| abstract |
PCT No. PCT/US91/03743 Sec. 371 Date Oct. 28, 1992 Sec. 102(e) Date Oct. 28, 1992 PCT Filed May 29, 1991.A dithering technique in accordance with an inventive arrangement saves two bits per sample in a wideband video signal. In accordance with this arrangement, a dither signal is added to an n-bit video signal. The adder should include a limiter to avoid overflows. The samples are truncated after the addition. In truncation, the least significant two bits are simply discarded. Usually, dither values are small positive integers which tend to increase the DC content of the signal. A dither signal which can provide significant improvement in a subsampled signal is a two frequency dither in which the higher frequency has the higher amplitude. The dither signal can have any repetitive sequence of the numbers 0, 1, 2, 3 in any order within said sequence, for example, 0, 2, 1, 3, 0, 2, 1, 3, . . . , etc. The quarter-frequency component is usually more objectionable than the half-frequency component, even though the quarter-frequency component has half the amplitude of the half-frequency component. Accordingly, a dedithering scheme can be chosen to suppress only the quarter-frequency component. A first signal path of the dedithering circuit is for delay and amplitude matching. A second signal path includes a combination inverted bandpass filter and limiter. The inverted bandpass filter cancels the frequency at the center of the passband when added to the delay and amplitude matched original signal. The limiter assures that only amplitudes of dither size will be cancelled. |