Video bandwidth reduction system employing interframe block differencing and transform domain coding

Abstract

Abstract Video type information signals are compressed for transmission and reproduction by comparing corresponding blocks of time domain information signals from successive fields, converting a block of the time domain information signals to a transform domain signal represented by discrete cosine transform coefficients when the difference between the corresponding blocks exceeds a block difference threshold, and encoding the transform domain coefficients for transmission to a decoding site. Corresponding blocks of time domain information signals from successive fields are compared by storing the successive fields in memory on a pixel by pixel basis, retrieving each block on a pixel by pixel basis, forming the difference between corresponding pixels from the successive blocks, squaring the resulting difference signal, summing the squares and dividing by the number of pixels per block. Successive fields are merged by weighted summing of corresponding pixels. Blocks are converted by first transforming individual samples along the horizontal direction, and then transforming the same block samples along the vertical direction, the transformed coefficients being stored in a diagonal memory unit along with a block address code and block averaged quadrature chrominance characters. Each converted block stored in the diagonal memory is encoded using a plurality of unique code tables. A dedicated block address code table is constructed using a unique algorithm; the remaining code tables are Huffman coded tables, one dedicated to the D.C. transform coefficient term, two other tables dedicated to the quadrature component characters, and the remaining tables (including the two chroma tables) being selected on a coefficient by coefficient basis using an algorithm based on the predictive mean value of the cosine coefficient terms. The cosine coefficient terms are also quantized prior to encoding by dividing the coefficient by a variable parametric value D k , which is a measure of the fullness of the transmission buffer, and which is changed in value after each block of codes is loaded into the buffer. The D k value is also used to adjust the value of the block difference threshold. The block codes are assembled in a transmission buffer in the order of generation and are transmitted to a decoding site along with initialization values for D k and a buffer fullness parameter B k . At the decoding site, the received code characters are decoded using an inverse processing resulting in recapture of the initial video signals. The luminance and chrominance components are initially processed by subsampling and averaging to produce further compression.

Inventors

• 👤 Eric R. Hamilton
• 👤 Stanley C. Fralick
• 👤 Robert D. Widergren
• 👤 Andrew G. Tescher

Bibliographic Details