FR2633472A1 - Device for temporal sub-sampling and motion-compensated temporal interpolation in an interlaced image sequence, use of such a device in the coding and decoding devices of a high-definition television picture transmission system, and coding and decoding devices for such a system - Google Patents

Abstract

Device for temporal sub-sampling and temporal interpolation in an interlaced image sequence including a spatial prefiltering circuit, a spatial sub-sampling circuit, a temporal sub-sampling circuit, and a motion-estimation stage. This device can be used in particular in an image transmission system comprising three processing branches 701, 702, 803 in parallel, the said motion-estimation stage 860, a circuit 870 for making a decision based on the original picture, on the pictures processed by the branches, and on a displacement vector selected by the said stage, and a circuit 740 for routing the outputs from the branches according to the output signal from the decision-making circuit. Application: high-definition television picture receivers.

Description

DESCRIPTION OF THE INVENTION Time-delayed subsampling and motion-compensated temporal interpolation device in an interlaced image sequence, use of such a device in the encoding and decoding devices of an image transmission system. high-definition television, and coding and decoding devices for such a system
The present invention relates to a device for temporal subsampling and temporal interpolation in a sequence of interlaced images divided into blocks of
I x J points (I, J positive integers) whose luminosity is expressed numerically. The invention also relates to the use of such a device in the coding and decoding parts of a high-definition television image transmission system, as well as coding and decoding devices for such a system.

The invention is indeed applicable essentially in the field of high definition television. In a high definition television transmission system according to the MAC standard, it reduces the bandwidth of television signals for transmission. It will be recalled here that said transmission is provided by means of an analog channel which conveys the data having undergone compression and that this analog channel is associated with an auxiliary channel known as digital assistance channel enabling the transmission of additional information relating to to the movements of the images transmitted by the analog channel.
The problem is in fact to maintain, despite the compression of information necessary to adapt the amount of this information to the limited bandwidth of the transmission channel the best possible spatial resolution, regardless of the speed of movement of the content of the images to transmit.

 An object of the invention is thus to propose a device allowing temporal subsampling and compensated temporal interpolation in motion without the appearance of the blur and the saccades traditionally observed, due to the temporal interpolation, in the presence of motion .

 To this end, the invention relates to a device for temporal subsampling and temporal interpolation, characterized in that it comprises a spatial prefiltering circuit of the interlaced image sequence, intended to deliver a sequence of sequential images while limiting the bandwidth, a spatial subsampling circuit for reducing in each of said sequential images the number of samples, a temporal subsampling circuit, for halving the temporal rhythm of said series of sequential images , and a transmit motion compensation stage, said stage itself comprising three image memories, provided in series for storing, respectively, on the one hand the images of rank 2k and 2k + 2 to be transmitted and on the other hand share images of rank 2k + 1 to eliminate before transmission, and a motion estimation device according to a method such as that of block correlation.

 Another object of the invention is to propose, in a high-definition television image transmission system, a reception stage comprising a motion compensation device which appropriately uses the motion estimation carried out at the same time. program.

 For this purpose, such a reception stage comprises in its decoding part a signal processing branch composed of a motion compensation device itself comprising a spatial post-filtering circuit intended to perform a spatial interpolation in the sequential images transmitted by the analog channel, then, in parallel on this circuit, a delay circuit and a motion compensation stage, and, to receive alternately the output of said delay circuit and that of said motion compensation stage, a switch intended to deliver a sequence sequential images then provided to a format converting circuit for transforming this sequence into a sequence of interlaced images, then to a multiplexer delivering the interlaced image sequence ready to be viewed, said motion compensation stage comprising itself, on the one hand, two image memories in series for storing the success images transmitted by the analog channel and postfiltered and secondly an adder to perform the half-sum of said transmitted images.

 Another object of the invention is to apply the principle and implementation thus described in a system for transmitting high definition television images to several parallel processing branches according to the greater or lesser importance of the movement in the original images.

The coding device according to the invention is, for this purpose, characterized in that it comprises itself
(a) three first, second and third processing branches, located in parallel, each receiving the original high definition image and each providing a spatio-temporal subsampling rate of 4
(b) after converting the original image to a non-interlaced format, said motion estimation stage
(c) a decision-making circuit starting on the one hand from the original image and the images processed by said three branches and on the other hand from the displacement vector selected by said motion estimation stage, and also sent to a so-called digital assistance channel associated with said analog channel
(d) a switching circuit of the outputs of said branches according to the output signal of said decision-making circuit, said decision signal being also sent to the digital assistance channel associated with said analog channel in that said branches comprise same
(i) the first, a first spatial filter followed by a spatial subsampler and a first format conversion circuit
(ii) the second, a 1/2 rhythm time sampler, a second spatial filter, a spatial subsampler, and a second format conversion circuit
(iii) the third, a time filter, a 1/4 time-rate sampler, a third spatial filter, a spatial sub-sampler, and a third format converting circuit, and in that said processed images received by said time-lapse circuit; decision making are those respectively available at the output of said spatial filters.

 Another object of the invention is also to provide on reception a decoding device appropriately using the processing performed on transmission in the coding device according to the invention.

Such a decoding device is then remarkable in that it comprises
(a) three first, second and third processing branches, located in parallel and each receiving the image transmitted to decompress these transmitted images and restore them in high definition format
(b) a switching circuit of the outputs of said branches according to the output signal of the decision-making circuit1 said signal having been transmitted via said digital assistance channel in that said branches themselves comprise
(i) the first, a dynamic interpolation circuit, a multiplexer, and a spatial post-filtering circuit
(ii) the second, a dynamic interpolation circuit, - a spatial post-filtering circuit, an image recovery circuit from said selected transmission vector on transmission, and a switch for conversion to an interlaced format, said displacement vector having been transmitted via said digital assistance channel
(iii) the third, a dynamic interpolation circuit, a multiplexer, a time filtering circuit, a spatial filtering circuit, and an interlaced conversion circuit.

Furthermore, in an improved embodiment of the invention, the coding device is characterized in that
(a) said motion estimation stage also comprises, in parallel with the first set of said first three image memories and said first motion estimation device, a second temporal subsampling circuit for dividing by two the temporal rhythm of the sequence of sequential images supplied to said first set and followed by a second set comprising a second set of three second image memories and a second motion estimation device according to a method such as that of correlation by block, each motion estimation device delivering a distinct motion vector supplied on the one hand to the decision-making circuit and on the other hand to the digital assistance channel
(b) the temporal filter of said third processing branch is a motion-compensated temporal filter on a horizon equal to the period of the images of the second branch, also receiving the displacement vector delivered by said first motion estimation device.

The corresponding decoding device is then remarkable in that it comprises
(a) three first, second and third parallel processing branches each receiving the transmitted image
(b) a circuit for switching the outputs of said branches according to the output signal of the decision-making circuit, said signal having been transmitted via the digital assistance channel in that said branches themselves comprise
(i) the first, a dynamic interpolation circuit, a multiplexer, and a spatial post-filtering circuit
(ii) the second, a dynamic interpolation circuit, a spatial post-filtering circuit, an image reconstruction circuit from said displacement vector selected for transmission by said first displacement estimation device and transmitted by the intermediate of the digital assistance channel, and a switch for conversion to interlaced format
(iii) the third, a dynamic interpolation circuit, a spatial postfiltering circuit, an image reconstruction circuit from said displacement vector selected on transmission by said second displacement estimation device and transmitted by the intermediate of the digital assistance channel, a multiplexer, and an image reconstruction circuit from half of the displacement vector selected on transmission by said second displacement estimation device the dynamic interpolation circuit of the second branch including a multiplexer which also receives the output of the image recovery circuit of the third branch, and each processing branch comprising a selective disconnect switch occupying the same open or closed position as the corresponding switch of the processing branches of the coding device when such a switch is provided in the trailing branches itement of the coding device.

The features and advantages of the invention will now appear in greater detail in the description which follows and in the accompanying drawings, given by way of non-limiting examples and in which:
FIGS. 1a and 1b respectively show the coding side, on the transmitting side, and decoding, on the receiving side, of a motion estimation and compensation device of known structure, in the case of a picture transmission system, television
FIGS. 2 and 4 show, respectively in the stringing part, on the transmitting side, and decoding, on the receiving side, an embodiment of a device according to the invention, in the case of a system for transmitting high-level television images. definition
FIG. 3a shows in more detail an exemplary motion estimation stage in the device of FIG. 2, FIGS. 3b and 3d explain the contents of the estimation circuits of the stage of FIG. 3a, and FIG. 3c shows an exemplary embodiment of the cells composing these estimation circuits
FIGS. 5 and 6 show alternative embodiments incorporating the devices of FIGS. 2 and 4 respectively
FIG. 7 shows an exemplary embodiment, in a system for transmitting high definition television images, of a coding device according to the invention.
FIGS. 8a to 8c represent the three processing branches of the device of FIG. 7, and FIGS. 9a to 9c show the corresponding image formats at the output of said branches.
FIG. 10 shows the decision-making circuit of the device of FIG. 7
FIG. 11 shows the decoding device associated with the coding device of FIG. 7 in the transmission system described.
FIG. 12 shows an improved variant embodiment of the coding device according to the invention
FIGS. 13a to 13c show in detail the three processing branches of the device of FIG. 12, and FIG. 14 the temporal filter of the third of these processing branches.
FIGS. 15 and 16 show in greater detail the motion estimation circuit and the decision circuit of the coding device of FIG. 12.
FIG. 17 shows the modified decoding device associated with the coding device variant of FIG. 12.

 The device represents in FIG. T in the case of the application to a high-definition television image transmission system comprises, in known manner, a transmission coding part (FIG. 1a) and a decoding part at the reception (FIG. 1b), which cooperate to detect and estimate the movement within the images to be transmitted and to adapt the processing of the image data to the greater or lesser importance of this movement. The images are captured here by a high-definition television camera (not shown) that analyzes the scene using an interlaced scan at 1250 lines and at a rate of 50 frames per second. Of course, the camera provides, after stamping of the signals R, V, B, three types of signals: the luminance signal Y and the two color difference signals U and V (or luminance signal). Subsequently, the description relates for example to the luminance signal but would apply equally well to the chrominance signal. It will therefore simply be specified that the output signal of the camera is sampled, and that the resulting samples are presented at the input of the coding part at a rate of 54 Megahertz. As the transmission channel, in the case of the MAC standard, only tolerates a rate of 13.5 Megahertz, a subsampling must be performed prior to said transmission.

 It will be specified that the images could, at the limit, be processed point by point but that it is simpler to cut them into N blocks of m x n points. Instead of scanning the points, the blocks are scanned, to which N representative points of said blocks correspond.

 The motion estimation mentioned above is provided as follows. The coding part shown in FIG. 1a consists of several branches in parallel, three for example, called here 1, 2 and 3. These branches receive the samples formed as indicated above and each comprise a pre-filtering circuit 101 and a circuit 102. Although the sampling structures are different from one branch to another, the subsampling rates are identical and here equal to 4. The filter templates are chosen so that the folding The outputs of the three subsampling circuits are sent to a switching circuit 103 which, according to the command received on a fourth input connection 105, assures the selection of one or the other. other of said outputs for subsequent transmission via the analog channel 10 of the transmission system.

 The control present on the connection 105 of the switching circuit, normally identical for all the points of a block, is determined by a decision circuit 106, according to a criterion generally related to a quantity measured from the image. input, or the energy of the gap between the pre-filtered images, from circuits 101 for example, and the original image. In the first case (a priori decision), the measured quantity can be for example the movement or the speed of the objects present in the image, and the decision is taken directly according to the value taken by this quantity. In the second case (a posteriori decision), the energy of the gap makes it possible to determine the branch that leads to the best image reconstruction using the transmitted samples, and therefore to make the referral accordingly.

The information delivered by the decision circuit 106 is sent to a digital assistance channel 20.

 Similarly, on reception, the corresponding decoding part, shown in FIG. 1b, firstly comprises a demultiplexing circuit 152 which, from the signal transmitted via the analog channel 10, provides three parallel post-filtering circuits 153. images with appropriate regular structures. Finally, a multiplexing circuit 154 receives the outputs of these post-filtering circuits and makes it possible, from the multiplexed signal, to generate an image that can be displayed on a screen 155 at a high resolution. The signal transmitted via the digital assistance channel 20 is supplied in parallel with the circuits 152 and 154.

 Subsampling structures, different from one branch to another as we have seen, can be purely spatial or allow, in addition, the elimination of a number of images in the temporal direction. We then have a proportionally higher number of samples to represent the spatial contents of the images, but in return, in case of movement, the temporal contents reflecting this movement are degraded.

 Two types of degradation can be more particularly observed on the reconstructed image: on the one hand the uniform motions are altered, the objects moving in fits and starts, on the other hand the resolution decreases suddenly as soon as a fixed object becomes mobile because of prefiltering and post-filtering. Both of these defects are visually very annoying, and the presence of an estimate and a motion compensation will remedy very significantly, eliminating jerks and maintaining the resolution for a range of speeds more large.

 The principle of motion compensation according to the invention is as follows. In the image sequence considered, one image out of two is first eliminated (that is to say the spatial information available at a given moment t). Thus, if the rate or temporal frequency is for example 1 / T where T corresponds to the time interval separating two successive images, the time interval after temporal sub-sampling will be 2T. By calling 2k-1, 2k, 2k + l, etc., the successive ranks of the image sequence.

Originally, this means that the images associated for example with the instants t + (2k-lfT, t + (2k + 1) T, etc. ..., or images here of odd rank, are eliminated.

 In parallel with this elimination of images, motion information is determined by a motion estimation method providing the allocation to each block of the images to be eliminated, here odd images, a displacement vector D such that the error of reconstruction of the block is minimal. This motion information is then used on reception to reconstruct the eliminated images before transmission, each block being reconstructed from the average of the information of two consecutive images in the direction of movement associated with the block.

This limits the defects due to the inaccuracy of the estimator, when the latter used until now the conventional solution of a reconstitution of an odd (or respectively even) frame only from the opposite parity frame previous, a solution that had the disadvantage of.déform the contours of solid objects.

 The principle thus defined is applicable for example in a high-definition television image transmission system and first of all in the coding part of the transmission stage of this system.

 In what follows, the spatiotemporal subsampling performed allows to obtain a sampling rate of 4 (2 in space, 2 in time). The motion estimator that will be used is based on the so-called block matching method, with a search range equal to: horizontal movement +3, vertical displacement t3). However, this choice is not imperative and must not limit the present invention, for the implementation of which an estimator of another type could absolutely be used. It will be specified here also that the branches 1, 2, 3 correspond to different speeds of movement on the images, the basic interval between images being, in the example described, 20, 40 and 80 milliseconds for the branches 1, 2 and 3 respectively. It is obviously in the branches 2 and 3 that there is interest, the movement being slower than in the case of the branch 1, to maintain the best resolution. The invention is therefore applicable to the branch 2, the extension to the branch 3 being described below.

 According to the example shown in FIG. 2, the device according to the invention firstly comprises, on transmission, for the branch referenced 2, a spatial pre-filtering circuit 201 receiving the input image, which is an interlaced image 50 Hz, 2: 1, 1250 lines, 54 M-samples (= 54.106) per second. This circuit 201 makes it possible to obtain a sequential image, while limiting its spatial bandwidth in order to avoid the folding due to temporal subsampling. The circuit 201 is followed, in series, by a temporal sampling circuit 202 which halves the temporal rhythm of the image (so we go to 25 images per second), then a subsampling circuit 203 space which makes it possible to reduce the number of samples in each image plane (for example by means of a sub-sampling staggered line which removes one point out of two) .In output of the circuit 201 is also provided, in parallel on the series connection of the circuits 202 and 203, a motion estimation stage 204 which will now be described in detail.

The motion estimation carried out by the stage 204 has the objective of determining for each block of the image of rank 2k + 1 which is eliminated a displacement vector D such that it is possible to obtain an approximation of said eliminated image to from the half-sum of the non-eliminated images that
Around it, in the present case from the half-sum of the images 2k and 2k + 2. This approximation is here expressed by the relation (1), given in the appendix as the other mathematical expressions which appear in the remainder of the description. In this relation, X denotes the current block of the 2k + 1 image, D the motion vector when the motion estimation has been applied to the 2k and 2k + 2 images, and the approximation of the intensity of the motion. point X of the current block of the image 2k + l.

 This objective can also be formulated by expressing that we want to associate with each block X of the image 2k + 1 a vector Dx such that the expression (3) is minimal (this expression, in which DFD comes from the corresponding English terms * Display Frame Difference ", is the approximation error attached to the current and equivalent block, for this block, as indicated by the expression (2), to the sum of the squares of the DFD approximation errors on all the points of the block) This known principle of examining the correlation between blocks (described in particular in the article by JR Jain and AK

Jain, "Displacement measurement and its application in interframe image coding", published in the journal IEEE Transactions on Communications, vol.COM-29, n012, December 1981, pages 1799 to 1808) is implemented, in the stage of motion estimation 204 here described, in two distinct but extremely similar steps.

 The motion estimation stage 204, represented by way of non-limiting example in FIG. 3a, comprises, for the execution of these two steps, a set 340 of two substantially identical estimation circuits 300 and 350, as well as Three of the series of image memories 341, 342 and 343. The estimation circuit 300, for example, comprises, as indicated in FIG. 3b, which gives a more detailed representation thereof, on the one hand nine identical cells 301 to 309. determining nine distortions (or estimation error as defined by expression (3) or expression (2)) relating to the nine following displacements Dx, Dy = (2,2), (2,0), (2) , -2), (0.2), (0.0), (0, -2), (-2.2), (-2.0), (-2, -2). These nine displacements are stored in a memory 345.Each of the cells 301 to 309 itself comprises identical elements, 311 to 331 for the first, 312 to 332 for the second, etc., and 319 to 339 for the ninth . These elements, considered for example for the first of the nine cells, comprise, first of all, as indicated in FIG. 3c showing this first cell an adder 311, which is intended to produce the half-sum of the images of rank 2k and 2k + 2, then a subtractor 321 and, in series with these two elements, a circuit 331 for squaring and summing. The adder 311 receives the output of the image memories 341 and 343, and the half-sum of the images 2k and 2k + 2 thus obtained is supplied to the input, for example positive of the subtractor 321 which receives on its opposite sign input. the output of the image memory 342 storing the image of rank 2k + 1. The output of the subtractor 321 is supplied to the circuit 331 for squaring and summing whose output constitutes the output of the cell 301.

 The nine respective outputs of the nine cells 301 to 309 are then supplied to a distortion comparison circuit 344 which compares the nine distortion values thus coming from the nine cells and determines the one which is the weakest. That of the nine displacements which leads to this minimum block distortion is called Dmin 1 and, after extraction of the memory 345, is sent to the second estimation circuit 350. This circuit 350, shown in FIG. 3d, repeats exactly the same operations. than the estimation circuit 300, but on nine other displacement values which are the following: Dx, Dy = Dmin1 + (1, 1), Dmin1 + (1.0), Dmin1 + (1, -1), Trin1 + (O, 1), Dmin + (O, O), Dmin I + (O, -1), Dmin + (-I, 1), Dlin + (-1, O), Dmin + (-t, -1) , and which are this time stored in a memory 395 receiving Dminl.

 The estimation circuit 350 comprises nine cells 351 to 359, which themselves comprise elements 361 to 381 for the first, 362 to 382 for the second, and so on, and which, as previously, are respectively, for each cell, an adder 361 to 369, a subtracter 371 to 379 and a squaring and summing circuit 381 to 389, provided in series. The outputs of the nine cells 351 to 359 are supplied to a distortion comparison circuit 394 which determines the lowest distortion and allows the selection of the corresponding Din2 displacement which minimizes the distortion for the current block X of the 2k + image. 1.

 The displacement thus selected is then sent to the digital assistance channel 20, while the output of the spatial subsampling circuit 203 is sent to the switching circuit 103. At the reception, the motion compensation device receives a signal. a sequence of images with a frame rate of 25 frames per second, these images being spatially undersampled, and renders an image sequence of 50 frames per second, 1250 lines, 2: 1 interlaced format, 1440 points per line, and 54.106 samples per second.

 This reception motion compensation device firstly comprises, as indicated in the embodiment of FIG. 4, a spatial post-filtering circuit 401 performing spatial interpolation to obtain a sequence of 25 frames per second, 1250 lines. per image, 1440 points per line. This circuit 401 is followed by a delay circuit 402 (the delay brought here is 20 milliseconds), then by a switch 403 which, from two image sequences each having a period of 40 milliseconds but shifted by 20 milliseconds, to reconstruct a sequence having a period of 20 milliseconds. At the output of the spatial post-filtering circuit 401 is also provided, in parallel with the series connection of the circuits 402 and 403, a motion compensated temporal interpolation stage 404.

 This stage 404 comprises on the one hand two series image memories 441 and 443, which store the two images successively transmitted by the analog channel 10 and post-filtered, that is to say the two images of rank 2k and 2k + 2 respectively, and on the other hand an adder 444 which is placed at the output of said memories and which makes it possible to carry out the half-sum of the transmitted images, according to the expression (4) where X represents the coordinates of the current point, Dmin2 the displacement assigned to the point and delivered by the digital assist channel 20, I (X-Dminn, 2k) and I (X + DXin2, 2k + 2) the intensity at the points associated with X on the transmitted images of rank 2k and 2k + 2 respectively (taking into account the estimated movement), and the intensity at point X of the eliminated image to be reconstructed. The output of the adder 444 constitutes the second input of the switch 403.

 The switch 403 thus receives, on the one hand, 1: 1 images which are the 2k, 2k + 2, etc. images transmitted every 40 milliseconds and, on the other hand, 1: 1 images which are the estimated I images. after the displacement transmitted by the channel 20 and whose period is also 40 milliseconds with an offset of 20 milliseconds compared to the transmitted images. This switch 403 therefore delivers a sequence of images having a rate of 20 milliseconds between images.

A format converting circuit 405 transforms this series of sequential images into a sequence of interlaced images, which is then supplied to a multiplexer 406. The output of this multiplexer 406 constitutes the interlaced high definition interleaved image sequence. displayed.

 Of course, the present invention is not limited to the embodiments described above and shown, from which variants or improvements can be provided without departing from the scope of the invention.

 The device structures previously described can indeed be modified in order to obtain a higher temporal subsampling rate, for example equal to 4. These modified structures are represented in FIG. 5, for the transmission part, and in the figure 6, for the reception part.

 The device for estimating movement on transmission then comprises, as indicated in FIG. 5, on the one hand the device of FIG. 2, here designated by reference 510, and on the other hand, at the input of FIG. this device 510, a time-holding filtering circuit consisting of a delay circuit 501 imposing a delay equal to T and an adder 502, and a circuit 503 of temporal subsampling. The hold time filtering circuit (501, 502) receives the 1250 line, 50 Hz, 2: 1 images and outputs a series of sequential images (1250 lines, 50 Hz, 1: 1) whose sampling provides at the input of the motion estimation device 510 a series of sequential images 1250 Q, 25 Hz, 1: 1. This sequence of images is processed by the device 510 which finally delivers a series of images. sequential images of period 80 milliseconds.

 Similarly, on reception, the movement compensation device comprises, as shown in FIG. 6, on the one hand the device of FIG. 4 designated here by the reference 520 and, on the other hand, at the output of this device 520 , an interpolation circuit composed of a delay circuit 521 imposing a delay equal to T and a switch 522. This interpolation circuit (521, 522) makes it possible to transform the series of sequential images 1250 lines, 25 Hz, 1440 points per line present at the output of the device 520 in a sequence of interlaced images having a time rate of 20 milliseconds, that is to say in a series of images 1250 lines, 50 Hz, 2: 1, 54 H-samples per second, which is provided to the multiplexer whose output is the sequence of interlaced high-definition images ready to be viewed.

 Furthermore, we have seen, above, that the invention concerned in the first place the branch 2, said branch 40 milliseconds, but it is also possible to apply the principle and implementation described in a transmission system including such a branch and constituted as follows. FIG. 7 shows a possible embodiment, in a high-definition television image transmission system, of an encoding device according to the present invention, FIG. 11 correspondingly showing the decoding device associated with this invention. encoding device in the transmission system (Figs. 12 and 17 will likewise show an improved variant of the encoding device and the corresponding decoding device).

 More precisely, the coding device of FIG. 7 firstly comprises, in parallel, three branches 701, 702, 703, here called 20 milliseconds branch, 40 millisecond branch, and 80 millisecond branch, respectively. These three branches 701 to 703 each receive, on their common input E, the high definition image, denoted 1250 lines, 50 Hz, 2: 1, 1440 points / line, and consisting of a sequence of interlaced images, constituted as indicated now.

 In the second branch 702, said branch 40 milliseconds, represented in FIG. 8b, the processing described above, carried out in the case of FIG. 2 by the circuits 201 to 203 and, in the present case of FIG. circuits 721, 722, 723. Specifically, a timing sampler 721 at the 1/2 rate delivers images 1250 Q., 25 Hz, 2: 1, 1440 p./line, which are then received by a spatial filter 722, then by a 1/2 rhythm spatial sub-sampler 723 and staggered line delivering images 1250 Q., 25 Hz, 2: 1, 720 p./line. The output images of the spatial sub-sampler 723, in accordance with the image format shown in FIG. 9b, are supplied to a circuit 725 for modifying the format (in English: shuffle circuit) which, in two frames and in 40 milliseconds ( therefore every 20 milliseconds) sends them in groups of lines (1, 5, 9, 13, etc ... then 3, 7, 11, 15, etc ...) to an input of a switching circuit 740 whose function is specified below. The images present at the input of the spatial subsampler 723 (connection S2) are also sent to a decision-making circuit 770 which is described below.

 In the third branch 703 called the 80 millisecond branch, represented in FIG. 8a, the interlaced image sequence is first converted into a series of non-interlaced images in a known type of time filter 731, which delivers images. 1250 2., 50Hz, 1: 1, 1440 p./line, which is followed by a time sampler 732 and then a spatial filter 733. This time sampler at a rate of 1/4 delivers images 1250 2., 12 , 5 Hz, 1: 1, 1440 p./line, which are then spatially filtered to avoid folding due to the subsampling performed. The output S3 of the filter 733 is sent on the one hand to another input of the circuit 770 of FIG. decision-making, and on the other hand to a spatial sub-sampler 734 of 1/2 rhythm and staggered line, which delivers images 1250 2., 12.5 Hz, 1: 1, 720p./line in accordance with the format of images shown in Figure 9a, to be associated with Figure 8a. The output images of the spatial sub-sampler 734 are then supplied to a format modification circuit 735 which, in four frames and in 80 milliseconds (hence every 20 milliseconds), sends them in groups of lines (1, 5, 9, 13, etc ..., then 2, 6, 10, 14, etc ..., and so on for 80 milliseconds) to the switching circuit 740.

Finally, in the first branch 701 called branch 20 milliseconds, represented in FIG. 8c, the sampling structure is this time such that only one point out of four is retained. The branch 701 comprises a spatial filter 711, and then a spatial subsampler. 712 1/4 rhythm and staggered line, which provides images 1250 2, 50
Hz, 2 :: 1, 370 p./line. These output images of the spatial subsampler 712, in accordance with the image format shown in FIG. 9c, are supplied to a format modification circuit 715 which, in two frames and in 40 milliseconds (hence every 20 milliseconds), sends to the third input of the routing circuit 740 first the samples located in zig-zag on the broken line denoted 1 then those also located in zig-zag but on a broken line marked 2. As before, the images of Sub-sampler input 712 (S1 connection) is also sent to a third input of the decision-making circuit 770.

 From the preceding description, made with reference to FIGS. 7, 8a to 8c, and 9a to 9c, it follows that the switching circuit 740 has on its three inputs, respectively denoted 741 to 743, three image sequences which are compressed images, since, in each of the three branches 701 to 703, a number of image points have been eliminated. It will further be noted that in each of the three sequences thus formed, the images contain the same number of points or samples to be transmitted in increments of 20 milliseconds.

 The switching circuit 740 then provides on its output a sequence of points or samples in which the content corresponding to each block of the original images will come from one or the other of the three branches according to the value of a signal. decision received on an input 746 of this circuit 740 and from the decision-making circuit 770.

 This decision-making circuit 770, described in the following paragraph, is preceded by a motion estimation circuit 760 similar to the motion estimation stage 204 of FIG. 2. This circuit 760 is itself preceded by a spatial filter 750 to switch from an interlaced image format to a non-interlaced format. The purpose of the circuit 760 is to tell the stage 204 to determine, for each block (or set of M x N samples), non-interlaced images of a certain rank (for example 2k + 1 images of odd rank) which are eliminated before transmission, a displacement vector D.

More precisely, this vector D must be such that it is possible to obtain an approximation of the eliminated image of rank 2k + 1 from the half-sum of the non-eliminated images of rank 2k and 2k + 2 which surround it, the DFD approximation error attached to each block being minimal (it has been seen above that this search to make the minimum DFD error was already described in previous documents, and that the example given to it does not was only as a preferred embodiment).

 The decision-making circuit 770 can now be described in detail. This circuit 770, shown in FIG. 10, comprises three parallel channels each comprising a comparison circuit, a squaring circuit, and a block-by-block summation circuit, the outputs of these three channels being sent to three inputs. corresponding ones of a distortion comparison and branch index selection circuit 1040 corresponding to the smallest of them.

 The first channel, corresponding to the branch 20 milliseconds, comprises first a subtractor 1011, which receives on the one hand the input image 1250., 50 Hz, 2: 1, 1440 p./line and other the output Si of the filter 711 of the branch 701 appears. This subtracter 1011 is followed by a squaring circuit 1017 and then by an adder 1018 on each block, the output of which expresses the distortion relative to the non-compensable branch. and measured block by block.

 The third, corresponding to the 80 millisecond branch, likewise comprises a subtracter 1031, which receives, on the one hand, via a delay circuit 1032 intended to compensate for the delay introduced by the spatio-temporal filtering of the fixed branch 703, input image 1250 Q, 50 Hz, 2: 1, 1440 p./line and secondly, through a non-interlaced format conversion circuit 1039 in format interleaved, the output 53 of the filter 733. This subtractor 1031 is followed by a squaring circuit 1037 and a block block adder 1038 whose output expresses the distortion relative to the fixed branch.

 The second channel, corresponding to the 40 millisecond branch, also comprises a subtracter 1021 receiving on an input the input image 1250 2., 50 Hz, 2: 1, 1440 p./line, and, on its other input, the resulting image follows from the output Sz of the filter 722. This output S2 is first sent to a spatial filter 1022 to change from an interlaced image format to a non-interlaced format. The output of this filter 1022 is supplied on the one hand to an input terminal of a switch 1026 and on the other hand to two serial memories 1023 and 1024 which respectively store the images of rank 2k and 2k + 2 successively transmitted. These two memories 1023 and 1024 also receive the displacement vector D, determined for each block by the motion estimation circuit 760, in order to obtain an approximation of the eliminated image of rank 2k + 1 from the half -like 2k and 2k + 2 images.

This half-sum is performed by an adder 1025 provided at the output of the two memories 1023 and 1024. The output of the adder 1025 is itself connected to the other input terminal of the switch 1026, the output of which, alternately the output of the filter 1022 or that of the adder 1025 to reconstruct an interlaced format image, is then supplied to the said other input of the subtractor 1021. This subtracter 1021 is followed, as in the two previous cases, by a circuit squaring 1027 then a block block adder 1028 whose output expresses the distortion relative to the branch 40 milliseconds.

 The distortions, thus available at the output of the three parallel channels which have just been described, are supplied, as indicated above, to the circuit 1040 which compares them and selects the smallest of them to send the corresponding branch index. to the input 746 of the switching circuit 740.This branch index constitutes said decision signal which controls in the switching circuit 740 the selection of either the output samples of the branch 701 called 20 milliseconds, or those of output of the branch 702 called 40 milliseconds, that is to say the output of the branch 703, said 80 milliseconds, with this restriction that, if it is found in the sequence of decisions, the presence of a decision branch 80 ms "isolated, it constrains this last to be finally a decision 'branch 20ms', so the selection thus made controls the transmission of one of the three branch outputs.

 Conversely, on reception, the images actually transmitted will be processed in the decoding device of FIG. 11 in order to reconstruct the original high definition images. This decoding device firstly comprises, for this purpose, as in the case of FIG. 7, three parallel branches 1701, 1702, 1703 which each receive the images actually transmitted and whose outputs are respectively received on the inputs 1741. , 1742, 1743 of a switching circuit 1740. These branches 1701 to 1703 are also called branches 20, 40 and 80 milliseconds, respectively.

 In the branch 1702 called 40 ms, the sequence of the transmitted images is supplied to a dynamic interpolation circuit comprising a zero insertion circuit 1721 between the transmitted signals, as well as a circuit 1722 placed at the output of this signal. last and introducing a delay of 20 milliseconds. This circuit 1721 generates, from two successive frames, an image in the format of FIG. 9b, that is to say with a rate of 40 milliseconds, in a non-interlaced format. This dynamic interpolation circuit is followed by an adder 1723 of the outputs of the circuits 1721 and 1722 respectively. The image 1250 2, 25 Hz, 1: 1, 1440p / output line of the adder 1723 is supplied to a spatial post-filtering circuit 1724, then to an image reconstruction circuit comprising two series memories 1725 and 1726 and an adder 1727 performing the half-sum of the outputs of these memories, according to the process already described above, concerning the adder 444 of FIG. 4. The two memories 1725 and 1726 receive the displacement vector estimated at transmission and transmitted by the digital assistance channel 20. A switch 1728, which receives on the one hand the output of the memory 1725 and on the other hand that of the adder 1727, finally delivers an image 1250 Q., 50 Hz, 2: 1, 1440 p./line which is sent to the input 1742 of the switching circuit 1740.

 In the branch 1703 called 80 ms, the sequence of the images effectively transmitted 625 2., 50 Hz, 2: 1, 720 p./line is first provided to a circuit 1731 said dynamic interpolation, intended to ensure previously a re-insertion of zeros between the signals actually transmitted for this branch 80 ms. This circuit 1731 generates, from four successive frames, an image in the format of FIG. 9a, that is to say with a rate of 80 milliseconds, in non-interlaced format. In the sequence of images thus obtained, the non-zero samples, in each image of the sequence, are located in staggered rows. These images 1250 i, 12.5 Hz, 1: 1, 1440 p./circuit output line 1731 are then supplied to a multiplexer 1732, then to a time filter 1735, then to a spatial filter 1736 at the output of which is available an image 1250 Q, 50 Hz, 1: 1, 1440p./line. Finally a non-interlaced format conversion circuit in interlaced format, comprising a delay circuit 1737, which delays said image by 20 milliseconds, and a switch 1738 controlled by a 50 Hz signal, delivers an image 1250 2., 50 Hz, 2: 1, 1440 p./line, which is sent to the input 1743 of the switch circuit 1740.

 The branch 1701 called 20 ms comprises, it, simply a dynamic interpolation circuit 1711, for the insertion of zeros as before. This circuit 1711 generates from an input frame an output frame in the format of Figure 9c, i.e., a 20 millisecond frame rate or a 40 millisecond frame rate in interlaced format. The branch 1701 then comprises a multiplexer 1712 and a spatial post-filtering circuit 1714 which delivers an image 1250 2., 50 Hz, 2: 1, 1440 p./line then sent to the input 1741 of the switching circuit 1740.

 The output of the decision-making circuit 770, which, on transmission, was sent to the switching circuit 740, is also sent to the nuseric assistance channel 20, with a view to restoring this information to the decoding. The switching circuit 1740, as well as the multiplexers 1712 and 1732, receive said output information of the circuit 770 transmitted by the channel 20. The circuit 1740 uses this decision signal to select correspondingly that of the outputs of the branches 1703, 1702, or 1701 which is suitable: the multiplexers 1712 and 1732 either simply deliver the output signal of the circuit 1711 or 1731 respectively if the decision signal corresponds precisely to the branch concerned (respectively the branch 20 ms 1701 or the branch 80 ms 1703) or, in the opposite case, deliver the output of the switch 1728 of the branch 40 ms 1702, restoring the format of FIG. 9a (case of the multiplexer 1732) or that of FIG. 9c (case of the multiplexer 1712) as the case may be . The reconstructed high definition image 1250 2., 50 Hz, 2: 1, 1440 p./line is thus finally available at the output of the switching circuit 1740.

 An improved embodiment of the coding device can still, we have seen, be proposed. FIG. 12 shows this other embodiment, and FIG. 17 shows correspondingly the decoding device associated with this coding device in the transmission system.

 The coding device of FIG. 12 firstly comprises, in parallel, as in the case of FIG. 7, three processing branches 20, 40 and 80 ms each receiving, on their common input E, a sequence of interlaced images. 1250 2., 50 Hz, 2: 1, 1440 p./line, and constituted as shown in Figures 13a to 13c.

The first two branches are identical to the branches 701 and 702 of FIG. 7, that is to say that they respectively comprise the same elements 711, 712, 715 and 721, 722, 723, 725 as the latter, such as they have been shown in detail in FIGS. 8c and 8b. The third branch 803, it differs from the branch 703 in that it comprises, instead of the simple temporal filter 731, a temporal filter 831 compensated in motion and operating over a 40 millisecond horizon, and comprising for this purpose, as shown in FIG. 14 showing this temporal filter, three image memories 81, 82, 83 and an adder 84.This temporal filter 831 delivers images 1250 2., 50 Hz, 1: 1, 1440 p./line, and is then followed by the same circuits as those encountered in the branch 703, namely the time sampler 732 at a rate of 1/4, which delivers images 1250 2., 12.5
Hz, 1: 1, 1440 p./line, the spatial filter 733, which makes it possible to limit the band of the signal and to avoid the aliasing of the spectrum due to the subsampling carried out, and the spatial sub-sampler 734 of rhythm 112 and staggered line, which delivers images 1250 2., 12.5 Hz, 1: 1, 720 lines conforming to the image format of Figure 9a. The output images of the .734 sub-sampler are, as in the branch 703, supplied to a format modification circuit identical to the circuit 735 and which sends them itself to the switching circuit 740.

 As before, the switching circuit 740 provides at its output a sequence of dots or samples in which the content corresponding to each block of the original images comes, from one of the inputs 741 to 743, from one or the other. other of the three branches 701, 702, 803 according to the value of the decision signal received on the input 746. This decision signal comes from a decision circuit 870, itself preceded by an estimation stage consisting of a motion estimation circuit 860.

 This circuit 860, represented in FIG. 15, comprises on the one hand a first set of circuits identical to the motion estimation circuit 760 and thus composed of three image memories 861, 862, 863 and a device of FIG. motion estimation 864. In parallel with this first set 861 to 864 there is provided a temporal subsampling circuit 865 for halving the timing of the sequence of sequential images supplied to said first set. This circuit 865, which also receives the output of the motion compensated time filter 831, is followed by a second set also comprising three image memories 866, 867, 868 and a motion estimation device 869.

 The motion estimation circuit 860, itself preceded (see FIG. 12) by an interlaced format conversion spatial filter 750 in non-interlaced format, is intended to provide either a sequence of motion vectors, but two groups of such displacement vectors, denoted by Vio and VgO in relation to the respective temporal rhythm of the corresponding sequence of images.

 The decision circuit 870 is also of the same nature as the circuit 770, with the only difference that the signal Ss (see FIG. 8a) received by the circuit 870 undergoes a motion compensated filtering here. As shown in FIG. 16, the circuit 870 therefore comprises three parallel channels but two of which, the second and third channels, are identical to those in the circuit 770 and comprise the same elements 1011, 1017, 1018 and 1021. 1028. The third way, it is modified in that it now comprises, as the second channel of the decision circuit 770 of Figure 10, elements 1131 to 1138 absolutely identical to the elements 1021 to 1028 of this figure 10 and contributing to the same goal.

 Conversely, on reception, the images actually transmitted after coding in the device of FIG. 12 will be processed in the decoding device of FIG. 17 with a view to reconstructing the original high-definition images. This decoding device comprises first of all, as in the case of FIG. 7, on transmission, and of FIG. 11, on reception, three branches in parallel 1701, 1802, 1803, say 20, 40 and 80 Bs, receiving the images transmitted and whose outputs are received on the inputs 1741 to 1743 of the routing circuit 1740.

 The first branch 1701 is identical to what it was in the embodiment of FIG. 11. The second branch 1802 is practically identical to the branch 1702 of FIG. 11, with the only difference that the interpolation circuit is modified and now also comprises a multiplexer 1729, provided in series between the adder 1723 and the spatial post-filtering circuit 1724. This modified dynamic interpolation circuit is intended to generate a regular link by taking either the data transmitted on two successive frames for the blocks processed in 40 ms and 20 ms, soid the data from the 80 ms branch.

 The third branch 1803 firstly comprises a dynamic interpolation circuit 1831 which, from four successive frames of the transmitted image sequence, reconstructs an image of the format 1250 Q., 12r5 Hz, 1: 1, 1440 p. / 2r then a spatial filter 1832 at the output of which is available an image 1250 2., 12.5 Hz, 1: 1, 1440 p./line.

This image is then supplied to an image reconstruction circuit comprising two series memories 1833 and 1834, receiving the displacement vector Vso estimated at transmission and transmitted by the digital assistance channel 20, an adder 1835 performing the half as the output of these memories, and a switch 1836 which receives on the one hand the output of the memory 1833 and on the other hand that of the adder 1835 and delivers an image 1250 2., 25 Hz, 1: 1 , 1440 p./line. This image is transmitted on the one hand to a multiplexer 1837, which also receives the output of the spatial post-filtering circuit 1724, and on the other hand to the multiplexer 1729 of the dynamic interpolation circuit of the second branch 1802. The multiplexer 1837 is even followed by another image reconstruction circuit comprising, as the previous one, two image memories 1838 and 1839, an adder 1840 performing the half-sum of these memories, and a switch 1841 which receives, on the one hand, the output of the memory 1838 and on the other hand that of the adder 1840 and delivers an image 1250 2., 50 Hz, 2: 1, 1440 p./line. The two memories 1838 and 1839 receive, this time, only the half-displacement vector Viol2, since the interpolation interval is 40 ms, that is to say half amplitude, and the output of the switch 1841. is sent to the input 1743 of the switching circuit 1740.

 This switching circuit 1740 receives not only the outputs of the three branches 1701, 1802, 1803, but also, on its input 1746, the output of the decision-making circuit 870 obtained on transmission and sent as the estimated displacement vectors , to the digital assistance channel 20 for the return of this information to the decoding. This output of the decision-making circuit 870 is also supplied to the multiplexer 1837, as well as to the dynamic interpolation circuits of the branches 20 ms 1701 and 40 ms 1802. The switching circuit 1740 uses this decision signal as before to select correspondingly that of the outputs of the branches 1701, 1802, 1803 which is appropriate.

 After the description of the various encoding and decoding devices which have just been detailed, it will be finally specified that it is possible to provide, in a manner corresponding to the transmission as well as the reception, in each of the first, second and third branches of treatment, a switch to turn off the treatment branch in which it is placed. Thus, a coding device according to the invention can it be constituted, as described, of the three branches mentioned, or consist of only two of them, the first and third, or first and second, or second and third, or even consist of only one of them only three. Of course, the structure of the decoding device is directly linked on this point to that of the coding device, and the openings or closings of the respective switches of the corresponding branches, coding and decoding will be controlled in a strictly similar manner. The different embodiments that result are not described in more detail, because they do not pose any particular problem of implementation.

APPENDIX (1) i (X, 2k + 1) XI (XD 2k) + I (X + D, 2k + 2) biocs [I (X, 2k + 1) - (X, 2k + 11 2

<tb><SEP> 2
<tb> (3) <SEP> r <SEP> DFD <SEP> (X, <SEP> Dx)
<tb><SEP> blocks
<tb> (4) I = I (X - Dmin2, 2k) + I (X + Min2 ^ 2k + 2)
2

Claims (16)

1. A device for temporal subsampling and temporal interpolation in a sequence of interlaced images divided into blocks of I x J points (I, J positive integers) whose luminosity is expressed numerically, characterized in that it comprises a spatial prefiltering circuit of the interlaced image sequence, intended to deliver a series of sequential images while limiting the bandwidth, a spatial subsampling circuit intended to reduce in each of said sequential images the number of samples, a temporal subsampling circuit for halving the timing of said series of sequential images, and a motion estimation stage on transmission, said stage including itself three memory memories; image, provided in series to respectively store on the one hand the images of rank 2k and 2k + 2 to be transmitted and secondly images of rank 2k + 1 to eliminate before t transmission, and a motion estimation device according to a method such as that of block correlation. 2. Device according to claim 1, characterized in that it is preceded, in series, a time-holding filtering circuit comprising a delay circuit imposing a delay equal to the time interval T between two successive images. source and an adder, and a temporal subsampling circuit of the output of said adder, providing at the input of said device a series of sequential images with a half-time rate of time. Transmitting stage for a high-definition television image transmission system via a limited bandwidth analog channel involving a processing for reducing the amount of information to be transmitted, characterized in that it comprises, in its coding part, a temporal interpolation device according to one of claims 1 and 2. 4. A high-definition television picture transmission system via a limited bandwidth analog channel involving a reduction processing of the quantity of information to be transmitted, this system comprising at least one transmission stage and a reception stage and characterized in that said transmission stage comprises in its coding part a signal processing branch composed of a device according to one of claims 1 and 2 and connected to an assistance channel digital device providing transmission to the reception stage of information relating to said motion estimation 5.A receiving field for a transmission system according to claim 4, characterized in that it comprises in its decoding part a signal processing branch composed of a motion compensation device itself comprising a spatial post-filtering circuit for performing spatial interpolation in the sequential images transmitted by the analog channel, then, in parallel on this circuit, a delay circuit and a motion compensation stage, and for alternately receiving the output of said delay circuit and that of said motion compensation stage, a switch for outputting a series of sequential images then provided to a format converting circuit for transforming this sequence into a series of interlaced images, then to a multiplexer delivering the image sequence interleaved ready to be visualized, said motion compensation stage itself comprising on the one hand two image memories in series for the storage of images successively transmitted by the analog channel and postfiltered and secondly an adder to perform the half-sum of said transmitted images. 6. Stage according to claim 5, characterized in that it is followed by an interpolation circuit comprising a delay circuit imposing a delay equal to T and a switch and intended to transform the series of sequential output images of said device in a series of interlaced images of twice the rate. 7. Application of the device according to claim 1 to the realization, in a system of transmission of high definition television images via a limited bandwidth analog channel involving a reduction of the amount of information processing to transmit, a coding device characterized in that it comprises itself  (a) three first, second and third processing branches provided for processing cadence images successively double one of the following, said branches being located in parallel, each receiving the original high definition image and each ensuring a rate of spatio-temporal subsampling equal to 4  (b) after converting the original image to a non-interlaced format, said motion estimation stage  (c) a decision-making circuit starting on the one hand from the original image and the images processed by said three branches and on the other hand from the displacement vector selected by said motion estimation stage, and also sent to a so-called digital assistance channel associated with said analog channel  (d) a switching circuit of the outputs of said branches according to the output signal of said decision-making circuit, said decision signal being also sent to the digital assistance channel associated with said analog channel in that said branches comprise same  (i) the first, a first spatial filter followed by a spatial subsampler and a first format conversion circuit  (ii) the second, a 1/2 rhythm time sampler, a second spatial filter, a spatial subsampler, and a second format conversion circuit  (iii) the third, a temporal filter, a 1/4 time sampler, a third spatial filter and a spatial subsampler, and a third format converting circuit, and that said processed images received by said timing circuit; decision making are those respectively available at the output of said spatial filters. 8. Encoding device according to claim 7, characterized in that the period of the images processed by the first, second and third branches is 40 and 80 milliseconds, respectively. 9. Encoding device according to one of claims 7 and 8, characterized in that each processing branch comprises a selective switch off switch of the corresponding branch. 10. System for transmitting high definition television images via a limited bandwidth analog channel involving a processing for reducing the quantity of information to be transmitted, this system comprising at least one transmission stage and a reception stage and characterized in that said transmission stage comprises in its coding part a coding device according to one of claims 7 to 9. 11. In the receiving stage of a transmission system according to claim 10, decoding device characterized in that it comprises  (a) three first, second and third processing branches, located in parallel and each receiving the image transmitted to decompress these transmitted images and restore them in high definition format  (b) a circuit for switching the outputs of said branches according to the output signal of the decision-making circuit, said signal having been transmitted via said digital assistance channel in that said branches themselves comprise  (i) the first, a dynamic interpolation circuit, a multiplexer, and a spatial post-filtering circuit  (ii) the second, a dynamic interpolation circuit, a spatial postfiltering circuit, an image reconstruction circuit from the said transmission vector selected on transmission, and a switch for the conversion to an interlaced format, said vector displacement transmitted via said digital assistance channel  (iii) the third, a dynamic interpolation circuit, a multiplexer, a temporal filtering circuit, a spatial filtering circuit, and an interlaced conversion circuit. Coding device according to one of Claims 7 to 9, characterized in that the decision-making circuit comprises, in parallel, three ways of calculating the distortion between the original image and the three processed images respectively. at the output of said spatial filters, and a comparison circuit of said three distortions and selection of the branch index corresponding to the weakest of them. 13. Encoding device according to claim 12, characterized in that, in said decision-making circuit, the selected branch index is modified to the index corresponding to the first branch when, in the sequence of decisions, one finds in the presence of an isolated decision of the index of the third branch. Coding device according to one of Claims 7 to 9, characterized in that  (a) said motion estimation stage also comprises, in parallel with the first set of said first three image memories and said first motion estimation device, a second temporal subsampling circuit for dividing by two the temporal rhythm of the sequence of sequential images supplied to said first set and followed by a second set comprising a second set of .three second image memories and a second motion estimation device according to a method such as that of block correlation, each motion estimation device delivering a distinct motion vector supplied on the one hand to the decision-making circuit and on the other hand to the digital assistance channel  (b) the temporal filter of said third processing branch is a motion-compensated temporal filter on a horizon equal to the period of the images of the second branch, also receiving the displacement vector delivered by said first motion estimation device. 15. High definition television image transmission system via a limited bandwidth analog channel involving a reduction processing of the quantity of information to be transmitted, this system comprising at least one transmission stage and a receiving stage and being characterized in that said transmitting stage comprises in its coding part a coding device according to claim 14. 16. In the receiving stage of a transmission system according to claim 15, decoding device characterized in that it comprises  (a) three first, second and third parallel processing branches each receiving the transmitted image  (b) a circuit for switching the outputs of said branches according to the output signal of the decision-making circuit; said signal having been transmitted via the digital assistance channel in that said branches themselves comprise  (i) the first, a dynamic interpolation circuit, a multiplexer, and a spatial post-filtering circuit  (ii) the second, a dynamic interpolation circuit, a spatial postfiltering circuit, an image reconstruction circuit from said displacement vector selected on transmission by said first displacement estimation device and transmitted via the digital assistance channel, and a switch for conversion to interlaced format  (iii) the third, a dynamic interpolation circuit, a spatial postfiltering circuit, an image reconstruction circuit from said displacement vector selected on transmission by said second displacement estimation device and transmitted by the intermediate of the digital assistance channel, a multiplexer, and an image reconstruction circuit from half of the displacement vector selected on transmission by said second displacement estimation device the dynamic interpolation circuit of the second branch including a multiplexer which also receives the output of the image recovery circuit of the third branch, and each processing branch comprising a selective disconnect switch occupying the same open or closed position as the corresponding switch of the processing legs of the coding device when such a switch is provided in the branches of tr the coding device.