AU606816B2 - Method for encoding/transmitting images - Google Patents

Description

L 1 -I i' -s I i j g

AUSTRALIA

PATENTS ACT 1952 Form COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE 606816 Short Title: Int. Cl: Application Number: Lodged: Complete Specification-Lodged: ;Accepted: Lapsed: Published: o 0 a P a 01~ 0 Priority: Related Art: This document contains the ainmndments made under Scction 49 and is corrcct for printing.

@0 I a 0a TO BE COMPLETED BY APPLICANT Name of Applicant: MITSUBISHI

KAISHA

DENKI KABUSHIKI S Address of Applicant: L' Actual Inventor: Address for Service: 2-3 MARUNOUCHI 2 CHOME

CHIYODA-KU

TOKYO 100

JAPAN

GRIFFITH KACK CO., 601 St. Kilda Road, Melbourne, Victoria 3004, Australia.

Complete Specification for the invention entitled: METHOD 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 guidance in completing this part DECLARED at Tokyo, Japan this 6 thdayof November, 1990 METHOD 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 o 10 Patent Application No. 73379/87, the contents of which are 0 0 incorporated herein by reference. There are also other S divisional applications of the noted parent application.

0" Description of the Prior Art As a result of the remarkable advance of the image processing technology in recent years, there have o 0°o been made various attempts to put, for example, the TV o°oi° conference system and the TV telephone system to the o o practical use by mutually and bidirectionally transmitting the image information. In such a technological field, the quantization technique has been used in which the image Goo 20 signals as the analog quantity are classified into a 8 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

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multidimensional signal space; thereby accomplishinq 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.

00 0 oo°" 84 00 00 0 o0 10 "On the Structure of Vector Quantizers" by A. Gersho 0 00 0 (IEEE TRANSACTION ON INFORMATION THEORY, Vol. IT28, No. 2, 0 O .oo March 1982, pp. 157 166) 0 "Speech Coding Based Upon Vector Quantization" by.

A. Buzo, A. H. Gray Jr., R. M. Gray and J. D. Markel 0001o 5 (IEEE TRANSACTION ON ACOUSTICS, SPEECH, AND SIGNAL o O 00 1 0 0 PROCESSING, Vol. ASSP28, No. 5, October 1980, pp. 562 0 4 574) 0 G C 0 0 o Moreover, the following U.S. Patents have been obtained by the assignee of the present invention.

U.S.P.N. 4,558,350 "VECTOR QUANTIZER", Murakami U.S.P.N. 4,560,977 "VECTOR QUANTIZER", Murakami et al.

4- 2 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 S2, a movement detecting circuit 2 for comparing a threshold value T with the estimated o 0 0 error signal S 2 to detect a movement or a change and for oa oo 2 o 0 .0 So 10 generating and outputting a movement or change detect 0. signal S 3 and a differential signal S a quantization o 0 circuit 3 for quantizing the movement or change detect ooo0 signal S 3 and the differential signal S 4 to output a quantization signal S5, a variable length encoder 4 for o 15 generating from the quantization signal S 5 an encoded o 'signal S 6 with a variable length and for outputting the 0s6, encoded signal S 6 a transmission data buffer circuit 0 0 for temporarily storing the encoded signal S6 and for outputting the encoded signal S 6 to the transmission side, 20 a local decoding circuit 6 for generating a reproduced 6 4 1 differential signal S 7 from the quantization signal S delivered from the quantization circuit 3 and outputting the reproduced or regenerated differential signal an adder 7 for achieving an addition on the reproduced differential signal S 7 and the estimation signal S 9 and for outputting a reproduced input signal S8, an estimating circuit 8 for outputting an estimation signal S 9 based on 'i 3 0 a O a 00 the reproduced input signal S. and a threshold generating circuit 9 for mohitoring the amount of the encoded signal S 6 accumulated in the tran smission data buffer circuit 5 and for generating an appropriatc threshold value T.

The movement detecting circuit 2 comprises, as showqn f.

in FIG. 2, an absolute value circuit 10 for, -calculating the absolute value Is 21 of the estimated error signal S~2' a comparing circuit 11 for effecting a comparison between he bsoute alu Is of the estimated error signal and the threshold value T and for outputting the movement 0 40 or change detect signal S 3 ,0 and a zero allocator 12 for allotting 0 and outputting 0 as the differential signal S4 when the mbvement or change is not detected as a 1,5 result of the comparison in the comparing circuit 11.

The movement detect signal S 3 is converted into a running 0~record R by use of the running length encode table 4a to generate serial data. In addition, only when the movement detect signal S 3is indicating the validness, the 0! '20 quantization signal S~ 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 80 8 80 0 00 88 0 8 00 -4 2 0000 o o o o o o0 00 00 0 0 0 00 o o 0 0 0 0 00oo 0 buffer circuit 13 for receiving and for temporarily storing the encoded signal S 6 delivered from the transmission data buffer circuit 5 on the transmission side, a variable length decoder 14 for decoding the encoded signal S 6 stored in the receiving data buffer 13 to output a reproduced quantization signal Sli, a local decoding circuit 15 for outputting a reproduced differential signal S 1 2 based on the reproduced quantization signal Sil, an adder circuit 16 for obtaining 010 the difference between the reproduced differential signal 0

S

1 2 and the reproduced estimation signal S13 and for o reproducing the input signal S 1 4 which corresponds to the 0 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 S 6 undergone the 0 multiplexing in the variable-length encode circuit 4 is received by the receive buffer circuit 13, the data is distributed to the respective decode tables of variable 20 codes under control of the multiplex separation control 0 0 circuit 14a. As a result of the decoding, the movement o 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 S11 (FIG. 3B).

000oooo o o oo 0 0 0 o 0 0 000 oo 0 0 001 0 000 00 0 0 0 5 r r 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, bnd the delay of the time t to be Z the following relationships are satisfied.

2 S S 9 S0 4

S

2 0 0 o o0

S

4 S 2 Q 0o 0 000 0 o S 7

S

4

S

ooo0 8 S7 +S9= S 1 Q d ooooo5=.

$9 A S Z t 0 0 9 8 T!L subtractor 1 calculates the estimated error signal S 2 representing the difference between the input signal S 1 and the estimated signal S9. whereas the movement 0 o0 detecting circuit 2 outputs the movement or change detection signal S 3 and the differential signal S 4 based on the estimated error signal S 2 calculated by the 20 subtractor 1.

0400 0 0 0. a A detailed description will be given of the operation 00 0 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 S2 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.

-6o o 00 00 0 I 00 0 109 The movement detection signal S 3 is output in conformity with the following conditions.

S

3 0 (invalid) IS 2

T

S3 1 (valid) IS21 T When the movement or change is not detected, namely, for

"S

3 zero allocator 12 outputs for the differential signal S 4 On the other hand, the quantization circuit 3 converts the inputted differential signal S 4 according to 10 an arbitrary characteristic. The variable encoding 0 circuit 4 receives the quantization signal S 5 only when 05 the movement detection signal S 3 is valid, namely, for t "S 3 1" and, for example, conducts a run-length encoding on the movement detection signal S3. For the quantization signal S, a code having a smaller code length is assigned to a value in the neighborhood of for which the S generation frequency is high and then the code is stored in the transmission data buffer circuit 5. The t transmission data buffer circuit 5 outputs the 20 accumulated datum as the encoded signal S 6 to a 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 (0 0 0 oQ 00 oa. 0 4 00 00 4 a 0 0 0

I

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',Sl. If the movement detection signal S 3 indicates the invalidness, 0000 o 0 0 the variable length decoder 14 outputs Next, the 00 00 &o od 1 local decoding circuit 15 decodes the reproduced o oo .0 0° quantization signal S 1 1 and outputs the reproduced 00.00 0o differential signal S 1 2 to the adder 16. The adder 16 0000 adds the reproduced differential signal S 12 to the reproduced estimation signal S 13 from the estimation 15 circuit 17 thereby to reproduce the input signal S 14 0 0 0 0o The operation to effect the data compression and C 0 0 transmission by use of the differential signal is 00 o referred to as the differential pulse code modulation (to be abbreviated as DPCM herebelow) system.

However, in the image encoding/transmitting apparatus 0o 0o using the DPCM system, the variable length encoding is achieved on the datun 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 neighborhood of "0" cannot be generated and hence the efficiency of the encoding is deteriorated; moreover, there has been a 8 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 It is an object of the present invention to provide an image encoding/transmitting apparatus and a method; thereof in. which a correction can be accomplished ooo oo0 a 0 in a case where a mismatching is detected for a block 0 0 o 0 selected by the movement compensation.

0 00 According to one aspect of the invention there 0 4 is provided an image encoding/transmitting method o 0 eo 0 comprising: a preprocessing step for generating blocks of pixels, each block containing a. plurality pixels in the 0 a I neighborhood of each other in an image of an image input 0 44 signal, for generating a vector signal for each said 0440 block, and for outputting said vector signal; a movement compensation processing step for 4«00 generating a plurality of reference blocks by use of a o frame memory storing an image of vector signals ahead in time by one frame with respect to a current vector signal, each said reference block including a block existing at a same position as a current input block, for respectively 9 1 calculating a reference vector signal, for achieving a distortion computation between the vector signal, and each said reference vector signal, for selecting a block having a minimum distortion, and for outputting a position information of the selected block; an encoding processing step for calculating a differential vector signal by executing a subtraction between the input block and the selected block, for encoding only the position information of the selected o ()10 block in a case where an average value and a variance of QO 00 0 the differential vector signal each are within a range of 0 00 o D a threshold value and for calculating an encoded signal, o and for sending the encodAsignal to a transmission data aoo buffer; and for encoding the position information of the selected block and the differential vector signal in a Va Ue case where the averageAand the variance of the 0 0 0 differential vector signal -is beyond the range of the 0 threshold and for sending the encoded signals to the 0 0o o transmission data buffer; a threshold value control step for controlling oo- the threshold value depending on an amount of the encoded o0 o °0 o signals temporarily stored in the transmission data "uffer, for decreasing the threshold value when the encoded signal amount is great, and for increasing the threshold value when the encoded signal amount is small; and 10

I

I an auxiliary threshold control step for reducing the threshold value when a distance between the current input block and the selected block calculated by the movement compensation step is great.

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 wherein: Goon 0°o013 FIG. 1 is a block diagram showing the 00 00 oo 0 configuration on the transmission side of the prior art o 00 00 0 image encoding/transmitting apparatus utilizing the DPCM 000000 system; o 000 FIG. 2A is a block diagram illustrating a detailed configuration of the movement detecting circuit o0 of FIG. 1, FIG. 2B is a block diagram illustrating a 0 0 0 000 0 0 00 detailed configuration of the variable-length encode 0 o 0 0 00 circuit 4, FIG. 2C is a schematic diagram illustrating an o 0 example of the multiplexing of the circuit of FIG. 1; FIG. 3A is a block configuration diagram depicting the reception side of the prior art image od 0 o o o encoding/transmitting apparatus, FIG. 3B is a block diagram showing the details of the variable-length decode circuit of FIG. 3A; FIG. 4 is a block configuration diagram depicting a general example as a basis of embodiment of the image encoding/transmitting apparatus according to the present invention; 11 time by one frame with respect to a current vector signal, each said reference block including a block existing at a same position as a current input block, for respectively /2 II- I i FIG. 5A is a block construction diagram depicting the overall constitution of the image encoding/transmitting apparatus of the embodiment according to the present invention, FIG. 5B is a detailed block diagram showing the tnreshold value control circuit, FIG. 5C is a schematic diagram illustrating positions of pixels in a reference block, FIG. 5D is a table depicting an example of the map data of the reference block; FIG. 6 is an explanatory diagram conceptually illustrating the disadvantage of the general transmitting 0 apparatus of FIG. 4.

a 0 0 0 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS o 9 0 Prior to the description of the embodiment of 0 *0 the present invention, description will be given of the 0.00 technology adopted as the basis of the embodiment.

I

FIG. 4 shows an image encoding/transmitting apparatus to which the frame-to-frame encoding method utilizing the vectorizing method, namely, the image encoding/transmitting method as the basis of '-he embodiment including the movement compensation is applied.

As shown in this diagram, the image encoding/transmitting apparatus primarily includes a preprocessing 12 the threshold value when a distance between the current input block and the selected block calculated by the movement compensation step is great.

A a section 41, a movement compensation section 42, and a vector quantization section 43.

The preprocessing section 41 generates from the image input signal 400 blocks each containing k pixels existing in the neighborhood of each other in the image to form a k-dimensional vector signal 401 for each block, whereas the frame memory 44 is provided to store the imagi signal formed in a block in advance in time by a frame of the current image signal.

00 o oi0 The movement compensation section 42 includes a 0 0 0 reference block generating section 42a for generating as S a reference blocks a plurality of blocks each including 0 o the current vector signal 401, a block corresponding to the current vector signal 401, and a block stored in the 15 frame memory corresponding to the same position in the 0 4 C image and for calculating the block position information o o i' 402a and the vector signal 4 0 2 a2 and a distortion 0 a2 o computation section 42b for calculating the distortion (for example, the Euclid distortion, the absolute 20 distortion, etc.) between the current vector signal 401 S0 and the reference vector signal 4 0 2 a2 and for selecting a block having the minimum distortion from the reference blocks.

The subtractor 45 achieves a subtraction between the current vector signal 401 and the vector signal 4 0 2 b2 of the block selected by the movement compensation section S13

AI

\r 42 -d sends the differential vector signal 405 to the vector quantizing/encoding section 43.

The vector quantizing/encoding section 43 comprises an arithmetic section 43a for computing the average value m and the variance a from the differential vector signal 405, a validness/invalidness judgment circuit 43b for judging the validness or invalidness of the selected block based on the average value m, the variance a, and Oe the threshold values T 1 and T 2 controlling the 0 0 0 1 2 00 0 o0 10 compression amount of the information volume, a 0 0 o normalizing section 43c for normalizing the differential 00 0 vector signal 405, a code block 43d for storing patterns 0 4 of a plurality of the normalized image vector signals, and a vector quantizing section 43e for selecting a pattern from the code book 43c which is the same as or similar to the normalized differential vector signal 403c t normalized by the normalizing section 43c and for encoding the selected pattern number, the average m, and the variance a.

Next, the flow of the signal will be described.

First, the image input signal 400 is subjected to the block generation in the preprocessing section 41 and is thereby converted into the vector signal 401.

Thereafter, the reference blocks are generated in the movement compensation section. From the reference blocks, a block having the smallest distortion with re'-ect to the vector signal 401 is selected, and then 14

C-

1 i a, ti n- i-~ 0000 0 1 oo oo o o 00 00 0 0 o oo 000f0 000 o a oo o 0 0 0 ooeo 0000 00 0 o 0000 0 0 00 the selection block position information 402b1 and the selection vector signal 4 0 2 b2 are supplied to the subtractor In the subtractor 45, a subtraction is then accomplished between the vector signal 401 and the selection vector signal 402b2, and the differential vector signal 405 is delivered to the vector quantizing/encoding section 43.

In'the vector quantizing/encoding section 43, the °10 differential vector signal 405 is processed by the arithmetic section 4 3a to calculate the average value m and the variance a of the differential vector signal 405.

S Thereafter, the validness/invalidness judgment circuit 43b judges the validness or invalidness as represented by the following expressions by use of the threshold S value T for the average value and the-threshold value S T 2 for the variance.

m T 1 and o T Invalid m T or ao T Valid If the judgment results in the invalidness, the If the judgment results in the invalidness, the

O

00 0 U 0 current block is assumed to be identical with the 0 0 selected block and hence only the selection block position information 4 0 2 b1 is encoded and the resultant signal is temporarily stored in the transmission data buffer 46.

On the other hand, if the judgment results in the validness, the differential vector signal 405 is 15 4 71 'It r~ -i 1, normalized as the datum to be transmitted in the normalizing section 43c according to the following formula.

Yi m)/o 0.

0~' o o 00 000 0 oO 00 o 0 0 0 0 0 0 66 0 (where, i 1, 2, k) i-th element of the normalized vector i-th element of the differential vector Thereafter, the normalized differential vector S signal 403c is quantized and encoded in the vector quantizing section 43e as follows.

SFirst, a pattern which is most similar to the o3, normalized differential vector signal 403c is selected from the code book 43d. As the transmission information, the pattern number, the selection position information 4 0 2 b1, the average value m, and the variance a are S encoded and the resultant signals are temporarily stored in the transmission data buffer 46.

The image encoded signals temporarily stored in the transmission data buffer 46 are transmitted in the o0 frame-by-frame fashion.

On the other hand, the threshold values T 1

T

2 are controlled according to the amount of the image encoded signals stored in the transmission data buffer 46 associated with the previous frame such that the threshold values are set to great values for the great amount of the signals and are set to small values for the small 16

J,

il amount of the signals, thereby controlling the degree of the compression for each frame.

According to the image encoding/transmitting apparatus shown in FIG. A as described above, as a result of the movement compensation processing step, when the differential data between the input blodk and the selected block is within the threshold value range in the encoding processing step, the selected block is a directly reproduced as an image.

In this operation, if the selected block or the input block has a strong contour line even when the differential datum is within the threshold value range, there has been a problem that the contour line is shifted in the image as shown in FIG. 6. This phenomenon is emphasized in a case where the distance between the input block and the selected block is great.

Such a problem takes place because the mismatching in the movement compensation cannot be fully compensated.

Next, the embodiment implemented to solve ?0 the problem above will be concretely described.

FIG. 5A is a block configuration diagram showing the image encoding/transmitting apparatus to which the fourth embodiment is applied. In FIG. 5A, the same reference numerals are assigned to the same components as those of FIG. 4 and the description thereof will be omitted.

17 i i~i SI4 The characteristic item of the embodiment is a threshold control section 47 which includes a threshold generating circuit 47a controlled'by the amount of the encoded signals temporarily stored in the transmission data buffer 46 for effecting a threshold control such that the threshold value is increased when the amount of the encoded signals is great and the threshold value is decreased when the amount of the encoded signals is small and a distance calculating circuit 47b for calculating 0 00 the distance between the current input block and the 0 "selection block selected by the movement compensation section 42. The threshold generating circuit 47a includes, as shown in FIG. 5 B, a threshold generating section 471 and an auxiliary threshold control circuit 472 for decreasing the threshold values based on the calculated distance when the distance is great.

0 0 Next, the flow of the signal will be described.

The image input signal 400 is first subjected to the o0°° block generation in the preprocessing section 41 so as to °0 be converted into the vector signal 401.

In the movement compensation section 42, reference blocks are generated and a block having the smallest distortion with respect to the vector signal 401 is selected from the reference blocks. Thereafter, the selection block position information 4 0 2 b and the selection vector signal 4 0 2 b2 are supplied to the subtractor 45, while the selection block position -18 i i .I_ information 402 bl is sent to the distance calculating section 47b of the threshold control section 47.

The details of the operation will be described with reference to FIGS. 5 C .5 D. FIG. 5'C is a schematic diagram showing positions of pixels of a reference block, namely, pixels exist as indicated by small circles 1 13 From the distortion operation section 42b sends to the distance calculating section 47b the number (one of the numbers 1 13 in this case) of the block having the smallest distortion among the reference Sblocks. The distance calculating section 47b converts the number into a distance by use of a map data beforehand set as shown in FIG. 5 D and then transmits the distance to the threshold generator circuit 47a.

The threshold values T 1

T

2 are controlled according to the amount of the image enicoded signals stored in the transmission data buffer 46 associated with the previous frame such that the threshold values are set to great values for a large amount of the signals and are set to small values for a small amount of the signals; however, when the distance of the output 4 0 7 b from the distance calculating circuit 47b exceeds a fixed value, the auxiliary control is conducted to reduce the threshold values.

The subtractor 45 effects a subtraction between the vector signal 401 and the selection vector signal 402 b2, and then the differential vector signal 405 is delivered to the vector quantizing/encoding section 43.

19 I Thereafter, in the vector quantizing/encoding section 43, the differential vector signal 405 is processed in the arithmetic section 43a to calculate the average value m and the variance a of the differential vector signal 405. In the validness/invalidness judgment circuit 43b, the validness or invalidness is judged by use of the threshold value T 1 for the average and the threshold value T 2 for the variance according to the following expressions.

m T 1 and a T 2 Invalid o m T or> T or Valid *i In this operation, if there exists a great distance o..o between the current block and the selected block, the control is effected to reduce the threshold values by the threshold control section 47 as described above; consequently, when the distance between the current block 4 and the selected block is large, the possibility of the invalidness is lowered.

If the judgment results in the invalidness, the current block is assumed to be identical with the selected block and only the selection block position information 402b is encoded and the resultant signal is I temporarily stored in the transmission data buffer 46.

On the other hand, if the judgment results in the validness, the differential vector signal 405 is normalized as the datum to be transmitted in the normalizing section 43c according to the following formula.

20 S t yi (xi m)/a (where, i l, 2, k).

fYi: i-th element of the normalized vector x i i-th element of the differential vector Thereafter, the normalized differential vector signal 403c is quantized and encoded in the vector quantizing section 43e as follows.

First, a pattern most similar to the normalized odifferential vector signal 403c is selected from the code book 3d. As the transmission information, the pattern number, the -selection position information 4 0 2 bl, the oo0 average value m, and the variance a are encoded and the resultant signals are -temporarily stored in the transmission data buffer 46.

1" 5s The image encoded signals temporarily stored in the o 4° transmission data buffer 46 are transmitted in the 0 0 o frame-by-frame fashion.

According to the embodiment, for a selected block with a great distance for which the possibility of the o, 7,0 mismatching is high as a result of the movement compensation, the control is effected to lower the Sthreshold values and to conduct the encoding and transmission of the differential vector signal between the input block signal and the selected block signal, which leads to an effect that the occurrence of the shift of the contour of the block is minimized.

21 encoding is deteriorated; moreover, there has been a 8 9 i ;z In addition, according to the embodiment, although a description has been given of an example of the auxiliary threshold control in which the threshold values are set to the lower values as the distance between the distance selection block and the input block is increased, the same effect can be attained by conducting a s'tepwise control in which several kinds of threshold values are provided depending on the distances.

0 0 0 0 0 0~ 00 0 000B 400.Q A AQ Ow 0 A 00 0 0 A 0.rst 22

Claims (1)

1. 3. A method as claimed in either of claims 1 or 2 and substantially as herein described with reference to any one of the examples shown in Figures 4 to 6 of the accompanying drawings. DATED THIS 20th DAY OF September 1989 MITSUBISHI DENKI KABUSHIKI KAISHA By Its Patent Attorneys GRIFFITH HACK CO Fellows Institute of Patent Attorneys of Australia ~I a 25