GB1592486A

GB1592486A - Method and apparatus for frame frequency conversion

Info

Publication number: GB1592486A
Application number: GB4830677A
Authority: GB
Original assignee: BTS Systementwicklungs GmbH
Current assignee: BTS Systementwicklungs GmbH
Priority date: 1976-11-22
Filing date: 1977-11-21
Publication date: 1981-07-08
Also published as: DE2652935C3; FR2371837A1; DE2652935A1; NL188381C; NL188381B; NL7712712A; JPH0136305B2; JPS5368123A; DE2652935B2; FR2371837B1

Description

(54) A METHOD AND APPARATUS FOR FRAME FREQUENCY CONVERSION (71) We, BTS - SYSTEMENTWICKLUNGS GmbH a German Company of R6bing- strasse 136, D-1000 Berlin 42, Germany, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method and apparatus for frame frequency conversion of television signals.

In a TV receiver the pictures are reproduced at a fixed frame frequency df for example 25 frames per second on the picture screen. If therefore moving pictures are to be recorded on a video recording medium, for example a picture disc, in order to be able to reproduce them later using a suitable play-back device on the screen of the TV receiver, it is necessary to record the moving frames at this frame frequency. This means that a comparatively large number of pictures per unit time must be recorded, which in turn results in rapid exhaustion of the limited recording capacity of the picture recording medium. If a picture recording medium is to have a performance time of 20 minutes, with the picture frequency mentioned it will be necessary for it to have a capacity of 30,000 pictures.

In many cases known recording media have an even lower storage capacity so that with such media it is not possible to obtain longer performance times, that is, if the storage capacity of the picture storage medium cannot be improved.

According to the invention, a method of frame frequency conversion of television signals, comprises storing each input signal sequence corresponding to a single picture or a component of a picture (as herein defined) in a first memory, extracting the stored sequences from the first memory in such a way as to produce a first extracted signal of which the sequences are each of shorter duration but have the same repetition frequency as the input signal sequences, then storing each first extracted signal sequence in a second memory, and extracting the stored sequences from the second memory in such a way as to produce a second extracted signal of which the sequences are each of the same duration but have a greater repetition frequency than those of the first extracted signal.

The term "component of a picture" in the present specification is taken to mean a component of a whole picture obtained by interlaced scanning, so that therefore one component of a picture can consist of the first, third, fifth etc. lines, that is to say of the odd lines while the other component of the picture consists of the second, fourth, sixth etc. lines, that is to say consists of the even lines.

Preferably each signal sequence of the first extracted signal is repeated at least twice in the second extracted signal, the first repetition being carried out simultaneously with the storage in the second memory of the corresponding sequence of the first extracted signal, and the second and any subsequent repetitions being carried out by extracting the stored sequence from the second memory.

In an alternative preferred method, each signal sequence of the first extracted signal is repeated at least twice in the second extracted signal by repeated extraction of the sequence stored in the second memory, storage of each signal sequence in the second memory being carried out during the final extraction from the second memory of the preceding signal sequence.

Preferably each sequence of the second extracted signal is re-stored in the second memory a predetermined number of times by feeding back the output of the second memory to its input.

In the method of the invention the stored signal sequences are converted at a playback frequency, which differs from the storage frequency, into pictures or components of pictures.

This is preferably carried out in such a manner that each stored signal sequence is stored simultaneously with its conversion into a picture or component of a picture and following this is extracted and converted into a picture or a component of a picture so that the storage of the signal sequence and its conversion into a picture or component of a picture occurs n times before the signal sequence corresponding to the next picture or component of a picture is converted into a picture or component of a picture, n being a whole number larger than unity.

On the basis of such a method it becomes possible in very many cases, without impairing the optical impression which an observer has on the playback of pictures, to record a substantially smaller number of pictures on a picture recording medium per unit time than is as such required by the reproduction frequency of the TV receiver (which will normally be used in the method of the invention.) The method in accordance with the invention assumes that the picture frequency, that is to say the number of picture changes per second, which is necessary before natural kinetic events appear "jerky" to the observer in most cases can be substantially lower than the usual value of 25 pictures per second of normal TV receivers.

Thus for the representation of natural kinetic events so that such events appear to occur continuously to the observer, 10 pictures per second are sufficient and it is only in the case of very rapid movements that 60 to 80 pictures per second are necessary. What is important is that in the clear majority of cases for the representation of natural kinetic events, a picture frequency of 16 pictures per second and less is sufficient. Accordingly, in the method of the invention it is sufficient in a very large number of cases to record a substantially smaller number of pictures per unit time, so that the duration of playback of a given picture recording medium can be substantially increased.

The method in accordance with the invention can also be used to repeat any desired parts of a TV programme, as for example a football game which has just been broadcast, on the picture screen in slow motion. This will be explained below in more detail with reference to one embodiment of the invention.

The invention includes an arrangement which is suitable for performing a method of frame frequency conversion in accordance with any one of the preceding claims, comprising a first memory connected to receive input signal sequences each of which corresponds to a single picture or a component of a picture (as herein defined), and being adapted to store those signal sequences and to extract the stored sequences in such a way as to produce a first extracted signal of which the sequences are each of shorter duration but of the same repetition frequency as the input signal sequences, a second memory connected following the first memory and adapted to store each first extracted signal sequence and to extract the stored sequences in such a way as to produce a second extracted signal of which the sequences each have the same duration but a greater repetition frequency than those of the first extracted signal.

Further featurcs and developments of the invention will be gathered from the following description.

The invention will now be described with reference to a few particularly preferred embodiments, which are represented diagrammatically in the accompanying drawings, in which: Figure 1 is a block circuit diagram of a first embodiment; Figure 2 is a block circuit diagram of a second embodiment; Figure 3 is a block circuit diagram of a further embodiment, which includes an encoding device; Figures 4 to 7 are traces showing the manner of operation of the memory device of Figures 1 and 2; and Figure 8 is a further embodiment showing how the arrangement in accordance with the invention may be used for slow motion replay.

Figure 1 shows a signal sequence generator 1 of which the output is connected to a memory device 2, which is connected to a signal sequence converter 3, which can for example be a conventional TV monitor having a picture screen 4.

The signal sequence generator 1 produces a succession of signal sequences, of which each sequence corresponds to an individual picture or a component of a picture. The signal sequence generator 1 can for example be a playback device for a video disc or record, which comprises the actual record player 5 with the associated scanning device, and a scanning signal conversion device 6 for converting the signals obtained on scanning the video disc or record (which for example can be optical signals) into electrical signals. When the scanning device of the record player 5 directly supplies electrical signals, the scanning signal conversion device 6 can be omitted. Therefore, at the output 7 of the signal sequence generator 1, which also forms the input of the memory device 2, signal sequences are available, of which each sequence corresponds to one picture or a component of a picture. In the present case it is assumed for brevity that each signal sequence corresponds to a complete picture.

The input signal sequences fed into the memory device 2 first pass to an electronic switch 8, which has two outputs 9 and 10, the output 9 being connected to the input of a first receiving memory 11 and the output 10 being connected to the input of a second receiving memory 12.

(These receiving memories each constitute a "first memory" referred to above.) The electronic switch 8 operates at the picture line frequency so that a first half picture is passed to the receiving memory 11, this half picture consisting of the odd lines, while a second half picture which consists of the even lines is stored in the receiving memory 12. This switching of the pictures to the memory device 2 is carried out on the input signal which has a predetermined frame frequency fs, which can for example amount to 12 1/2 pictures per second. The output of each of the two receiving memories 11 and 12 is connected by a respective clock 13 and 14 to the respective input of one output memory 15 and 16 so that therefore the half pictures stored in the receiving memories 11 and 12 are transmitted at the clock frequency of the clocks 13 and 14 to the output memories 15 and 16. The frequency of the clocks 13 and 14 will be referred to the clock frequency FT. (The output memories 15, 16 each constitute a "second memory" referred to above.) The outputs of the output memories 15 and 16 are connected by further respective clocks 17 and 18 and feedback devices 19 and 20 to an electronic switch 21, of which the output 22 forms the output of the memory device 2 and the input of the signal sequence converter 3.

Each of the feedback devices 19 and 20 is connected via a line 23 and 24 to the input of the associated output memory 15 and 16.

The clocks 17 and 18 operate at a different clock frequency fT to that of the clocks 13 and 14, the clock frequency fT being higher than the clock frequency FT.

The inputs 19a and 20a of the feedback devices 19 and 20 respectively, receive the half pictures synchronously at the frequency fT. These feedback devices are electronic switches, for example gates, which have two ouputs 19b, 19c and 20b, 20c, of which in each case the one output 19b and 20b is connected to the respective circuit line 23 or 24, while the other output 19c and 20c is connected to a respective input of the electronic switch 21. This electronic switch 21 operates in such a manner that its output 22 is connected, in synchronism with the half pictures, alternately to the output l9c of the feedback device 19 and the output 20c of the feedback device 20. Thus, the signal sequences, corresponding respectively to a whole picture, and which consist of two half picture signal sequences, appear at the output 22 at a repetition frequency fA, which in accordance with the accepted television standard comprises 25 pictures per second or 50 half pictures per second.

The manner of operation of the memory device 2 represented in Figure 1 will now be described with reference to an example, in which the signal sequences appearing at the input 7 correspond to a frame frequency of 12 1/2 pictures per second, while the signal sequences appearing at the output 22 correspond to a frame frequency of 25 pictures per second. For more detailed explanation reference is made to Figure 4, which indicates the progress of the signal sequences with time so that accordingly the horizontal axis is to be considered the time coordinate. This applies for all traces of Figure 4.

At the input 7, signal sequences A, B, C, D etc. occur, of which each corresponds to a whole picture, which has been scanned line for line, that is to say without leaving out any lines. In the present case the frame frequency fs is 12 1/2 pictures per second. The electronic switch 8 divides up each signal sequence A, B etc. in the above mentioned manner into two signal sequences Al, A2, B1 and B2 etc., which are represented at Ia and Ib and correspond respectively to half a picture in accordance with the interlaced scanning method. The signal sequences Al, B1 etc. are therefore also stored in the receiving memory 11 at the storage frequency fs. The same applies for the signal sequences A2, B2 etc. with respect to the receiving memory 12. The signal sequences Al, A2 etc. are transferred in the manner indicated at IIa and IIb from the receiving memories 11 and 12 to the output memories 15 and 16 by the clocks 13 and 14. These clocks, which are responsible for the passage of the signal sequences Al, A2, B1, B2 etc. from the receiving memories to the output memories, admittedly operate with a clock frequency FT which is equal to the storage frequence fs, but they have a line transmission frequency fz which is four times the line transmission frequency Fz with which the signal sequences, corresponding to the individual picture lines, are passed to the receiving memories 11 and 12. Thus, the sequences are transmitted to the output memories at the same sequence repetition frequency but at an increased speed. The clocking of transmission is such that the end of storage of one signal sequence in the receiving memory coincides with the end of storage of the same signal sequence in the output memory, as is indicated by the broken lines in Figure 4.

It would be possible to operate the clocks 17 and 18 and the feedback devices 19 and 20 in such a manner that simultaneously with the storage of the respective signal sequence Al, A2, B1, B2 etc. in the output memory 15 and 16 this same signal sequence would appear via the lines 23 and 24 respectively at the outputs 1 9c and 20c respectively and then the clocks 17 and 18 and the feedback devices 19 and 20 would be operated so that the signal sequences stored in the output memories 15 and 16 would be stored two more times in succession (i.e. three times in all) and would be extracted three times in succession from the output memories 15 and 16 so that each signal sequence Al, B1, A2, B2 would appear four times in all at the output l9c and 20c of the associated feedback device 19 and 20 respectively, these transfers or transmissions occurring with the line transmission frequency fz. Such a manner of operation would however make it necessary for the clocks 17 and 18 to be so operated that they would become non-conducting during each fourth clock pulse (each clock pulse corresponding to the time taken to pass a signal sequence Al, A2, B 1, B2 etc.).

A manner of operation of the clocks 17 and 18 which is simpler than that just described and in which these clocks conduct during each transmission of half a picture from the output memories, can be achieved if the signal sequences Al, A2 etc. are only extracted from the output memories after first being stored and are stored four times in all, and are then fed to the outputs l 9c and 20c, and on the extraction of the last signal sequence Al or A2, the next signal sequence B1, B2 is stored in the output memories 15 and 16. These operations are indicated at IIIa and IIIb in Figure 4, in which these representations relate to the signal sequences appearing at l 9c and 20c. The first extraction of a signal sequence Al and A2 etc.

can take place immediately after it has been stored, as is also shown in Figure 4.

Irrespective of which manner of operation of the clocks 17 and 18 and the feedback devices 19 and 20 is in fact chosen, the electronic switch 21 is operated at four times the storage frequency fs in synchronism with the signal sequences Al, A2 etc. so that these signal sequences, corresponding to half pictures, appear, as desired, at twice the issue or read out frequency fA at 22. The signal at the output 22 of the memory device 2 is represented in Figure 4 at IV. It will be seen from this that each complete picture A, B, C etc., as indicated in Figure 4 at V, is displayed twice in succession on the screen 4, that is to say the read out or issue frequency fA amounts to twice the storage frequency fs.

An illustration of a case in which the storage frequency fs is 16 2/3 pictures per second and the issue or read out frequency fA is 25 pictures per second is indicated in Figure 5. Since the display and the manner of operation are in principle similar to those of Figure 4, a more detailed explanation is not called for and it is only appropriate to point out that in this case, in which there is no simple doubling, quadrupling etc. of the storage frequency, the ratio between the storage frequency and the read out frequency being 2 to 3, one half picture Al, A2 or Bl, B2 of each picture A, B etc. appears twice and the other half picture only appears once on the screen, as is indicated at IV in Figure 5 so that alternately the first and the second half picture occur twice. In this manner will be displayed on the screen 4 not only entire pictures A, B, C but also "mixed" pictures, of which the first half picture will be the same as the first half picture of the preceding picture and the second half picture will be the same as the second half picture of the following picture, as indicated at V in Figure 5.

If one assumes the following general relationsllip fA = fs a/b to apply, the above described method can be operated so that a is a whole number larger or equal to 2 and b is a whole number larger or equal to 1. If n is taken to denote the occurrence frequency of a certain component of a picture at the input 19c and respectively 20c of the electronic switch 21, we then have the relationship n = 2fA/fs. If furthermore N is taken to denote the occurrence frequency of storage of half a picture, this number then depends upon which of the two of the above mentioned procedures is selected for the clocks 17 and 18 and the feedback devices 19 and 20. In the first of these two cases N = n - 1 while in the second case N = n.

The occurrence frequency n', with which a picture appears on the picture screen 4 is equal to a/b so that, as has already been explained with reference to Figure 5, a picture consisting of half pictures can also appear 1 1/2 times and in a corresponding manner a picture made up of half pictures can also appear 2 1/2 times, 3 1/2 times etc. on the screen. The possible frequency relationships a /b would appear to be quite sufficient for practical requirements; if a still finer graduation were to be desired, a picture would have to be broken down into more than two picture components (interlaced scanning), for b is equal to the number of component pictures, which are used to make up a whole picture.

Different possible storage frequencies fs and the corresponding values of a, b and n are given in Table I for the practical case of two components of a picture and an output or read out frequency fA of 25 pictures per second.

TABLE I fA fs a b a/b n 25 162/3 3 2 3/2 3 25 121/2 2 1 4/2 4 25 10 5 2 5/2 5 25 81/3 3 1 6/2 6 The same procedure as described above can also be employed if two half pictures Al and A2 are fed in successively at 7 instead of being fed in simultaneously. The representations of traces in Figures 4 and 5 will then apply, apart from I, k and Ib, in just the same manner, providing that the half pictures are fed in at 7 with twice the line transmission frequency Fz.

The memory device 2 must be set so that the electronic switch 8 is switched over in synchronism with the half pictures, and the line transmission frequencv fz with which the picture line signal sequences are transferred from the receiving memory 11 or 12 to the output memory 15 or 16, only needs to amount to twice the line transmission frequency Fz at the input 7. In the case of a successive input of the components of a picture it is however also possible to use a memory device 25 as is shown in Figure 2. This memory device only comprises one receiving memory 26, which is directly connected to the input 7, and has only one output memory 27, of which the feedback device 28 has its output 2 & directly connected to the output 22. In other respects the arrangement of Figure 2 corresponds with the circuit of a memory pair 11, 15 or 12, 16 of Figure 1, as regards the clocks 29 and 30, the feedback connection 31 and the input 28a and the output 28b of the feedback device 28, so that it is not necessary to provide a more detailed explanation.

The manner of operation of the memory arrangement 25 in accordance with Figure 2 will now be explained with reference to Figures 6 and 7, in which the respective signal sequences are indicated along the same lines as in Figures 4 and 5. In accordance with Figure 6 a storage frequency of 12 1/2 pictures per second is converted into a read out or output frequency of 25 pictures per second, and in accordance with Figure 7 a storage frequency of 16 2/3 pictures per second is converted into the same output frequency.

The signal sequences occurring at the input 7 of the storage device 25 are represented at I in Figures 6 and 7, in which the symbols Al, A2, B1, B2 etc. have the same meaning as in Figures 4 and 5. These signal sequences are transmitted from the receiving memory 26 to the output memory 27 at a line transmission frequency fz which amounts to twice the line transmission frequency Fz with which they are supplied to the receiving memory 26. The transfer or transmission between these two memories occurs in such a manner that the first storage operation for the two half pictures in the output memory 27 as shown at II is terminated practically simultaneously with the storing of the half pictures in the receiving memory 26, as is indicated by the broken line in Figures 6 and 7. The frequency of picture transfer is equal to the storage frequency fs.

As will furthermore be seen from Figures 6 and 7, the signal sequences Al, A2 andBl, B2 etc., corresponding to the components of pictures, are simultaneously supplied, on first being entered into the output memory 27, and via the circuit line 31 and the feedback device 28 to the output 22, of which the signal sequences are indicated at III in Figures 6 and 7. With such a manner of operation in the case successive components of pictures, regular clock sequences of the clock 30 occur. As a consequence in Figure 6 each picture only has to be stored once in memory 27, and in Figure 7 only half of each picture has to be stored in the output memory 27. Alternatively each picture may be stored twice or 16 times respectively in the output memory. In other respects the equations specified in Table I apply, in which case however the occurrence frequency n' for half a picture at the output of the feedback device amounts to half the value of n and furthermore the number N" of storage operations for half a picture in the output memory is equal ton'.

Figure 3 shows a modified form of the storage device of Figure 1. This storage device can be used in cases where the picture scanned in the disc player 5 consists of three successively scanned pictures, that is to say a red component, a green and simultaneous luminance component, and a blue component of the same picture, which in what follows are denoted as the R, Y and B pictures. The input 7 is connected to the input of an electronic switch 33, which has two outputs, of which the one is connected to the input of the electronic switch 34 and the other is connected to the input of the electronic switch 35. The two last mentioned electronic switches each have three outputs, connected respectively to receiving memories 1 lea, 1 ib, 1 inc and 12a, 12b and 12c. The clocking of the electronic switches 33, 34 and 35 is such that in the receiving memories 1 lea and 12a one respective R half picture is stored while in the receiving memories 1 lb and 1 2b one respective Y half picture is stored while in the receiving memories 1 1c and 1 2c one respective B half picture is stored. The half pictures in the receiving memories 1 la to 1 lc consist of the odd lines and the half pictures in the receiving memories 1 2a to 12c consist of the even lines. In other respects the clocks 1 3a to c and 14a to c and also 17a toc and 1 8a toc are the same as the clocks 13 and 14 and 17 and 18 respectively.

Furthermore the feedback devices 19d to 19f and 20d to 20f are the same as the feedback devices ] 9 and 20. The lines 23a to c and 24a to c correspond to the lines 23 and 24 in Figure 1. These parts corresponding to each other also operate in accordance with the manner of operation explained in conjunction with Figure 1 so that at the outputs (indicated by the arrows in Figure 3) of the feedback devices 1 9d to f and 20d to f, R, Y and B half pictures appear in the form of signal sequences at an output or read out frequency fA differing from the frequency fs of storage, and from them an R, Y and B picture results. In order to ensure that these pictures occur simultaneously, in two of the receiving memories 1 la to 1 1c and 1 2a to 1 2c delay circuits are provided, which serve to provide compensation timing.

Between the outputs of the feedback devices in Figure 3 and the output 22 of the memory device, an encoding circuit arrangement 45 is provided, which undertakes the R, Y and B encoding so that the signals at the output 22 can be fed directly to a TV receiver. At the input 46 audio signals can be supplied to the audio part 47 so that the signal taken from the output 22 can if necessary have an audio component.

Finally Figure 8 shows a further embodiment of the invention, which can be connected with the receiving part 37 and the reproduction part 38 of a TV receiver and with which instantaneous scenes, for example the scoring of a goal in a football match, can be repeated on the picture screen 48 in slow motion. For this purpose a memory device 25 of the type shown in Figure 2 is provided, but it differs from the memory device shown in Figure 2 in that the receiving memory 26' has a substantially higher capacity than the receiving memory 26, for example a capacity of 500 pictures, something which corresponds to a playback time of 1 minute at a normal speed. The input 7 of the memory device 25 is connected to the output 37a of the receiving part of the TV set via a switch 39, while the output 22 can be connected via a switch 40 to the input 38a of the reproduction part of the TV set. Furthermore an electronic switch 41 is provided, via which the output 22 can be connected to the input 7. Finally the arrangement has a switching device 42, which can be used to temporarily interrupt the normally existing connection between the output 37a and the input 38a, and which simul taneously actuates the electronic switch 41, the clocks 29 and 30 and the feedback device 28.

(The control connections are not shown in the drawing in order to simplify it). Finally the switching device 42 can also be used to change the clock frequency of the clock 29.

The attachment shown in Figure 8 operates in the following manner: During normal TV reception there is a connection not only from the input 38a, via the switch 42, to the output 37a but also from the latter, via the switch 39, to the input 7 of the memory device 25. Accordingly the receiving memory 26' has supplied to it the TV pictures which have just been received and this receiving memory is connected so that the signals of the TV pictures stored are fed through continuously from the input 7 to the output of the clock 29, but the signals arriving there are not passed on, when the clock 29 is not switched on.

Therefore in the memory 26' the respective last-received TV pictures are stored, in the present case the last-received 500 pictures. During normal reception the switches 40 and 41 are open.

When the user of the TV receiver wishes to repeat a scene which has just appeared, for example a goal scene, in slow motion, then he will operate, immediately at the end of this s the clock 29, operates in such a manner that the pictures are returned to the receiving memory 26' in the same manner as such pictures are otherwise supplied to it from the receiving part 37, that is to say in such a manner that the clock 44 passes the pictures at a lower line transmission frequency from the intermediate memory 43 than that line transmission frequency with which the pictures are fed to the intermediate memory. As a consequence of this, after performance of the repeated scene, the receiving memory 26' is in the same condition as at the beginning of operation of the switching device 42. It is therefore possible to repeat the scene as often as desired on the screen and it is furthermore possible to change the clock frequency of the clocks 29 and 44 and of the electronic switch 41, so that in this manner the slow motion replay can be made even slower or can be speeded up. Preferably the clock sequences can be so changed that between a normal speed and an extreme slow motion form several possible intermediate stages can be selected.

WHAT WE CLAIM IS: 1. A method of frame frequency conversion of television signals, comprising storing each input signal sequence corresponding to a single picture or a component of a picture (as herein defined) in a first memory, extracting the stored sequences from the first memory in such a way as to produce a first extracted signal of which the sequences are each of shorter duration but have the same repetition frequency as the input signal sequences, then storing each first extracted signal sequence in a second memory, and extracting the stored sequences from the second memory in such a way as to produce a second extracted signal of which the sequences are each of the same duration but have a greater repetition frequency than those of the first extracted signal.

2. A method in accordance with Claim 1, in which each signal sequence of the first extracted signal is repeated at least twice in the second extracted signal, the first repetition being carried out simultaneously with the storage in the second memory of the corresponding sequence of the first extracted signal, and the second and any subsequent repetitions being carried out by extracting the stored sequence from the second memory.

3. A method in accordance with Claim 1, in which each signal sequence of the first extracted signal is repeated at least twice in the second extracted signal by repeated extraction of the sequence stored in the second memory, storage of each signal sequence in the second memory being carried out during the final extraction from the second memory of the preceding signal sequence.

4. A method in accordance with any preceding claim, in which each sequence of the second extracted signal is restored in the second memory a predetermined number of times by feeding back the output of the second memory to its input.

5. A method in accordance with Claim 1, in which each stored signal sequence is stored simultaneously with its conversion into a picture or component of a picture and following this is extractd and converted into a picture or a component of a picture so that the storage of the signal sequence and its conversion into a picture or component of a picture occurs n times before the signal sequence corresponding to the next picture or component of a picture is converted into a picture or component of a picture, n being a whole number larger than unity.

6. A method in accordance with Claim 5, in which after its (n + 1)th conversion into a picture or component of a picture the stored signal sequence is erased or is replaced by the signal sequence corresponding to the next picture or component of a picture, and this signal sequence is if required stored m times and then again converted into a picture or a component of a picture, before the signal sequence corresponding to the next picture but one is converted into a picture or a component of a picture, m being a whole number larger than unity and which can differ from n.

7. A method in accordance with Claim 5, in which each signal sequence is stored n times and is converted into a picture or a component of a picture.

8. A method in accordance with any one of the preceding claims, in which during or before the conversion of a stored signal sequence into a picture or a component of a picture at least the signal sequence corresponding to the next picture or component of a picture Is stored.

9. A method in accordance with claim 8, in which a predetermined number of signal sequences, which correspond to a number of sequentially occurring pictures or components of pictures, is stored, and before the beginning of the conversion of these signal sequences into pictures or components of pictures the respective signal sequence which has been stored for the longest time is erased at a predetermined frequency and simultaneously, at the same frequency, a signal sequence is stored, which directly follows the last signal sequence stored.

10. An arrangement which is suitable for performing a method of frame frequency conversion in accordance with any one of the preceding claims, comprising a first memory connected to receive input signal sequences each of which corresponds to a single picture or a component of a picture (as herein defined), and being adapted to store those signal sequences and to extract the stored sequences in such a way as to produce a first extracted signal of which

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the clock 29, operates in such a manner that the pictures are returned to the receiving memory 26' in the same manner as such pictures are otherwise supplied to it from the receiving part 37, that is to say in such a manner that the clock 44 passes the pictures at a lower line transmission frequency from the intermediate memory 43 than that line transmission frequency with which the pictures are fed to the intermediate memory. As a consequence of this, after performance of the repeated scene, the receiving memory 26' is in the same condition as at the beginning of operation of the switching device 42. It is therefore possible to repeat the scene as often as desired on the screen and it is furthermore possible to change the clock frequency of the clocks 29 and 44 and of the electronic switch 41, so that in this manner the slow motion replay can be made even slower or can be speeded up. Preferably the clock sequences can be so changed that between a normal speed and an extreme slow motion form several possible intermediate stages can be selected. WHAT WE CLAIM IS:

1. A method of frame frequency conversion of television signals, comprising storing each input signal sequence corresponding to a single picture or a component of a picture (as herein defined) in a first memory, extracting the stored sequences from the first memory in such a way as to produce a first extracted signal of which the sequences are each of shorter duration but have the same repetition frequency as the input signal sequences, then storing each first extracted signal sequence in a second memory, and extracting the stored sequences from the second memory in such a way as to produce a second extracted signal of which the sequences are each of the same duration but have a greater repetition frequency than those of the first extracted signal.

the sequences are each of shorter duration but of the same repetition frequency as the input signal sequences, a second memory connected following the first memory and adapted to store each first extracted signal sequence and to extract the stored sequences in such a way as to produce a second extracted signal of which the sequences each have the same duration but a greater repetition frequency than those of the first extracted signal.

11. An arrangement in accordance with Claim 10, in which the second memory has feedback means for feedback of the signal sequences one or more times.

12. An arrangement in accordance with Claim 10, or 11 in which the first memory possesses a storage capacity which corresponds to a plurality of pictures.

13. An arrangement in accordance with Claim 12, in which between the input of the first memory and the output of the second memory there is connected an intermediate memory having a clock.

14. An arrangement in accordance with Claim 13, in which an electronic switch is connected to the input of the intermediate memory.

15. An arrangement in accordance with any one of Claims 10 to 14, in which the first and the second memory and any intermediate memory that is present consist of two half picture memories connected in parallel.

16. An arrangement in accordance with Claim 15, in which each half picture memory consists of three parallel memories, that is to say an R half picture memory, a Y half picture memory and a B half picture memory.

17. An arrangement in accordance with Claim 16, in which it comprises time delay circuits are connected to the parallel half picture memories for compensation for differences in time, which arise owing to the sequential entry of the signals in the parallel half picture memories.

18. An arrangement in accordance with Claim 10 substantially as described above and as illustrated in Figure 1 of the accompanying drawings.

19. An arrangement in accordance with Claim 10 substantially as described above and as illustrated in Figure 2 of the accompanying drawings.

20. An arrangement in accordance with Claim 10, substantially as described above as as illustrated in Figure 3 of the accompanying drawings.

21. An arrangement in accordance with Claim 10 substantially as described above and as illustrated in figure 8 of the accompanying drawings.

22. A method of frame frequency conversion which is substantially as described with reference to the accompanying drawings.