Abstract:
A bad editing detection device is provided to pre-detect a bad editing of image signal, so as to avoid zigzag effect in the television image. When the input image is from a film, instead of from a video source, the line doubler performs a de-interlace for the film signal to increase the vertical resolution of the television signal. The detection device detects a bad editing before the image signal is played and adjusts the de-interlace of the line doubler to avoid zigzag effect.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a detection device and, more particularly, to a device for detecting a bad editing in image signals.  
         [0003]     2. Description of the Related Art  
         [0004]     Due to the bandwidth limitation, the current television signals are transmitted and displayed by an interlaced manner. As shown in  FIG. 1 , an image frame is generated by interlacing one even field  11 ,  13  and one odd field  10 ,  12 , wherein the odd field  10 ,  12  contains only odd lines ofthe image frame, and the even field  11 ,  13  contains only even lines of the image frame. In order to improve the vertical resolution, next generation televisions require a line doubler to perform a frequency multiplication process to increase the vertical resolution. One of the simplest frequency multiplication processes involves directly combining two adjacent fields (an odd field and another even field) to form a progressive scan frame. However, due to a time difference between the two fields, the progressive scan frame yields zigzag patterns on moving objects in the image.  
         [0005]     In order to avoid the above-mentioned problem, an advanced line doubler is provided with a motion detector to detect the moving objects in the image, and applies an inter-field interpolation of a de-interlaced process to the still parts of an image, and an intra-field interpolation of the de-interlaced process to the moving parts of an image.  
         [0006]     Another frequency multiplication process is achieved by determining whether the image source is from a film. It is known that a film is formed by recording 24 frames per second. Thus, if the film is to be displayed following the NTSC television standard, the 24 frames per second must be transformed into 60 fields per second. As shown in  FIG. 2 , this transformation technique is known as “3:2 pull down”; in other words, two continuous frames of the film are respectively transformed into 3 fields and 2 fields. For example, a frame  14  of the film is transformed into a field  18  (an odd field), a field  19  (an even field) and a field  20  (an odd field), and a frame  15  of the film is transformed into a field  21  (an even field) and a field  22  (an odd field), and so on. Therefore, if the image source is recognized as originally from a film, a perfect output, without any zigzag effect, can be obtained by combining only the odd field and the even field originally from the same film frame, and thus the moving object can be provided with the highest possible vertical resolution.  
         [0007]     In order to determine the type of image resource, a prior art technique utilizes frame motion data or field motion data to determine whether the image source is from a film.  FIG. 3  shows a frame motion detector  31  providing frame motion data. As shown in  FIG. 3 , every frame motion detector  31  is used for detecting whether two continuous odd fields or even fields are identical; if they are, a “0” is outputted; if they are not, a “1” is outputted. Therefore, if the television image is from a still picture, regardless of whether the image source is from a film or a video, the frame motion detector  31  continuously outputs a sequence “00000,00000, . . . ”; if the television image is from a moving video, the frame motion detector  31  continuously outputs a sequence “11111,11111, . . . ”; if the television image is from a moving film, the frame motion detector  31  continuously outputs a sequence “01111,01111, . . . ”.  
         [0008]     According to the output from the frame motion detector  31 , a state transition diagram of film detection, as shown in  FIG. 4 , is utilized for determining whether the television image is from a film processed by 3:2 pull down. In the state transition diagram, states A˜F are corresponding to the video mode, and states G˜K are corresponding to the film mode. As shown in the drawings, the state A is an initial state of the state transition diagram. When the input sequence is “01111”, the state will transit to state E, and a counter  41  is incremented. When the count value of the counter  41  exceeds a threshold value, the state transits from E to G, i.e., from the video mode to the film mode.  
         [0009]     If the image is processed by 3:2 pull down, the frame motion detector  31  outputs “01111” or “0000”. After the frame motion detector  31  outputs a predetermined number of the sequence “01111”, the state of the state transition diagram transits from the video mode to the film mode. Under the film mode, as long as the input remains “0XXXX”, the state remains in the film mode.  
         [0010]     The prior art technique can detect whether the image resource is from a film so as to provide a perfect frequency multiplication process. However, a bad editing of the film will impair the 3:2 pull down process, which causes zigzag effect in the television image. As shown in  FIG. 5 , fields  1 ˜ 8  are from a film segment A, and fields  9 ˜ 16  are from another film segment B. Due to a bad editing in the film segment B, field  9  and the following fields are not consistent with the 3:2 pull down process. Please refer again to  FIG. 4  and the state transition diagram can only determine that the image is fit to the film mode at field  11 . Therefore, when the field  9  is used as a basis to generate the television image, the field  9  and the field  10  originally from different film frames are combined into one image frame, and the television image incurs zigzag effect as a result.  
         [0011]     In order to solve the above-mentioned problem, U.S. Pat. No 6,201,577 granted to Peter D. Swartz for a “Film source video detection” discloses a method of detecting bad editing on current television image. The method notifies a film detector to leave the film mode when there is a bad editing detected, so as to avoid combining two fields from different frames into an image frame. However, because the detection is performed on the current television image, when the bad editing is detected, the line doubler has already outputted an image frame with zigzag effect.  
         [0012]     Therefore, it is desirable to provide a bad editing detection device for video signal to mitigate and/or obviate the aforementioned problems.  
       SUMMARY OF THE INVENTION  
       [0013]     An objective of the present invention is to provide a bad editing detection device to overcome the aforementioned problems.  
         [0014]     Another objective of the present invention is to provide a bad editing detection device that can pre-detect bad editing of image signal to avoid zigzag effect in the television image.  
         [0015]     In order to achieve the above-mentioned objective, the bad editing detection device of the present invention includes first to fourth buffers for respectively storing a first field, a second field, a third field and a fourth field, wherein the second field is a basis field for generating current output of an output frame, and the fourth field, the third field and the first field are respectively a second following field, a first following field and a previous field of the second field; a frame motion detector for determining whether the first field and the third field are identical; if they are, a “0” is outputted; otherwise, a “1” is outputted; a first counter for being reset when the frame motion detector outputs 0, and being incremented when the frame motion detector outputs 1; and a bad editing detector for determining bad editing according to the third field and the fourth field when a value of the first counter is 0, 1 or 3, and according to the third field and the second field when the value of the first counter is 2 or 4.  
         [0016]     Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a schematic drawing of odd and even fields of an image frame;  
         [0018]      FIG. 2  is a schematic drawing of 3:2 pull down process for transforming film frames into video fields;  
         [0019]      FIG. 3  is a schematic drawing of using a frame motion detector to provide frame motion data;  
         [0020]      FIG. 4  is a state transition diagram of film detection;  
         [0021]      FIG. 5  is a schematic drawing of a bad editing film signal;  
         [0022]      FIG. 6  is a functional block drawing of a bad editing detection device of the present invention; and  
         [0023]      FIG. 7  is a functional block drawing of a bad editing detector. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]      FIG. 6  is a functional block drawing of a bad editing detection device in accordance with a preferred embodiment of the present invention. The bad editing detection device comprises four buffers  61 ,  62 ,  63  and  64 , a frame motion detector  65 , a film detector  66 , a bad editing detector  67 , a line doubler  68 , two multiplexers  691  and  692 , and a counter  693 . The buffers  61 ,  62 ,  63  and  64  are provided for temporarily storing continuously inputted odd and even fields. The buffer  62  stores a field f 1  to be outputted currently; the field buffers  64 ,  63  and  61  are used for respectively storing a second following field f 3 , a first following field f 2  and a previous field f 1  of the field f 1 , and the line doubler  68  generates an output frame based upon the field f 1 .  
         [0025]     The frame motion detector  65  is provided for determining whether the field f 1  and the field f 2  are identical, i.e., whether two continuous odd fields (or even fields) are identical; if they are, a “0” is outputted; otherwise, a “1” is outputted.  
         [0026]     The film detector  66  is provided for determining whether an input filed is from the film according to the output from the frame motion detector  65 . The state transition diagram shown in  FIG. 4  can be used for determining whether the input field is from the film or the video.  
         [0027]     The counter  693  is reset to zero when the frame motion detector  65  outputs “0”, and is incremented when the frame motion detector  65  outputs “1”. When the input field is from a moving film, the frame motion detector  65  outputs a sequence “01111,01111, . . . ”; therefore, the counter  693  is provided with the value of 0,1,2,3,4,0,1,2,3,4, . . . , which can be used for determining whether the field f 1  and the previous field f 0  or the following field f 2  are combined to form one single frame.  
         [0028]     When determining the input field is from the moving film, the film detector  66  controls the multiplexer  691  to select the field f 0  or the field f 2 . The line doubler  68  combines the field f 1  with the field f 0  or the field f 2  to generate one frame for output. If the value of the counter  693  is “0” (indicating that the field f 1  and the following field f 2  are from the same frame), the multiplexer  691  selects the field f 2  to combine the field f 1  with the field f 2  to generate one frame for output. If the value of the counter  693  is “1” (indicating that the field f 1  and the following field f 2  are from the same frame), the multiplexer  691  selects the field f 2  to combine the field f 1  with the field f 2  to generate one frame for output. If the value of the counter  693  is “2” (indicating that the field f 1  and the previous field f 0  are from the same frame), the multiplexer  691  selects the field f 0  to combine the field f 1  with the field f 0  into one frame for output. If the value of the counter  693  is “3” (indicating that the field f 1  and the following field f 2  are from the same frame), the multiplexer  691  selects the field f 2  to combine the field f 1  with the field f 2  into one frame for output. If the value of the counter  693  is “4” (indicating that the field f 1  and the previous field f 0  are from the same frame), the multiplexer  691  selects the field f 0  to combine the field f 1  with the field f 0  into one frame for output. Accordingly, the field f 1  for current output can be combined with field f 0  or f 2 , which is from the same frame as field f 1 , to yield one frame.  
         [0029]     The bad editing detector  67  is provided for determining whether there is any bad editing according to the field f 2  and the fields f 1  or f 3 , wherein the selection of f 1  or f 3  is achieved by controlling the multiplexer  692  when the film detector  66  determines that the input field is from a moving film. If the value of the counter  693  is “0”, the multiplexer  692  selects the field f 3 , and the bad editing detector  67  determines whether there is a bad editing according to the field f 2  and the field f 3 . If the value of the counter  693  is “1”, the multiplexer  692  selects the field f 3 , and the bad editing detector  67  determines whether there is a bad editing according to the field f 2  and the field f 3 . If the value of the counter  693  is “2”, the multiplexer  692  selects the field f 1 , and the bad editing detector  67  determines whether there is a bad editing according to the field f 2  and the field f 3 . If the value of the counter  693  is “3”, the multiplexer  692  selects the field f 3 , and the bad editing detector  67  determines whether there is bad editing according to the field f 2  and the field f 3 . If the value of the counter  693  is “4”, the multiplexer  692  selects the field f 1 , and the bad editing detector  67  determines whether there is a bad editing according to the field f 2  and the field f 1 .  
         [0030]      FIG. 7  is a functional block drawing of the bad editing detector  67 . The bad editing detector  67  comprises a line buffer  671 , two subtractors  672  and  673 , a comparator  678 , and a counter  679 . The field f 2  (having pixels denoted as f 2 (i,j)) and field f 1 /f 3  (having pixels denoted as f 1 /f 3 (i,j)) are utilized to perform a subtraction operation by the subtractor  673  to obtain a luminance difference between the field f 2  and the field f 1 /f 3 . Since the field f 2  and the field f 1 /f 3  are respectively an odd field and an even field, f 2 (i,j) and f 1 /f 3 (i,j) are one pixel away from each other in the vertical direction, and the luminance difference between the field f 2  and the field f 1 /f 3  is termed the frame vertical energy of the field f 2 .  
         [0031]     The line buffer  671  is provided for buffering a line in the field f 2 . Thus, pixel f 2  (i,j) in the field f 2  becomes pixel f 2  (i- 1 ,j) after being buffered by the line buffer  671 . The buffered field f 2 ′ and the field f 2  are applied to the subtractor  672  for performing a subtraction to obtain a luminance difference between the buffered field f 2 ′ and the field f 2 . Since f 2  (i- 1 ,j) is the buffered f 2 (i,j), f 2 (i- 1 ,j) and f 2 (i,j) are two pixels away from each other in the vertical direction, and the luminance difference between the buffered field f 2 ′ and the field f 2  is termed the field vertical energy of the field f 2 .  
         [0032]     The frame vertical energy and the field vertical energy of the field f 2  are compared with each other by the comparator  678 . Since the distance (one pixel away from each other in the vertical direction) between the field f 2  and the field f 1 /f 3  is smaller than the distance (two pixels away from each other in the vertical direction) between the buffered field f 2 ′ and the field f 2 , the frame vertical energy is smaller than the field vertical energy. When the comparator  678  finds that the frame vertical energy exceeds the field vertical energy, it indicates that there may be a bad editing, and so the value of the counter  679  is incremented. This continues until the value of the counter  679  exceeds a threshold value, upon which a bad editing signal is outputted to notify the film detector to leave the film mode. On the other hand, when the comparator  678  finds that the frame vertical energy is smaller than the field vertical energy, the counter  679  is reset.  
         [0033]     In view of the foregoing, it is known that the bad editing detection device of the present invention is able to detect a bad editing at the field f 2  following the field f 1  of current output to predict the bad editing conditions. Therefore, the film detector can leave the film mode before the output frame generates zigzag effect, and a de-interlace process of the video mode is thus employed to generate the subsequent frame, which completely avoids zigzag effect in the output image.  
         [0034]     Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.