JPS6342987B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an apparatus for predictively encoding an image signal such as a TV (Television) signal, and more particularly to a predictive encoding apparatus for encoding a prediction error signal with unequal length. As a typical device that predictively encodes digitized image signals such as TV signals,
DPCM (Differential Pulse Code Modulation)
Encoding devices are well known. This DPCM encoding device is a DPCM encoder configured to subtract a prediction signal obtained by a predictor from an input signal to obtain a prediction error signal, and quantize the prediction error signal by a quantizer. It is equipped with and,
The quantized prediction error signal is encoded and transmitted. The system is equipped with a feedback loop that adds the prediction error signal quantized by the quantizer and the prediction signal output from the predictor to obtain a locally decoded signal, and sends the locally decoded signal to the predictor. .
The predictor outputs the next predicted signal based on the received locally decoded signal. That is, it includes a predictor and a quantizer.
The DPCM encoder consists of a recursive type predictive encoder with a feedback loop. In recent years, methods have been developed in which the quantization characteristics and prediction functions of a quantizer are adaptively switched. However, when applying these methods to a DPCM encoding device, since the DPCM encoder is constructed of a recursive type, ultra-high-speed circuit elements are required to perform complex processing such as the above-mentioned adaptive encoding. There is a drawback. Another disadvantage is that the processing time of the encoding loop is not long enough to perform real-time DPCM processing. On the other hand, a predictive encoding device with a non-recursive type predictive encoder without a feedback loop does not have a quantizer to quantize the prediction error signal.
This is a reversible predictive coding device that can decode an original signal from a prediction error signal. In other words, it is a predictive coding device that can store information. The prediction error signal is converted into an unequal length code and transmitted. According to this predictive encoding device, processing time for quantization is unnecessary. In addition, since the predictive encoder is configured as a non-recursive type (also called a forward type because there is no feedback loop), the relative phase of the input signal and the predicted signal output from the predictor is By delaying both signals by an appropriate amount while matching the
Signal processing time can be extended. As a result, a circuit configuration using low-speed elements is possible, and complex signal processing such as the above-mentioned adaptive predictive coding can be performed. However, with this non-recursive type (i.e., forward type) predictive encoding device, it is not possible to control the amount of information in the input/output signal, so long-term continuous TV signals, etc., are encoded in real time and transmitted at a constant transmission bit rate. The drawback was that it was not possible to do so. SUMMARY OF THE INVENTION An object of the present invention is to provide a non-recursive type (ie, forward type) predictive encoding device that can encode and transmit an image signal such as a TV signal at a constant transmission bit rate. Another object of the present invention is to monitor the amount of information input to a buffer memory for temporarily storing and smoothing output information before sending it out, or the amount of information stored in the buffer memory, so that the amount of information of the input signal can be reduced in a preprocessing section. An object of the present invention is to provide a non-recursive type (ie, forward type) predictive encoding device that adaptively controls the amount of information to be transmitted. According to the present invention, there is provided a preprocessing circuit that receives a digitized image signal and controls the amount of information of the image signal according to a control signal, and a preprocessed image signal that is output from the preprocessing circuit. a prediction encoder that outputs a prediction error signal using reversible logic; an unequal-length encoding circuit that converts the prediction error signal into an unequal-length code in response to the operation of the preprocessing circuit; A buffer memory for temporarily storing, smoothing and transmitting the unequal length code information and control information necessary for decoding output from the equal length encoding circuit, and the amount of information input to the buffer memory or information in the buffer memory. A predictive encoding device is obtained, which includes a control circuit that outputs the control signal to be given to the preprocessing circuit based on the accumulated amount, and uses information sent from the buffer memory as output information. In the present invention, the preprocessing circuit specifically includes:
(1) a quantization circuit capable of quantizing the digitized image signal according to a quantization characteristic selected by the control signal from the control circuit; or (2) from the control circuit. a first control that determines pixels to be thinned out from the digitized image signal according to a thinning characteristic selected by a control signal; and a second control that actually thins out the pixels to be thinned out. and a third control in which the signal of the pixel to be thinned out is interpolated from the signal of the surrounding pixel that should not be thinned out is performed on the digitized image signal. (3) among the spatial frequency and the frequency in the time axis direction of the digitized image signal according to the band-limiting characteristic selected by the control signal from the control circuit; It is constituted by a band-limiting circuit capable of band-limiting at least one of them, or (4) a circuit combining at least two of the quantization circuit, the decimation control circuit, and the band-limiting circuit. Here, thinning means not only removing pixels in appropriate pixel units, but also removing all pixels in an appropriate section, removing all pixels in one field for each appropriate field, etc. It is used to mean reducing the number of pixels by removing pixels. According to the predictive encoding device of the present invention, since the predictive encoder can be configured as a forward type, there is no need for a quantizer that quantizes the prediction error signal, and the time required for signal processing to obtain the prediction error signal is reduced. It can be stretched out. Therefore, it becomes possible to configure a circuit using circuit elements that operate at low speed, and it becomes possible to perform complex signal processing such as adaptive predictive coding. Furthermore, in the present invention, since the preprocessed signal is reversibly encoded, the difference between the image signal reproduced on the receiving side and the original image signal occurs only in the preprocessing section. Therefore, if no distortion occurs in the preprocessing, the reproduced image can be exactly the same as the original image. In the present invention, preprocessing is controlled according to the amount of information input to the buffer memory or the amount of information stored in the buffer memory, so if the amount of information in the original image signal is less than the amount of transmitted information, there will be no distortion at all. Enables encoded transmission,
Extremely high quality TV signal transmission can be achieved. Next, embodiments of the present invention will be described with reference to the drawings. Referring to FIG. 1, a predictive encoding device 3 and a predictive decoding device 14 according to a first embodiment of the present invention are shown. In this embodiment, a quantization circuit 4 is used as a preprocessing circuit of the predictive encoding device 3. Analog input to input terminal 1
The image signal of the NTSC color TV signal is converted into a digital signal, for example, a 5-bit signal with a level range of -16 to 15, by an A/D converter 2 whose sampling frequency s is selected to be three times the subcarrier frequency sc. of
It is converted to a PCM (Pulse Code Modulation) image signal. If the sampling frequency s is s=3sc,
The number of samples n _H during one horizontal scanning period is n _H =682.5. The output signal of the A/D converter 2 is sent to the quantization circuit 4 of the predictive encoding device 3. The quantization circuit 4 can quantize the input image signal according to a quantization characteristic selected by a control signal sent from the control circuit 11. The control circuit 11 selects a fine quantization characteristic with the same accuracy as the input signal to the quantization circuit 4 when the amount of information stored in the buffer memory 10 is small. As a result, the quantization circuit 4 has, for example, 5
Outputs the bit PCM image signal as is. On the other hand, when the amount of information stored in the buffer memory 10 is large, the control circuit 11 selects coarse quantization characteristics. As a result, the quantization circuit 4 outputs a coarsely quantized image signal, for example, a 3-bit PCM image signal. The image signal quantized by the quantization circuit 4 is sent to a subtraction circuit 7 of a predictive encoder 5 and a predictor 6. The predictor 6 performs prediction from the quantized image signal according to the characteristics of a predetermined prediction function P(z) P(z)=Z ^-1 +Z ^-2nH -Z ^-2nH-1 (1) Find and output a signal. The predicted signal output from the predictor 6 is sent to a calculator 7. The subtracter 7 subtracts the prediction signal from the quantized image signal and outputs a prediction error signal. This prediction error signal is sent to the unequal length encoding circuit 9 of the unequal length encoder 8. The unequal length encoding circuit 9 has multiple types of code conversion characteristics corresponding to the quantization characteristics of the quantization circuit 4, and according to the code conversion characteristics selected by the control signal from the control circuit 11. Convert the prediction error signal to an unequal length code. The unequal length code output from the unequal length encoding circuit 9 is sent to a buffer memory 10. The amount of information sent to the buffer memory 10 changes over time depending on the image signal input to the predictive encoding device 3. The buffer memory 10 is
Information on the unequal length code sent from the unequal length encoding circuit 9 and control information such as control signals and synchronization signals required for decoding are temporarily stored in the buffer memory 10, and the transmission speed of the transmission line is adjusted. The speed is converted to suit the speed and the output information is sent to the transmission line from the output terminal 12. It is also conceivable to write the output information of the output terminal 12 to a storage device such as magnetic tape. The control circuit 11 monitors the amount of information stored in the buffer memory 10. The control circuit 11 determines whether to switch the quantization characteristic at appropriate intervals based on the amount of information stored from the buffer memory 10, and changes the quantization characteristic of the quantization circuit 4 and the code conversion characteristic of the unequal length encoding circuit 9. Outputs a control signal for switching. The above is an explanation of the operation of the predictive encoding device 3. In the predictive decoding device 14, information sent from the transmission line is sent from the input terminal 13 to the buffer memory 16 of the unequal length decoder 15. Information is temporarily stored in the buffer memory 16 at the transmission speed sent from the transmission path. The once stored information is sequentially read out in accordance with requests from the unequal length decoding circuit 17 of the unequal length decoder 15, and the information on the quantization control signal is sent to the control circuit 18, and the information on the unequal length code is is sent to the unequal length decoding circuit 17. The control circuit 18 outputs a control signal for switching the inverse code conversion characteristic of the unequal length decoding circuit 17 based on the information of the control signal sent from the buffer memory 16. The unequal length decoding circuit 17 has inverse code conversion characteristics corresponding to the code conversion characteristics of the unequal length encoding circuit 9 of the predictive encoding device 3. When the unequal length decoding circuit 17 obtains each unequal length code from the unequal length code string sent from the buffer memory 16, the unequal length decoding circuit 17 decodes the unequal length code sent from the control circuit 18 for the next obtained unequal length code. Inverse code conversion is performed in accordance with the inverse code conversion characteristic selected by the incoming control signal, and a quantized prediction error signal is output. The obtained prediction error signal is sent to the adder 20 of the prediction decoder 19.
This signal is added to the predicted signal sent from the predictor 21, and becomes a decoded signal. The decoded signal is sent to a predictor 21 and a D/A converter 22. The predictor 21 has the same prediction function P(z) as the predictor 6 of the predictive encoding device 3, and outputs and adds a predicted signal at the next sampling time according to the prediction function from the decoded signal. Send to container 20. The D/A converter 22 performs D/A conversion on the digital decoded signal and outputs the analog decoded signal to the output terminal 23 . Note that in order to reset the propagation of errors due to errors in the transmission path, the signals of each part are initialized with appropriate synchronization. The above is an explanation of the operation of the predictive decoding device 14. FIG. 2 shows a specific circuit example of the quantization circuit 4 of the predictive encoding device 3 in the first embodiment of the present invention. The quantization circuit 4 quantizes the 5-bit PCM signal X expressed in two's complement into 3 to 5 bits according to the control signal QS from the control circuit 11 and outputs the quantized signal. The least significant digit (LSD) of the above-mentioned 5-bit PCM signal X is x ₁ and has a magnitude of 1. The most significant digit (MSD) is a sign digit that indicates positive or negative at _xs . In the 5-bit PCM signal X input to the quantization circuit 4, the upper 3 bits from x ₃ to x _s are sent as they are to the output terminals y ₃ to y _s , and the lower bits from x ₂ and x ₁ are respectively sent to the output terminals y 3 to y s. It is sent to AND circuits 28 and 29. Of the 3-bit control signal QS sent from the control circuit 11,
The bits of QS ₂ are connected to the inversion circuit 26, the bits of QS ₁ are connected to the inversion circuit 27, and QS ₀ is left unconnected. The control signal QS sets one of the bits QS ₀ to QS ₂ to a high level indicating a positive logic 1, and sets all other bits to a low level indicating a positive logic 0. Inversion circuit 2
6 is sent to AND circuits 28 and 29, and the output of inversion circuit 27 is sent to AND circuit 29.
Therefore, when the _QS0 bit of the control signal QS becomes High level and the first quantization characteristic is selected, the 5-bit input signal is output as the output signal Y as it is. Further, when QS ₁ becomes High level and the second quantization characteristic is selected, the bit of y ₁ becomes Low level and a 4-bit quantized signal is output. Furthermore, when QS ₂ is at High level and the third quantization characteristic is selected, y ₁ and y ₂ are always at Low level and a 3-bit quantized signal is output. FIG. 3 shows a specific circuit example of the predictor 6 of the predictive encoding device 3 in the first embodiment of the present invention. This predictor 6 uses the above as the prediction function P(z).
The function shown in equation (1) is used. The prediction function P(z) in equation (1) can be used to efficiently directly predictively encode an NTSC color TV signal when sampling is performed with the sampling frequency s selected to be three times the subcarrier frequency sc. can do. However, s=3sc
Therefore, in equation (1), n _H = 682.5,
Z ^-1 = e ^-j2 〓 ^{/ s} . The predictor 6 converts the input signal into
Output terminals 102, 103 and 104 which are delayed by 1, 1365 and 1366 sampling clock periods and output.
A non-recursive type digital filter consisting of a shift register 101 with be. The prediction coefficients in equation (1) are all integers. The predictor 21 of the predictive decoding device 14 is also configured similarly to the predictor 6. Next, a specific example of the code conversion characteristics of the unequal length encoding circuit 9 and the inverse code conversion characteristics of the unequal length decoding circuit 17 will be shown. In this case, since the image signal is 5 bits, 32 unequal length codes whose code numbers are -16 to 15 shown in the following table are used.

[Table] The shortest code length is 2 bits, and the longest code length is 9 bits. Let the magnitude of the LSD of the 5-bit PCM signal output from the A/D converter 2 be 1, and let the prediction error signal sent from the subtracter 7 to the unequal length encoding circuit 9 be e, and the unequal length When the code number of the code is N and x is a certain real number, the symbol [x] represents the value of n that satisfies the inequality nx<n+1, where n is an integer. In other words, the symbol [ ] represents conversion into an integer by truncation. 1st, 2nd and 3rd
The first, second, and third code conversion characteristics corresponding to the quantization characteristics of
It has the characteristic of converting into an unequal length code of code number N shown by equation (4). N=[e]...(2) N=[e/2]...(3) N=[e/4]...(4) For example, in the case of the second code conversion characteristic, e=-2
The prediction error signal of is ``11'' as N=-1 from equation (3).
is converted to an unequal length code. Here, since the prediction coefficients are integer coefficients, unless the quantization characteristics are changed, the quantization accuracy of the input signal to the predictive encoder 5 and the prediction signal match. That is, the accuracy of the input signal of the predictive encoder 5 and the prediction error signal match,
The prediction error signal e when each of the first, second, and third quantization characteristics is selected is an integer, an integer multiple of 2, and an integer multiple of 4. There is a one-to-one correspondence between the error signal and the code number. Even where the quantization characteristics change, if you want to match the quantization precision of the input signal to the predictive encoder 5 and the predicted signal, that is, if you want to have a one-to-one correspondence between the predicted error signal and the code number. In this case, the value in the predictor 6 is reset each time the quantization characteristic is switched, or a quantization circuit, for example, a quantization circuit with the same characteristics as the quantization circuit 4 is added to the output side of the predictor 6. The predicted signal may be quantized. In this case, the values in the predictor 21 are reset on the predictive decoding device 14 side, or the same quantization circuit as the quantization circuit on the output side of the predictor 6 is added to the output side of the predictor 21. In this way, the input signal to the predictive encoder 5 and the decoded signal of the predictive decoding device 14 can be completely matched. Next, the inverse code conversion characteristics of the unequal length decoding circuit 17 are as follows. If the code number of the unequal-length code decoded by the unequal-length decoding circuit 17 is N, and the prediction error signal obtained by inverse transformation is e, the first, second, and third quantization characteristics The first, second, and third inverse code conversion characteristics corresponding to It has the property of converting. e=N...(5) e=2×N...(6) e=4×N...(7) For example, in the second code inversion characteristic, an unequal length code of "11" has a prediction error of e=-2. converted into a signal. In order to perform information-preserving encoding, that is, to obtain a decoded signal of the predictive decoding device 14 that matches the input signal to the predictive encoder 5, the outputs of the predictors 6 and 21 must be It is necessary to provide a quantization circuit on each side and perform quantization so that the quantized prediction signal matches the quantization precision of the input signal to the prediction encoder 5. However, when the prediction coefficients are only integer coefficients, information preservation encoding can be performed without providing a quantization circuit on the output side of the predictor as shown in the first embodiment. Next, referring to FIG. 1, a method of performing information preservation encoding when the coefficients of the prediction functions P(z) of the predictors 6 and 21 are not integers will be described. In the first method, as described above, the predictors 6 and 21
In this method, a quantization circuit is provided on the output side of the quantization circuit. The second method is a method that equivalently realizes the first method by devising the code conversion characteristics of the unequal length encoding circuit 9 without providing a quantization circuit on the output side of the predictor 6. . Hereinafter, FIG. 4, which shows a configuration for achieving the second method, will be explained. Referring to FIG. 4, a predictive encoding device 3 and a predictive decoding device 14 according to a second embodiment of the present invention
It is shown. FIG. 4 shows a quantized image signal outputted from the quantization circuit 4 of the predictive coding device 3 and a decoded signal of the predictive decoding device 14 using a prediction function of coefficients including decimal points in FIG. 1. A quantization circuit 40 is added so that the values match. Furthermore, in FIG. 4, the predictor 10
7 and 41 prediction functions and unequal length encoding circuit 1
The code conversion characteristics of 08 are different from those shown in FIG.
The other parts have the same functions as the same parts in FIG. 1 and perform similar operations. The decoded signal output from the adder 20 of the predictive decoding device 14 is sent to the D/A converter 22 and the predictor 41.
is supplied to The predictor 41 obtains a predicted signal according to the prediction function and sends it to the quantization circuit 40 . The quantization circuit 40 quantizes and outputs the predicted signal according to the quantization characteristic selected by the control signal from the control circuit 18 , and supplies the quantized predicted signal to the adder 20 . The adder 20 adds the output signal of the quantizer 40 and the reproduced prediction error signal sent from the unequal length decoding circuit 17 to generate a decoded signal that is equal to the signal input to the predictive encoder 5. Output. The quantization circuit 40 has the same quantization characteristic as the quantization characteristic of the quantization circuit 4 of the predictive encoding device 3, and is configured similarly to that shown in FIG. That is, quantization by truncation is performed. FIG. 5 shows a specific circuit example of the predictor 107 shown in FIG. This predictor 107 has a sampling frequency s
There are two prediction functions that can efficiently predict a color TV signal when the subcarrier frequency is three times the subcarrier frequency sc, and the prediction signal is obtained by adaptively switching between the two prediction functions. There is. The first prediction function P <sub>1</sub> (z) is a prediction function having prediction coefficients below the decimal point, and is expressed by equation (8). P <sub>1</sub> (z) = 0.5Z <sup>-1</sup> +Z <sup>-3</sup> -0.5Z <sup>-4</sup> ...(8) The second prediction function P <sub>2</sub> (z) is a prediction function that predicts from two lines in advance, and is expressed by equation (9). It will be done. P <sub>2</sub> (z) = Z <sup>-2nH</sup> (however, n <sub>H</sub> = 682.5) ...(9) Then, the predicted signals by the two prediction functions and the input signal to the predictor 107 (locally decoded signal) are compared, and the predicted signal by the predictor 107 is The function that outputs a prediction signal close to the input signal is used for the next prediction. The quantized image signal input to the predictor 107 is processed by a first prediction circuit 42 having the characteristics of the prediction function of equation (8), and a second prediction circuit 42 having the characteristics of the prediction function of equation (9).
is input to the prediction circuit 43 and the determination circuit 44. The first prediction signal output from the first prediction circuit 42 is sent to the terminal a of the switching circuit 45 and to the determination circuit 4.
The second prediction signal input to terminal b of the switching circuit 45 and output from the second prediction circuit 43 is input to terminal b of the switching circuit 45.
and is input to the determination circuit 44. Judgment circuit 44
determines which predicted signal is closer to the quantized input signal to the predictor 107, and if the first predicted signal is closer to the input signal to the predictor 107, a selection signal of 0 is sent. If the second predicted signal is closer, a selection signal of 1 is output. The selection signal is delayed by one sampling clock cycle in the register 46 and then sent to the switching circuit 45. The switching circuit 45 is
When the selection signal is 0, the first prediction signal of the switch terminal a is output, and when the selection signal is 1, the second prediction signal of the terminal b is output. In this way the first
or the second predicted signal is selected, and the predicted signal is output from the output of the predictor 107. The predictor 41 of the predictive decoding device 14 is also the predictor 10
It is configured similarly to 7. In this adaptive prediction, switching is performed using information from one sample before, so there is no need to transmit a signal for switching the prediction function. FIG. 6 shows the first predictor in the predictor 107 shown in FIG.
This is a specific circuit example of the prediction circuit 42 and the second prediction circuit 43. The first prediction circuit 42 includes registers 32, 34, 35, and 38 that delay the input signal by one sampling clock period and output the signal, and a subtracter 3.
3, an adder 37, and multipliers 31 and 36 with a coefficient of 0.5. Second prediction circuit 43
consists of a shift register 39 which delays the input signal by 1365 sampling clock cycles and outputs the delayed signal. FIGS. 7a and 7b show other circuit examples of the predictive decoder 24 including the quantization circuit 40 in the embodiment of FIG. 4, respectively. In FIG. 7a, the prediction signal output from the predictor 41 and the reproduced prediction error signal sent from the unequal length decoding circuit 17 are added together in the adder 20, and then the quantization circuit 40
The signal is quantized and made into a decoded signal. In FIG. 7b, the decoded signal obtained from the adder 20 is quantized by the quantization circuit 40 and then sent to the predictor 41.
7a and b are the predictive decoder 2 of FIG. 4, respectively.
Perform the same operation as in step 4. The code conversion characteristics of the unequal length encoding circuit 108 in FIG. 4 are as follows. When the prediction error signal sent to the unequal length encoding circuit 108 is e, the code number for unequal length encoding is N, and x is a certain real number,
The symbol <x> is n-1<xn+, where n is an integer.
Let it represent the value of n that satisfies the inequality of 1. That is, the symbol <> represents rounding up to an integer. The first, second, and third code conversion characteristics corresponding to the first, second, and third quantization characteristics are expressed by equations (10), (11), and (12), respectively, for the prediction error signal e. It has the characteristic of converting to an unequal length code of code number N. N=<e>...(10) N=<e/2>...(11) N=<e/4>...(12) For example, in the case of the second code conversion characteristic, e=-3
The prediction error signal of is ``11'' as N=-1 from equation (11).
is converted to an unequal length code. The inverse code conversion characteristics of the unequal length encoding circuit 17 in FIG. 4 are the same as those in FIG. 1, and are expressed by equations (5), (6), and (7). Referring to FIG. 8, a predictive encoding device 3 and a predictive decoding device 14 according to a third embodiment of the present invention are shown. In this embodiment, the preprocessing circuit of the predictive encoding device 3 performs thinning control on the digitized image signal according to the thinning characteristics selected by the control signal from the control circuit 11. A thinning control circuit 50 is used that can perform the following. The thinning process may be performed in an equivalent manner. Therefore, first, the thinning control circuit 5
The first method is to actually perform thinning at 0' (the circuit in Figure 10, which will be described later) to reduce the number of samples, and then perform predictive coding using a predictive encoder. The second method involves feeding the image signal as it is to the predictive encoder, then actually thinning it out in the unequal-length encoding circuit and performing code conversion, and the second method in which the pixels to be thinned out are determined in the thinning control circuit and the pixels are thinned out. A third method can be considered, in which the signal of a pixel that should not be thinned out is interpolated from the signal of the surrounding pixel that should not be thinned out, and the unequal length encoding circuit actually thins out the signal and performs code conversion. This embodiment employs the third method. The image signal input to terminal 1 is processed by A/D converter 2 at a sampling frequency s that is three times the subcarrier frequency.
It is converted into a 5-bit PCM signal sampled at (s=3sc) and sent to the thinning control circuit 50.
The thinning control circuit 50 determines the pixels to be thinned out and the pixels not to be thinned out according to the thinning characteristics selected by the control signal, and also determines the pixels to be thinned out using the signals of the surrounding pixels that should not be thinned out. Signal values are interpolated in advance. The image signal output from the thinning control circuit 50 is input to the subtracter 7 and the predictor 107 of the predictive encoder 5. In the subtracter 7, a thinning control circuit 50
The prediction signal output from the predictor 107 is subtracted from the image signal output from the predictor 107, and a prediction error signal is output. The prediction error signal is input to the unequal length encoding circuit 51 of the unequal length encoder 8. In accordance with the control signal from the control circuit 11, the unequal length encoding circuit 51 converts only the prediction error signals corresponding to pixels that should not be thinned out into unequal length codes according to code conversion characteristics, and decodes them. Buffer memory 10 along with control information necessary for
send to The buffer memory 10 includes an unequal length encoding circuit 51
The information sent from the buffer memory 10 is temporarily stored, the speed is converted to match the transmission speed of the transmission line, and the information is sent to the transmission line from the output terminal 12.
The control circuit 11 is informed of the amount of information stored in the. The control circuit 11 determines whether to switch the thinning characteristics at appropriate intervals based on the amount of information stored from the buffer memory 10, and switches the thinning characteristics of the thinning control circuit 50 and the code conversion characteristics of the unequal length encoding circuit 51. Outputs a control signal. Control circuit 1
In No. 1, control is performed so that the number of samples to be thinned out increases as the amount of information storage increases, and so that no thinning is performed when the amount of information storage is small. The above is an explanation of the operation of the predictive encoding device 3. In the predictive decoding device 14, information sent from the transmission path is sent from the input terminal 13 to the buffer memory 16 of the unequal length decoder 15, and is temporarily stored therein. This stored information is sequentially read out in accordance with requests from the unequal length decoding circuit 52 of the unequal length decoder 15. Information on the thinning control signal is sent to the control circuit 18, and information on the unequal length code is sent to the unequal length decoding circuit 52. The control circuit 18 sends a control signal for switching thinning characteristics to the unequal length decoding circuit 52 and the interpolation processing circuit 53 based on the information of the control signal sent from the buffer memory 16. The unequal length decoding circuit 52 obtains individual unequal length codes from the unequal length code string sent from the buffer memory 16. Then, the unequal length decoding circuit 52 corresponds to pixels that have not been thinned out according to the inverse code conversion characteristic selected by the control signal from the control circuit 18 for the obtained unequal length code. At that time, reverse code conversion is performed and a prediction error signal is output. An appropriate value, for example 0, is set at the time corresponding to the pixel where the thinning was performed.
A prediction error signal with a value of is output. The obtained prediction error signal is sent to the adder 20 of the prediction decoder 24, where it is added to the prediction signal sent from the predictor 41, and becomes a decoded signal. The decoded signal is sent to the interpolation processing circuit 53. Since a correct decoded signal is not obtained for the thinned out pixels, the interpolation processing circuit 53 determines whether the surrounding pixels are not thinned out according to the interpolation characteristics selected by the control signal from the control circuit 18. Adaptive interpolation is performed using pixel signals. The decoded signal that has undergone interpolation processing is sent to the D/A converter 2.
2 and the predictor 41. D/A converter 2
2 outputs an analog decoded signal to a terminal 23.
The predictor 41 outputs a predicted signal from the decoded signal according to the prediction function P(z) from the decoded signal, and outputs a predicted signal from the decoded signal to the adder 20.
send to The above is an explanation of the operation of the predictive decoding device 14.
Note that the specific circuit example of the predictors 107 and 41 in this third embodiment (FIG. 8) includes the third embodiment.
The predictor 6 shown in the figure or the predictor 107 shown in FIG. 5 is used. In addition, the unequal length encoding circuit 5
The code conversion characteristics of 1 and the inverse code conversion characteristics of the unequal length decoding circuit 52 include the first code conversion described in the first embodiment (FIG. 1) or the second embodiment (FIG. 4). A characteristic and a first inverse transcoding characteristic are used. FIG. 9 is a diagram showing the spatial arrangement of sampled pixels for explaining the thinning characteristics in the thinning control circuit 50 of the third embodiment of the present invention. The sampling frequency s is three times the subcarrier frequency (s=
3sc), the number of samples n _H in one horizontal scanning line is n _H =682.5. The arrangement of pixels sampled from a portion of the screen from the (l-3)th line to the lth line of one field is as shown by the O marks shown in FIG. 9a. FIG. 9b is a diagram showing pixels to be thinned out using the first thinning characteristic. The x mark indicates the pixel to be thinned out. In the horizontal direction, thinning is performed every three samples, and in the vertical direction, thinning is performed every other line, reducing the number of effective samples to 5/6. The x-marked pixels to be thinned out are shifted by one sampling period for each line to be thinned out. Figure 9c is
FIG. 7 is a diagram showing pixels to be thinned out using a second thinning characteristic. All lines are thinned out every 3 samples in the horizontal direction, and the number of effective samples is reduced to 2/3. Interpolation of signals of pixels to be thinned out is performed as shown in FIG. 9c. Interpolation of the pixel x on the l-th line where the thinning is performed uses neighboring pixels a, b, c, d, and e where the thinning is not performed, and the signals of each image are 0.5, 0.25, -0.5, 0.5, and The value added after weighting by 0.25 is set as the signal of pixel x. This interpolation is expressed as Z-function interpolation filter characteristic H(z)
If expressed as (13), H(z)=0.5Z ^-1 +0.5Z ^-681 -0.5Z ^-682 +0.25Z ^-684 +0.25Z ^-1365 ...(13) Figure 10 shows a thinning control circuit 50' that can actually perform thinning. This is a specific circuit example.
The image signal input to the thinning control circuit 50' is
Terminal 63 of switching circuit 62 and interpolation filter circuit 61
sent to. The interpolation filter circuit 61 is composed of a digital filter having interpolation filter characteristics expressed by equation (13), and outputs an interpolation signal. The interpolated signal is sent to terminal 64 of switching circuit 62. In the switching circuit 62, the control signal sent from the control circuit 11 determines the non-thinning characteristic (FIG. 9a).
) and the first thinning characteristic (characteristic in Figure 9b)
and the second thinning characteristic (the characteristic shown in FIG. 9c) is selected. Then, according to this thinning characteristic, a switch 65 is connected to a terminal 64 for a pixel to be thinned out, and an interpolation signal is obtained. On the other hand, for pixels that are not thinned out, a switch 65 is connected to the terminal 63, and the original image signal without any processing is output. The interpolation processing circuit 53 of the predictive decoding device 14 in the third embodiment (FIG. 8) is configured in the same manner as the thinning control circuit 50' in FIG. When the prediction function has coefficients with values below the decimal point, quantization by truncation can be performed by inputting only integer values from the output of the adder 20 in FIG. 8 to the interpolation processing circuit 53. FIG. 11 is a third embodiment of this invention (FIG. 8)
This is a specific example of a circuit configured by combining both the thinning control circuit 50 and the predictive encoder 5 in FIG. This circuit example is configured such that the interpolation filter circuit 61 of the thinning control circuit 50' in FIG. 10 is also used by the delay element of the second prediction circuit 43 of the predictor 107 in FIG. An image signal is input from a terminal 70, a control signal is input from a terminal 78, and a prediction error signal is output from a terminal 79. The switching circuit 62 has the same function as the switching circuit 62 in FIG. The first prediction circuit 42, determination circuit 44, switching circuit 45, and register 46 have the same functions as the first prediction circuit 42, determination circuit 44, switching circuit 45, and register 46 shown in FIG. 5, respectively. Subtractor 7 has the same function as subtracter 7 in FIG. The second prediction circuit 43 is composed of a shift register with taps, and has output terminals 431,
432, 433, 434 and 435 have 680 and 68 input signals respectively to the shift register.
Signals delayed by sampling clock periods of 1,683, 1364 and 1365 are output. Multipliers 73, 74, 75, 76 and 77 each have 0.5,
It has coefficients of 0.5, -0.5, 0.25, and 0.25, and performs multiplication respectively. The output signals of those multipliers are sent to the adder 7
2 and added, and then delayed by one sampling clock period in register 71. An interpolated signal is obtained at the output of this register 71. That is, the second
The relationship between the input signal of the prediction circuit 43 and the output signal of the register 71 is determined by the interpolation filter characteristic shown in equation (9). The interpolation processing circuit 53 and the predictor 41 in the predictive decoding device 14 shown in FIG. 8 can be similarly configured to share a delay element. Referring to FIG. 12, a predictive encoding device 3 and a predictive decoding device 14 according to a fourth embodiment of the present invention
It is shown. In this embodiment, a combination of a quantization circuit 4, a thinning control circuit 50, and a band limiting circuit 80 is used as a preprocessing circuit. The image signal input to terminal 1 is processed by A/D converter 2 at a sampling frequency s that is three times the subcarrier frequency.
The signal is converted into a 5-bit PCM signal sampled at (s=3sc) and sent to the band limiting circuit 80. The band-limiting circuit 80 band-limits at least one of the spatial frequency and the frequency in the time axis direction of the digitized image signal according to the band-limiting characteristic selected by the control signal from the control circuit 82. be able to. Band-limiting characteristics can also be determined to remove noise components in the image signal. The image signal band-limited by the band-limiting circuit 80 is quantized by the quantization circuit 4 using a quantization characteristic selected by a control signal from the control circuit 82 . The image signal quantized by the quantization circuit 4 is sent to a thinning control circuit 50. The thinning control circuit 50 performs interpolation processing on the pixels to be thinned out according to the thinning characteristics selected by the control signal from the control circuit 82. The image signal subjected to interpolation processing by the thinning control circuit 50 is sent to the predictive encoder 5, and the predictive encoder 5 outputs a prediction error signal. The prediction error signal is sent to an unequal length encoding circuit 81 of the unequal length encoder 8. The unequal length encoding circuit 81 has code conversion characteristics corresponding to the quantization characteristics, and corresponds to pixels that should not be thinned out according to the code conversion characteristics selected by the control signal from the control circuit 82. Convert only the prediction error signal to an unequal length code. The unequal length code information is sent to the buffer memory 10 together with control information necessary for decoding, and is temporarily stored in the buffer memory 10. The buffer memory 10 smoothes the information and sends it out to the transmission line from the output terminal 12, and also notifies the control circuit 82 of the amount of information stored in the buffer memory 10. The control circuit 82 determines whether to switch between the band-limiting characteristic, the quantization characteristic, and the thinning-out characteristic at appropriate intervals based on the amount of information stored from the buffer memory 10, and determines whether the band-limiting characteristic, the quantization characteristic, and the thinning-out characteristic are unequal. A control signal for switching the code conversion characteristics of the long encoding circuit 81 is output. The above is an explanation of the operation of the predictive encoding device 3. In the predictive decoding device 14, the information sent from the transmission path is sent to the buffer memory 16 of the unequal length decoder 15 and temporarily stored. This stored information is sequentially read out in accordance with requests from the unequal length decoding circuit 83 of the unequal length decoder 15. The control information is sent to the control circuit 93, and the information on the unequal length code is sent to the unequal length decoding circuit 83. Control circuit 9
3 sends a control signal for switching the quantization characteristic, thinning characteristic, and inverse code conversion characteristic to the unequal length decoding circuit 83, the quantization circuit 40, and the interpolation processing circuit 53 based on the control information sent from the buffer memory 16. The unequal length decoding circuit 83 converts the unequal length code into a prediction error signal according to the inverse code conversion characteristic corresponding to the code conversion characteristic selected by the unequal length encoding circuit 81 of the predictive encoding device 3. do. At this time, the prediction error signal for the thinned out pixels is interpolated with an appropriate value, for example, 0. The prediction error signal is sent to the adder 20 of the prediction decoder 24, where it is added to the prediction signal from the predictor 41 to become a decoded signal. The decoded signal is sent to a quantization circuit 40. The quantization circuit 40 performs quantization according to the quantization characteristic selected by the control signal from the control circuit 93. The quantized decoded signal is sent to an interpolation processing circuit 53. The interpolation processing circuit 53 adaptively performs interpolation on the thinned pixels using signals of surrounding non-thinned pixels according to the interpolation characteristics selected by the control signal from the control circuit 93. . The decoded signal subjected to interpolation processing is sent to the D/A converter 22 and the predictor 41. D/A converter 22 outputs an analog decoded signal to output terminal 23 . The above is an explanation of the operation of the predictive decoding device 14. According to this embodiment, the band limiting circuit 80, the quantization circuit 4, and the thinning control circuit 50 serve as preprocessing circuits.
Because it uses a combination of
Encoding can be performed in which the deterioration of image quality is not visually noticeable. Fine-grained control that takes into account the above visual characteristics includes, for example, relatively preferentially performing band limiting or thinning in flat image parts that contain low frequency components, and limiting by quantization in parts that contain many high frequency components. be carried out relatively preferentially,
Control that restricts information in an overall well-balanced manner is conceivable. FIG. 13 shows a specific circuit example of the band limiting circuit 80 of the fourth embodiment (FIG. 12). This band-limiting circuit 80 limits the spatial frequency band, and is configured as a product of a horizontal band-limiting filter and a vertical band-limiting filter. The image signal input to the input terminal 84 is supplied to a band pass filter A87 and a subtracter 89. A control signal from the control circuit 82 input to the input terminal 85 is supplied to attenuation circuits 88 and 91. The bandpass filter A87 is composed of a digital filter represented by the function H _A (z) of equation (14), and has a filter characteristic that allows a frequency band in the horizontal direction to pass. H _A (z)=1−(0.5Z ⁻¹ +Z ⁻³ −0.5Z ⁻⁴ ) (14) The bandpass signal output from the bandpass filter A87 is sent to the attenuation circuit 88. Attenuation circuit 8
8, the magnitude of attenuation is controlled by a control signal from the control circuit 82, and outputs a bandpass signal that is k _A (0≦k _A ≦1) times as large. The k _A times bandpass signal outputted from the attenuation circuit 88 is sent to a subtracter 89.
is supplied to The subtracter 89 subtracts the k _A times the bandpass signal from the input image signal of the terminal 84 and outputs a horizontally band-limited signal. Subtractor 8
The output of 9 is the bandpass filter B90 and subtractor 9.
2. Bandpass filter B90 (15)
It is composed of a digital filter represented by the function H _B (z) in the equation, and has filter characteristics that allow frequency bands in the vertical direction to pass. H _B (z)=1−Z ^−2nH (15) where n _H is the number of samples for one line, and when s=3sc, n _H =682.5. The bandpass signal output from bandpass filter B90 is supplied to attenuation circuit 91. The magnitude of attenuation of the attenuation circuit 91 is controlled by a control signal from the control circuit 82, and k _B (0
≦k _B ≦1) Outputs a bandpass signal twice as large. The k _B times bandpass signal output from the attenuation circuit 91 is supplied to a subtracter 92 . Subtractor 92
subtracts k _B times the vertical bandpass signal from the horizontally band-limited signal, and outputs the horizontally and vertically band-limited signal to the output terminal 86 . The filter function H'(z) representing the band-limiting characteristic of the band-limiting circuit 80 is expressed by equation (16). H′(z)={1−k _A (1−0.5Z ⁻¹ −Z ⁻³ +0.5Z ⁻⁴ )}×{1−k _B (1−Z ⁻¹³⁶⁵ )}…(1
6) k _A and k _B are each 1 if the amount of information accumulated is large.
Alternatively, if a value close to 1 is selected and the amount of information stored is small, a value of 0 or a value close to 0 is selected. k _A
and k _B are both 0, H′(z) in equation (16)
becomes 1, and the input image is output as is. k _A
When both of and k _B approach 1, only frequency components near the frequencies of 0 and sc and near integer multiples of _H /2 ( _H is the horizontal scanning frequency) are passed. As is clear from the above description, according to the present invention, preprocessing circuits such as a band limiting circuit, a quantization circuit, and a thinning control circuit are provided, and by adaptively controlling these circuits, it is possible to perform coding in real time. Accordingly, it is possible to provide a non-recursive type predictive encoding device that can be easily configured and configured. Since a non-recursive type predictive coding device can decode the same signal that is input to the predictive coding device, if the predictive coding device of this invention is used, the information of the image is less than the transmission bit rate. Basically, it is possible to perform encoding to preserve information. Note that the quantization characteristics and configurations of the quantization circuits 4 and 40 are not limited to those shown in FIG. 2. The prediction functions and configurations of the predictors 6, 21, 41, and 107 are not limited to those shown in FIGS. 3 and 5. The code conversion characteristics, inverse code conversion characteristics, and unequal length codes are not limited to those shown in the first embodiment or the second embodiment. The thinning characteristics of the thinning control circuit 50 are not limited to the characteristics shown in FIG. The thinning control circuit 50' and the interpolation processing circuit 53 are
The filter characteristics of the interpolation filter circuit 61 are not limited to those shown in the figure, and the filter characteristics of the interpolation filter circuit 61 are not limited to the function shown in equation (13). The circuit configured by combining the thinning control circuit 50 and the predictive encoder 5 is the 11th
It is not limited to what is shown in the figure. The band limiting circuit 80 is not limited to that shown in FIG. 13. The unequal-length codes with code conversion characteristics used in the unequal-length encoding circuit 9 do not use one type of fixed unequal-length code, but adaptively switch between several different types of unequal-length codes. It may also be used while Furthermore, in the first to fourth embodiments, the image signal is an NTSC color TV signal, but it is not limited to an NTSC system signal, and for example,
A PAC method may also be used. Also, the sampling frequency is not limited to three times the subcarrier frequency. Furthermore, the control circuit that outputs the control signal to the preprocessing circuit may determine the control signal to be given to the preprocessing circuit based on the amount of information input to the buffer memory 10. That is, the control signal to be given to the preprocessing circuit is determined based on the cumulative amount of information input to the buffer memory 10 in a certain section (whether the amount of information input to the buffer memory 10 increases rapidly or gradually). It's okay.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of a specific configuration of the quantization circuit 4 shown in FIG. 1, and FIG. A circuit diagram showing an example of a specific configuration of the predictor 6,
FIG. 4 is a block diagram showing the configuration of a second embodiment of the present invention, FIG. 5 is a circuit diagram showing an example of a specific configuration of the predictor 107 in FIG. 4, and FIG. A circuit diagram showing an example of a specific configuration of the first prediction circuit 42 and the second prediction circuit 43, FIGS. 7a and 7b
are a circuit diagram showing another specific configuration of the predictive decoder 24 in FIG. 4, FIG. 8 is a block diagram showing the configuration of a third embodiment of the present invention, and FIGS. 9a, b
10 is a circuit diagram showing the decimation control circuit 50', and FIG. 11 is an example of a specific configuration when the decimation control circuit 50 and the predictive encoder 5 are combined. A circuit diagram showing,
FIG. 12 is a block diagram showing the configuration of a fourth embodiment of the present invention, and FIG. 13 is a circuit diagram showing an example of a specific configuration of the band limiting circuit 80 of FIG. 12. 4 is a quantization circuit as a preprocessing circuit; 50 and 50' are thinning control circuits as preprocessing circuits;
0 is a band limiting circuit as a preprocessing circuit, 5 is a predictive encoder, 9, 108, 51 and 81 are unequal length encoding circuits, 10 is a buffer memory, and 11 and 82 are control circuits.

Claims (1)

[Scope of Claims] 1. A preprocessing circuit that receives a digitized image signal and controls the amount of information of the image signal according to a control signal, and a preprocessed circuit that is output from the preprocessing circuit. a prediction encoder that receives an image signal and outputs a prediction error signal using reversible logic; and an unequal length encoding circuit that converts the prediction error signal into an unequal length code in response to the operation of the preprocessing circuit. A buffer memory for temporarily storing and smoothing the unequal length code information and control information necessary for decoding output from the unequal length encoding circuit, and transmitting the unequal length code information and the control information necessary for decoding, and the amount of information input to the buffer memory or the buffer memory. and a control circuit that outputs the control signal to be given to the preprocessing circuit based on the amount of accumulated information, and the predictive encoding device uses information sent from the buffer memory as output information. 2. In the predictive encoding device according to claim 1, the digitized image signal may be quantized in accordance with the quantization characteristic selected by the control signal from the control circuit. 1. A predictive encoding device characterized in that a quantization circuit that can perform the above-mentioned functions is used as the preprocessing circuit. 3. In the predictive encoding device according to claim 1, thinning control is performed on the digitized image signal according to the thinning characteristic selected by the control signal from the control circuit. 1. A predictive encoding device characterized in that a thinning control circuit capable of performing the following steps is used as the preprocessing circuit. 4. In the predictive encoding device according to claim 1, the spatial frequency and time axis of the digitized image signal are determined according to the band-limiting characteristic selected by the control signal from the control circuit. A predictive encoding device characterized in that a band-limiting circuit capable of band-limiting at least one of the frequencies in the directions is used as the pre-processing circuit. 5. In the predictive encoding device according to claim 1, the digitized image signal may be quantized in accordance with the quantization characteristic selected by the control signal from the control circuit. a quantization circuit capable of performing decimation control on the digitized image signal according to a decimation characteristic selected by the control signal from the control circuit; a band-limiting circuit capable of band-limiting at least one of a spatial frequency and a frequency in a time axis direction of the digitized image signal according to a band-limiting characteristic selected by the control signal from the circuit; A predictive encoding device characterized in that a combination of at least two of them is used as the preprocessing circuit.