Abstract: A method and apparatus for coding an image comprising (at least) two regions (e.g., a facial region and a background region) which are to be coded with different quantization error parameters (e.g., quantizer step sizes), wherein the respective quantization error parameters are determined with use of a feed-forward rate control technique. Initial quantization error parameters are assigned to each region, and the overall bit rate which would result for the coding of the given frame is computed based on these assigned quantization error parameters. The computed bit rate is compared to a given bit rate constraint which may, for example, represent a limitation of a transmission channel. Based on the result of this comparison, one or both of the assigned quantization error parameters are adjusted, thereby resulting in different quantization error parameters for the two regions.

Abstract: A method and apparatus for performing vector quantization in a video coder. The method includes obtaining a video frame and segmenting it into coding blocks of predetermined size. A predetermined number of the coding blocks is transferred to a first cache memory. A predetermined portion of a codebook is transferred into a first section of a second cache memory which is capable of being rotated or having addresses associated with bytes in the second cache memory interchanged or offset by a specified amount. Concurrently with computing the vector quantization for the first portion of the codebook with respect to the coding blocks in the first cache memory, a second section of the codebook is transferred into a second section of the second cache memory. The number of coding blocks transferred to the first cache memory is selected so that transferral of the second section of the codebook is completed at the same time as or prior to completion of the computation of the vector quantization.

Abstract: A method of coding a set of multi- level signals, such as video signals comprises filtering the set of multi-level signals into one or more sets of multi-level sub-band signals; allocating a first quantity of bits for use in coding a first set of sub-band signals; coding the first set of multi-level sub-band signals using zero or more of the first quantity of allocated bits; allocating a second quantity of bits for use in coding a second set of sub-band signals, the second quantity of bits comprising zero or more of the first quantity of bits not used in coding the first set of multi-level sub-band signals; and coding the second set of multi-level sub-band signals using zero or more of the second quantity of allocated bits. Three examples of the method am provided. A hardware implementation involving the use of digital signal processors operating in parallel is also provided.

Abstract: A method of coding a video signal at a fixed bit rate with use of a vector quantization codebook, wherein advantageous codebook updates are determined by comparing a coding error associated with a first provisional coding of a frame with a coding error associated with a second provisional coding of the frame. The first provisional coding uses a fixed available number of bits to code a frame with use of the unmodified codebook, whereas the second provisional coding uses a modified codebook to code the same frame. However, the second provisional coding codes both the frame and the codebook updates with the fixed available number of bits. The provisional coding having the smaller coding error is selected as the coding of the frame which will be adopted. In addition, the codebook may be replaced with the modified codebook when the second provisional coding is selected. In this manner, the coder will adapt the codebook to the characteristics of the scene.

Abstract: The present invention provides a method of coding a set of multi-level signals, such as video signals. The method comprises filtering the set of multi-level signals into one or more sets of multi-level sub-band signals; allocating a first quantity of bits for use in coding a first set of sub-band signals; coding the first set of multi-level sub-band signals using zero or more of the first quantity of allocated bits; allocating a second quantity of bits for use in coding a second set of sub-band signals, the second quantity of bits comprising zero or more of the first quantity of bits not used in coding the first set of multi-level sub-band signals; and coding the second set of multi-level sub-band signals using zero or more of the second quantity of allocated bits. Three examples of the method are provided. A hardware implementation involving the use of digital signal processors operating in parallel is also provided.

Abstract: In a private telecommunications network, a plurality of digital PBXs are interconnected via pairs of codecs. The codecs of each pair, or "tandem", are each operative to encode 64 kilobit/second (kbps) mu-law speech so as to compress it to 16 kbps speech for transmission to the other codec in the tandem. The latter is operative to thereafter decompress the 16 kbps speech back to 64 kbps. Each codec has a second mode of operation in which, rather than decode the encoded speech, it preserves the bits thereof in its own output signal. The codec transitions to this mode whenever it recognizes the presence of another codec on its high-bit-rate side of the connection. As a result, only one encoding/decoding cycle is performed across the connection, thereby minimizing the speech-coding-induced distortion and delay therein.

Abstract: Impulse response estimation is improved in an adaptive filter by compensating digital signals incoming to the filter to include a nonlinearity substantially identical to a nonlinearity included in a return signal path to the filter.

Abstract: Update gain normalization is employed in adaptive filters to control weighting of the filter impulse response updates in order to converge properly to a desired impulse response. Singing, i.e., oscillating, of the filter is overcome by adjusting the update gain when an incoming signal power estimate used to normalize the gain exceeds a prescribed threshold value. In one example, the normalized gain is adjusted to be a fixed value for power estimate values which exceed the threshold. In accordance with another aspect of the invention, a single normalized gain value is used to adjust the update gain in two adaptive filters employed as echo cancelers in a bidirectional voice frequency repeater.