AU606817B2

AU606817B2 - Apparatus for encoding/transmitting images

Info

Publication number: AU606817B2
Application number: AU41541/89A
Authority: AU
Inventors: Kenichi Asano; Naofumi Goda; Hiroaki Kikuchi; Okikazu Tanno
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1986-05-26
Filing date: 1989-09-20
Publication date: 1991-02-14
Anticipated expiration: 2007-05-25
Also published as: AU4154089A; JPS62276927A; AU4153889A; AU606816B2; AU606815B2; AU4153989A; AU4154189A; AU607636B2

Description

AUSTRALIA

PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: Int. Cl: Application Number: Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published: Priority: Related Art: i Form )g~l'A This document contai.n.- t ;rie'A ld r s r'::de ui. i.; c 0ion :r;d ."rrrcl i>.

I

i -rI

I

,i rtr TO BE COMPLETED BY APPLICANT Name of Applicant: Address of Applicant: Actual Inventor: MITSUBISHI DENKI KABUSHIKI

KAISHA

2-3 MARUNOUCHI 2 CHOME

CHIYODA-KU

TOKYO 100

JAPAN

Address for Service: GRIFFITH HACK CO., 601 St. Kilda Road, Melbourne, Victoria 3004, Australia.

Complete Specification for the invention entitled: APPARATUS FOR ENCODING/TRANSMITTING IMAGES The following statement is a full description of this invention including the best method of performing it known to me:- 1 j_ i ;.~c~ios~-~'iLnn~-acrrsrm~F----D I APPARATUS FOR ENCODING/TRANSMITTING IMAGES BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a technology for transmitting image signals obtained by encoding image information which utilizes the so-called vector quantization technique and which is applicable to the fields such as the television (TV) conference system and the TV telephone system This application is a divisional of Australian 0o a 10 Patent Application No. 73379/87, the contents of which are 0000oooo 0 incorporated herein by reference. There are also other 0 00 oo divisional applications of the noted parent application.

0 0000 0 0 0000 Description of the Prior Art 00 As a result of the remarkable advance of the image processing technology in recent years, there have been made various attempts to put, for example, the TV Li conference system and the TV telephone system to the practical use by mutually and by directionally transmitting the image information. In such a technological field, the quantization technique has been used in which the image signals as the analog quantity are S classified into a finite number of levels changing in a discrete fashion within a fixed width and a unique value is assigned to each of these levels. Particularly, there has been a considerable advance in the vector quantization technique in which a plurality of samples of the image signals are grouped in blocks and each block thereof is mapped onto a pattern most similar thereto, in a 1A i_ multidimensional signal space; thereby accomplishing the quantization.

The study of the vector quantization technology has been described in the following reference materials, for example.

"An Algorithm for Vector Quantizer Design" by Y. Linde, A. Buzo. and R. M. Gray (IEEE TRANSACTION ON COMMUNICATIONS, Vol. COM.28, No. 1, January 1980, pp.

84 0 .10 "On the Structure of Vector Quantizers" by A. Gersho 0 S0 9(IEEE TRANSACTION ON INFORMATION THEORY, Vol. IT28, No. 2, 0 0 0 o March 1982, pp. 157 166) o 0 0 o "Speech Coding Based Upon Vector Quantization" by A. Buzo, A. H. Gray Jr., R. M. Gray and J. D. Markel (IEEE TRANSACTION ON ACOUSTICS, SPEECH, AND SIGNAL So PROCESSING, Vol. ASSP28, No. 5, October 1980, pp. 562 oYo 0 0574) o 00 Moreover, the following U.S. Patents have been 0 0 00 obtained by the assignee of the present invention.

20 U.S.P.N. 4,558,350 "VECTOR QUANTIZER", Murakami 0000 o00 U.S.P.N. 4,560,977 "VECTOR QUANTIZER", Murakami et 00 4 o a i al.

2 2 00 4 Referring now to FIGS. 1 3B, the prior art technology of the present invention will be described.

The conventional image encoding/transmitting apparatus, as shown in FIG. 1, includes a subtractor 1 for obtaining a difference between an input signal S 1 such as an image signal and an estimation signal S 9 and for outputting an estimated error signal S 2 1 a movement dete&ting circuit 2 for comparing a threshold value T with the estimated error signal S 2 to detect a movement or a change and for 1 0 generating and outputting a movement or change detect signal S53 and a differential signal S 4 1 a quantization circuit 3 for quantizing the movement or change detect signal S 3 and the differential signal S 4 to output a quantization signal S51, a variable length encoder 4 for generating from the quantization signal S 5 an encoded signal S. with a variable length and for outputting 'the encoded signal S 6 a transmission data buffer circuit for temporarily storing the encoded signal S 6 and for outputting the encoded signal S 6 to the transmission side, a local decoding circuit 6 for generating a reproduced differential signal S 7 from the quantization signal delivered from the quantization circuit 3 and outputting the reproduced or regenerated differential signal S 7 an adder 7 for achieving an addition on the reproduced differential signal S 7and the estimation signal S 9 and for outputting a reproduced input signal 8 an estimating circuit 8 for outputting an estimation signal S 9 based on -3 i

'I

the reproduced input signal S8, and a threshold generating circuit 9 for monitoring the amount of the encoded signal S 6 accumulated in the transmission data buffer circuit 5 and for generating an appropriate threshold value T.

The movement detecting circuit 2 coiprises, as shown in FIG. 2, an absolute value circuit 10 for-calculating the absolute value IS21 of the estimated error signal .S2, a comparing circuit 11 for effecting a comparison between 10 the absolute value IS 2 1 of the estimated error signal S 2 and the threshold value T and for outputting the movement or change detect signal S 3 and a zero allocator 12 for allotting 0 and outputting 0 as the differential signal S4 when the movement or change is not detected as a result of the comparison in the comparing circuit 11.

f €The movement detect signal S3 is converted into a running a3 record R by use of the running length encode table 4a to I generate serial data. In addition, only when the movement detect signal S 3 is indicating the validness, the quantization signal S 5 is converted into a variable-length record through the variable-length encode table 4b to generate serial data (FIGS. 2B 2C). Reference numeral 4C indicates a multiplex operation control section.

In contrast to the configuration on the transmission side of FIGS. 1 2B, the configuration on the reception side is shown in FIGS. 3A 3B. In FIG. 3A, the equipment on the reception side includes a receiving data 4 buffer circuit 13 for receiving and for temporarily storing the encoded signal S6 delivered from the transmission data buffer circuit 5 on the t.ansmission side, a variable length decoder 14 for decoding the encoded signal S6 stored in the receiving data buffer 13 to output a reproduced quantization signal Sil a local decoding circuit 15 for outputting a reproduced differential signal S 1 2 based on the reproduced a a: quantization signal S1l, an adder circuit 16 for obtaining °o 10 the difference between the reproduced differential signal S12 and the reproduced estimation signal S 13 and for reproducing the input signal S 14 which corresponds to the o"" reproduced input signal S 8 on the transmission side, and an estimating circuit 17 for outputting the reproduced estimation signal S 1 3 After the encoded signal S6 undergone the multiplexing in the variable-length encode circuit 4 is B received by the receive buffer circuit 13, the data is distributed to the respective decode tables of variable 0 .20 codes under control of the multiplex separation control circuit 14a. As a result of the decoding, the movement detect signal and the quantization signal are attained.

Moreover, when the decoded movement detect signal indicates the invalidness the quantization signal is reset to by the flip-flop 14c, thereby outputting the output Sll (FIG. 3B).

5 Next, the operation on the transmission side will be described with reference to FIGS. 1 2.

Assuming first the non-effective error in the movement detecting circuit 2 to be d, the estimation coefficient to be applied to the reproduced input signal

S

8 in the estimating circuit 8 to be A, and the delay of the time t to be Z the following relationships are o0 satisfied.

o S S 1

S

o o0 o o o a o -10 S d S0010 d b t i s S A. S dS 0000 0 0 t a and the estimated signal S, whereas the movement detecting circuit 2 outputs the movement or change detection signal S3 and the differential signal S 4 based on the estimated error signal S 2 calculated by the subtractor 1.

A detailed description will be given of the operation of the movement detecting circuit 2 by referring to FIG. 2. The allotting absolute value circuit 10 obtains the absolute value of the estimated error signal S 2 and then the comparison circuit 11 achieves a comparison between the absolute value IS21 of the estimated error signal S2 and the threshold value T generated by the threshold value generating circuit 9.

6 11 I The movement detection signal S 3 is output in conformity with the following conditions.

S3 0 (invalid) IS21 T

S

3 1 (valid) IS21 T When the movement or change is not detected, namely, for

"S

3 zero allocator 12 outputs "for the differential signal S4.

SOn the other hand, the quantization circuit 3 o on converts the inputted differential signal S 4 according to 0000 So"o 10 an arbitrary characteristic. The variable encoding circuit 4 receives the quantization signal S 5 only when o 0 o0e. the movement detection signal S 3 is valid, namely, for

"S

3 1" and, for example, conducts a run-length encoding on the movement detection signal S For the quantization 0000 oo0 '15 signal S 5 a code having a smaller code length is assigned O 0 4 0 to a value in the neighborhood of for which the ooo generation frequency is high and then the code is stored in the transmission data buffer circuit 5. The transmission data buffer circuit 5 outputs the accumulated datum as the encoded signal S 6 to a transmission line. The threshold generating circuit 9 monitors the accumulated amount of the transmission data buffer circuit 5 and further controls the generation amount of the encoded data by generating an appropriate threshold value.

Next, the operation on the reception side will be described with reference to FIG. 3. The receiving data 7 1 .4 *1 0 0009e 0 00 00. 06 0 0 0.0* 8 0999 buffer circuit 13 first receives the encoded signal S6 undergone the variable length encoding on the transmission signal and outputs the signal S 6 to the variable length decoder 14. Only when the movement detection signal S 3 undergone the decoding operation indicates the validness, the variable length decoder 14 outputs the reproduced quantization signal'.Sll. If the movement detection signal S 3 indicates the invalidness, the variable length decoder 14 outputs Next, the 10 local decoding circuit 15 decodes the reproduced quantization signal Sl and outputs the reproduced differential signal S12 to the adder 16. The adder 16 adds the reproduced differential signal S 1 2 to the reproduced estimation signal S13 from the estimation 15 circuit 17 thereby to reproduce the input signal S 14 The operation to effect the data compression and transmission by use of the differential signal is 0 referred to as the differential pulse code modulation (to be abbreviated as DPCM herebelow) system.

However, in the image encoding/transmitting apparatus using the DPCM system, the variable length encoding is achieved on the datum which is judged to be effective at the step of the variable length encoding; consequently, as the threshold-value increases, the code having a short code length to be assigned in the neighbor'ood of "0" cannot be generated and hence the efficiency of the encoding is deteriorated; moreover, there has been a 0 0 0 0.

a o o c 0 000 o 0 0 9 8 "i ;iJ problem that as the threshold value becomes greater, the precision of the quantization is not improved for the quantization characteristic of the quantization circuit in the circuitry on the transmission side even when the dynamic range of the effective datum is narrowed.

SUMMARY OF THE INVENTION i It is an object of the present invention to f provide an image encoding/transmitting apparatus and a I method; thereof using the DPCM system having a high encoding efficiency in which the quantization error is minimized by use of the quantization characteristic corresponding to the threshold value.

According to one aspect of the invention there is provided an image encoding/transmitting apparatus using a differential pulse modulation system in a datum C tI 1 I compressing/transmitting apparatus utilizing a Sdiffserential pulse modulation system including a transmission circuit for effecting a datum compression and 4 transmission by achieving a differential pulse modulation on a digital input signal and a reception circuit corresponding to the transmission circuit wherein: said transmission circuit includes an estimating circuit for calculating an estimation signal to estimate the digital input signal; 25 a movement detection circuit for outputting a differential signal depending on an estimation error signal being a difference between the input signal and the -9- -i -L 1 estimation signal and a threshold value for smoothing an amount of a transmission data; a quantizing circuit for quantizing the differential signal; a transmission data buffer circuit for temporarily storing the quantized transmission signal; a threshold generating circuit for generating o and controlling the threshold value; and 0 0 o0o a local decoding circuit for locally decoding 0 00 o0 0 a0 the quantized signal to calculate the estimation signal, 00 0 °T said reception circuit includes: 0 :it 1. a receiving data buffer circuit for temporarily storing a received signal; a local decoding circuit for decoding the 000 °0 15 received signal; and 0 00 4 an adder for calculating a regenerated signal C0 from the decoded signal and the estimation signal, said quantizing circuit includes: e an adaption quantization circuit having a 0t plurality of quantization characteristics and a characteristic selecting circuit for selecting said quantizing characteristic depending on the threshold value, and said local decoding circuits of said 10 L. ,i L o oo 00 0 transmission circuit and said reception circuit each includes: an adaption local decoding circuit having a plurality of decoding characteristics corresponding to the quantizing circuit and a characteristic selecting circuit for selecting said decoding characteristic depending on the threshold value.

According to a further aspect of the invention 10 tLere is provided an image encoding/transmitting apparatus using a differential pulse code modulation system in a datum compressing/transmitting apparatus utilizing a differential pulse code modulation system including a transmission circuit for effecting a datum compression and transmission by achieving a differential pulse code modulation on a digital input signal and a reception circuit corresponding to the transmission circuit wherein: said transmission circuit includes an estimating circuit for calculating an estimation signal to estimate the digital input signal; a quantizing circuit for quantizing the differential signal; an adaptation local decoding circuit having a plurality of decoding characteristics corresponding to the quantizing circuit; a threshold generating circuit for generating and controlling the threshold value; and a characteristic selecting circuit for selecting said decoding characteristic depending on the threshold value.

I: Ii

'I

11 an adaption local decoding circuit having a plurality of decoding characteristics corresponding td the quantizing circuit and /3 4 I BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention can be more clearly ascertained, an example of a preferred embodiment will now be described with reference to the accompanying drawings, w.herein: FIG. 1 is a block diagram showing the configuration on the transmission side of Ahe prior art image encoding/transmitting apparatus utilizing the DPCM oooo0 system; 10 FIG. 2A is a block diagram illustrating a detailed configuration of the movement detecting circuit S of FIG.1, FIG. 2B is a block diagram illustrating a detailed configuration of the variable-length encode circuit 4, FIG. 2C is a schematic diagram illustrating an 15 example of the multiplexing of the circuit of FIG. 1; 0000 FIG. 3A is a block configuration diagram depicting the reception side of the prior art image encoding/transmitting apparatus, FIG. 3B is a block diagram showing the details of the variable-length decode circuit of FIG. 3A.

FIG. 4A is a block configuration circuit illustrating the transmission circuit section of an embodiment of the image encoding/transmitting apparatus using the DPCM system according to the present invention, FIG. 4B is a block circuit showing in detail the threshold value generating circuit 9 of FIG. 4A, FIG. 4C is a 12 Z1 00 0 00 0 00 00 0 00 0 0 0 0 0 0 0 0 characteristic graph depicting a conversion example; FIG. 5A is a block configuration diagram showing the details of the adaptation quantization circuit of FIG.

4A, FIG. 5B is a block configuration diagram illustrating the details of the adaptation local decoding circuit of FIG. 4A, FIG. 5C is a block circuit diagram showing in detail the characteristic selecting circuit 28 of FIG. FIG. 5D is a block circuit diagram illustrating in detail the characteristic selecting circuit 29 of FIG. o3pg FIG. 6 is a block configuration diagram 0 0o00 illustrating the circuit section on the reception side in 00 the transmission apparatus of the embodiment of FIG. 4; 0 o000 FIGS. 7(a) 7(b) are characteristic diagrams 0000 o. showing examples of the adaptive quantization and encoding characteristics according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 000 o" The datum compressing/transmitting apparatus 00 o o utilizing the differential pulse modulation system 0,0° according to the embodiment includes a transmission 0 0 circu.t section for effecting the data compression and transmission on the digital input signal by use of the Sdifferential pulse modulation and a reception circuit section associated with the transmission circuit section.

FIG. 4A shows the block construction diagram of the transmission circuit section of the embodiment.

In the embodiment, the quantization circuit comprises an adaptive quantization circuit 3 having a plurality of quantization characteristics. The adaptive quantization circuit 3 selects a characteristic depending 0 0 c 13 on the threshold value T, conducts an adaptive quantization on the differential signal S 4 and outputs the adapted quantization signal S The adaptive local decoding circuit 6 is disposed corresponding to the adaptive quantization circuit 6, decodes the adapted quantization signal Sg i and outputs the regenerated differential signal S 7 Incidentally, the same reference numerals are assigned to o*oo the same components as those of the prior art example and o 10 the description thereof will be omitted.

2 °d FIG. 5A is a block diagram for explaining the oo ooo adaptive quantization circuit 3 in details. The character r.ao selecting circuit 28 selects a quantization characteristic depending on the threshold value T and then quantizes the differential signal S 4 a o 01 FIG. 5B is a block diagram for explaining the adaptation local decoding circuit 6 in details. The "O character selecting circuit 29 selects a decoding 00 characteristic depending on the threshold value T and then 0 V20 decodes the quantization signal S5 furthermore, the 0 0 obtained signal passes the zero allocation circuit 0 00 2 g 14 so as to be subjected to the zero allocation depending on the movement detection signal S 3 Next, the flow of the signal will be described. As shown in FIG. 4A, assuming the digitalized input signal such as an image signal to be Si, the estimated signal calculated by the estimating circuit 8 (to be described later) to be S9, the estimation error signal to be S 2 0 0 °oS the differential signal to be S 4 the regenerated 0000 oa.

0oo differential signal to be S and the regenerated input 0 signal to be Sp, these exists the following relationships 0.00 among the respective signal values.

S

2 S 1 9

S

4

S

2 d oec O0 0 0 oo o

S

7 4 Q S' S A S 8 00 0 where, d is the non-effective error'in the movement detection circuit, Q stands for the quantization error, 0 A indicates the estimation coefficient, and Z denotes a delay of the time t.

The estimating circuit 8 delays the regenerated input signal S8 by a period of time t beforehand set, multiplies the obtained signal by the coefficient A, and outputs the estimation signal S9. Like FIG. 2, in the movement detecting circuit 2, assuming the absolute value of the estimated error signal S2 calculated by the absolute value circuit 10 to be IS21 15 1

FY

U

I~'

and the threshold value to be T, the value of the movement detection signal V calculated by the comparing circuit 11 is determined as follows.

If Is21 T, then V 0 (invalid) else V 1 (valid).

Furthermore, if the predetermined amount of movement oo...oS is not detected (within the invalid data range), the zero 0 0 allocation circuit 12 allocates to the estimated 00.0 0 error signal S 2 and hence the differential signal S 4 is 0 o 0 10 outputted as to the adaptive quantization circuit 3.

o00oo0 0 As shown in FIG. 5A, the differential signal S4 inputted to the adaptive quantization circuit 3 is converted into the quantization signal S 5 according to 0 00 o0 o the quantization characteristic specified by the 0 00 character selecting circuit 29 which changes over the 0o4 o a 9 characteristic depending on the threshold value T and the quantization signal S 5 is then outputted to the variable length encoding circuit 4.

oO A description will be here given of the quantization characteristic example in reference to FIG. 7 The dot-and-dash line indicates a characteristic example in the case of T 0, whereas the solid line denotes a characteristic example in the case of T 3.

As shown in this diagram, when the datum of the differential signal S 4 is in the invalid data range data the quantization is not accomplished, namely, the quantization is effected only for the datum 16 in the valid data range (data -T or +T data). As can be seen from FIG. 5A, the quantization characteristic selected by the character selecting circuit 28 is such that the quantization output on the differential signal within the invalid data range (within the specified range of the corresponding threshold value) becomes to be which improves the quantization accuracy.

o The characteristic selecting circuit 28, as shown no- o in detail in FIG. 5C, comprises a flip-flop 28a (FF) to 10 which the decoded quantization signal selected by the 04 characteristic selecting circuit 28 is delivered as an input signal and is reset to when the movement detect signal VD indicates the invalidness (V 0).

o o o .4 s The variable length encoding circuit 4 receives 0 only the quantization signal S 5 for which the movement O' detection signal S 3 is valid (V 1) and effects the run length encoding on the movement detection signal S 3 For the quantization signal S 5 a code with a short code length is assigned to the value in the neighborhood of 0 for which the generation frequency is high, and the resultant code is transmitted to the transmission data buffer circuit 5. The data accumulated in the transmission data buffer circuit 5 is sent as the encoded signal S 6 to the transmission path.

In addition, as shown in FIG. 4A, the quantization signal S 5 is also delivered to the adaptation quantization circuit 6.

-17 -4

M

7'r 1 lu.n.r .a ;_u 0400 0401 00 04 0 040004 009 0000 Moreover, as shown in FIG. 4 B, the threshold value generator circuit 9 includes a conversion table 9a used to convert an input data into a threshold value based on the accumulated amount of the data. FIG. 4C shows the relationsilips between the accumulated data amount and the threshold value.

On the other hand, as shown in FIG. 5B, the adaptive decoding circuit 6 selects a decoding characteristic by means of the character selecting circuit 29 corresponding '10 to the quantization characteristic selected by the adaptation quantization circuit 3. As shown here in FIG. 5D, the characteristic selecting circuit comprises a memory device such as an ROM and the selection signal thereof is determining by use of the mapping in which the 15 threshold value T is used as an address input. Moreover, the allocation zero circuit 25 allocates the invalid datum which is then delivered as the regenerated differenti:al signal S 7 FIG. 7B shows a decoding characteristic example. In the adder 7, the regenerated 20 differential signal S7 is added to the estimation signal

S

9 to obtain the regenerated input signal S 8 t- the supplied to the estimating circuit 8.

The threshold generating circuit 9 monitors the data accumulation amount of the transmission data buffer circuit 5, generates an appropriate threshold value according to the data accumulation amount, and thereby achieves a smoothing operation on the data code amount.

09000 OlII 0 0 I 00 0 II 0000 0(0 00, 0 4 001 4 18- UULjJULL.LY LlAU UulL-JUL Oil \r±3U. J01.

5- FIG. 6 is the block construction diagram illustrating the reception circuit section of the data compressing/transmitting apparatus utilizing the differential pulse modulation system according to the present invention. The reception data buffer circuit 13 temporarily stores the encoded signal S 6 the variable length decoding circuit 14 decodes the encoded signal

S

6 the adaptive local decoding circuit 15 outputs the regenerated differential signal S 12 and the estimating .12 circuit 17 estimates the regenerated signal S i i" Here, the detailed constitution of the adaptive local decoder circuit 15 is the same as that of the circuit 6 of FIG. 4 A. In addition, the quantization characteristic and the decoding characteristic associated with the memory device such as an ROM are the same as those shown in FIGS. 5A The regenerated signal S is calculated by the adder 1 16 from the estimated signal S13 and the regenerated differentia l signal S12" Next, the flow of the signal in the reception circuit section will be described. The encoded signal S6 subjected to the variable length encoding in the transmission circuit section is received by the receiving data buffer circuit 13 and is then transmitted to the variable length decoding circuit 14.

Only when the movement detection signal SI 1 c decoded in the variable length decoding circuit 14 indicates the IIt, 19 i i 1- i .1 valid data range (V the quantization signal S 1 1 a and the threshold value S 1 b are fed to the local decoding circuit 15. When the decoded movement detection signal S 3 indicates the invalid data range (V "0" is delivered to the local decoding circuit Moreover, like the adaptive local decoding circuit 6 of the transmission circuit section, the adaptive local decoding circuit 15 selects a decoding characteristic depending- on the threshold value Sllb.

The quantization signal Sll a is then decoded into the S regenerated differential signal S 1 2 and is added by means of the adder to the estimated signal S 1 3 from the 04 estimating circuit 17, thereby the encoded signal S 6 from the transmission circuit section is regenerated as 15 a signal S 14 0s s In this embodiment, the same effect can be attained by reducing the threshold value for the transmission °ao through an operation to generate (update) the threshold value at an interval of an arbitrary period of time T a frame period).

20

Claims

1. An image encoding/transmitting apparatus using a differential pulse modulation system in a datum compressing/transmitting apparatus utilizing a differential pulse modulation system including a transmission circuit for effecting a datum compression and transmission by achieving a differential pulse modulation 0 0 on a digital input signal and a reception circuit 0 correspor~ding to the transmission circuit wherein: 0 said transmission circuit includes 0 0 an estimating circuit for calculating an 0000 estimation signal tc estimate the digital input signal; a movement detection circuit for outputting a differential signal depending on an estimation error signal being a difference between the input signal and the estimation signal and a threshold value for smoothing an 000 amount of a transmission data; a quantizing circuit for quantizing the 04 differential signal; 0 a transmission data buffer circuit for temporarily storing the quantized transmission signal; a threshold generating circuit for generating and controlling the threshold value; and a local decoding circuit for locally decoding the quantized signal to calculate the estimation signal, said. reception circuit includes: a receiving data buffer circuit f or tewporarily 21 storing a received signal; a local decoding circuit for decoding the received signal; and an adder for calculating a regenerated signal from the decoded signal and the estimation signal, n said quantizing circuit includes: i an adaption quantization circuit having a plurality of quantization characteristics and a Vi characteristic selecting circuit for selecting said quantizing characteristic depending on the threshold 4 value, and said local decoding circuits of said transmission circuit and said reception circuit each includes: t an adaption local decoding circuit having a plurality of decoding characteristics corresponding to the quantizing circuit and a characteristic selecting circuit for selecting said decoding characteristic depending on the threshold value.

2. An image encoding/transmitting apparatus according to claim 1 wherein said quantizing characteristic selected by said quantizing circuit is such that a quantization output of the differential signal within an invalid data range (within a specification of the corresponding threshold -ralue) is

3. An image encoding/transmitting apparatus using a differential pulse code modulation system in a datum 22 i. i: i L ;i 10 I I compressing/transmitting apparatus utilizing a differential pulse code modulation system including a transmissio. circuit for effecting a datum compression and transmission by achieving a differential pulse code modulation on a digital input signal and a reception circuit corresponding to the transmission circuit wherein: said transmission circuit includes an estimating circuit for calculating an estimation signal to estimate the digital input signal; a quantizing circuit for quantizing the 0 C 0.00 differential signal; 000o o0o°0 an adaptation local decoding circuit having a o~0o° plurality of decoding characteristics corresponding to the 00 0oooo0 00oooo quantizing circuit; a threshold generating circuit for generating and controlling the threshold value; and 0000 ooo0 oooo000 a characteristic selecting circuit for selecting 0 on 0 O 0 said decoding characteristic depending on the threshold o°°°oO value.

4. An image encoding/transmitting apparatus 0 0 according to claim 3 wherein said quantizing o characteristic selected by said quantizing circuit is such that a quantization output of the differential signal within an invalid data range (within a specification of the corresponding threshold value) is 23 4 "'6f An image encoding/transmitting apparatus as claimed in any one of claims 1 to 4, and substantially as herein described with reference to any one of the examples shown in Figures 4 to 7 of the accompanying drawings. DATED THIS 20TH DAY OF SEPTEMBER, 1989 MITSUBISHI DENKI KABUSHIKI KAISHA By Its Patent Attorneys i GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia 2 I 24 L I