbh

Gerd Brand

Uwe Riemann

Wilhelm Moring

A test pattern generator provides a test pattern signal timed for insertion in the foreground signal of a chromakey mixer to occupy the area of particular shape in any desired part of a monitor screen. The test pattern signal provides a color scan signal which becomes part of the foreground signal within the test pattern area and which is also supplied to the decoder along with the foreground signal. Decoder responds to the color scan signal in the test pattern by substituting the background signal of the portion of the color scan displayed corresponding to colors to which the decoder responds by switching in the background signal. This enables determination of the exact range of response of the decoder while the mixer is operating also of observance of changing of the setting of the response of the decoder so that it can be more accurately set to the desired color range.

Method and apparatus for testing and checking the criteria of a key

A circuit arrangement for obtaining a control quantity which is dependent on the phase shift of a color burst signal comprising an amplitude factor with respect to a reference signal, preferably of approximately the same frequency, which is phase-locked to a clock signal with which the amplitude values of the color burst signal are sampled and whose frequency is the 4n-fold of the frequency of the reference signal. n is an integer and the keying occurs in such manner that a first sampled difference signal obtained by the sampling and a second sampled difference signal shifted by a quarter of a cycle of the color burst signal, are obtained which are proportional to the amplitude of the color burst signal. For evaluating as directly as possible the phase error independently of the amplitude factor, at least one sampled difference signal (X and Y, respectively) is divided by the amplitude factor (A) in a conversion stage (55) in such manner that at least one phase-sensitive control quantity is obtained which consists substantially of sin- and/or cos-members of the phase angle (.alpha.), optionally of a sum or a difference or a product thereof which is at least substantially independent of the amplitude factor.

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Didderse, Germany

Gerd Brand