JPS6052168A - Adaptive forecasting decoder - Google Patents

Abstract

PURPOSE:To improve forecasting effect and also to eliminate the need for a mode code by selecting a forecast value obtained from plural forecasting devices from the degree of failure in the forecasting of a forecast error signal after scanning. CONSTITUTION:Exclusive OR circuits 4a1-4an having a forecasting error signal Y from a decoder 41 and forecasting values P1-Pn from forecasting devices 3a1 -3an give the output of decoding signals X1-Xn. Then a selector 6 selects a decoding signal X from the decoding signals X1-Xn according to the selection signal from a forecast selecting circuit 5. An exclusive OR circuit 42 produce forecast error signals Y1-Yn from the decoding signal X and inputs them to a forecast selecting circuit 5. Then the selection circuit 5 selects a forecast error signal having the least failure in the forecast among picture elements after scanning already and outputs it as a selection signal. Thus, the forecasting effect is inproved and also the mode code is made unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides predictive coding of halftone photographs representing halftones in black and white binary image signals used in newspapers, etc., and an adaptive prediction method used when decoding the transmitted code. The present invention relates to a decoding device.

Conventionally, this type of adaptive predictive coding method compares the number of mispredicted pixels of a plurality of prediction error signals in a certain block unit, such as the prediction means shown in Japanese Patent Application Laid-Open No. 55-41080. However, there is a method of selecting a prediction error signal with a small number of prediction errors. This method has the disadvantage that the prediction effect is not sufficient when it is better to change the prediction method in the middle of a block, and a mode code is required to indicate which prediction method has been selected, resulting in insufficient data compression. there were.

An object of the present invention is to eliminate the drawbacks of the conventional prediction means described above, and to provide a decoding device for use in an adaptive predictive coding method that has a high prediction effect and does not require a mode code.

The predictive decoding device of the present invention calculates a plurality of predicted values P1wP2y, . . . for a sample value X of a pixel X on a halftone photograph.

pn, and generates the plurality of predicted values P1.pn. P2. ...
, Pn and the sample value X, the obtained prediction error signal Y□, Y2
．． ....

In an adaptive predictive decoding device that decodes a code obtained by an adaptive predictive coding device that selects and encodes one prediction error signal Y, means for decoding the prediction error signal Y; Prediction error signal Y and multiple predicted values P1, 12
A plurality of decoded signals X1°X3. ...
, Xn, neighboring pixels of the pixel X and 2 of the image
A plurality of pixels Yly)'fe... having the same phase relationship with the pixel X on the dimensional mesh periodic pattern.

ym and the plurality of pixels Y1tY2*..., the plurality of predicted values P1eP using sample values of neighboring pixels of ym
l+...

means for generating Pn, and a means for generating the sample value
Y2.・.

means for obtaining Yn, and prediction error signals Y, , Y2 . ..., the plurality of predicted values p from Yn
HPat..., Pn, and calculates the degree of prediction error of the plurality of decoded signals X1. X2. . . , means for selecting the sample value X of the decoded pixel X from xn.

In the adaptive predictive decoding device of the present invention, prediction error signals Y, Y2 . ..., predicted value PlIP2t of the pixel already scanned from Yn..., Pn
Since the prediction error signal Y with the least prediction error is selected by comparing the degree of prediction error, the number of prediction errors included in the prediction error signal Y is small, and there is no need for a mode code to indicate which predicted value has been selected. This has the effect of reducing the amount of information after encoding as a whole and making it compatible with international standard MH encoding.

Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing an example of reference pixels of a predictor used in the adaptive predictive decoding device of the present invention, that is, pixels used to generate a prediction signal and pixels used to compare prediction errors of prediction error signals. It is. In addition, Figure 1 is 45°
The target is a diagonal halftone image. In Figure 1, the distance P
Ittl (more specifically, D-10) represents the period of the halftone dot, and the pixels that have the same phase relationship (on the two-dimensional mesh periodic pattern of the image) with the sample value X of the pixel X are yl, y2 .
....

It is y. In the figure, neighboring pixels a, b,
c.

Sample values of d+ fy g A, B, C, D, F,
G, a sample value Y of a pixel y1 separated in the main scanning direction by the period of the halftone dot, and an example of a reference pixel included therein. Similarly, neighboring pixels a, b, c, d, fy of pixel X
Sample values A, B, C, D, F, G of g, sample value Y2 of pixel y2 diagonally separated by the period of the halftone dot, and an example of a reference pixel in the vicinity thereof are shown. A pixel y3yY41 that has the same phase relationship as the sample value X of .

Sample value Y of ym,,Y,...9 Using Ym, the second
An example of a reference pixel used in the picture predictor 3a3 is obtained.

Still pixel 'i, 12.13y 14. +5. t...
Icy +st Illsjlog iII t IH
t sst ft ladle 11! +'+6+'l? *
'll5 jlots at bt Ct dy ft
The prediction error signal of g is used in the prediction selection circuit 5 of FIG. 2(4).

FIG. 2 is a block diagram showing a first embodiment of an encoding device that generates a code to be decoded by the decoding device of the present invention, and when the reference pixels shown in FIG. 1 are used. This is a configuration example. In the figure, a sampled and binarized image signal is applied to terminal 1. Assuming that the sample value applied to terminal 1 at a certain time is X, this sample value X is stored in the line memory 2a.

Predictor 3a1.3a2. ...Supplied to Ban. The line memory 2a delays the signal by about one line, and to be more precise, if the delay amount for one line is H (= 5ooo samples), the output terminal will have a signal delayed by (H-6)-7994 samples. is obtained. Another line memo! J
2b,, 2b2? ..., 2bl each delays the input signal by one line, and each output terminal has a delay of 1°2, . . . compared to the output terminal of the line memory 2a.
, a signal delayed by l lines is obtained. As described above, using the combinations shown in FIG. 1 as reference pixels, the predicted values P, , P, . . . are obtained, respectively.

Output Pn. Predicted value PLtP2. . . . tan is then connected to exclusive OR circuits 4al, 4a2 . ..., 4a
An exclusive OR is taken with the sample value X at H, and the prediction error signal Y
,,Y,,...

Yn is obtained and input to the prediction selection circuit 5 and selector 6. The prediction selection circuit 5 selects pixels a, b, and c that have already been scanned, as shown in an example in FIG.

dy fy gt j5~ito prediction error signal Yl
t Y2 +...

A selection signal () that compares the number of prediction errors included in Y and selects the prediction error signal (maximum) with the least prediction error among the pixels that have already been scanned, and selects Y as the prediction error signal for the current pixel. b) is output. The selector 6 obtains a prediction error signal Y for each pixel according to the selection signal M. The prediction error signal Y is then encoded by an encoder 7 (eg, a conventionally used encoder such as a run-length encoder) and outputted as a code C at an output terminal 8.

Further, in the encoding of the encoder 7, when the prediction state signal is encoded in addition to the prediction error signal, this can be achieved by the embodiment 741J2 of the present invention shown in FIG. 2(B).

That is, the prediction state signal is a signal used to statistically examine the predicted hit probability for each reference pixel pattern in advance and to group the prediction error signals according to the magnitude of the predicted hit probability. For example, when the prediction state is two states, the prediction signal SI*S2t...-, Sn is
Predicted value PI + P2t "' t Predictor 3a' composed of a shift register and ROM similarly to Pfl
l, 3a'z *..., 33'. It will be outputted.

The selector 6' selects the prediction state signal S in the same manner as the prediction error signal Y, and the selected prediction state signal S is inputted to the reference numeral 7'. The encoder 7' uses the prediction state signal S to perform run-length encoding on the prediction error signal, for example. A run-length encoding method using such a prediction error signal and a prediction state signal is described in Japanese Patent Laid-Open No. 55-41080.

FIG. 3(4) is a block diagram showing an example of the embodiment of the predictor 3al used in FIG. The current scanning line and the previous scanning line, that is, the output signals of the line memory 2a shown in FIG. 2(4) are applied to terminals 1° and 11.

Letting the sample value applied to the terminal 10 be
11 samples time delayed, pixel "g" in FIG.
Sample values of t hl, yt and g+ Ft Gt Hl
eYl and G1 are obtained. Terminal 11 has the sample value
A signal delayed by (H-6)=7994 sample times is applied, but is further delayed by 4f sample times in the shift register 12d. In shift registers 12e, 12f and 12g, pixels d, c, b in FIG. 1 are delayed by 1-4 and 11-13 samples.

Sample value Dg Cy J A of a*dlp'l and
+DI+C8 and B are obtained. The signal thus obtained is applied and produces at its output terminal 14 the aforementioned predicted value P. Neighboring pixel a of pixel X as a reference pixel
t by C9'y 't g, pixel y2 diagonally separated by the period of the halftone dot, and its neighboring pixel b2*c2
The predictor 3a2 when using yd2t g2y h2 can also be implemented with a circuit configuration using a shift register and ROM.
The following pixels Y3e Y4m have the same phase relationship as pixel X.
....

Predictor 3a3.3a4. when using ym. ..., 3
al can also be implemented with a similar circuit configuration.

The above describes an example in which only one pixel having the same phase relationship with pixel X is selected as the reference pixel of the predictor, but it is also possible to simultaneously use multiple pixels having the same phase relationship with pixel X as the reference pixel. .

For example, the neighboring pixel b of X shown in FIG. 1 as a reference pixel
t Cs g and y1*)'2゜y, which have the same phase relationship with X, and its neighboring pixels C1s gl* C2t g2
．． C3t gs r sample value Bt Ct (L Yl,
Clt Glt y,, c,, o,.

Y8. Of course, a predictor using C3, G, etc. is included.

FIG. 3(B) shows the predictor 3 used in FIG. 2(I3).
The difference is that a ROM13' that generates 3'1 is added.
Everything else is exactly the same. The predicted state signal S1 is the predicted value P1
Similarly, several types of papers are prepared in advance.

FIG. 4 is a diagram showing an embodiment of the prediction selection circuit 5 used in FIG. 2(4) and FIG. 2(B). terminal 20
a1.20a2. ..., 20an contains prediction error signals y, y Y2 obtained from the results of each predictor.
*..., Yn is applied. The prediction error signal Y applied to the terminal 20a is delayed by a delay circuit 21a1 composed of a line memory and a shift register, and the prediction error signal Y is applied to the pixels It9+2t+3. +4.11 guns,
Prediction error signal Yly jl of i蒐89119+ and g
, yl, 1! t Yls Icy Yle j4yY
l, ,, Yl, 1. , Ylt 1+'l'
and Y1+g is R, OM.

1W +1 Prediction error measurement circuit 2 consisting of adder and register
It is input to 2a1. Prediction deviation measurement circuit 22a.

Then, the already scanned pixel i, ~11°lat b,
c.

Prediction error signal Yl, i −Yl+ + of dy fy g
・、Y、.

5 +'1 Y, Yl, il', Y,. * Yled
l ''+? (+ and Yltgy's total prediction error is counted. In other words, Yly, ', Y1+ +, Q, Ylt+7 i,,, y,, g is added to the total prediction error for the previous pixel, and Yll, □ ,, yl9,
2. By subtracting y, , , , Ylt9 14, the total sum of prediction errors with respect to the original pixel can be found. Similarly, prediction error signal Y2. Y.

, Yn are the delay circuits 21a2, 21a3 . =-,
21an and the prediction error measurement circuit 22a2.2
2a3. ....

22an counts the number of prediction errors, and the comparator circuit 23
is input. In the comparison circuit 23, the prediction error signal YI,
Y2. ..., already scanned pixel i for Yn,
~110'lat by Cv dy et fy g
The numbers of prediction errors are compared with each other, and a selection signal for selecting the prediction error signal Y for the current pixel X is outputted from the terminal 24.

Although the prediction selection circuit of the present invention has been described above, it goes without saying that these do not impose any limitations on the present invention. For example, when comparing the degree of prediction error, it is of course possible to use Toshin's method of adding weight proportional to the distance from the current pixel, and also use the range of the prediction error signal to compare the degree of prediction error. Of course, it is also possible to limit the number of pixels to pixels in an area corresponding to the size of the halftone dot around the pixel X, which has already been scanned.

FIG. 5 shows a delay circuit 21a used in FIG. 4.

It is a figure showing one example of this. A prediction error signal Y is applied to the terminal 20a2. Line memo') 30al delays the prediction error signal by about one line, and more precisely, the delay amount for one line is H (= 8000 samples).
Then, a signal delayed by ('H-2)-7998 samples is obtained at its output terminal. Also line memory 30
b, , 30b, , 30b each delay the input signal by one line, and each output terminal has 30
1. compared to the output terminal of a1. 2. A signal delayed by 3 lines is obtained. Shift register 31at j31a2
．． 31a3 and 31a4 are 1 to 7 and 4, respectively
Pixel jl +2+ 13y j4* jljy j in Figure 1 with a shift register delayed by ~7 sample times
Prediction error signal YI, ,' for 18tiso and g
,,Y,.

Attention Yu,,Y,,,Natsu Y,Two J Yl-,Y,,,Shizuku Y
II'112, 13l'+q1g'+9 and Ylt are obtained, and the terminals 32alt 32a2.
32a3゜32a4y 32a5.32a6.32a7
and 32a8.

FIG. 6(4) is a block diagram showing a first embodiment of the adaptive predictive decoding device of the present invention. In the figure, terminal 40
The code applied to is decoded into a prediction error signal Y by a decoder 41. Prediction error I5 @Y is exclusive logic circuit 4al, 4azg..., 4an and predictor 3a1
゜3a2. ..., predicted value PI that is output more than 3an
+P2+...

Pn and the decoded signals X, , X2 .・
....

Generate Xn. The selector 6 selects the decoded signals X1 . Decoded signal X is selected from X, . . . , Xn. The exclusive OR circuit 42 calculates the predicted value P1
From yP2+..., Pn and the decoded signal X, prediction error signals Y,, Y2... , Yn is generated and input to the prediction selection circuit 5. Other line memories 2a, zb, .
2b2°-, 2bn, predictor 3a3.3a2. ++
, 3aH, the prediction selection circuit 5 has exactly the same circuit configuration and the same operation as the 21st embodiment which is the first embodiment of the adaptive predictive encoder of the present invention. Moreover, the predictor 3a1 of the present invention
．． 3a2g(A) ..., as 3al, 3rd Je? A predictor designated TE is used.

FIG. 6(g)) shows the second
1 is a block diagram illustrating an embodiment of the present invention. The difference between the figure and FIG. 6 (4) is that the decoder 41' divides the prediction error signal into run lengths using the prediction state (No. 11).
The predictors 3a'1, 3a'2, . . . , 3a'n that generate a prediction error signal and a prediction state signal as shown in FIG. The point is that a method for selecting a decoded signal and a predicted state signal is used.

As described above, the present invention uses a plurality of predictors and selects the resulting predictor based on the degree of prediction error of the scanned prediction error signal, so the prediction effect is higher than that of the conventional prediction method. This is an adaptive #+lJ decoding device that can also be adapted to a large international standard MH encoder.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the reference pixel of the predictor used in the present invention and the pixel used for comparing the prediction error of the prediction error signal, and FIG. 2 (G) and FIG. 2 (J3) are
Block diagrams showing the first and second embodiments of the adaptive predictive coding device according to the present invention, FIG. 3(4) and FIG.
) is a block diagram showing first and second examples of the predictor 6 (1j) used in the present invention, FIG. 4 is a diagram showing an example of a prediction selection circuit used in the present invention, and FIG. Figures 6 (G) and 6 (B) showing an example of the delay circuit used in the present invention are block diagrams showing the first and second embodiments of the present invention. Numbers 2a, 2bI, 2b2...g
2bm-4g2bm and 30al, 3ob,,
aob,, 30bs is line memory, reference number 3al
t 3a2. ”' * 3an e 3a'lt
3a'2*"'+3a'H, is a predictor, reference number 4
a,, 4a2. ..., 4aH and 42 are exclusive OR circuits, reference numeral 5 is a prediction selection circuit, reference numerals 6 and 6' are selectors, reference numerals 7 and 7' are encoders, and reference numerals 12a and 12b. 12c, 12d, 12e, 12f, 1
2g t' 31a1.31a2, 31a3° and 3
1a4 is a shift register, reference numbers 13 and 13' are ROM % reference numbers 21at, 21a2, -. 2
1an-. and 21an is a delay circuit, reference number 22a1.22a
2. .... 22an-1 and 22an represent prediction error measuring circuits, and reference numerals 4 and 41' represent signal generators. △ △ Heo 3 Figure (A)

Claims (1)

Claims: A plurality of predicted values P1yP2y..., Pn are generated for a sample value X of a pixel X on a halftone photograph, and the plurality of predicted values P1. P2. ..., Pn (n: positive integer) and sample value X
The obtained prediction error signal Y1. Y2. ..., yn
In an adaptive predictive decoding device that decodes a code obtained by an adaptive predictive coding device that selects and encodes one prediction error signal Y, means for decoding the prediction error signal Y; Signal Y and multiple predicted values p, y P2
t"'?pn, a plurality of decoded signals x,,'x,..., a means for obtaining Xn, and a means for obtaining A plurality of pixels YItY2+..., ym(m
: positive integer) and the plurality of lateral funiculus Y1tY2. .... The plurality of predicted values P1. means for generating P2+..., Pn; means for obtaining prediction error signals y, ty, t..., Yn from the sample value - and a plurality of predicted values PltPty..., Pn; Prediction error signal Y, Y2 of corner pixel
．． . . .;Y, the plurality of predicted values P1tP2v・
.
..., means for selecting sample value X of decoded pixel X from xn.