JPH0132703B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adaptive predictive encoding device used when encoding an image signal.

Conventionally, this type of adaptive predictive coding device has been provided with a plurality of prediction means, as shown in Japanese Patent Application Laid-Open No. 55-41080, and the number of pixels of which the prediction of a plurality of prediction error signals is incorrect is determined in a certain block unit. There is a method of comparing the prediction error signals and selecting the prediction error signal with the least prediction error. This method has the disadvantage that the prediction effect is not sufficient when image signals with different characteristics, such as halftone photographs and characters, coexist in one block.

An object of the present invention is to eliminate the drawbacks of the conventional prediction means described above, and to provide an adaptive predictive coding device with high prediction effects.

The adaptive predictive coding device of the present invention includes means for generating predicted values P ₁ and P ₂ for the current sample value X using past sample values, and prediction from the predicted values P ₁ and P ₂ and the sample value X. means for generating error signals Y ₁ and Y ₂ ; means for selecting a prediction error signal Y from the prediction error signals Y ₁ and Y ₂ in accordance with a prediction selection signal M ₁ ; and means for at least predicting the prediction selection signal M ₁ . When the prediction error signal Y is a prediction error using the error signals Y ₁ and Y ₂ and the past prediction selection signal, the prediction selection signal M ₁ is generated under the condition that the prediction selection signal M ₁ is not changed. means for generating an error signal E from the prediction error signal Y and a selection error signal N representing a change in the prediction selection signal _M1 ; and means for encoding the error signal E.

The adaptive predictive encoding device of the present invention is applied to, for example, data compression encoding of newspaper facsimiles, and uses means for generating two types of predicted values P ₁ and P ₂ suitable for predicting halftone photographs and characters, respectively. value P ₁ ,
The prediction error signal Y is selected pixel by pixel so that the prediction error is smaller than the prediction error signals Y ₁ and Y ₂ obtained from P ₂ , and the prediction error signal Y and the selection error signal according to which prediction error signal is selected are Since the error signal E, which is the logical sum of N, is encoded, the present invention has the effect of reducing the amount of information after encoding, with a higher prediction effect than conventional predictive encoding devices.

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

FIG. 1A is a diagram showing an example of reference pixels of a halftone photo predictor used in the adaptive predictive coding apparatus of the present invention. Note that FIG. 1A is intended for a 45° diagonal halftone image. In FIG. 1A, the distance D (D=10 here) 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:
b ₀ and c ₀ . In the figure, the neighboring pixels of pixel x
Sample values A ₁ - A ₆ of a ₁ - _{a 6} , sample values B ₀ of pixel b ₀ separated in the main scanning direction by the period of the halftone dot, and sample values B ₁ - _{B 5} of its neighboring pixels b ₁ - b ₅ The combination of
It shows an example of reference pixels used in the predictor 3a ₁ in Figure A. Similarly, the sample values A ₁ to _{A 6} of neighboring pixels of pixel x, the sample values C ₀ of pixel c ₀ diagonally separated by the period of the halftone dot, and the sample values C 1 to C ₁ of its neighboring pixels c ₁ to c ₅ The combination of C ₅ is also the predictor 3 in Figure 2A.
This is an example used for a ₁ .

FIG. 1B is a diagram showing an example of reference pixels of a character predictor used in the adaptive predictive encoding device of the present invention. In the figure, the sample value X of pixel x is predicted by the sample values of neighboring pixels of pixel x. The combination of sample values A ₁ to _{A 12} of neighboring pixels a ₁ to _{a 12} of pixel x is an example used in the predictor 3a ₂ of FIG. 2A.

FIG. 2A is a block diagram showing a first embodiment of the adaptive predictive coding apparatus of the present invention, in which the predictor is centered on the reference pixel _b0 in FIG.
This is an example using diagram B. In the figure, a sampled and binarized image signal is applied to terminal 1. Assuming that the sample value applied to terminal 1 is X, this sample value X is sent to line memory 2 and predictor 3.
The line memory 2 supplied to a ₁ and 3a ₂ delays the signal by about one line, and if the delay amount for one line is H (=8000 samples), its output terminal has (H-6) = 7994 A sample-delayed signal is obtained. The predictors 3a ₁ and 3a ₂ are composed of a shift register and a read-only memory (ROM), and use the combinations shown in FIGS. 1A and 1B as reference pixels to calculate the predicted values P ₁ and 3a 2, respectively.
Output P ₂ . The predicted values P ₁ and P ₂ are exclusive ORed with the sample value X in exclusive OR circuits 5a ₁ and 5a ₂ , converted into prediction error signals Y ₁ and Y ₂ , and input to the multiplexer 6a. The selection signal generation circuit 4a (see FIG. 4A or 4B for details) generates a prediction selection signal _M1 and an error signal E from the prediction error signals Y, _Y1 , and _Y2 , and the error signal E is input to the encoder 7. be done. In the multiplexer 6a, the prediction error signal Y is selected pixel by pixel according to the prediction selection signal _M1 . The error signal E is encoded by the next encoder 7 (a conventionally used encoder such as a run-length encoder) and outputted from an output terminal 8.

FIG. 2B is a block diagram showing a second embodiment of the present invention.
(prediction error signal Y or selection error signal N), state signal S (prediction state signal S _Y or selection state signal
This shows an example of a case where _SN ) is encoded at the same time.

That is, the predicted state signal S _Y (or selected state signal S _N ) is calculated by statistically examining the predicted hit probability of the prediction error signal (selection error signal) for each reference pixel pattern in advance. This is a signal used to group the prediction error signal E (or selection error signal N) according to size. For example, when there are two prediction states (selection states), the prediction probability is greater than or equal to a certain value. The reference pixel patterns are divided into reference pixel patterns and other patterns.

In FIG. 2B, the predicted state signals S ₁ , S ₂ and the selected state signal _SN are sent to the predictor 3 which is composed of a shift register and a ROM in the same way as the predicted values P ₁ , P ₂ .
A _{' 1} , 3a' ₂ and _a selection state signal generation circuit ₉ which obtains a selection state signal from the sample value S _N is input to multiplexer 6b. The multiplexer 6a′ ₁ is
The prediction error signal Y and the prediction state signal S _Y are selected in accordance with the prediction selection signal M ₁ , the prediction error signal Y is input to the selection signal generation circuit 4a, and the prediction state signal S _Y is input to the multiplexer 6b. multiplexer 6b
selects the state signal S corresponding to the error signal E from the predicted state signal S _Y and the selected state signal S _N according to the error selection signal M ₂ and inputs it to the encoder 7'. The encoder 7' performs run-length encoding on the error signal E using the state signal S. Such an error signal E
A run-length encoding method using the state signal S and the state signal S is described in Japanese Patent Laid-Open No. 55-41080.

FIG. 3A is a block diagram showing an embodiment of the predictor _3a1 used in FIG. 2A, in which halftone dots in the main scanning direction of FIG. 1A are used as reference pixels. Current scan line and previous scan line signals are applied to terminals 10 and 11. If the sample value applied to the terminal 10 is X, then the shift registers 12a, 1
2b and 12c, the pixels a ₁ , a ₂ , b ₀ in FIG.
~ _b2 sample values _A1 , _A2 , _B0 ~ _B2 are obtained. A signal in which the sample value X is delayed by (H-5)=7995 sample times is applied to the terminal 11, and is further delayed by 4 sample times by the shift register 12d. In shift registers 12e, 12f and 12g, 1 to
4 and 12 to 14 sample times delayed, and the sample values A ₃ to _A 3 of pixels a 3 to _{a 6} and b ₃ to _{b 5} in FIG.
A ₆ and B ₃ to B ₅ are obtained. The reference pixel sample values A ₁ to A ₆ , B ₁ to B ₅ and
B ₀ is applied as an address to the ROM 13 and generates the aforementioned predicted value P ₁ at its output terminal 14 . The embodiment in the case of the character predictor _3a2 shown in FIG. 1B as a reference pixel also uses a shift register and
It can be similarly implemented with a circuit configuration using ROM.

Although an embodiment has been described above in which only one pixel having the same phase relationship with pixel x is selected as the reference pixel of the predictor, a plurality of pixels having the same phase relationship with pixel x can be used simultaneously as the reference pixel. For example, pixels a ₁ , a ₄ to a ₆ near x shown in FIG. 1A as reference pixels have the same phase relationship with x.
b ₀ , c ₀ and its neighboring pixels b ₂ , b ₄ , b ₅ , c ₂ , c ₄ ,
Sample values of c ₅ A ₁ , A ₄ to _{A 6} , B ₀ , B ₂ , B ₄ , B ₅ , C ₀ ,
Of course, predictors using C ₂ , C ₄ , and C ₅ are included.

FIG. 3B shows the predictor 3 used in FIG. 2B.
FIG. 3 is a block diagram showing an embodiment of _a'1 . The difference in the figure from the predictor 3a ₁ in FIG. 3A is that a ROM for generating a prediction state signal S ₁ is added.
Everything else is exactly the same. Predicted state signal S ₁ is the predicted value
As with P ₁ , it is statistically determined in advance from several types of papers.

FIG. 4A is a block diagram showing a first embodiment of the selection signal generation circuit 4a used in FIGS. 2A and 2B, and the predicted selection signal shown in FIG. 5A.
This is a circuit that generates _M1 and an error signal E. Note that FIG. 5A is a diagram for explaining the relationship between selection signals. In FIG. 4A, the register 24a is first reset so that the prediction selection signal _M1 selects the prediction error signal _Y1 at the beginning of the scan line. Next, according to the prediction error signals Y ₁ and Y ₂ applied from the terminals 20 and 21 and the prediction selection signal M ₁ of the previous pixel, which is the output of the register 24a, the ROM 2
3, the prediction selection signal M ₁ and the error selection signal M ₂
is generated, and the prediction selection signal M ₁ is output from the terminal 27 and the error selection signal M ₂ is output from the terminal 28 . The register 24a delays the prediction selection signal _M1 by one pixel, and the exclusive OR circuit 25 outputs the prediction selection signal _M1.
A selection error signal N, which is the change point of , is generated and input to the multiplexer 26 . The multiplexer 26 selects the error signal E from the prediction error signal Y and the selection error signal N according to the error selection signal _M2 , and outputs it from the terminal 29.

Next, using FIG. 5A, the prediction selection signal, error selection signal M ₁ , M ₂ , prediction error signal Y ₁ ,
The relationship between the _Y2 selection error signal N and the error signal E will be described. In the figure, the error signals, Y ₁ , Y ₂ ,
Shaded areas of Y and N, i.e. Y ₁ , Y ₂ , Y and N=
1 indicates an incorrect prediction; others, ie, Y ₁ , Y ₂ , Y, and N=0, indicate a correct prediction. The shaded part of the selection signal M ₁ or M ₂ , that is, M ₁ or M ₂ = 1, indicates that the prediction error signal Y ₂ or the selection error signal N is selected.
Others, ie, M ₁ or M ₂ =0, indicates that the prediction error signal Y ₁ or the prediction error signal Y is selected. Here, the prediction selection signal M ₁ and the error selection signal M ₂ are the prediction error signal Y from the prediction error signals Y ₁ and Y ₂ , respectively.
is a signal that selects the error signal E from the prediction error signal Y and the selection error signal N, and finally the error signal E
is chosen to reduce the number of mispredictions. In other words, if the prediction error signals Y ₁ and Y ₂ are signals obtained from predictions suitable for each of the photographs and characters, then the prediction error of the prediction error signals Y ₁ and Y ₂ is as shown in FIG. There is a strong possibility that prediction errors will occur continuously, such as in the prediction error signals Y ₁ and Y ₂ . In such a case,
If the prediction error signals Y ₁ and Y ₂ are automatically switched using the prediction selection signal M ₁ to reduce the prediction error, the number of mispredictions of the error signal E will be reduced, and the amount of information after encoding will be reduced. do.

In FIG. 5A, the prediction selection signal M ₁ and the error selection signal M ₂ are obtained as follows. The prediction selection signal _M1 is determined so that the prediction error of the prediction error signal Y is minimized. In other words, the prediction error signal Y is selected so that the prediction error signal Y is determined to be a misprediction only when both the prediction error signals Y ₁ and Y ₂ are mispredictions. Predicted selection signal for that
Switching of _M1 is performed when the prediction error signal side selected one pixel before is predicted incorrectly. At this time, the error selection signal _M2 is obtained as follows. The error selection signal _M2 selects whether the prediction error signal Y or the selection error signal N is incorrect (both predictions cannot be incorrect at the same time), and the selection error signal N is used to select the possibility that the prediction error signal N is incorrect. One day,
That is, when either prediction error signal results in a prediction error, the selection error signal N is selected. The contents of the ROM 23 in FIG. 4A, that is, the table used to implement the above logic, are shown in FIG. 6A, and the prediction selection signal
The result of expressing M ₁ and the error signal E in a logical formula is shown in the following formula. Note that "+" indicates exclusive OR, "+" indicates logical AND, and "X" indicates inversion.

M ₁ = (P ₁ P ₂ )・M′ ₁ + ₁・P ₂・X +P ₁・₂・E= ₁・₂・X+P ₁・P ₂・+M′ ₁ M _1In Figure 6A, M′ ₁ is It represents the prediction selection signal _M1 of one pixel before. Using the table in FIG. 6A and inputting the prediction error signals Y ₁ and Y ₂ in FIG. 5A,
The results of determining the prediction selection signal M ₁ , prediction error signal Y, selection error signal N, error selection signal M ₂ and error signal E are shown in the lower part of FIG. 5A. The number of prediction errors in the error signal E obtained in this way is 8.
Therefore, the number of prediction errors of the original prediction error signals Y ₁ and Y ₂ is smaller than 10 and 12. FIG. 4B is a block diagram showing a second embodiment of the prediction selection signal generation circuit 4a used in FIG. 2A, and a circuit for generating the prediction selection signal _M1 and error selection signal _M2 shown in FIG. 5B. It is. Note that FIG. 5B is a diagram for explaining the relationship between selection signals. Fourth
The difference between Figure A and Figure 4B is that in Figure 4B, the prediction selection signal M ₁ and the error selection signal M ₂ are determined.
The difference is that the prediction error signals Y ₁ and Y ₂ delayed by one pixel are used as inputs to the ROM 23'. Fifth
In Figure B, the prediction selection signal M ₁ and the error selection signal M ₂ are obtained as follows since prediction errors in the prediction error signal tend to occur continuously on only one side. The prediction selection signal _M1 is switched when only the prediction error signal selected one pixel before is predicted incorrectly and the previous prediction error signal is also predicted incorrectly. At this time, the error selection signal M ₂ selects the selection error signal N when there is a possibility that the selection error signal N will be unpredicted, that is, when the prediction error signal Y ₁ or Y ₂ will be unpredicted continuously. FIG. 6B shows the contents or table of the ROM 23' of FIG. 4B used to implement the above logic. In the figure,
Y′ ₁ , Y′ ₂ , and M′ ₁ represent the prediction error signal Y ₁ and Y ₂ prediction selection signal M ₁ of one pixel before, respectively. Using the table in FIG. 6B and inputting the prediction error signals Y ₁ and Y ₂ in FIG. 5B, the prediction selection signal M ₁ , prediction error signal Y, selection error signal N, error selection signal M ₂ , and error signal E are determined. The results are shown in the lower part of Figure 5B. The number of prediction errors in the error signal E at this time is 8, which is smaller than the 10 and 12 prediction errors in the original prediction error signals Y ₁ and Y ₂ . The difference between FIG. 5A and FIG. 5B appears in the 7th to 11th sample values and the 29th to 34th sample values. In the former case, the number of isolated prediction errors on the prediction error signal _Y1 side is as small as one, so the error signal E on the side of Figure 5B is small; in the latter case, the number of isolated prediction errors on the prediction error signal _Y2 side is 3. and 2 or more, the error signal E on the side of FIG. 5A decreases.

FIG. 7A shows the first embodiment of the invention, namely the second embodiment.
FIG. 2 is a block diagram of an adaptive predictive decoding device that decodes codes encoded by the adaptive predictive encoding device shown in the figure. In the figure, the symbol applied to the terminal 41 is
It is decoded into an error signal E by a decoder 42. The error signal E is generated by the selection signal generation circuit 4b (FIG. 7A or
In Figure B), the predictions P ₁ and P ₂ are converted into a prediction error signal Y and a prediction selection signal M ₁ . The prediction error signal Y is exclusive-ORed with the predicted values P ₁ and P ₂ output from the predictors 3a ₁ and 3a ₂ in exclusive OR circuits 5a ₁ and 5a ₂ , and decoded signals X ₁ and X ₂ are obtained. generate. Next, in the multiplexer 6a, according to the prediction selection signal _M1 , the decoded signals _X1 and
X is selected from X ₂ . The other parts, such as the line memory 2 and predictors 3a ₁ and 3a ₂ , have exactly the same circuit configuration and operate in the same way as in FIG. 2A, which is the first embodiment of the adaptive predictive encoder of the present invention.

FIG. 7B shows a second embodiment of the invention, namely FIG.
FIG. 2 is a block diagram of an adaptive predictive decoding device that decodes codes encoded by the adaptive predictive encoding device shown in the figure. The difference from the first embodiment shown in FIG. 6A is that the decoder 42' uses the state signal S (prediction state signal S _Y or selection state signal S _N ) to use the error signal E (prediction error signal Y or selection error signal N), and similarly to the encoder side shown in FIG. 2B, the predictor 3
a' ₁ and 3a' ₂ generate predicted state signals S ₁ and S ₂ , and a selection state signal generating circuit 9 and a multiplexer 6b are required.

Next, FIGS. 8A and 8B are block diagrams showing one embodiment of the selection signal generating circuit 46 used in FIGS. 7A and 7B. Figure 8A shows
This circuit 4b corresponds to the selection signal generation circuit 4a of FIG. 4A. That is, the error signal E shown in FIG. 5A
This circuit generates a prediction error signal Y and a prediction selection signal _M1 . In the figure, terminals 50, 5
The ROM 53 uses the predicted values P ₁ and P ₂ and the error signal E applied from the terminals 1 and 52 as addresses to generate a prediction error signal Y and a selection error signal N, and the prediction error signal Y is outputted from the terminal 56. The selection error signal N is sent to the register 54 and the exclusive OR circuit 55.
It is converted into a prediction selection signal M ₁ at step b, and is output from the terminal 57. Further, the error selection signal M ₂ is obtained by taking the exclusive OR of the predicted values P ₁ and P ₂ in the exclusive OR circuit 55a, and is output from the terminal 58. The contents of the ROM, that is, the table used here, are shown in FIG. 9A, and the result of expressing the prediction selection signal _M1 and the decoded signal X by a logical equation is shown in the following equation.

M ₁ = (P ₁ P ₂ )・E′ ₁ X= ₁・₂・E+P ₁・P ₂・+ ₁・P ₂・(M′ ₁ E)+P ₁・₂・(M′ ₁ ) Figure 8B is the selection signal generation circuit 4a of FIG. 4B.
This is a circuit 4b corresponding to.

That is, this circuit generates a prediction error signal Y and a prediction selection signal _M1 from the error signal E shown in FIG. 5B. In the figure, the predicted values P ₁ and P ₂ applied from the terminals 51 and 52 are connected to the exclusive OR circuit 55b,
At 55c, an exclusive OR is performed with the sample value X applied from the terminal 59 to generate prediction error signals Y ₁ and Y ₂ . The prediction error signals Y ₁ and Y ₂ are delayed by one pixel in the register 60, and are applied as addresses to the ROM 53' in the same way as the prediction values P ₁ and P ₂ and the error signal E, thereby generating the prediction error signal Y and the selection error signal N. do. The contents of the ROM 53', that is, the table used here, are shown in FIG. 9B.

As described above, the adaptive predictive encoding device of the present invention uses a predictor that generates two types of predicted values suitable for predicting halftone photographs and characters, respectively, and selects the prediction error signal Y obtained from the predictor on a pixel basis. , Furthermore, by simultaneously encoding the selection error signal N indicating which predictor is used, no mode code is required.
In other words, it is an adaptive predictive encoding device with a small amount of information after encoding.

[Brief explanation of drawings]

1A and 1B are diagrams showing an example of reference pixels of a predictor used in the present invention; FIGS. 2A and 2B are block diagrams showing first and second embodiments of the present invention; FIGS. 3A and 3B are block diagrams showing an example of a predictor used in the present invention, and FIGS. 4A and 4B are block diagrams showing an example of a selection signal generation circuit of the encoding device of the present invention. , FIGS. 5A and 5B are diagrams for explaining the relationship between selection signals of the present invention, and FIGS. 6A and 6B are diagrams for explaining the relationship between selection signals of the encoding device of the present invention. 7A and 7B are block diagrams showing an embodiment of an adaptive predictive decoding device according to the present invention, and FIG.
9 and 8B are block diagrams showing an example of the selection signal generation circuit of the decoding device according to the present invention, and FIG.
FIG. A and FIG. 9B are diagrams showing the contents of the ROM used in the selection signal generation circuit of the decoding device of the present invention. In the figure, reference number 2 is line memory, 3a ₁ ,
3a ₂ , 3a' ₁ and 3a' ₂ are predictors, 4a and 4
b is a selection signal generation circuit, 5a ₁ , 5a ₂ , 25, 55
a, 55b and 55c are exclusive OR circuits, 6
a, 6a', 6b and 26 are multiplexers, 7
and 7' is an encoder; 9 is a selection state signal generation circuit;
12a, 12b, 12c, 12d, 12e, 12
f, 12g, 24a, 24b and 60 are shift registers; 13, 13', 23, 23', 53 and 53' are ROMs; 42 and 42' are decoders;
4 represents a counter.

Claims (1)

[Claims] 1 In an adaptive predictive coding device that codes a binary image signal, the predicted value P ₁ for the current sample value
and P ₂ using past sample values; means for generating prediction error signals Y ₁ and Y ₂ from the predicted values P ₁ and P ₂ and _the sample value X; A prediction selection signal M ₁ is generated from Y ₂ and a prediction selection signal M ₁ ' for the past sample value, and an error selection signal M indicating that there is a high possibility that only one of Y ₁ and Y ₂ will be an incorrect prediction is generated. means for generating a prediction error signal Y in accordance with the prediction selection signal M ₁ by making one of the prediction error signals Y ₁ and Y ₂ into the prediction selection signal M ₁ ;
means for generating a selection error signal N indicating a change point of the predicted selection signal _M1 ;
It is characterized by comprising means for selecting one of the prediction error signal Y and the selection error signal N as the error signal E based on the error selection signal _M2 , and means for encoding the error signal E. adaptive predictive coding device.