Societe Anonyme De Telecommunications

British Telecommunications Corporation

Sat (Societe Anonyme De Telecommunications)

Daniel Pierre Devimeux

Jean-Claude R Jolivet

Francois-Xavier Antoine Stouls

Craig S Clapp

Norman L Shilston

Armand Riou

Coding and decoding of digital images by transformation of pixel blocks reduce the data bit rate. Transformation of blocks leads to discontinuities in brightness level for pixels bordering on block boundaries. These discontinuities are detected for each given bordering pixel by a change of sign of two level gradients respectively computed with the levels of two pixels adjacent to the bordering pixel. A brightness level of the bordering pixel is then corrected by a discontinuity correction factor evaluated from a discontinuity divergence equal to the absolute value of the difference between the brightness level of the bordering pixel and an arithmetical average of brightness levels of the two adjacent pixels, as a function of a quantization pitch associated with a block to which belongs the bordering pixel. The block is then corrected in its entirety to attenuate the differences of average brightness levels between two adjacent blocks generated by the coding and decoding.

Method and device for spatial filtering of digital images decoded by

This invention relates to digital transmission techniques whereby information produced in asynchronous form, for instance by variable-length coding and/or by conditional coding, is intended for transmission through a synchronous digital transmission path. More particularly, the invention concerns a receiving device comprising a picture buffer memory having a content that can be different from that of a picture buffer memory included in a transmitting device of the system, a circuit for detecting picture line and field synchronizations, a circuit for transcoding video information prior to its writing in the receiving device buffer memory and a circuit for monitoring writing and reading addresses in the buffer memory in terms of the detected synchronizations. A partial decoding of the video information is performed prior to entry in the receiving device buffer memory, and a synchronization of this memory is independent of the content in the transmitting device buffer memory.

Receiving device in an asynchronous video information transmitting system

A conditional replenishment video data transmission system involves the transmission of updating digital data for clusters of consecutive picture elements, all or most of which show a change since the previous frame, in lines of a raster over an image to be transmitted. The lines of the raster are numbered cyclically in groups of 8, the numbers being part of line synchronizing code words, and the position along a line of the first element of each cluster is identified by a number. The data are transmitted at a constant rate from a transmitter buffer to a receiver buffer and an auxiliary data store records the addresses of the line synchronizing code words in the receiver buffer. The address of the receiver buffer read by a reading means can be corrected by reference to the address data in the auxiliary storage means if for example the line numbers do not follow in sequence or the element addresses are not in ascending order due to corruption during transmission. Alternatively, the reading means may be controlled at all times by the address data in the auxiliary storage means and not only when a tracking error has occurred. The tracking of the received data in the receiver buffer by the reading means may show a consistent error relative to the position predicted by the assumed transmission delay time; preferably such tracking errors are corrected by a whole frame jump using a receiver buffer of more than one frame capacity.

Digital data transmission/reception having adaptive error control

A digit rate reducing method in the transmission of video-telephone signals, wherein each frame is scanned by means of two consecutive fields comprising each the lines of same parity, each frame dot being represented by a word of n, in particular 3, binary digits comprising transmitting a frame every three frames, storing a frame of each parity at the receiving equipment in a frame storage device, systematically freshening-up a stored frame by the next transmitted frame of same parity, and regenerating intermediate frames by interpolating between the stored frames, further comprising forming a pseudo-field I.sub.n with opposite parity to a stored field T.sub.n by interpolating between T.sub.n and the stored field T.sub.n+3 or T.sub.n-3, and regenerating an intermediate field T.sub.n+1 or T.sub.n-1 from I.sub.n and T.sub.n+3 or T.sub.n-3, respectively.

Growing community of inventors

Perros Guirec, France

Daniel Pierre Devimeux