British Telecommunications Public Limited Company

British Telecommunications Corporation

Roger J Clarke

Richard C Nicol

Brian A Fenn

Wai K Cham

King N Ngan

A method of transmission or storage of a television picture involves dividing it into a plurality of blocks, subjecting them individually to a two-dimensional unitary transformation, transmitting or storing the transform coefficients and reconstructing the original blocks by the use of the inverse transformation. To reduce the data rate, the zero sequency coefficient is omitted for most or all the blocks, and the mean levels of the reconstructed blocks are adjusted to reduce visible brightness changes between them. The adjustment may be made to reduce the means square differences between the elements in two blocks along the common boundary. The division into blocks may give common elements in two blocks along each inter-block boundary. If a picture transition coincides with a block division an indication of this may be sent so that differences between elements along the division are ignored.

Omission and subsequent estimation of zero sequency coefficients of

A method and an apparatus for transmitting an image in which the image is sampled at a first plurality of points. The samples are then subjected to a two-dimensional unitary transform to produce a second plurality of transform coefficients, the second plurality being smaller than the first plurality and being obtained either by selection or truncation of the transform to provide the coefficients containing only the lower frequency components of the image. The transform coefficients are transmitted and on receipt converted by the inverse transform to a second plurality of image samples. Suitable transforms include the Hadamard and the discrete cosine. The image transmission is described as part of a viewdata system.

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Burton on the Wold, United Kingdom

Roger J Clarke