US 6,714,717 B1 · Time base corrector

Abstract

A time base corrector apparatus for removing time base errors from video signals. A voltage-controlled oscillator (VCXO) is locked to the chroma burst of the input signal. The VCXO is used to digitize the input video, to comb filter and to demodulate chroma signals. Time base correction is accomplished by lengthening or shortening each video line in sub-pixel increments by using an interpolator circuit to interpolate consecutive pixels. A sync error detector circuit determines the sync threshold position to sub-pixel accuracy. Sync error process logic circuit determines the integrated line length and line to line error. A coefficient generator determines the coefficients necessary to correct this error for every pixel. The interpolator then uses a polynomial interpolation technique. The interpolator compensates for too few pixels per line by compressing the stretched pixels to the proper size and by creating new pixels from a portion of the pixels immediately before and after the created pixel. Interpolator compensates for too many pixels per line by incorporating the values of the input pixels into the proper number of pixels by an interpolation technique. The pixel values are decimated and written to a write buffer.

Claims36

Dependent claims

A time base corrector apparatus for removing time base errors from composite video signals, comprising:

a digital sync error detector that detects a time that a sync crosses a sync detect threshold to determine the exact start of each line of video in pixel clock and sub-clock increments;
a sync error process logic circuit coupled to the sync error detector for calculating a correction required to reposition each video line and stretch or compress the video line to correct for time base errors;
a luminance interpolator for receiving luminance data from an output of a digital comb filter and cooperative with the sync error process logic circuit to calculate corrected pixel values for the luminance output of the digital video signal;
a pair of chrominance interpolators for receiving two demodulated data streams that are generated from a chrominance output of the digital comb filter, and cooperative with the sync error process logic circuit to calculate corrected pixel values for the chrominance output of the digital video signal;
and
a write buffer for receiving a decimated digital video signal output from an associated interpolator.

3 more elements

A method for removing time base errors from composite video signals, comprising:

determining the exact start of each line of video in pixel clock and sub-clock increments by a digital sync error detector detecting a time that a sync crosses a sync detect threshold;
calculating a correction required to reposition each video line and stretch or compress the video line to correct for time base errors by a sync error process logic circuit;
receiving luminance data from an output of a digital comb filter, receiving a plurality of calculated values from the sync error process logic circuit by a luminance interpolator, and calculating corrected pixel values for the luminance output of the digital video signal based on the luminance data and the plurality of calculated values;
receiving two demodulated data streams that are generated from a chrominance output of the digital comb filter, receiving a plurality of calculated values from the sync error process logic circuit by a pair of chrominance interpolators, and calculating corrected pixel values for the chrominance output of the digital video signal base on the two demodulated data streams and the plurality of calculated values;
decimating the digital video signal output from each chrominance interpolator;
and
receiving a decimated digital video signal output from an associated interpolator into a write buffer.

4 more elements

Dependencies are inferred from the claim text.

Time base corrector

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Time base corrector

Life of this patent

Abstract

Claims36