JPS6199419A - Predictive encoding system - Google Patents

Abstract

PURPOSE:To reduce DC components without increasing the redundancy to compress a band by assigning the code of a smaller CDS value to a data signal whose absolute value of the prediction error level is smaller. CONSTITUTION:A prediction error signal E is led to a quantizer 12 to transmit an output data signal D0. A representative value setting device 13 has the reverse characteristic with respect to the quantizer s12. The output signal from a predicting device 15 is fed back to the input side of an adder 14, and this output is added to a representative value signal R, and thereby, the adder 14 executes the integrating function. A local decoder 16 transmits a predicted value signal P. A specific output characteristic is given to the quantizer 12. That is, such a code is assigned to the error signal E of a narrow range that the absolute value of CDS is small, and bit patterns of prediction error signals having the same absolute value are inverted and arranged in a digital signal D0. Thus, a bit pattern whose absolute value of CDS is small is assigned to the prediction error signal E of about zero of high frequency to transmit the digital signal D0 having less DC components.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a predictive coding system configured to reduce the direct current component of a predictive error signal.

In other words, the present invention performs predictive coding using the correlation of data signals (for example, for video signals such as television signals, intra-scanline predictive coding, intra-frame predictive coding, or The present invention relates to a predictive coding method for efficiently transmitting signals, such as interframe predictive coding.

[Prior art]

2. Description of the Related Art For example, a digital VTR is known as a device that embodies a conventionally known predictive encoding method.

In this type of apparatus, in order to record an image signal with a large amount of information onto a recording medium such as a magnetic tape, the correlation of the image information is utilized to compress the transmission band.

However, it is difficult for ordinary magnetic recording devices to record and reproduce very low frequencies and DC components. This will be explained in detail based on the recording/playback principle of a digital VTR as follows.

Recording and playback on magnetic tape is performed via several heads attached to a rotating cylinder, but the heads normally used detect changes in magnetic flux over time (differential value) by converting them into voltage. Therefore, DC components and low frequency components are difficult to reproduce. Moreover, since the head is always rotating at high speed, the signal supply to the head and signal reception from the head are performed via a rotary transformer attached to the cylinder, and for this reason, the DC component of the signal is not transmitted. It turns out.

Therefore, band-compressed image data is not recorded as is, but is scrambled using a pseudo-random pattern to suppress the direct current component before being recorded or reproduced. However, even in this case, the scrambled image data contains a DC component, however small, so in systems that cannot transmit such DC components, it is difficult to reproduce the recorded pattern of low frequency components. Many detection errors will occur. Such an increase in the error rate results in a disadvantage that the image quality deteriorates.

Also, various DC-free modulation methods are known (8
-10 block code, interleaved NRZI, etc.), conversion methods that do not have a DC component, such as 8-10 conversion, have the drawback that redundancy increases and the transmission bit rate increases, making it difficult to achieve high-density recording. Moreover,
In order to realize such a modulation method, complicated processing is required, and the hardware cost also increases.

〔the purpose〕

In view of the above-mentioned points, an object of the present invention is to provide a predictive coding method configured to reduce DC components and perform band compression without increasing redundancy.

In order to achieve this object, the present invention is characterized in that a code with a small CDS value is assigned to a data signal with a small absolute value of the prediction error level.

The present invention will be described in detail below with reference to one drawing.

〔Example〕

Fig. Em1 shows an embodiment of a predictive encoder to which the present invention is applied, where 11 is a subtracter that subtracts a predicted value signal P from the input image data signal theory and sends out a prediction error signal E; A quantizer which introduces a prediction error signal E and sends out an output data signal Do (for example, 4 bits) to be described later; 13 is a representative value setter having inverse characteristics to the quantizer 12; 14 is a signal from the predictor 15; An adder 16 is made up of a representative value setter 13, an adder 14, and a predictor 15, and is configured to feed back the output signal to the input side and add it to the representative value signal R, thereby performing an integral function. It is a local decoder that delivers a value signal P.

Next, the input/output characteristics of the quantizer 12 will be explained using Table 1. That is, Table 1 shown below is a table showing the relationship between the level of the prediction error signal E and the bit configuration of the output data signal Do.

Addendum - L - - ］＼ - In addition, the CD
.

Digital Sum) is the output bit pattern D
When the level rlJ of each bit of o is +1°° and the level "0" is "-1", it represents the sum of each bit in a single code. Therefore, the sum of the numbers of rlJ and "0" When the sum of the numbers is equal, the CDS becomes an army.

As shown in FIG. 2, the prediction error signal E is known to have a statistical property that it has a large frequency distribution around °O''' based on the correlation of images. Therefore, in the present invention, the prediction error signal E is For a small range of , a code is assigned so that the absolute value of CDS becomes small, and on the other hand, a code that makes the absolute value of CDS large is assigned to a region where prediction error signal E is large.

In addition, since the prediction error signal E is symmetrically distributed around °"0, the output bit pattern 7 is as shown in Table 1.
For 0 entries, the bit patterns of prediction error signals having the same absolute value are reversed. The inverted arrangement of such bit patterns is explained in more detail as follows. -3'', the arrangement of the upper bits and lower bits is reversed to '1011'.Similarly, for '0010' which corresponds to the prediction error +6°, the prediction error '- However, for '+7' and °'-7pa, which are the maximum values of the prediction error in this example, ''1111°° and 'oooo' are respectively set. In addition, if the prediction error is zero, the value of 0110"
+001". In this way, by assigning a bit pattern with a small absolute value of CDS to the vicinity of E = 0, where the probability frequency of the prediction error signal E is high, it is possible to create a digital signal D with a small DC component.
O is sent.

FIG. 3 shows another embodiment of the predictive encoder according to the present invention, where 20 is a subtracter that subtracts the predicted value signal P from the input image data signal Di and sends out the predicted error signal E.

22 is a changeover switch, 24A and 24B are a second quantizer and a second quantizer, respectively.
It is a quantizer, and the second
Shown in the table.

Table 2 Also, 26 is an up/down counter, which counts up when the output data Do is 1''', and the output data is
It is configured to count down when it is 0'°.

28 is a changeover switch; 30A and 30B are a first representative value setter and a second representative value setter having inverse characteristics of the first quantizer 24A and second quantizer 24B, respectively; 32 is an adder; 34 is a predictor It is.

The first and second quantizers 24A described above.

As is clear from Table 2, the difference between 24B and 24B is, respectively, when the prediction error is 7'
The configuration is such that the bit pattern of "oooo" is transmitted.Therefore, the other prediction error is "+6'
+ -7, , are configured in advance to transmit exactly the same bit pattern.

The changeover switches 22 and 28 also indicate that the sign bit information sent from the 7-up down counter 26 is negative.
When indicating ", the A side (the first quantizer layer 24A side)
Select side B).

Next, the operation of this embodiment will be explained. For convenience of explanation, it is assumed that the changeover switches 22 and 28 have previously selected the A side.

As is clear from the distribution curve shown in the second figure, the prediction error signal E is probabilistically distributed symmetrically in both positive and negative directions, so the prediction error signal E with such distribution is as shown in Table 2. When introduced into the first quantizer (Q), the probability of successive "1"s is greater than the probability of successive "1"s as its output bit pattern. Therefore, the up/down counter 26 counts up more times, and the output sign bit becomes positive.

When the sign bit of the up/down counter 26 indicates positive,
Changeover switch 22.28 is the second quantizer (Q2)
24B and the second representative value setter (R2) 30B. Thus, since the quantization is performed by the second quantization table (Q2), the output bit pattern is
The bit pattern is changed to a bit pattern with more °0°° than "1", and the up/down counter 26 counts down. Due to this feedback action, 0" and "1" appear with equal probability in the output data signal Do. Thus, a DC-free code string can be obtained.

〔effect〕

As explained above, in the present invention, a code is assigned such that the absolute value of CDS is small in a region where the probability density of the prediction error level is high, so a complicated modulation circuit etc. is not required to realize DC-free. Instead of , just DP
CM (Differential Pulse Cod
The output bit pattern string can be made DC-free by simply rewriting the quantization table of e Modulation.

Furthermore, the fact that the output data has a small DC component also has the effect of facilitating subsequent clock demodulation.

Furthermore, the output data obtained by the present invention can be magnetically recorded.
Even when reproducing data, it is possible to remove the error rate caused by the DC component of data.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a predictive encoder to which the present invention is applied. FIG. 2 is a diagram showing the probability density distribution of a prediction error signal, and FIG. 3 is a block diagram showing another embodiment of the present invention. Dl...Input image data signal, Do...Output data signal, P...Prediction value signal, E...Prediction error signal, R...Representative value signal, (゛"2O-43(!i) !. +2.24A, 24B...Quantizer, 13.3OA
, 30B...Representative value setting device. 14.32... Adder. 15.34... Predictor, 16... Local decoder, 22.28... Changeover switch, 26... Up/down counter. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1) A predictive coding method characterized in that a code with a small CDS value is assigned to a data signal with a small absolute value of a prediction error level. 2) A code in which all bits are "1" or "0" is selectively assigned to a data signal that causes a predetermined prediction error, according to the accumulated information of the code that has already been output. A predictive encoding method according to claim 1, characterized in that: