FI92540B - MAC decoder for the chrominance signal of a high resolution television - Google Patents

Description

5,92540

High Definition Television Receiver Chrominance Signal MAC Decoder - High Definition MAC Decoder for Chrominance Signal

The invention relates to a block of a high-definition television receiver in which the original subsampling patterns are formed from the chrominance samples of the received signal.

10 HDTV in the European High Definition Television System

(High Definition Television) transmission is via satellite or cable using a MAC system that is not compatible with any other traditional TV system. For this reason, current receivers need a special decoder to receive the MAC transmission.

The HDTV studio standard has an aspect ratio of 16: 9 and comprises 1250 lines displayed at an interleaving ratio of 2: 1 (or later 1: 1) and a field frequency of 50 Hz. Of the 20 lines, 1152 are active, visible on the image surface, and one line has 1440 luminance pixels and half less, i.e. 720 chrominance pixels. The image is encoded when transmitted into a MAC-compatible HDMAC signal by compressing the luminance signal into its fourth part and the chrominance signal into its eight-to-25th part in a bandwidth reducing encoder (separate encoder for luminescence and chrominance) so that the original picture can be restored at the receiver. The line number of the transmission signal is thus half of the original, i.e. 625 lines, and the interleaving ratio is 2: 1. For the encoder that reduces the bandwidth, the input signal format is currently agreed to be 1250/2: 1/50 Hz, but later the interleaving ratio is likely to change to 1: 1, in which case the compression must be further increased. In view of the receiver, the so-called A DATV signal that conveys information about the motion-35 content of an image.

Compression is based on controlled subsampling controlled by motion information. This means, 92540 2 that the less motion there is in the image, the higher the spatial resolution is used, and when the motion content of the image is large, the temporal resolution is added at the expense of the spatial.

5

In the above-mentioned bandwidth reduction encoder BRE (Bandwidth Reduction Encoder), the image to be transmitted is divided into blocks of 16 * 16 pixels, so that the entire image is divided horizontally into 90 ree blocks and vertically into 72 ree blocks. The blocks, 10 of which total 6480, are treated differently based on their business content. Furthermore, the processing is different for the chrominance signal components U, V than for the luminance signal Y. Since the image sensation in the human eye is largely based on luminance, the horizontal density of the luminance pixels 15 of the HDTV image is twice that of the chrominance pixels. In this case, the above-mentioned 16 * 16 pixel block is reduced to an 8 * 16 pixel block when looking at chrominance pixels, and due to the sensitivity of the eye, as few sub-sampling patterns as for chrominance samples cannot be used for luminance samples when lowering the bandwidth.

Thus, bandwidth reduction is more complex for luminance samples than for chrominance samples.

Referring now to Figures 1-3, it is described to reduce the bandwidth of the chrominance signal 25 to match the MAC signal. The • sampling frequency of the chrominance signal is 27 MHz. As stated above, the color resolution in the horizontal direction is lower than the luminance resolution. Since for the human eye most of the image resolution effect comes from the luminance component, in the complete HDTV image, the chrominance components along the line are reduced so that only every other pixel contains chrominance information. Since the U and V components are transmitted on the MAC channel in alternating lines, the vertical resolution of the color signal must also be reduced. Compression 35 proceeds in such a way that the second field of the image is completely ignored and chrominance samples from the second field are taken thinned. Depending on the motion content of the HDTV sub picture (8 * 16 chrominance pixels) under consideration,

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92540 3 the color signal is combined into one of three image processing branches, each of which is first filtered with anti-crease filters and then subsampled using a different sampling pattern in each branch. Thus, each of the 5 branches operates in its own mode, which are 80 ms mode, 40 ms mode and 20 ms mode.

If there is no movement, the signal is controlled. 80 ms to the mode branch where only one HDTV image is sampled.

10 The subsampling pattern (decimation) is as shown in Figure 1. In the image, the squares represent the chrominance pixels of a complete HDTV image, and for simplicity, the image represents only 1/4 of the entire 8 * 16 pixel block. In the 80 ms branch, only those Kro minans pixels with a number inside are included in the 15 subsampling patterns. It can be seen from the image that every other line of the image is ignored (i.e., the second field) and only every other chrominance pixel of every other line is sent to the MAC channel. In one MAC field of 20 ms, the samples from the line are not placed in order, but the samples 20 are decomposed into different fields. The number inside the square indicates in which field the chrominance information of each pixel is placed. Thus, for example, the chrominance pixels of the first line are placed alternately in the MAC fields 2 and 4. It is essential to note that the chrominance information of one image is placed in four four consecutive MAC fields. Conversely, this means that * when decoding an image at the receiver, information from four consecutive MAC fields is required to produce one original HDTV image.

30 If there are slow-moving objects in a part of the image, the chrominance signal to be compressed is directed to the 40 ms mode branch, where the field transmission time is increased from 20 ms to 40 ms. This is shown in Figure 2. It compresses two complete HDTV images into four 20 ms MAC fields. The subsampling pattern 35 is now such that every other chrominance sample of every other line of one field of one image is included and samples of the second field of the image are not included at all. The numbers refer to the MAC field in which the chromium 4 92540 nance sample is placed. Thus, the samples of one line of the second field of the first HDTV image, denoted by 1, are placed in the MAC field 1, skipped over one line in the same field, and the samples of the next line, denoted by the number 2, are placed in the MAC field 2. The result is that the chrominance samples of the first HDTV image are in MAC fields 1 and 2 and the samples of the second HDTV image are in MAC fields 3 and 4. Compared to Figure 1, the chrominance information of two HDTV images is placed in a period of 80 ms instead of one. Thus, the 80 ms period has become temporal. Thus, essential in this 40 ms mode is that the subsampled chrominance information of one image is placed in two consecutive MAC fields. Conversely, this means that when decoding an image at a receiver, information from two 15 consecutive MAC fields is required to produce a single original HDTV image.

If there are fast-moving parts in the image, the chrominance signal to be compressed is directed to a 20 ms branch, where the chrominance information from four 20 HDTV images is compressed into four consecutive MAC fields. For each image, samples are taken only from the second field, and even extremely sparsely, only every 8th sample from every other line is included. The numbers indicate in which MAC field the 25 mic sample is placed. It is observed that the samples of one MAC field always come from one image. Thus, the chrominance information of the four HDTV images is included in the 80 ms period. Thus, the temporality is even greater than in the case of Figure 2, where two images are compressed into an 80 ms period.

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According to the information provided by the motion detector, a switch is controlled which switches only one mode at a time to the output of the BRE. This information, in which branch the output signal is generated, is encoded into a DATV signal, according to which the encoder directs the signal to the correct branch.

The compression of the transmission signal briefly described above will be apparent to one skilled in the art and the subject has been discussed in one step.

in detail e.g. F.W.P. Vreeswijk, M.R. Haghiri and C.M. Carey-Smith, HDMAC Coding for Compatible Broadcasting of High Definition Television Signals, 16th International TV Symposium, Montreaux, Switzerland, June 17-22-1989, and 5 F.W.P. Vreeswijk and M.R. Haghiri, HDMAC Coding for MAC

Compatible Broadcasting of HDTV Signals, Third International Workshop on HDTV, Turin, Italy, August 30 - September 1, 1989.

10 In the receiver's MAC decoder, the compressed picture 625/2: 1/50 Hz must be restored to the original HDTV format, ie 1250/2: 1/50 Hz. The analog television signal received at the decoder is converted into video, data and audio signals. The decoder can be called a Bandwidth Restoration Decoder (BRD) and is analogous to the BRE described above. The BRD encoder will now be described in more detail with reference to Figure 4, and the description relates to chrominance. The received sample frequency is 6.75 MHz and the output frequency of the BRD is 27 MHz. The encoder comprises a "line 20 deshuffler" block 41, at least 3 field memories 42 connected, e.g., to a cascade, a subsampling pattern converter 43 and three interpolator branches 44, 45 and 46. The SSPC 43 of the subsampling pattern returner has four consecutive MAC fields input at the same time. 25 l 1 has the "oldest" field, i.e. the first field received, and input 4 has the youngest field, i.e. the last field received. The SSPC generates from its input location the original subsampling patterns shown in Figures 1-3, from which the missing chrominance pixels are interpolated in the interpolation branches. Each interpolator branch produces a complete HDTV field with respect to the color signal, and the output of the selected branch is connected by a switch C to a demultiplexer 47, which separates the time-multiplexed U and V components from the chrominance signal. The components are the output signals of the BRD. The position of the switch 35 is controlled by the motion information contained in the received DATV signal.

6 92540

The chrominance components U and V are transmitted on the alternating line and the sampling frequency of the chrominance signal is 6.75 MHz.

In the deshuffler 41, the lines of the received MAC fields must be arranged so that each line contains only 5 samples from one of the original HDTV lines. In this case, the SSPC 43 can be implemented without using line memories. The SSPC only needs 4 field inputs, so 3 field memories 42 are needed. The memories can be cascaded so that the field just received is fed to both the first memory and the fourth input of the SSPC (input 4) and samples of the last field memory are taken to the SSPC. to the first input (input 1).

As stated above, the task of the SSPC 43 is to return the subsampling patterns of the 15 different modes shown in Figures 1-3. It combines the successive MAC fields it receives and compiles a subsampling image of the original HDTV image from them. In addition, it interpolates any missing samples. In the received DATV signal, the SSPC receives information about the min-20 subsampling pattern it must generate at any given time. It can be seen from Figures 1-3 that the 20 ms mode subsampling pattern can be restored from one MAC field, the 40 ms mode subsampling pattern can be restored when two MAC fields are available, but all four MAC fields are required to restore the 80 ms mode subsampling pattern. field. The SSPC always generates a subsampling pattern field during the time it takes to receive one MAC field, i.e., one subsampling field per 80 ms basic period (i.e., one HDTV picture), numbered 30 also 1-4 and hereinafter referred to as HDTV field 1, HDTV field 2, HDTV field 3 and HDTV field 4. It can be assumed that HDTV field 1 corresponds to MAC field 1, HDTV field 2 corresponds to MAC field 2, etc. For example, when the SSPC inputs have the MAC field of Figure 1. fields 1-4, the SSPC processes the HDTV field 2 of these. 35 If the next 40-ms mode block of the next picture sequence, Fig. 2, is received, after processing the HDTV field 2 of the first sequence, the situation is that the SSPC inputs is the MAC fields 2, 3 and 4 of Figure 1 and Figure 2

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92540 7 MAC field 1, which already belongs to the next image sequence.

The SSPC should further process the 80 ms mode block into the HDTV field 3, although not all of the 80 ms mode MAC fields in the same image sequence block are available. Later-5 min, after 20 ms, fields 3 and 4 of Figure 1 and fields 1 and 2 of Figure 2 are input, but the SSPC should still process the 80 ms mode block to the HDTV field 4, although not all of the 80 ms mode blocks MAC fields of the same image sequence are no longer available.

10

The problem is how to restore the 80 ms mode subsampling pattern when the SSPC has to switch from the 40 ms or 20 ms subsampling pattern to the 80 ms subsampling pattern, or when the SSPC has to switch from 80 ms to 15 ms: n pattern recovery to form a 20 ms or 40 ms subsampling pattern. In other words, the problem arises when, when looking at the same area in time on the image surface, the image motion decision "motion-containing image area" precedes or follows the decision "stationary image area", where all four fields required to reproduce the 80 ms mode in the same block subsampling pattern are not. available.

The prior art subsampling pattern restorer 25 SSPC solves this problem simply by horizontally copying the missing samples from the nearest adjacent known samples. Copying is performed when one of the consecutive 80 ms MAC fields in the same block is missing. If two consecutive fields are missing, the interpolation of the missing samples is given to a 20 ms interpolator, which improves the result. However, copying leads to errors in the image, because when an image or, rather, a block becomes stationary, that is, when the boundaries of these blocks are within range and when copying missing pixels from stationary (80 ms) pixels, horizontal line and stamp errors, i.e. vertical - and diagonal edges and lines will have horizontal line segments and the vertical and diagonal edges may become toothed.

92540 θ

The same is true when a block changes from stationary to motion. The image error is visible throughout the block.

5 These problem areas are illustrated in Figure 5. It looks at the same block (part of the image) over time. The block is initially stationary, with the information placed in four consecutive 80 ms mode MAC fields, represented by numbers within the block. The chronological order of the fields is from left to right. Each MAC field has its own relative field number, which is 1, 2, 3, or 4. In the next step, the block becomes motionful, so the information is placed in four consecutive 40 ms MAC fields 1, 2, 3, and 4. Then again the block becomes stationary-15, so the information is in the 80 ms mode MAC fields 1, 2, 3, and 4. Next, the motion content is large, so the block information is in four consecutive 20 ms mode MAC fields 1, 2, 3, and 4. the number below the field indicates which mode the field belongs to. The successive field numbers 20 to 4 thus always form one block, as shown in Figures 1-3. Each block 1-4 of the four fields is associated with its own motion information received on a separate DATV channel, decoded, and transmitted to the SSPC, whereby it is able to return the correct subsampling pattern based on the DATV information.

When the input to the SSPC has fields marked with an arc a, the HDTV field 2 should first be processed to form the SSPC's 80 ms mode subsampling pattern, which it does because 30 consecutive fields in the same mode are available.

But when the input has fields marked with an arc b,; only three consecutive 80 ms mode fields are available.

The known SSPC then generates the missing samples required for the processing of the HDTV field 3 by horizontal copying, which results in image errors. When the input has fields marked with an arc line c, i.e. two 80 ms mode fields of the block to be processed are missing, the known SSPC gives the interpolation of the missing samples to a 20 ms interpolator instead of an 80 ms interpolator (i 92540 9). field interpolation is given to the 20 ms interpolator only when switching from stationary mode to motion mode and then only for the last 5 fields.These cases are indicated by circled mode numbers in Figure 5. However, image errors always occur when switching from motion detection mode to stationary mode. and vice versa.These image errors are not corrected by the prior art subsampling pattern restorer SSPC 10.

The present invention provides a way in which image errors caused by the use of the prior art can be eliminated. The invention is characterized by what is stated in claim 1.

The inputs of the subsampling pattern restorer can be marked as the first, second, third, and fourth inputs. The fourth input is the MAC field just received, the third is the previous Kent-20 delayed by the field delay, the second is the field delayed by two field delays, and the first is the field delayed by three field delays. That is, the input is affected by four consecutive MAC-Fields such that input 1 has the oldest field. According to the invention, the sub-sampling pattern restorer SSPC is forced to process a 20 ms field every time a) when the situation where the MAC field of the 80 ms mode affecting all inputs has changed to the situation where the fourth or fourth and third inputs are affected by either 40 ms or 20 ms field, and 30 b) when the MAC fields of the 80 ms mode are affected by the last three inputs and the first input is affected by: the field of another mode.

The operation of (a) means that the stationary block is changing to a motion-containing block, while the operation of (b) means that the motion-containing block is becoming a stationary block.

10 92540

Since the DATV information associated with each received MAC field indicates the mode of the block, a function can be constructed by simple logic to monitor the state of the inputs and force the stationary picture HDTV fields to the 5 SSPC 20 ms interpolator under the conditions of a or b. interpolation.

The invention is illustrated by the accompanying figures, in which Fig. 1 shows a subsampling pattern of stationary block chrominance samples 10, Fig. 2 shows a subsampling pattern of a motion block, Fig. 3 shows a subsampling pattern of a fast motion block, the subsampling pattern restorer, Fig. 6A is a table of SSPC input combinations when processing different 20 HDTV fields, Fig. 6B is a table corresponding to Table 6A with cases where the processing of the invention is used, Fig. 7 is a view corresponding to Fig. 5 with points marked, 25 using the processing of the invention, Figure 8 illustrates the use of a DATV signal in decision making, Figure 9 shows a block diagram of one possible constraint arrangement, and Figure 10 is a block diagram of another possible constraint arrangement. 30 arrangements.

Figures 1-5 have already been described above and will be referred to below as needed. Table 6A shows the problem areas involved in using the prior art SSPC. In the left column of the table, "Field" refers to the HDTV subsampling pattern field to be processed, "RFN" refers to the MAC field number at each input of the SSPC (see Figures 1-3), and "Case" refers to a combination of li 92540 11 input fields when processing each subsampling field. that is, HDTV fields 1, 2, 3, or 4. Cases where prior art causes problems are shown in bold. Let us start with an example of case 6, i.e. Case 6. In this case, the input fields of the SSPC are the MAC fields 1, 2, 3 and 4 of the 80 ms mode block. The SSPC has all four fields of this mode of the block at its disposal, so it can form a subsampling pattern field without any problems. i.e. HDTV field 2's. This corresponds to the situation in Figure 5, where the input 10 is the first four fields from the top left, i.e. the fields marked with an arc a.

After a period of 20 ms, the MAC fields have "moved" one input forward and the fourth input already has the first MAC field of the next block, in this case a 40 ms mode block, whose number (RFN) is thus 1. Figure 5 with reference, the inputs are now the fields marked with an arc b, i.e. the 80 ms mode fields 2, 3, 4 and the 40 ms mode field 1. In Table 6A, we have now moved to Case 10 20 and processed the 80 ms mode HDTV field 3. It is observed that all four 80 ms mode fields in the block are no longer available, so that the SSPC's 80 ms interpolator does not have all the necessary samples available. According to the state of the art, as mentioned in connection with Figure 5, the missing samples would be copied by horizontally copying from existing adjacent samples, so that there would be image defects in the final HDTV image. Accordingly, according to the invention, the SSPC is forced to form a 20 ms mode subsampling pattern and a 20 ms interpolator branch is connected to the output of the 30 BRD (switch C Fig. 4). This means that the 80 ms mode HDTV field 3 is processed by the 20 ms mode interpolator. The samples it needs are all available, so there is no need to undertake horizontal copying. This reduces image errors.

35 Again, after a period of 20 ms, the fields have "shifted" by one. the input forward, the first and second inputs having the first two fields of the next block, the 40 ms mode block, 92540 12, the numbers (RFN) of which are thus 1 and 2. Referring to Figure 5, the input is now the fields marked with an arc c, i.e. 80 ms: n mode block fields 3, 4, and 40 ms mode block fields 1 and 2. In Table 6A, we have now moved to Case 15 and further processed the same 80 ms mode block field, HDTV field 4. It is observed that two more of this 80 ms mode field is available.

Accordingly, in accordance with the invention, the interpolator of the SSPC is now forced to further interpolate in the 20 ms mode and the 10 80 ms mode HDTV field 4 is processed by the 20 ms mode interpolator, the samples of which are all available.

After another 20 ms, the input combination is as in Table 6A Case 4, so a 40 ms field is processed. After the four 15 received MAC fields, the input fields are the fields marked with the dashed line d in Figure 5, i.e. 40 ms mode field 4 and 80 ms mode fields 1, 2 and 3. In Table 6A, the situation corresponds to Case 2 and the interpolator should process 80 ms mode HDTV field 1. Now, we do not use horizontal-20 pairing of samples, but force the interpolator to 20 ms mode, so that the necessary samples are available. Thus, the 80 ms mode HDTV field 1 is processed by a 20 ms mode interpolator. In the next step, after one 20 ms period, all 80 ms mode fields in this block are available, 25 so the situation is according to Case 6 and HDTV field 2 is normally processed by the 80 ms mode interpolator.

In the next step, the inputs are the fields marked with an arc line e, ie field 3 of the HDTV-30 block 80 should be processed, but only the three fields of this mode in the block are available. The fourth input field is the MAC field 1 of the 20 ms mode of the block. In Table 6A, the situation corresponds to Case 11. Instead of horizontal copying of samples according to the prior art, the interpolator is forced into 20 ms mode, whereby all 35 samples it needs are available.

The interpolator is likewise forced from the 80 ms mode to the 20 ms mode also in the next step, where the input fields

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92540 13 is marked with an arc line f in Fig. 5. The HDTV field 4 of the 80 ms mode is to be processed. The situation is therefore according to Table 6A Case 16. Even now, the interpolator is forced into a 20 ms mode so that all the samples it needs are available.

5

A suitable Case can be found in Table 6A for any of the sequences of successive blocks, and it can be stated that the maximum number of possible cases is 18. In the table, a small horizontal line means that there can be a field in any mode at that point.

In Fig. 7, which corresponds to Fig. 5, the mode markings of the fields of the 80 ms blocks, which the corresponding field of the sub-sampling pattern is processed in the forced 20 ms mode, are marked in a circle. In Figure 5, the fields in which 20 ms mode processing is used in the prior art solution are marked in a corresponding manner. A comparison of the figures clearly shows the difference between the prior art and the invention.

Correspondingly, the table in Fig. 6B, which corresponds to the table in Fig. 6A, shows in bold the cases in which a 20 ms interpolator is forcibly used in stationary field processing. Thus, it can be seen that when processing field 1, the cases Case 2 and Case 3 in Figure 6A are replaced by Case 5, when processing field 3, cases 10 and Case 11 replace Case 13, and when processing field 4, cases 15 and Case 16 replaced by Case 18. The maximum number of different cases has thus been reduced by six to 12.

30

Figure 8 shows the principle of forced processing decision making. As is known, the received DATV signal is decoded to obtain the motion information of each block. The DATV information is fed to three cascaded field memories 35 84, 85 and 86. Since the HDTV image is divided into 90 * 72 blocks, and each block is associated with its motion information, a DATV memory size of 90 * 72 items is sufficient. The motion information associated with each image is thus stored in the DATV field memory. As before 92540 14

said, the received MAC image signal is stored in three field memories, memories 81, 82 and 83 in Figure 8, from which the SSPC reads the received MAC fields with the current received field being one SSPC input No. 5. The output of the field memory 82 corresponds to that field, by SSPC

processes, i.e. if the field memory has a MAC field 2, the field HDTV field 2 must be processed. The contents of the DATV field memories and the MAC field memories are completely synchronous, so e.g. when transferring the received MAC field from the field memory 81 10 to the subsample pattern return SSPC, DATV is simultaneously the current memory of the current block of the field to be transferred can be read from the field memory 84. Knowing this, control logic is provided, which monitors the motion information 15 obtained from the outputs datv (1), datv (2) of the outputs of the DATV field memories 84, 85, and the motion information information datv (4) of the field just received. When the logic detects that one of the shaded areas in Table 6A is valid, it provides a first control signal that forces the SSPC to form a 20 ms subsampling pattern and a second control signal that forces a 20 ms branch to output the BRD, i.e. turns switch C, Fig. 4, to the output of a 20 ms decoder.

Forcing is performed when the following logical condition is valid: 25 Stationary image processing is performed in 20 ms mode when

datv (2) = "80 ms block" and datv (l) is different from "80 ms block" OR

30 datv (2) = "80 ms block" and datv (4) is different from "80 ms block"

Coercion can be done in several different ways. In the first embodiment shown in Fig. 9, this inference can be made in the known DATV modifier block 92 (DATV modifier) after the DATV decoder 91 as a subroutine thereof.

The modifier block makes the decision information of the interpolator to be used. The motion data decoded by the DATV decoder is fed to the field memories A, B, C and the data just received

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92540 15 also for the DATV editing block. The memory arrangement is the same as in Fig. 8. The decision information "branch decision", which is the same as the output of the DATV field memory B and corresponding to the output of the field memory 82, Fig. 8, is applied to the SSPC 942 and the demultiplexer 5 947. The decision information sets the SSPC mode. In addition, the datv (l) and datv (4) data and the field number RFN to be processed are exported to the SSPC. The RFN information and the input signal of the DATV field memory A are further applied to the line deshuffler 101. The DATV modification block 92 examines whether the above logic condition is valid and, if valid, forces the decision signal to "branch" for 20 ms. mode.

According to the second embodiment shown in Figure 10, the SSPC makes a forcing decision. It needs the 15-digit RFN of the field to be processed, as well as the datv (i), datv (3), and datv (4) information. These are obtained from the DATV decoder 108 and the DATV field memories B and C. The output of the field memory B is normally a branch decision signal, but if said logical condition is met, the monitoring logic in the SSPC raises a flag indicating "forced 20 20 ms mode". The demultiplexer 107 monitors the flag and when it detects the flag is up, it does not care about the branch decision signal received from the DATV memory B but switches to the 20 ms branch 104. The flag is raised when there is a temporal limit in the received MAC fields. Thus, the flag is raised 25 in the case of Case 2, 3, 10, 11, 15, or 16 of Table 6A. The flag forces the SSPC to 20 ms mode regardless of the branch decision information.

The present invention does not cause major changes to the prior art subsampling pattern restorer SSPC. A variable indicating forcing a 20 ms interpolator must be added to the control logic, or the control logic changes the received problem point decisions to 20 ms mode. The invention makes it possible to prevent the sawing of the vertical and diagonal edges of saturated colors, the so-called "stamp effect", as well as horizontal lines of line at the vertical and diagonal edges. In addition, the various processing options are reduced from eighteen to twelve.

Claims (10)

92540 16 A method for controlling an HDMAC decoder for generating a stationary high-definition picture area from a MAC video signal, comprising chrominance samples of a high-definition picture divided into picture areas 5 and subsampled according to motion content, wherein the encoder: - simultaneously derives (SSPC) such that its first input has a first field in time, the second input has a second field in time, the third input has a third field in time, and the fourth input has a last field in time, and the subsample pattern restorer (SSPC) forms one of three samples derived therefrom. al-15 from the original subsampling pattern, - deriving the formed subsampling pattern into three signal link processing branches, the first branch of which forms a high-definition image of the stationary image area the second branch forms a high-resolution image of the slow-motion image area formed from the subsampled pattern, and the third branch forms a high-resolution image of the high-motion image image control area. high-definition television image • at a time to the output of the decoder, characterized in that when the samples of the second input belong to the stationary image area, the subsampling pattern restorer (SSPC) is forced to form a fast-moving image area subsampling pattern and said third signal processing branch is then decoded the samples of the first or last si input field belong to the motion image area. 35 A method according to claim 1, characterized in that the forcing is performed when the second, third and fourth inputs have samples representing the stationary image area II 92540 17 but the first input has samples representing the image area containing motion. A method according to claim 1, characterized in that the forcing is performed when the first and second inputs have samples representing a stationary image area but the third and fourth inputs have samples representing an image area containing motion. A method according to claim 1, characterized in that the forcing is performed when the first, second and third inputs have samples representing a stationary image area but the fourth input has samples representing an image area containing motion. 15 A method according to claim 1, characterized in that in each MAC field, the motion information of each image area (DATVj) is stored in a data field memory from which it can be read when the area subsampling pattern is formed. A method according to claim 5, characterized in that the image area of the field entering the first input of the subsampling pattern restorer corresponds to the first motion data datv (1), the image area of the field entering the second input corresponds to the second motion data datv (2) and the image input of the fourth input the image area of the field corresponds to the fourth motion data datv (4), where the forcing is performed when datv (2) = "stationary area" and datv (l) = "area containing motion", or datv (2) = "stationary area" and datv (4) = "area with motion 30". An HDMAC decoder for generating a high definition picture from a MAC video signal, comprising chrominance samples of a high definition picture divided into picture areas and subsampled according to motion content, the encoder comprising: - a subsampling pattern restorer (SSPC) (103; 943) which is simultaneously routed; field samples such that its first input 92540 18 (1) has a temporal first field, the second input (2) has a second temporal field, the third input (3) has a third temporal field, and the fourth input (4) has a temporal last field, wherein 5 the subsampling pattern restorer (SSPC) generates one of the three original subsampling patterns from the samples derived from its inputs, and - three signal processing branches (104, 105, 106; 944, 945, 946) connected to the subsampling pattern restorer, of which 10 form the first branch (106; 946). a subsampling pattern formed from the stationary image area of the high definition image, and a second branch (105; 945) generates a high-definition image of the subsampling pattern formed of the slow-motion image area, and the third branch (104; 944) 15 forms a high-definition image of the subsampling pattern formed of the fast-moving image area, wherein the branch decision signal is connected to decode one at a time. 20. first means (A, B, C) for recording the motion content (datv (1), datv (2), datv (4)) of the image areas entering the first (1), second (2) and fourth inputs, - second means (92; 103) coupled to the first means and provided with a forced branch decision signal 25 forcing a stationary high definition image area to be formed. providing a subsampling pattern of the fast moving image area of the sub-sampling pattern restorer (103, 943) and forcing the encoder output of the third signal processing branch whenever the motion content (datv (1)) of the first incoming field 30 or the motion content (datv) of the last incoming field indicates that the field contains motion. HDMAC decoder according to claim 7, characterized in that the first means comprise successive outputs of a first (A), a second (B) and a third (C) DATV field memory and a third memory (C) indicating a first incoming input. The output of the MAC field motion content (datv (1)), the output of the second li 92540 19 memory (B) indicates the motion content of the second incoming MAC field (datv (2)) and the input of the first memory (A) indicates the motion content of the last incoming field (datv (4)). ); wherein the output (datv (2)) of the second memory (B) is also a branch decision signal. HDMAC decoder according to claim 7, characterized in that the second means (92) comprise a DATV modification block which provides both a branch termination signal and a forced branch termination signal. HDMAC decoder according to claim 8, characterized in that the second means are included in the subsampling pattern restorer (103), whereby it provides a forced branch termination signal. 92540 20