Abstract:
A system for detecting poor video editing detects a television (TV) image signal. When a TV image originates from a film signal rather than a video signal, a de-interlacing device performs a de-interlacing at a film signal mode to thereby increase a vertical resolution of a TV image signal. A sawtooth detector can detect a poor video editing, which causes a sawtooth occurrence to TV image signals, on an unbroadcasted TV image signal. Accordingly, the poor video editing is found in advance. Also, the invention uses a scene change in combination with the sawtooth detector to thereby avoid a poor edited image and obtain a preferred image quality.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a detecting system and, more particularly, to a system for detecting poor video editing. 
     2. Description of Related Art 
     For the limited broadcast bandwidth, current TV broadcasting typically uses alternate odd/even fields. As shown in  FIG. 1 , odd fields  10  and  12  have only odd-line video data, and even fields  11  and  13  have only even-line video data. New generation of TVs requires a higher vertical resolution, and accordingly a line doubler is used in a TV to perform a double frequency processing in order to increase the vertical resolution. The simplest double frequency processing is to directly merge adjacent odd and even fields to thereby form a progressive scan frame. However, because of a time difference between the adjacent odd and even fields, such a processing presents a sawtooth to a motion image. 
     To overcome the aforementioned problem, a line doubler preferably is equipped with a frame motion detector to detect a motion image. In addition, the line doubler can perform an inter-field interpolation of de-interlacing process on a still image and an intra-field interpolation of de-interlacing process on the motion image. 
     Another double frequency processing is achieved by determining if an image originates from a film. It is known that a film is formed by recording 24 frames per second. Accordingly, for displaying a film signal on an NTSC TV, it converts the 24 frames into 60 fields per second. As shown in  FIG. 2 , such a conversion is typically referred to as a “3:2 pull down”, i.e., two temporally successive film frames are converted into three fields and two fields respectively. For example, frame  14  is converted into field  18  (odd field), field  19  (even field) and field  20  (odd field), frame  15  is converted into field  21  (even field) and field  22  (odd field), and so on. Thus, upon such a double frequency processing, a perfect double frequency output can be obtained by combining all odd and even fields that correspond to the same frame when an image is determined to originate from a film signal. In this case, an image has no sawtooth and a motion image can have the highest vertical resolution. 
     For detecting an image source, frame or field motion data is used to determine whether the image source is a film signal or not.  FIG. 3  shows an example of using frame motion detectors  31  to provide the required frame motion data. As shown in  FIG. 3 , each frame motion detector  31  can detect two successive odd or even fields to thereby output ‘1’ when the two successive odd or even fields are the same and ‘0’ when different. Accordingly, if a TV image is a segment of still frames, whether the image source is a film signal or not, the frame motion detector  31  outputs a sequence ‘11111, 11111, . . . ’. If the TV image is a segment of motion video signal, the frame motion detector  31  outputs a sequence ‘00000, 00000, . . . ’. If the TV image is a segment of motion film signal, the frame motion detector  31  outputs a sequence ‘10000, 10000, . . . ’. 
     The output of the frame motion detector  31  is applied to  FIG. 4  in which a film detection state transition diagram is shown, thereby determining if an input image is of a 3:2 pull down film. States  0 - 5  of the film detection state transition diagram are video mode states, and states  6 - 10  are film mode states. As shown in  FIG. 4 , the diagram starts at state  0 . For every input with ‘10000’, the state transition has to pass through state  4 , which causes an increase on the counter  41 . When the counter  41  exceeds a threshold, a state transition from state  4  to state  6  is performed, i.e., a TV image (video) mode state is changed into a film mode state. 
     As cited above, when an input image is of the 3:2 pull down film, the frame motion detector outputs ‘10000’ or ‘1111’. When the frame motion detector outputs a certain amount of ‘10000’, the film detection state transition diagram is changed from a video mode state to a film mode state and remains at the film mode state as long as the input is met with ‘1XXXX’. 
     The aforementioned technique can effectively detect whether an image originates from a film signal or not, and have a perfect double frequency output. However, it also causes the poor film editing, which impairs the 3:2 pull down proportion and outputs the image with a sawtooth. 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 sawtooth effect as a result. 
     To overcome the aforementioned problem, U.S. Pat. No. 6,201,577 granted to Peter D. Swartz for a “Film source video detection” discloses a method for detecting a poor editing. The method detects the poor editing on a current output image and informs a film pattern detector to leave the film mode to thereby avoid combining two fields, which are not of a same frame, into a frame. However, such a detection is operated on the current output image, which cannot totally avoid an image from presenting a sawtooth because a line doubler outputs a frame with a sawtooth before a poor editing is detected. In addition, the prior art cannot leave the film mode in states  7 - 10  and thus possibly combines two fields of different frames into a frame, resulting in likely presenting a sawtooth to a TV image. 
     Therefore, it is desirable to provide an improved system for detecting poor video editing to mitigate and/or obviate the aforementioned problems. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a system for detecting poor video editing, which can reduce the use amount of frame buffers and line buffers to thereby reduce the hardware cost. 
     Another object of the present invention is to provide a system for detecting poor video editing, which can detect and process various poor editing to thereby obtain a preferred image quality. 
     In accordance with one aspect of the present invention, there is provided a system for detecting poor video editing. The system receives plural fields of a video datastream for detecting a poor editing in the video datastream. The system includes a film mode detector, a sawtooth detector and a scene detector. The film mode detector receives a previous field F[N−1] and a next field F[N+1] respectively of the video datastream to accordingly determine whether the video datastream is of a film mode or not. The sawtooth detector receives a current field F[N] and the next field F[N+1] respectively of the video datastream to thereby determine whether a sawtooth is present to the next field F[N+1] based on a field energy of the current field F[N] and a frame energy of the current field F[N] and next field F[N+1]. The scene detector receives the current field F[N], the next field F[N−1] and the previous field F[N−1] in order to calculate a field brightness difference between the current field F[N] and the previous and next fields F[N−1] and F[N+1], and accordingly determines whether a scene change occurs. When the video datastream is of the film mode and the scene change occurs, the video datastream is determined to have the poor editing, for the poor editing mostly occurs at the scene change. 
     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 
         FIG. 1  is a schematic view showing display fields of a video signal; 
         FIG. 2  is a schematic view of typical fields converted from a film signal; 
         FIG. 3  is a schematic view of typically using a frame motion detector to provide the required frame motion data; 
         FIG. 4  is a film detection state transition diagram; 
         FIG. 5  is a schematic view showing a typical poor edited film signal; 
         FIG. 6  is a block diagram of a system for detecting poor video editing in accordance with the invention; 
         FIG. 7  is a block diagram of a sawtooth detector in accordance with the invention; 
         FIG. 8  is a schematic view of using a scene detector to calculate a field brightness difference of a current field in accordance with the invention; and 
         FIG. 9  is a state transition diagram of a system operation in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 6  is a block diagram of a system for detecting poor video editing in accordance with the invention. As shown in  FIG. 6 , the system receives plural fields F[Z] of a video datastream for detecting a poor editing in the video datastream, wherein Z=N indicates a current field in processing. The system includes a film mode detector  610 , a sawtooth detector  620 , a scene detector  630 , a de-interlacing device  640 , a direct coupler  650 , a determinator  660  and a multiplexer  670 . 
     The de-interlacing device  640  receives a current field F[N], a previous field F[N−1] and a next field F[N+1] respectively of the video datastream and accordingly uses a de-interlacing to produce the frame for the current field F[N]. 
     The direct coupler  650  receives the previous field F[N−1], the current field F[n] and the next field F[N+1] respectively of the video datastream to accordingly produce the frame for the current field [N] directly. 
     The film mode detector  610  receives the previous field F[N−1] and the next field F[N+1] respectively of the video datastream to accordingly determine whether the video datastream is of a film mode or not. When the video datastream is not of a film mode, the film mode detector  610  outputs states  0  to  5 , and when the video datastream is of a film mode, the film mode detector  610  sequentially outputs states  6  to  10 , i.e., film mode  6  to  10 , which can be implemented by those skilled in the prior art in accordance with the state transition diagram of  FIG. 4  and thus a detailed description is deemed unnecessary. 
     The sawtooth detector  620  receives the current field F[N] and the next field F[N+1] respectively of the video datastream to thereby determine whether a sawtooth is present to the next field F[N+1] in accordance with a field energy of the current field F[N] and a frame energy of the current field F[N] and next field F[N+1]. When the frame energy is greater than the number of pixels of the field energy of the current field F[N] and exceeds a threshold, the sawtooth detector determines that the sawtooth is present to the next field F[N+1]. 
     The field energy of a pixel can be expressed by:
 
|Luma F[N] [i][j]−Luma F[N] [i+1][j]|,   (1)
 
where Luma F[N] [i][j] indicates a brightness of pixel (i, j) of the current field F[N] and Luma F[N] [i+1][j] indicates a brightness of pixel (i+1, j) of the current field F[N]. The frame energy of a pixel can be expressed by:
 
|Luma F[N] [i][j]−Luma F[N+1] [i][j]|,   (2)
 
where Luma F[N] [i][j] indicates a brightness of pixel (i, j) of the current field F[N] and Luma F[N+1] [i][j] indicates a brightness of pixel (i, j) of the next field F[N+1].
 
       FIG. 7  is a block diagram of the sawtooth detector  620  in accordance with the invention. In  FIG. 7 , the sawtooth detector  620  includes a line buffer  621 , subtractors  622  and  623 , absolute devices  624  and  625 , comparators  626  and  627  and a counter  628 . For a sawtooth detection, the sawtooth detector  620  first uses a reset signal to reset the counter  628 . The subtractor  623  subtracts the current field F[N] (with the pixel brightness Luma F[N] [i][j]) from the next field F[N+1] (with the pixel brightness Luma F[N+1] [i][j]) and a brightness difference between the fields F[N] and F[N+1] is obtained. Because one of the fields F[N] and F[N+1] is an odd field and the other is an even field, the distance between the fields F[N] and F[N+1] is one pixel in vertical. In addition, the brightness difference between the fields F[N] and F[N+1] is referred to as a frame energy of the current field F[N]. 
     The line buffer  621  buffers a line of the current field F[N]. Accordingly, the pixel (i, j) of the current field F[N] is passed through the line buffer  621  to obtain a pixel (i+1, j), which is of a line buffered field F[N]′, and the fields F[N]′ and F[N] are subtracted by the subtractor  622  to thereby obtain a brightness difference between the fields F[N]′ and F[N]. Because the pixel (i+1, j) is obtained by line buffering the pixel (i, j), the distance between the pixels (i+1, j) and (i, j) is two pixels in vertical. The brightness difference between the fields F[N]′ and F[N] is referred to as a field vertical energy of the current field F[N]. 
     The frame energy and field energy of the current field F[N] are passed through the absolute devices  624  and  625  to obtain the absolute values respectively for further comparison by the comparator  626 . Since the distance between the fields F[N] and F[N+1] is smaller than the distance between the fields F[N]′ and F[N], i.e., one pixel is smaller than two pixels, the frame energy is smaller than the field energy. If the comparator  626  finds the frame energy greater than the field energy, it may indicate an occurrence of sawtooth and the counter  628  is increased by one. When the counter  628  exceeds a threshold, a sawtooth present signal is output to inform the film mode detector  610  of leaving the film mode. 
     In this embodiment, the sawtooth detector  620  receives the current field F[N] and the next field F[N+1] respectively of the video datastream to thereby determine whether a sawtooth is present to the next field F[N+1] in accordance with the field energy of the current field F[N] and the frame energy of the current field F[N] and next field F[N+1]. In other embodiments, the sawtooth detector  620  can receive the current field F[N] and the previous field F[N−1] respectively of the video datastream to thereby determine whether a sawtooth is present to the current field F[N] in accordance with the field energy of the previous field F[N−1] and the frame energy of the previous field F[N−1] and current field F[N]. 
     The scene detector  630  receives the current field F[N], the next field F[N+1] and the previous field F[N−1] in order to calculate a field rightness difference Diff_Luma between the current field F[N] and the previous and next fields F[N−1] and F[N+1], and accordingly determines whether a scene change occurs. 
       FIG. 8  is a schematic view of using the scene detector  630  to calculate the field brightness difference Diff_Luma of the current field F[N] in accordance with the invention. The scene detector  630  depends on the following equation to calculate the field brightness difference Diff_Luma of the current field F[N]:
 
Diff_Luma=max(| Y   F[N−1]   −Y   F[N]   |, |Y   F[N+1]   −Y   F[N] |),   (3)
 
where Y F[N−1 ] indicates a brightness average of the previous field F[N−1], Y F[N]  indicates a brightness average of the current field F[N] and Y F[N+1]  indicates a brightness average of the next field F[N+1]. The brightness average of the current field F[N] is expressed by:
 
                       Y     F   ⁡     [   N   ]         =       ∑     i   =   0       X   -   1       ⁢       ∑     j   =   0       Y   -   1       ⁢         Luma     F   ⁡     [   N   ]         ⁡     [   i   ]       ⁡     [   j   ]             ,           (   4   )               
where Luma F[N] [i][j] indicates a brightness of pixel (i, j) of the current field F[N], X indicates the row number of the current field F[N] and Y indicates the column number of the current field F[N].
 
     When the field brightness difference Diff_Luma corresponding to the current field F[N] is greater than a previous field brightness difference and a field brightness threshold Diff_Luma_Th, the scene detector  630  determines that the scene change occurs. The previous field brightness difference is obtained by selecting the maximum field brightness difference from the previous fields F[N−2], F[N−3], F[N−4] and F[N−5]. Namely, the scene detector  630  determines that the scene change occurs as the following equation (5) is found.
 
Diff_Luma&gt;max(Diff_Lum — 2, 3, 4, 5) and Diff_Luma&gt;Diff_Luma_Th,   (5)
 
where Diff_Lum_ 2 , Diff_Lum_ 3 , Diff_Lum_ 3  and Diff_Lum_ 5  indicate field brightness differences respectively of the previous fields F[N−2], F[N−3], F[N−4] and F[N−5], and Diff_Luma_Th indicates the field brightness threshold.
 
     In other embodiments, the previous field brightness difference can be obtained by selecting the maximum field brightness difference from the previous fields F[N−2], F[N−3], F[N−4] and F[N−5] and performing a weighting operation. Namely, the scene detector  630  determines that the scene change occurs as the following equation (6) is found.
 
Diff_Luma&gt;max(Diff_Luma — 2, 3, 4, 5)×gain and Diff_Luma&gt;Diff_Luma_Th   (6)
 
     The determinator  660  is connected to the film mode detector  610  and the scene detector  630 . When the video datastream is of the film mode and the scene change occurs, the video datastream possibly containing a poor editing is determined. Namely, when the current field F[N] is at the film mode state  8  or  10  and the scene detector  630  determines at the previous state  7  or  9  that a scene change occurs, the current field F[N] possibly containing a poor editing can be determined. In this case, the multiplexer  670  selects the de-interlacing device  640  as the output to thereby produce the frame for the current field, but the state still remains at the film mode. 
     When the current field F[N] is at the film mode state  6 ,  7  or  9  and the sawtooth detector  620  determines at the previous state  10 ,  6  or  8  that a sawtooth is present to the next field F[N+1], the current field F[N] is determined to have a poor editing and the multiplexer  670  selects the de-interlacing device  640  as the output to thereby produce the frame for the current field F[N] and return to the state  0  (out of the film mode). 
     For the other conditions different from the cited above, the multiplexer  670  selects the direct coupler  650  as the output. 
       FIG. 9  is a state transition diagram of a system operation in accordance with the invention. As shown in  FIG. 9 , for one of the film mode states  6  to  10 , a poor editing can be detected due to a scene change or sawtooth effect and further processed to thereby obtain a preferred image quality. 
     The prior art uses the sawtooth detector to determine whether a poor editing occurs or not, which can predict a poor editing of the next field F[N+1] and accordingly avoid the sawtooth occurrence when the current field F[N] and the next field F[N+1] are combined. However, when the next two fields F[N+1] and F[N+2] are combined, a frame buffer and a line buffer are required in combination with the sawtooth detector for detecting the poor editing, which increases the hardware cost. Otherwise, the sawtooth effect still occurs. By contrast, the invention uses the sawtooth detector  620  in combination with the scene detector  630  to thereby predict a poor editing. When the sawtooth effect is detected by the detector  620  and the film mode is at state  6 ,  7  or  9 , it immediately goes out of the film mode. When a scene change is detected by the scene detector  630  and the film mode is at state  8  or  10 , the multiplexer  670  selects the de-interlacing device  640  as the output to thereby produce the frame for the current field F[N] but still remain at the film mode. Thus, the different conditions for a poor editing occurrence are properly responded but no sawtooth effect occurs. 
     In view of foregoing, it is known that the invention combines the sawtooth detector  620  and the scene detector  630  to thereby avoid the video datastream from producing the sawtooth effect caused by a poor editing in directly coupling two adjacent fields. In addition, the use number of frame buffers and line buffers are reduced to further reduce the hardware cost. Thus, the different conditions for a poor editing presentation are detected and processed to thereby obtain a preferred image quality. 
     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.