Digital modulators for use with sub-nyquist sampling of raster-scanned samples of image intensity

Apparatus for processing a video signal that is raster scanned, with successive scan lines occurring at a prescribed scan line rate within image fields and occurring in first and second spatially interleaved sets of scan lines within each image field, said video signal being a baseband signal of a prescribed bandwidth extending up to a prescribed maximum frequency, said apparatus comprising:

• means for providing a digitized video signal by digitizing said video signal;
• a digital band-splitter filter with a cross-over frequency at one-half said prescribed maximum frequency, for separating said digitized video signal into samples of a lower-frequency-band component and samples of a higher-frequency-band component;
• means for generating first and second weighted sums of said lower-frequency band component and said higher-frequency-band component, said lower-frequency-band component and said higher-frequency-band component both being weighted by a first weighting factor in generating said first weighted sum, and both being weighted by second weighting factors of the same amplitude but of opposite polarities in generating said second weighted sum;
• and
• means for selecting alternate samples of said first and second weighted sums to generate a folded-video signal.

Apparatus for processing a video signal that is raster scanned with successive scan lines occurring at a prescribed scan line rate and being apportioned to first and second sets of scan lines, said video signal being a baseband signal of a prescribed bandwidth extending up to as high a frequency as a prescribed maximum frequency that is a multiple of said prescribed scan line rate, said apparatus comprising:

• means for sampling said video signal at the Nyquist rate for said maximum frequency, whereby there is a prescribed integral number of sequential samples per scan line;
• a band-splitter filter with a cross-over frequency at one-half said prescribed maximum frequency, for separating said video signal into a lower-frequency-band component and into a higher-frequency band component having a polarity associated with each of its successive samples, each component having said prescribed integral number of samples per scan line identified by consecutive modulo two numbers assigned in accordance with the sequential occurrence of those said samples beginning with zeroeth;
• means for generating first and second weighted sums of said lower-frequency-band component and said higher-frequency-band component, said lower-frequency-band component being weighted by the same weighting factor in generating both said first and said second weighted sums, and said higher-frequency-band component being weighted by weighting factors of the same amplitude but of opposite polarities in generating said first and said second weighted sums;
• and
• means for generating a folded-video signal having said prescribed integral number of samples per scan line identified by consecutive modulo two numbers assigned in accordance with the sequential occurrence of said samples, during scan lines of said first set each zeroeth sample of said folded-video signal corresponding to the current zeroeth sample of said first weighted sum in magnitude and being of the same polarity, during scan lines of said first set each first sample of said folded-video signal corresponding to the current first sample of said second weighted sum, during scan lines of said second set each zeroeth sample of said folded-video signal corresponding to the current zeroeth sample of said second weighted sum and during scan lines of said second set each first sample of said folded-video signal corresponding to the current first sample of said first weighted sum.