Abstract:
A method for processing video signals including three fields which are sequentially related involves: determining whether field motion exists between the first field and the second field and generating a first detection signal corresponding to the second field; and determining whether the first field is capable of being combined with the second field according to the first detection signal.

Description:
BACKGROUND OF INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to an apparatus for processing video signals, and more particularly, to an apparatus for determining a film mode of the video signals.  
         [0003]     2. Description of the Prior Art  
         [0004]     In interlaced scanning, odd scan lines and even scan lines of a frame are scanned in sequence. Thus, each frame is actually composed of two fields: an odd field and an even field. Progressive scanning, which is also referred to as non-interlaced scanning, combines the odd and the even field into one frame and then sequentially scans the frame in double horizontal frequency so that the quality of the display image is improved.  
         [0005]     Since field motion may exist between two fields, combining two fields having field motion into a frame may result in a sawtooth phenomenon within the frame and thereby deteriorate image quality. Therefore, before determining a merge direction of each field of a video data, the film mode, e.g., 2:2 pull-down or 3:2 pull-down, of the video data should be determined first.  
         [0006]     The conventional method needs to determine a specific number of fields to identify the film mode of the video data. However, the film mode of the video data may not be consistent from the beginning to the end, and furthermore, switching the film mode may have no regulation. As a result, it may be impossible to identify the film mode of the video data of the prior art and thereby impossible to determine the merge direction of each field within the video data. In this situation, the image quality of the video data is decreased.  
       SUMMARY OF INVENTION  
       [0007]     It is therefore an objective of the claimed invention to provide a method and apparatus for determining the merge direction of a field according to the detection results of field motion.  
         [0008]     According to the claimed invention, a method for processing video signals is disclosed. The method includes: determining whether field motion exists between the first field and the second field and thereupon generating a first detection signal corresponding to the second field; and determining whether the first field is capable of being combined with the second field according to the first detection signal.  
         [0009]     A device for determining video signals is disclosed in the invention. The device includes: a first motion detector for determining whether field motion exists between the first field and the second field and for thereupon generating a first detection signal; and a decision unit coupled to the first motion detector for determining whether the first field is capable of being combined with the second field according to the first detection signal. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0010]      FIG. 1  is a block diagram of a video detector according to the invention.  
         [0011]      FIG. 2  is a diagram of a video sequence according to the film mode of 2:2 pull-down.  
         [0012]      FIG. 3  is a diagram of a video sequence according to the film mode of 3:2 pull-down.  
         [0013]      FIG. 4  is a diagram of a video sequence having different film modes.  
         [0014]      FIG. 5  is a flowchart of a method for determining video signals according to the invention.  
         [0015]      FIG. 6  is another diagram of a video sequence having different film modes. 
     
    
     DETAILED DESCRIPTION  
       [0016]     Please refer to  FIG. 1 , which depicts a block diagram of a video detector  100  according to the invention. The video detector  100  comprises a first motion detector  110  for determining whether field motion exists between a first field and a second field, and for thereupon generating a first detection signal corresponding to the second field, wherein the first and the second fields are adjacent fields. A buffer  120  is for temporally storing the data outputted from the first motion detector  110 . A decision unit  130  is for determining the merge direction of the second field according to the first detection signal. A pattern detector  140  is for determining the pattern of a plurality of detection signals to assist the decision unit  130  to decide the merge direction of the second field. Additionally, a second motion detector  150  is for determining frame motion to generate a frame motion signal. The frame motion signal is regarded as a reference by the decision unit  130  to improve the detection correctness of the video detector  100  of the invention.  
         [0017]     In an embodiment, the first motion detector  110  is used as a field motion detector, and the second motion detector  150  is used as a frame motion detector. As the architecture of the first motion detector  110  and the second motion detector  150  are well known in the art, further details are omitted here.  
         [0018]     In one embodiment, the pattern detector  140  comprises a first pattern comparator  142  for determining whether a plurality of detection signals matches a first pattern; and a second pattern comparator  144  for determining whether a plurality of detection signals matches a second pattern. In an embodiment, the first pattern corresponds to the film mode of 2:2 pull-down, and the second pattern corresponds to the film mode of 3:2 pull-down. In addition, the second pattern comparator  144  can verify the determined film mode according to the frame motion signals outputted from the second motion detector  150 .  
         [0019]      FIG. 2 ,  FIG. 3 , and  FIG. 4  are diagrams of video sequences. Each field is labeled with a letter plus a number. Fields having the same letter are generated from the same film frame and each of the fields is assigned with a corresponding number. If one detection signal corresponds to a first value (such as logic 0), it means no field motion exists between the two fields corresponding to the detection signal, e.g. the fields A 1  and A 2  in  FIG. 2 . If one detection signal corresponds to a second value (such as logic 1), it means field motion exists between the two fields corresponding to the detection signal, e.g. the fields B 2  and C 1  in  FIG. 2 . In addition, if one frame motion signal corresponds to the second value (logic 1), it means frame motion exists between the two fields corresponding to the frame motion signal, e.g. the fields A 1  and B 1  in  FIG. 2 . Similarly, if one frame motion signal corresponds to the first value (logic 0), it means no frame motion exists between the two fields corresponding to the frame motion signal, e.g. the fields C 1  and C 3  shown in  FIG. 3 .  
         [0020]     When the film mode of the video sequence is 2:2 pull-down, as shown in  FIG. 2 , a pattern of “01” repeatedly appears in the sequence of the detection signal and all frame motion signals are logic 1.  
         [0021]     When the film mode of the video sequence is 3:2 pull-down, as shown in  FIG. 3 , a pattern of “00101” repeatedly appears in the sequence of the detection signal and a pattern of “01111” is repeatedly presented in the sequence of the frame motion signal.  
         [0022]      FIG. 4  depicts a diagram of a video sequence with a portion of 2:2 pull-down and a portion of 3:2 pull-down. Please refer to  FIG. 5 , which depicts a flowchart of a method for determining video signals according to the invention. The steps of the flowchart  500  are described as follows:  
         [0023]     In step  504 , the first motion detector  110  determines field motion and generates a detection signal. For example, receiving a field E 1 , the first motion detector  110  generates a detection signal  406  corresponding to the field E 1  according to the field E 1  and the neighboring field D 1 .  
         [0024]     In step  506 , receiving the detection signal  404 , the decision unit  130  decides a possible merge direction for the field D 1  based on the detection signal  404 . For example, the detection signal  404  is logic 0. Thus, the decision unit  130  maybe concludes that the field D 1  can be merged with the preceding field C 2 , accordingly.  
         [0025]     In step  508 , the decision unit  130  further determines the possible merge direction for the field D 1  according to the detection signal  406 . As shown in  FIG. 4 , the detection signal  406  is logic 1, which represents that field motion exists between the fields E 1  and D 1 . Thus, to avoid sawtooth images, the decision unit  130  decides that the field D 1  cannot merge the succeeding field E 1 .  
         [0026]     In this embodiment, the decision unit  130  decides the merge direction of the field D 1  based on one or both of the results obtained in steps  506  and  508 , and thereupon outputs a first indication signal in step  512 . The first indication signal represents the merge direction of the field by different values and characters. For example, the first indication signal represents that the field can only be merged with the preceding field by value “0”; represents that the field can only be merged with the succeeding field by value “1”; represents that the field can only be merged with the preceding field or the succeeding field by value “2”; and represents that field cannot be merged with other fields by value “3”. In this embodiment, the decision unit  130  can output a value “0” as the first indication signal to represent that the field D 1  can be merged with the preceding field C 2 .  
         [0027]     If two improper fields are merged into one frame, it easily results in sawtooth phenomenon within the frame. Avoiding an incorrect decision, the method of the invention can further utilize the second motion detector  150  to verify the determining result of the first motion detector  110 .  
         [0028]     In a second embodiment of the invention, the second motion detector  150  of the video detector  100  determines whether frame motion exists between two fields. The determining result of the second motion detector  150  can be employed to verify the correctness of the detection signal generated by the first motion detector  110 . In a preferred embodiment, a threshold value used by the second motion detector  150  while detecting frame motion is smaller than a threshold value used by the first motion detector  110  while detecting field motion. In other words, the determination of the second motion detector  150  is stricter than the first motion detector  110 .  
         [0029]     The threshold value of the first motion detector  110  needs to be set properly. For example, the fields D 1  and C 2  of  FIG. 4  are assumed from different film frames and therefore field motion exists between the two fields, so the detection signal  404  should be logic 1. If the threshold value used by the first motion detector  110  is too large and the pixel difference between the fields D 1  and C 2  is smaller than the threshold value (i.e. the fields D 1  and C 2  are similar), the first motion detector  110  mistakenly concludes that there is no field motion between the fields D 1  and C 2  and outputs an incorrect detection signal  404  (at logic 0 state) as shown in  FIG. 4 . The incorrect detection signal  404  leads the decision unit  130  to make an inaccurate decision. In  FIG. 4 , for example, both the detection signals  402  and  404  are logic 0, which represents that no field motion exists between the fields C 2  and C 1 , and that no field motion exists between fields D 1  and C 2 . Accordingly, the decision unit  130  concludes that the fields D 1  and C 1  are generated from the same film frame. However, a frame motion signal  414  corresponding to the field D 1  is logic 1 as shown in  FIG. 4 , which represents there is frame motion between fields D 1  and C 1 . Accordingly, it can be determined that the fields D 1  and C 1  do not come from the same film frame. As a result, in the second embodiment of the invention, the decision unit  130  overthrows the correctness of the detection signal  404  according to the frame motion signal  414  in step  506  or  512  and determines that the field D 1  cannot be merged with the field C 2 . In addition, according to the determining result in step  508  as mentioned above, the field D 1  cannot be merged with the field E 1 . The decision unit  130  outputs a value “3” as the indication signal corresponding to the field D 1  accordingly. In other words, the field D 1  should be de-interlaced by using intra-field interpolation.  
         [0030]     In general, a steady video sequence has specific film mode, such as 3:2 pull-down, 2:2 pull-down, or another pull-down ratio. In a preferred embodiment, the video detector  100  can use the film mode information of the video sequence to assist in determining the merge direction of the field. Before the film mode of the video sequence is determined, the video detector  100  can use detection signals or both the detection signals and the frame motion signals to determine the merge direction of fields. As in the above illustration, the method and architecture of the invention can be applied in regular, part regular, and irregular video sequences to avoid merging incorrect fields.  
         [0031]     In a third embodiment of the invention, the video detector  100  first utilizes the pattern detector  140  to detect whether the detection signals match a predetermined film mode in step  510 . In a preferred embodiment, the pattern detector  140  simultaneously uses the first pattern comparator  142  and the second pattern comparator  144  to perform a pattern comparison in order to determine whether the video sequence matches the first pattern, the second pattern or without regulation. In practice, the number of the detection signals compared by the first pattern comparator  142  and the second pattern comparator  144  are not necessarily the same.  
         [0032]     For example, receiving the detection signal  404  of the field D 1 , the first pattern comparator  142  detects if the last two detection signals including the detection signal  404  match “0X” or “X0” pattern to determine whether the current video sequence matches the film mode of 2:2 pull-down. In this example, “X” means the detection signal can be logic 0 or logic 1. As shown in  FIG. 4 , the detection signal  404  and a previous detection signal  402  are both logic 0 and that matches the “0X” or “X0” pattern. Accordingly, the first pattern comparator  142  concludes that the current video sequence may be 2:2 pull-down. Concurrently, the second pattern comparator  144  detects if the last five detection signals including the detection signal  404  match “00X0X,” “0X0X0,” “X0X00,” “0X00X,” or “X00X0” pattern to determine whether the current video sequence matches the film mode of 3:2 pull-down. As shown in  FIG. 4 , the field D 1  and preceding four fields (i.e. fields B 1 , B 2 , C 1  and C 2 ) correspond to detections “10100”, which matches the “X0X00” pattern. Thus, the second pattern comparator  144  concludes that the current video sequence may be 3:2 pull-down.  
         [0033]     In step  510 , if any of the comparisons of the first and second pattern comparators  142  and  144  is positive, this means that the current video sequence is steady. As a result, the decision unit  130  can apply the above methods to determine the merge direction of the field D 1  in step  512 . In practice, the video detector  100  can use only one pattern comparator to determine whether the received video sequence is steady.  
         [0034]     In a fourth embodiment of the invention, the pattern detector  140 , in step  510 , further uses the detection result of the second motion detector  150  to verify the correctness of pattern detection. For example, as shown in  FIG. 4 , the frame motion signals correspond to the five fields prior to the field D 1 , i.e. fields A 3 , B 1 , B 2 , C 1 , and C 2 , are “01111” and that matches the sequence pattern of 3:2 pull-down in  FIG. 3 . Therefore, if the frame motion signal  414  corresponding to the following field D 1  is logic 0, the pattern of 3:2 pull-down is confirmed. However, if the frame motion signal is logic 1, not logic 0, this means the film mode determined by the second pattern comparator  144 , 3:2 pull-down, may be incorrect. As a result, the second pattern comparator  144 , in step  510 , changes its determination to indicate that the film mode of the current video sequence is not 3:2 pull-down according to the detection result of the second motion detector  150 .  
         [0035]     In step  512 , the decision unit  130  outputs a value “0” as the first indication signal to represent that the field D 1  can only be merged with the preceding field C 2  based on the result of the above steps.  
         [0036]     Regarding another field F 1  in  FIG. 4 , a detection signal  408  corresponding to the field F 1  is logic 1, and this means there is field motion between the field F 1  and a preceding field E 3 . Accordingly, the decision unit  130  concludes that the field F 1  cannot be merged with the preceding field E 3  in step  506 . A detection signal  410  corresponding to a field G 1  posterior to the field F 1  is also logic 1, and this means there is also field motion between the field F 1  and the succeeding field G 1 . Therefore, the decision unit  130  concludes that the field F 1  cannot be merged with the succeeding field G 1 , either. As a result, the decision unit  130 , in step  512 , outputs a value “3” as the first indication signal to indicate that the field F 1  cannot be merged with its neighboring fields, E 3  or G 1 . In other words, the field F 1  should be de-interlaced by using interpolation. According to the video determining method of the invention, when the decision unit  130  concludes that one field cannot be merged with its preceding or succeeding field in steps  506  and  508 , the decision unit  130 , in step  512 , can directly output a value “3” to indicate that the field cannot be merged with neighboring fields without the detection results obtained by the pattern detector  140  and the second motion detector  150 . On the other hand, when the decision unit  130  concludes that one field can be merged with its preceding or succeeding field in steps  506  and  508 , the decision unit  130  determines in step  512  the merge direction of the field by the detection result obtained by the pattern detector  140  in step  510  to verify the conclusions obtained in steps  506  and  508 . As a result, the detection correctness of the invention is thereby greatly improved.  
         [0037]     In practical implementations, in order to facilitate the following stages to perform other video processing functions, such as merging fields or pixel interpolation etc., the decision unit  130  can generate a second indication signal to represent the film mode of the current video sequence according to the detection results of the first and second pattern comparators  142  and  144  of the pattern detector  140 . The second indication signal can employ different values or characters to represent the film mode of the video sequence. For example, the second indication signal can use value “0” to represent that the film mode of the video sequence is 2:2 pull-down; use value “1” to represent that the film mode of the video sequence is 3:2 pull-down; and use value “2” to represent that the video sequence is irregular.  
         [0038]     Note that the first and second pattern comparators  142  and  144  of the pattern detector  140  operate independently and both update their detection result depending upon the latest detection signal outputted from the first motion detector  110 . In  FIG. 6 , for example, when the video detector  100  only receives fields L 1  and L 2 , the first motion detector  110  outputs a detection signal  602  corresponding to the field L 2 . At that moment, both the pattern comparators  142  and  144  cannot determine the film mode for the received fields due to the sequence of detection signals being too short. When the first motion detector  110  outputs a detection signal  604 , the second pattern comparator  144  still cannot determine the film mode of the received fields due to the sequence of detection signals being not long enough. The first pattern comparator  142 , however, needs only two detection signals to determine the film mode. As shown in  FIG. 6 , the detection signals  602  and  604  are logic 0 and logic 1, respectively. Since the two detection signals match the “0X” pattern, the first pattern comparator  142  concludes that the current video sequence may be 2:2 pull-down.  
         [0039]     The second pattern comparator  144  determines whether the film mode of the video sequence is 3:2 pull-down when receiving five detection signals. For example, the five detection signals  602 ,  604 ,  606 ,  608 , and  610  form a “01010” sequence and that matches the “0X0X0” pattern. At that moment, the second pattern comparator  144  concludes that the current video sequence may be 3:2 pull-down accordingly. On the other hand, the last two detection signals  608  and  610  form a “10” sequence and that also matches the “X0” pattern, so that the first pattern comparator  142  concludes that the current video sequence may be 2:2 pull-down. As mentioned above, the detection results of the first pattern comparator  142  and the second pattern comparator  144  are independent of each other. As shown in  FIG. 6 , when receiving a next field O 1 , a detection signal  612 , logic 1, corresponds to the field O 1  is generated. At that moment, the first pattern comparator  142  concludes that the latest film mode may be 2:2 pull-down due to the last two detection signals  610  and  612  form a “O 1 ” sequence. The second pattern comparator  144 , however, concludes that the latest film mode is not 3:2 pull-down due to the last five detection signals  604 ,  606 ,  608 ,  610 , and  612  form a “10101” sequence which does not match the sequence of 3:2: pull-down.  
         [0040]     As illustrated above, the video determining method of the invention can conclude the film mode of the video sequence after receiving only a few fields. In addition, each of the pattern comparators for determining different film modes operates independently. Thus, when the film mode of the video sequence is changed, the invention can conclude that the video sequence is steady if any of the detection results of the pattern comparators is positive. As a result, the number of detection signals required for the pattern detector  140  to determine film mode is greatly reduced. Additionally, while determining the new film mode of the video sequence, the merge direction of each field can be determined simply based on the detection results obtained in steps  506  and  508 , or each field can be de-interlaced using a pixel interpolation method.  
         [0041]     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.