Patent ID: 7336843
Filing Date: 2008-02-26
Classification: H04N

Abstract:
1. A method of compressing and transmitting digital data, in particular images, at a constant bit rate, the method comprising: Splitting input data into blocks of data, Applying an orthogonal or bi-orthogonal transform to a current block, Quantizing coefficients obtained by applying the transform, Entropically coding the quantized coefficients, Temporarily saving the data resulting from coding in buffer memory, Removing a particular number of bits from the memory for each block of digital data, and adjusting the quantizing step by applying a control function to obtain, for the current block, after coding, a number of bits close to the number of bits removed from the memory for each block of data, said control function being based on measurement of the bit rate produced by the entropic coding, and said control function taking account of the data bit rate measured for at least a preceding block, Wherein the coefficient obtained by applying the orthogonal or bi-orthogonal transform are ordered in order of decreasing moduli and quantizing step is obtained from the modulus of the coefficient whose rank is equal to the integer nearest the ratio of the target bit rate and a parameter which is estimated for each block based on at least one preceding block.