Abstract: A method for synchronization of a digital audio signal sampled at a standard audio frequency with the corresponding digital video signal sampled at a standard video frequency associates an integer number of samples of the digital audio signal with each video field of the digital video signal. The number of audio samples per video field is determined by the audio sample rate rounded up to the nearest integer. Every N video fields where the number of digital audio samples is an integer value, the digital audio signal is resynchronized with the digital video signal by repeating the digital audio samples at the end of video field N that correspond to video field N+1. At reception the same digital audio samples are skipped at the end of video field N.

Abstract: A circuit for driving a transmission line composed of first and second conductors, comprises input transistors for providing a differential signal, and first and second output transistors having their bases connected to receive the differential signal, their collectors connected to a first reference potential level, and their emitters connected to the first and second conductors respectively. An output enable circuit selectively places the output transistors either in a conductive condition, in which they apply the differential signal to the transmission line, or in a non-conductive condition, in which the isolate the transmission line from the input transistors.

Abstract: A shaped video having an input key control signal associated therewith is processed by carrying out a first operation on the input key control signal to provide a first processed signal, carrying out a second operation on the first processed signal to provide a second processed signal, and combining the shaped video signal and the second processed signal to provide an output video signal. One of the first and second operations comprises translation. In this manner, a simulated shadow is added to the shaped video signal.

Abstract: A simple compositing system for combining sequences of images, including graphics and video images, records the sequences onto a disk recorder. A frame from each sequence in turn is processed by a digital picture manipulator channel and stored in a respective frame store. Once one frame from each sequence is processed and stored, the frames from the frame stores are combined in a video combiner to form a composite frame, which is read back into the disk recorder. All of the frames of the sequences are combined in this manner to form composite frames, the totality of composite frames producing a final composite image sequence stored in the disk recorder. The final composite image sequence is then transferred to an output device in real time.

Abstract: A chroma keyer with fringe control offset adds a fringe control offset value to a correlation output produced by a hue selector. The hue selector compares the hues of a foreground image, representing a foreground object in front of a reference matte background, with a reference hue corresponding to the reference matte background to produce the correlation output. The adjusted correlation signal is then negatively clipped and provided at the output of the hue selector as a hue select signal that is used for deriving a chroma key signal and for providing background suppression to the foreground image.

Abstract: A control panel for a television digital special effects device comprises a plastic shroud that has an internal conductive coating and defines a key panel cavity. A key panel plate fits within the key panel cavity. A thin stainless steel EMI screen is adhesively bonded to the upper surface of the key panel plate and an overlay sheet is adhesively bonded to the upper surface of the EMI screen. Apertures for the keys, controls and displays of the control panel are present in registration in the key panel plate, the EMI screen and the plastic overlay. The EMI screen has a main body with fingers projecting from its periphery. The dimensions of the main body of the EMI screen are smaller than the corresponding dimensions of the key panel cavity in the plastic shroud, while the finger-tip-to-finger-tip dimensions of the screen are larger than those corresponding dimensions.

Abstract: An enhanced video special effects system architecture is based on deinterlacing (16) incoming fields of interlaced video and processing the deinterlaced video through video special effects operations (18, 30), each of which benefits from operating on a progressive scan video signal rather than an interlaced video signal.

Abstract: A switcher with depth processing includes a depth processor module. External depth data, or internally generated depth data, are input to the depth processor to generate a priority signal for combining key video signals as layers between a background and a foreground video signal. Further a composite depth signal is generated for the combined key video signals for subsequent processing so that additional key video layers may be intersected and intertwined with the key video layers in the combined video signals.

Abstract: A method of pattern generation for a screen using a wipe solid generator and a recursive memory includes generating from operator inputs a wipe solid. An extent of the generated wipe solid is measured to produce maximum and minimum values. These maximum and minimum values are extended to encompass a desired border size and softness. A lever-arm scaling function is selected based upon whether a change in operator input causes a reversal in pattern and/or causes the pattern to "breathe." The selected lever-arm scaling function uses prior values from the recursive memory to generate new values that are stored in the recursive memory. From the stored values clip levels are determined such that completion of lever-arm movement to a limit position coincides with completion of the pattern without distortion of the size of the pattern.

Abstract: A depth-based video combiner that combines two video signals to produce a combined video signal as a function of respective key signals and a priority signal derived from respective depth coefficient signals also combines the respective depth coefficient signals as a function of the respective key signals and the priority signal to produce a combined depth coefficient for the combined video signal to provide smooth depth transitions at intersecting edges between the two video signals. A mix coefficient for the depth coefficient signals is generated from the respective key signals and the priority signal. The mix coefficient signal is used to combine the respective depth coefficient signals to produce the combined depth coefficient signal.

Abstract: Depth-based recursive video effects are generated by including depth information in the recursive loop. A combined depth coefficient signal output from a depth-based video combiner is modified by a recursive key signal from the recursive image output from the recursive loop. The resulting depth coefficient signal may then be blurred when a recursive blur effect is selected by using an appropriate filter corresponding to that used in the luminance and key recursive loops. The recursive depth coefficient signal from the depth recursive loop is used, together with the depth coefficient signal associated with an incoming image, to produce the priority signal used in the depth-based video combiner.

Abstract: A sampling rate converter for converting an input digital signal, such as D2 PAL, into an output digital signal, such as D1 PAL, has a pair of polyphase filters. The input digital signal is input in parallel to the two polyphase filters, with the phase selected by one of the filters being offset by one from that of the other. The outputs of the polyphase filters are input to a linear interpolator to produce the output digital signal. The resolution of the sampling rate conversion is a function of the number of phases N of the polyphase filters and the number of interpolation steps M of the interpolator.

Abstract: A single loop analog-to-digital conversion and video clamping circuit includes a low-pass filter and analog amplifier that present the incoming analog video signal to an analog-to-digital converter and to the input of a limit detector and protection circuit. The output of the analog-to-digital converter is sampled an integer multiple of four times during the black interval, with the results being summed and averaged. The resulting value is then scaled and limited, and compared to the desired level for a representation of black. Any resulting error quantity is converted from digital back to, analog and modified if necessary by the output of the limit detector and protection circuit. The signal that results from that modification is low-pass filtered and converted to a current by a transconductance amplifier. The resulting feedback current is then applied to a capacitor in the input circuitry, thereby clamping the input and resulting digital output of the overall circuit to the desired level.

Abstract: An inverse hyperbolic comb filter decodes an encoded signal by subtracting a vertically filtered and horizontally filtered version of the encoded signal from a delayed version of the encoded signal whereupon the resulting output is further horizontally filtered to provide a first decoded output. A twice delayed version of the input signal then has the first output signal subtracted therefrom to provide a second output. Optional further vertical filtering may be employed to vertically filter the output of the first subtractor before the final horizontal filtering is performed. The filter may also be employed in encoding signals wherein the components to be encoded are first filtered prior to combining. The inverse hyperbolic comb filter is applicable to any system employing combining of two-dimensional signals via quadrature modulation and may also be employed in three-dimensional systems.

Abstract: A reduced viewport feature for a graphics display system allows an operator to observe manipulations on a graphics display of video image planes that are wholly or partially outside a viewing area. A two-dimensional input image plane in the form of a wireframe is transformed to a three-dimensional image plane due to manipulation, such as rotation and/or translation. The resulting three-dimensional image plane is subsequently mapped as a two-dimensional projection onto the graphics display. Transformation matrix coefficients are multiplied by a variable reduction coefficient to cause all points of the image plane to converge toward the center of the graphics display, resulting in the ability to view space which originally was not visible to the operator on an output video monitor.

Abstract: An improved chroma keyer has a secondary hue selector for chrominance suppression of "blue fringing" effects. The second hue selector provides a second chroma key signal from a foreground video signal, with the selected hue being offset from that of a primary hue selector. A matte generator having a hue corresponding to the hue of a backing in the foreground video signal is modulated as a function of the second chroma signal. The modulated hue from the matte generator is subtracted from the foreground video signal to produce a modified foreground video signal. The modified foreground video signal is converted into a shaped foreground video signal. The shaped foreground video signal is combined with a shaped background video signal to produce a composited output video signal. The shaped background video signal is a function of a background video signal and a primary chroma key signal from the primary hue selector.

Abstract: A chroma key generation method and apparatus are provided (for both composite and component video) in which an operator selects a reference portion of a color television image to identify it as the background of the image, and a strobe signal is then generated whenever the video data that is presently passing through the keyer is within the reference portion of the color video image. This strobe causes the video data corresponding to that portion of the image to be stored. A microprocessor then determines attributes of the video in the reference portion of the color image from the stored video data, these attributes including a reference hue, .alpha.. The image hue .THETA. at each pixel in the color image is correlated with the reference hue .alpha. to produce a correlation signal that has a first range of values for points of the color image at which the image hue matches the reference hue and a second range of values for points of the color image at which the image hue does not match the reference hue.

Abstract: A pseudo-random pattern generator has modifiable feedback so that a variety of pseudo-random video patterns can be generated and used either directly, or after further manipulation, to control the mixing of two video sources. Control of a multiplexer allows a variety of pattern lengths to be selected by altering which stages of a shift register are supplied to a feedback exclusive-OR gate. Patterns with controllable granularity can be achieved by stretching each part of the noise pattern a selectable number of times along either or both axes. Horizontal stretching is achieved by clocking the shift register more slowly than the rate at which it is being read out. Vertical stretching is achieved by repeating the same pattern on each of a selectable number of consecutive lines. Varying the ratio of the stretching along the horizontal axis to the stretching along the vertical axis allows the aspect ratio of the grains of the pattern to be controlled.

Abstract: An interpolating digital signal clipping circuit provides pre-clipping of the luminance component of a video signal. A difference circuit adjusts each sample so that a single bit indicates whether the sample value is closer to a positive or negative clipping limit. Interpolated samples are produced by phase shifting FIR filters and are applied, along with the actual current sample, to a minimum or maximum selecting circuit that selects the minimum or maximum sample depending on the state of the indicating bit. The selected sample is compared with the clipping limits to produce an excess signal that indicates how much the selected sample exceeds the relevant clipping limit. A gain control signal is generated to be a "1" when no clipping is required and less than one when clipping is required. A digital video signal clipping circuit receives this pre-clipped luminance signal and adjusts each sample as above.