Abstract: The central difference along a selected axis through a point (u, v) of a rectangularly-sampled luminance field and at an arbitrary angle .alpha. is computed by interpolation. The octant in which the selected axis lies is identified, and first and second pixels through which the lines that limit the identified octant are identified. The first and second pixels are adjacent each other in the luminance field array and lie on a common ordinate or a common abscissa. The difference between the luminance values of the first and second pixels is calculated. Third and fourth pixels, which are symmetrically disposed with respect to the first and second pixels respectively about the point (u, v), are identified, and the difference in luminance values of the third and fourth pixels is calculated. The central difference along the selected axis is calculated by applying the MIX operator to the two difference values and a mix ratio coefficient which is the tangent of an angle which is related to .alpha.

Abstract: A digital wipe generator has a digital waveform generator to generate X and Y digital waveforms from a composite sync signal. A digital wipe solid generator processes the X and Y digital waveforms to produce a digital wipe solid waveform. The wipe solid generator has a circle generator using a square root function which preshifts the sum of the squares prior to access to a look-up table, and then post shifts the output of the look-up table by one-half the amount of the preshift to produce a desired curve pattern for the digital wipe solid waveform. The digital wipe solid waveform is input to mixer circuits where it is processed to produce an anti-aliased key signal for mixing external video signals, the anti-aliasing being based upon an interpolation/decimation scheme using fractional bits of the digital wipe solid waveform. The output of the mixer circuits is a desired wipe transition.

Abstract: A video difference key generator has a stored reference video image. An input video image is compared with the reference video image by an absolute difference circuit which substracts corresponding pixels of the two video images, the smaller from the larger, to produce a difference video image. The difference video image may be filtered, and then is input to a transfer function circuit to produce an output which may be used as a key signal for compositing video images.

Abstract: A multifunction amplifier uses a finite transconductance amplifier to provide an amplifier with a high impedance input and a desired output impedance. A pair of appropriate polarity binary signals are summed to form a ternary signal which may be filtered by a filter circuit upon command. The ternary signal, filtered or unfiltered, is input to one input of a differential transconductance amplifier while a feedback signal via a feedback path from an output node of the finite transconductance amplifier is input to the other input. The outputs of the differential transconductance amplifier are equally amplified by a pair of output current gain amplifiers. A unity gain bias level shifter is provided between one of the differential outputs and one of the pair of output amplifiers. The output amplifiers combine the amplified output currents at the output node.

Abstract: A method for orientating and animating video images using quaternions to provide smooth, predictable rotations in a digital video effect device. Euler angles for a new orientation are input by an operator and are converted into an appropriate quaternion. For incremental orientation changes the appropriate quaternion is combined with the current quaternion of the video image in either source or target space to form a new quaternion for the new orientation of the video image. A selected plurality of such new quaternions in a sequence make up the video effect keyframes. In executing the video effect a Bezier spherical linear algorithm is used to interpolate intermediate quaternions on a video field by field basis between neighboring pairs of keyframe quaternions based upon the source keyframe quaternion, the destination keyframe quaternion, a source outgoing keyframe quaternion, a destination incoming keyframe quaternion and an inbetweening time coefficient.

Abstract: A low power, differential ECL line driver has a switching network that applies a constant current source as the emitter load to only one of the output transistors at a time while applying a constant current source to the base of the other output transistor.

Abstract: An adaptive DCPM video encoder operates directly upon a digitized composite video signal to generate a bit reduced serial digital output signal. The encoder has a feed back loop in the form of a recursive filter with zero's at d.c. and the color subcarrier frequency of the digitized encoded video signal that determines a predicted value for subtraction from the digitized composite video signal to produce a difference signal having the color subcarrier frequency nulled out. The difference signal is quantized to produce a quantized difference signal from which the predicted value is derived. An inner loop determines from the quantized difference signal an offset value from which the presence of large step transitions in the digitized encoded video signal are detected. For large step transitions the offset signal is subtracted from the difference signal to produce an offset difference signal for input to the quantizer.

Abstract: A video signal is used to create a mosaic effect by carrying out a first sample and hold operation on the video signal so as to generate a second video signal, rotating the effective scanning direction of the second video signal through a predetermined angle to generate a third video signal, and carrying out a second sample and hold operation on the third video signal so as to generate a fourth video signal.

Abstract: A wipe-only effects apparatus has a video mixer with video input terminals for receiving respective input video signals. The mixer combines the input video signals in dependence upon a control signal received at a control input terminal of the mixer. A ramp generator a repetitive ramp signal and applies it to a control input terminal of the video mixer as the control signal. The repetitive ramp signals start at the beginning of the active picture interval of a video field and terminate at a position determined by an operator controlled knob. The transition from one video signal to the other is caused by decreasing the slope of the repetitive ramp signal to zero.

Abstract: A digital clip and gain circuit compares an input waveform with a clip level to produce a difference waveform. The difference waveform is shifted by an exponent representing a power of two portion of a gain value, and is then multiplied by a mantissa representing a fractional portion of the gain value. The resulting product is input to a lookup table which provides level shifting and limiting to output a control waveform. A parallel overflow logic circuit processes the difference waveform and the exponent portion of the gain value to determine if the resulting product is out of range. If the resulting product is out of range, the lookup table outputs either a maximum or a minimum value for the control waveform according to the sign of the difference waveform.

Abstract: The color burst of a first video signal is brought into a desired phase relationship with the color burst of a second video signal by generating a first number which is representative of the phase relationship between the burst of the second video signal and a calibration reference signal and generating a second number which is representative of the phase relationship between the burst of the first video signal and the calibration reference signal. The second number is compared with the first number, and the phase of the burst of the first video signal is adjusted automatically in a manner such as to achieve a predetermined relationship between the second number and the first number.

Abstract: A digital timing generator using a state machine detects the presence of a predetermined pulse pattern at the input to generate a valid pulse output, and from the periodic repetition of the valid pulse output indicates the presence or absence of an input signal having the predetermined pulse pattern. The edges of the pulses at the input are detected and the pulse widths are determined by a time duration counter as being within the limits corresponding to the predetermined pulse pattern. A valid pulse counter is incremented for each pulse having the proper pulse width, and when the count of the counter reaches a predetermined value a valid pulse output is indicated. The valid pulse output may be delayed before being input to a signal presence detector. Each valid pulse output restarts a time interval counter and increments a valid input counter so long as the time interval timer does not reach a maximum time interval.

Abstract: A circuit for quantizing television horizontal phase to subcarrier zero crossings has a voltage variable delay circuit to delay the leading edges of incoming horizontal pulses to produce a delayed horizontal pulse output. The corresponding leading edges of the delayed horizontal pulse output are input to the clock input of a flip-flop to store the level of a square wave input which has a given transition (high to low, for example) for each zero crossing of the subcarrier. The stored levels are integrated to produce an error signal which is used to delay the leading edges of the incoming horizontal pulses so that the leading edges of the delayed horizontal pulse output are time quantized within a narrow window at a subcarrier zero crossing.

Abstract: A matte generator for generating a video signal representative of a matte having a uniform color, has an operator interface for generating signals representing three independent variables which are sufficient to characterize a color. A processor receives the input signals and derives three numerical values from the input signals and from calibration values provided to the processor, and a quadrature modulator receives a subcarrier signal and signals representing the three numerical values and generates an encoded video signal in response thereto. The encoded video signal and a calibration signal are applied to a calibration circuit for comparing the encoded video signal and the calibration signal and providing an output signal representative of the relationship therebetween. The output signal of the calibration circuit is applied to the processor and is used to generate calibration values such that the encoded video signal is brought into predetermined relationship with the calibration signal.

Abstract: A tracking modulation limiter for laser diodes tracks from the output of a laser diode the maximum forward current. The maximum forward current is multiplied by a factor less than one to generate a control current representative of the maximum negative modulation for the laser diode. The control current is modulated by an input modulation signal and combined with the maximum forward current to drive the laser diode so that the drive current does not fall below threshold.

Abstract: An intra-field recursive interpolator reads stored output video from one field store while writing output video into a second field store. The read stored output video is spatially corrected by vertical interpolation prior to being multiplied by a decay constant and being combined with an input video which has been multiplied by the inverse of the decay constant to produce the output video. The resulting output video is a combination of the current input field of video and each preceding field of the output video.

Abstract: A digital audio transmission system which is compatible with common carrier digital hierarchy systems converts two channels of analog data, such as precision stereo audio, into high resolution digital data words sampled at a high frequency. The data words are parity checked with the addition of one bit and divided into odd and even bit words for each channel. The bit words are time domain multiplexed into a common carrier frame with separate words for the parity bits and alternating channel data consisting of an odd and an even bit word. Each bit word is checked for all zeros and modified accordingly to assure that ones density and consecutive zero restraints are achieved. The resulting common carrier frames are transmitted over the appropriate common carrier cross-connects to a receiver which decodes the frames, recovering the bit and parity words. The bit words are recombined into data words and checked for parity.

Abstract: A picture transformation memory has three field stores which rotatively store a next field of video data, output a prior field of video data and output a current field of video data to provide a full frame output for each field input period. Each field store has four planes which contain identical fields of data and are read from sequentially pixel by pixel. Each plane has four banks with the field data being read into the banks sequentially pixel by pixel such that when one pixel is addressed, a local address generator addresses the neighboring pixels as well to produce a multi-pixel output to an interpolator. Four half bandwidth data the first and third planes contain identical data and the second and fourth planes contain identical data in the same address locations as the corresponding data in planes one and three.

Abstract: A multiple television standards input selector and convertor selects a video signal from among a plurality of television standard format input sources including encoded video, analog component video and digital video. The selected video signal is converted to a predetermined standard format video signal for further processing by a digital video effects device. The selection of the video signal occurs within a vertical interval period so that no visible effect is detectable on a display when switching between video sources.

Abstract: A mixer controlled, variable passband, finite impulse response filter has a plurality of individual filter function blocks which are cascaded. The filter function of each of the individual filter function blocks is represented by a fixed filter function block having a linear phase response. The junctions between successive filter function blocks form signal taps. The signal from each signal tap is delayed by a compensating delay device so that the signals from each of the plurality of signal taps have the same phase function. Signals from selected signal taps are then combined in a predetermined manner to achieve a desired filter transfer function.