Picture signal processing mode control

Abstract: The invention relates to a method of and apparatus for controlling a picture signal processing mode. The picture signal processing mode may indicate whether the picture signal originates from movies-film and, more specifically, how the fields of the picture signal relate to the pictures of the movie-film, or whether motion vectors are reliable enough to allow for a motion-compensated picture signal processing mode. First and second motion vectors are determined (ME, D T ) for first and second fields, and a picture signal processing mode control signal is obtained by comparing (D T ), -, COMP-R) the first and second motion vectors.

Description: The invention relates to a method of and apparatus for controlling a picture signal processing mode. The picture signal processing mode may indicate whether the picture signal originates from movie-film and, more specifically, how the fields of the picture signal relate to the pictures of the movie-film, or whether motion vectors are reliable enough to allow for a motion-compensated picture signal processing mode. The invention further relates to a television signal receiver including such a picture signal processing mode controlling apparatus. Many recent proposals for novel High-Definition Television (HDTV) systems include the requirement that a control signal is to be transmitted along with the HDTV signal which gives an indication about the origin of the picture signal, because in some respects, picture signals originating from movie-film require a different treatment, i.e. picture signal processing mode, than picture signals which are picked up by a camera. For similar reasons, up-conversion algorithms to be used in Improved Definition Television (IDTV) receivers require a picture signal processing mode control signal which provides information about the origin of the picture signal. Up till now, no reliable and yet simple method of automatically detecting whether the picture signal originates from movie-film has been reported. Another problem met in IDTV receivers is that motion-compensated picture signal processing methods are potentially very suitable to provide an improved display quality of the picture signal, but that artifacts caused by motion vector estimation errors are very disturbing. Consequently, there is a need to determine when motion vectors are reliable enough to allow for a motion-compensated picture signal processing mode, and when the motion-compensated picture signal processing mode should be switched off in view of the unreliability of the motion vectors. US-A-4,864,398 discloses a television standards converter comprising a motion analyzer for analyzing the motion between consecutive fields of an input television signal. Its Fig. 12 shows a comparator receiving motion vectors from three consecutive fields to determine some erroneous conditions and some picture content information. From the comparison it can be determined whether the motion of an object stopped, whether there has been a motion vector calculation error, or whether there exists a continuous motion. EP 359 334 A discloses a method of generating picture signal processing mode control signals which indicate whether the picture signal originates from movie-film. It further discloses the indication of whether picture signals originate from movie-film by detecting whether motion is only present per picture period. In another context, it discloses determining first motion vectors for a first field and second motion vectors for a second field. US 4 998 287 A compares field n and field n-2 to determine whether the video signal received was derived from film. This document refers to a motion detector. It is, inter alia , an object of the invention to provide a simple and reliable picture signal processing control. For this purpose, the invention provides a picture signal processing control as well as a receiver for television signals using such a picture signal processing control signal, as defined in the independent claims. Advantageous embodiments of the invention are defined in the subclaims. The invention is based on the recognition that when a picture signal processor already comprises a motion vector estimator for furnishing motion vectors, a simple comparison of the motion vectors estimated for successive fields provides a reliable indication of whether the picture signal originates from film and, more specifically, how the television picture signal fields relate to the movie-film pictures. As 24 Hz film pictures are usually converted into 50 Hz television fields by scanning each film picture twice, there is no motion between the television fields which correspond to the same film picture, while there will be a finite amount of motion between television fields which do not correspond to the same film picture. A comparison of the sum of the lengths of the motion vectors of two successive fields will thus provide sufficient information about the source of the picture signal. As the transition between two successive film pictures may occur either between an even and an odd television field or between an odd and an even television field, two different film phases are possible. The first option is standardized for broadcasting, while television signals on laser vision discs have been recorded by using the second option. The option which has been used can easily be detected by a similar observation of the lengths of the motion vectors. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the drawings: Fig. 1 shows an embodiment of a first apparatus in accordance with the invention for determining whether picture signals originate from movie-film. In Fig. 1, a picture signal is applied to a motion vector estimator ME. The motion vectors estimated by the motion vector estimator ME are applied to a length-determining circuit L, which may determine the true length of the motion vectors by taking the root of the sum of the squares of horizontal and vertical components of the motion vectors, or which may simply sum the absolute values of these components. The output of the length determining circuit L is applied to a first summing circuit Σ 2T which determines the sum of the motion vectors of two subsequent field periods. This sum is a measure of the amount of activity in the picture signal and is thus called the activity signal. The output of the first summing circuit Σ 2T is compared to an activity threshold ThA by an activity comparator COMP-A to obtain an activity enable signal. The arrangement will only change its decisions about whether the picture signal originates from film if there is sufficient motion in the picture to warrant a reasonably reliable decision. The output of the length determining circuit L is also applied to a second summing circuit Σ T which determines the sum of the motion vectors of the present field period. The output of the second summing circuit Σ T is delayed by a field period T by a delay circuit D T which furnishes the summed vector lengths of a previous field period. The output of the delay circuit D T is multiplied by 1-Th and by 1+Th so as to ensure that a decision that the picture fields originate from movie-film is only taken if the summed vector length of the present field is smaller than the summed vector length of the previous field by more than a first given threshold or if the summed vector length of the present field is larger than the summed vector length of the previous field by more than a second given threshold. To this end, the output of the second summing circuit Σ T is applied to first inputs of first and second comparators COMP1 and COMP2, whose second inputs are coupled to the output of the delay circuit D T through multipliers which multiply by 1-Th and 1+Th, respectively. A logic OR-circuit combines the outputs of the comparators COMP1 and COMP2. The output of the logic OR-circuit is applied to a non-inverting input of a first logic AND-circuit AND1 and to an inverting input of a second logic AND-circuit AND2, which logic AND-circuits further receive the activity enable signal from the comparator COMP-A. The output of the first logic AND-circuit AND1 is coupled to a set input S of a set-reset flipflop FF. The output of the second logic AND-circuit AND2 is coupled to a reset input R of the set-reset flipflop FF. A data output D of the flipflop FF supplies a film indication signal F. To determine whether the transition between two successive film pictures is between an even and an odd field or between an odd and an even field, the data output D of the flipflop FF is coupled to a clock input of a D-flipflop DFF, whose data input is coupled to the output of the first comparator COMP1. The D-flipflop DFF supplies a transition mode indication signal M which is positive if the transition between two film pictures is between an even and an odd television field. The indication signals F and M can be applied for controlling the operation of a subsequent picture signal processing unit. The arrangement shown in Fig. 1 operates as follows: if the summed vector lengths of two successive fields do not differ too much, the output of the logic OR-circuit will be logic zero, and the flipflop FF will be reset to indicate that the television picture fields do not originate from film. If on the other hand, either one of the comparators COMP1 and COMP2 indicates a difference between the summed vector lengths by more than a given threshold, the output of the logic OR-circuit will be logic one, and the flipflop FF will be set to indicate that the television picture fields originate from film. When the comparisons are made during even field periods, a positive output of comparator COMP1 which indicates that the vectors of the present even field to the previous odd field are smaller than the vectors of the previous odd field to its preceding even field, also indicates that the present even field and the previous odd field correspond to the same film picture, so that the transition between two film pictures will take place between the present even field and the next odd field. Such a positive output of the first comparator can thus easily be used to indicate that the movie-film source material is scanned in the manner standardized for broadcasting. The above description clearly shows that a simple comparison of motion vectors determined for successive fields can easily be used to determine the picture signal processing mode and, more specifically, whether and how the picture signal processing should be adapted for movie-film originated pictures. The comparisons are preferably related to the total amount of motion in the picture, which can very simply be determined by adding the motion vector lengths of a television frame period. Switching between a movie-film adapted processing mode and a non-movie-film adapted processing mode is preferably only made when there is enough motion in the picture to warrant a reliable decision. As there will be no motion between the two television fields which originate from the same movie-film picture, the presence of movie-film originated television signals can very simply be determined by comparing the sums of the motion vector lengths of two field periods. More specifically, movie-film originated picture signals can be deemed to be present when the sum of the motion vector lengths of one field does not differ from the sum of the motion vector lengths of the other field by more than given thresholds. These thresholds are preferably related to the sum of the motion vector lengths, which can easily be obtained by multiplying the vector length sum of one of the fields by 1-Th and by 1+Th to obtain the range between which the vector length sum of the other field should be when non-movie-film originated picture signals are present.

Claims: A method of generating picture signal processing mode control signals (F, M), the method comprising the steps of: determining (ME) first motion vectors for a first field, and second motion vectors for a successive second field of a picture signal; and comparing (L, ΣT, DT, COMP1, COMP2) said first and second motion vectors to obtain picture signal processing mode control signals (F, M) that indicate whether said picture signal originates from movie-film. A method as claimed in claim 1, wherein said comparing step comprises the further steps of: determining (L, Σ2T) a sum of lengths of said first and second motion vectors to obtain an activity signal; and changing (COMP-A, AND1, AND2, FF) said picture signal processing mode control signals (F, M) only when said activity signal has a predetermined relation (COMP-A) with an activity threshold (ThA). A method as claimed in claim 2, wherein said picture signal processing mode control signals (F, M) are only changed when said activity signal exceeds (COMP-A) said activity threshold (ThA). A method as claimed in claim 1, wherein said comparing step comprises the further steps of: determining (ΣT, DT) a first total of lengths of said first motion vectors, and a second total of lengths of said second motion vectors; and changing said picture signal processing mode control signals (F, M) to indicate movie-film when (COMP1, COMP2, OR) said first and second totals differ by more than given thresholds (Th), and to indicate non-movie-film when said first and second totals differ by less than said given thresholds (Th). A method as claimed in claim 4 wherein said given thresholds (Th) depend on said first or said second total (ΣT). A method as claimed in claim 4, wherein said picture signal processing mode control signals (F, M) indicate a first type of movie-film originating picture signals when said first total is smaller than said second total by more than a first given threshold (Th), while said picture signal processing mode control signals (F, M) indicate a second type of movie-film originating picture signals when said first total is larger than said second total by more than a second given threshold (Th). A method as claimed in claim 1, wherein said picture signal processing mode control signals (F, M) indicate how the fields of the picture signal relate to pictures of the movie film. An apparatus for generating picture signal processing mode control signals (F, M), the apparatus comprising: means (ME) for determining first motion vectors for a first field, and second motion vectors for a successive second field of a picture signal; and means (L, ΣT, DT, COMP1, COMP2) for comparing said first and second motion vectors to obtain picture signal processing mode control signals (F, M) that indicate whether said picture signal originates from movie-film. A receiver for television signals, comprising: means for receiving and decoding said television signals to obtain picture signals; means coupled to said receiving and decoding means for enhancing said picture signals; characterized in that said enhancing means include an apparatus for generating picture signal processing mode control signals as defined in claim 8.

Inventors: BIEZEN PAUL W A C, DE HAAN GERARD, HUIJGEN HENDRIK, OJO OLUKAYODE ANTHONY, BIEZEN, PAUL W. A. C., DE HAAN, GERARD, HUIJGEN, HENDRIK, OJO, OLUKAYODE ANTHONY, BIEZEN, PAUL W. A. C., INT. OCTROOIBUREAU B.V., DE HAAN, GERARD, INT. OCTROOIBUREAU B.V., HUIJGEN, HENDRIK, INT. OCTROOIBUREAU B.V., OJO, OLUKAYODE ANTHONY, INT. OCTROOIBUREAU B.V.
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 1993
Main classification: H04N5
IPC codes: H04N5, H04N7