Field of the Invention:
The present invention relates to an arrangement for difference pulse code modulation (DPCM) coding of television signals, in which respective estimated values are subtracted from digitized picture element signals and the difference signals obtained are utilized for signal transmission following quantization and coding, and comprising a recursive signal path that, in turn, comprises a first adder for forming reconstructive picture element signals from the quantized difference signals and the estimated values, and comprises a limiter, a predictor for forming the estimated values and a subtractor for forming the difference signals.
Description of the Prior Art
An arrangement of the type set forth above is generally known from the publication Proc. IEEE, vol. 73, No. 4, Apr. 1985, pp. 592-598, particularly FIGS. 1, 2 and 4, and will be explained here with reference to a basic circuit diagram as shown in FIG. 1 of the present application. A sequence of digitized picture element signals s is received at an input 1 of the arrangement, the picture element signals s being supplied via sample and hold stages that are not illustrated. In order to reduce the data flow, efforts have been undertaken to remove redundant and irrelevant portions of the video signal in order, for example, to reduce the bit transmission rate without thereby deteriorating the picture quality. In detail, this occurs in that it is not the successive picture element signals that are transmitted via the transmission channel to a receiver, but only the difference signals that are formed by forming the difference between a respective current picture element signal s and an estimated value s identified in a predictor on the basis of the preceding picture element signals. Such a method is also referred to as difference pulse code modulation (DPCM).
The difference formation required for a DPCM coding is carried out in a subtractor 2 whose first input is connected to the input 1 and whose second input is connected to a predictor 3. Each difference signal .DELTA. that is also referred to as an estimated error is quantized in a quantizer 4, whereby the difference signal .DELTA..sub.q =.DELTA.+.sub.q that occurs and is affected by the quantizing error q, is coded in a coder 5 and is supplied to a transmission channel by way of an output 6. A recursive signal path that extends from the circuit point 7 at the output of the quantizer 4 contains a first adder 8, a limiter 9 and a predictor 3, and is connected to the second input of the subtractor 2 for forming the estimated value The output of the predictor 3 is further connected to a second input of the first adder 8 that forms what is referred to as a reconstructed picture element signal s.sub.R by addition of the quantized difference signal .DELTA..sub.q and the estimated value The predictor 3 supplies the estimated value s from at least one of the preceding picture element signals for every current picture element signal s.
When, according to FIG. 2, the current picture element lying in the line n in a television picture is referenced X, the picture element sampled immediately therebefore is referenced A, the picture element of the preceding line n-1 corresponding to X is referenced C and the picture elements aligned adjacent the latter and sampled immediately before or, respectively, after the element C are referenced B and D. When the corresponding picture elements of the preceding picture m-1 are referenced X' and A'-D', then the following occurs. For forming the estimated value s for the picture element signal of the picture element X, the picture element signals of at least one of the points A-D are utilized, whereby one speaks of a 2-dimensional (2D) prediction. When, in addition thereto or exclusively therefrom, the picture element signals of at least one of the picture elements X' and A'-D' are used, then a 3-dimensional (3D) prediction is present. In the former case, the estimated value s can be identified, for example, according to the 2D-estimating equation EQU s=.alpha.s.sub.A +.beta.s.sub.B +.gamma.s.sub.C +.delta.s.sub.D ( 1)
and in the latter case can be estimated, for example, according to the 3D-estimating equation EQU s=s.sub.X ( 2)
wherein s.sub.A is the reconstructed picture element signal of the picture element A, s.sub.B is the reconstructed picture element signal of the picture element B, etc, and wherein the coefficients .alpha., .beta., .gamma. and .delta. represent weighting factors that are assigned to the individual picture element signals. The estimated equation (2) is recommended when the contrast of the current picture element X to the picture elements surrounding the picture element X is low, this being referred to as "activity".