Patent Publication Number: US-7212246-B2

Title: Image signal format detection apparatus and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application Nos. 2002-80504, filed on Dec. 16, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image signal format detection apparatus and method, and more particularly, to an image signal format detection apparatus and method capable of detecting images converted from progressive format images to interlace format images by an application of a 2:2 pull-down algorithm. 
     2. Description of the Related Art 
     In general, an image display device employs either an interlace scan mode or a progressive scan mode. The interlace scan mode is used for general TVs and the like, and includes a division of one image frame into two fields and a display of the fields on a screen one after the other, in order, when displaying one image. At this time, the two fields are referred to as a top field and bottom field, an upper field and lower field, an odd field or even field, and so on. On the other hand, the progressive scan or non-interlace scan mode is used for computer monitors, digital TVs, and so on, and includes a display of an entire frame image, all at once, by dealing with one image frame, as a frame unit, e.g., film being displayed on a screen. 
     For example, in case of 480-line National Television System Committee (NTSC) interlace scan mode (precisely, 487 valid lines in 525 lines), one frame is divided into two 240-line fields for display, and the divided 240-line fields, as noted above, are displayed on a screen one after the other every 1/60 seconds (480/60 i). On the other hand, the progressive scan mode completely displays the entire frame image, e.g., a 480-line image, all at once every 1/60 seconds (480/60 p). Accordingly, a progressive format image based on the progressive scan mode has a better image quality compared to an interlace format image. 
     One of the typical video formats that is closely related to such a progressive scan mode is a DVD movie formatted for display on an analog television and initially produced on film, since the original sources for almost all DVD movie titles released in recent years are produced on film first. Movies are produced at 24 frames per second, differently from NTSC TV programs. In the case of a DVD movie, it is, of course, possible to directly manufacture a DVD including the original images of 24 frames, as in an original film movie. However, since a majority of image display devices, such as general analog televisions, at present adopt the interlace scan mode, it is more practical to produce DVD movie titles in the interlace scan mode. 
     Accordingly, a process is required for converting a 24-frame progressive film into 60-field interlace images, which is typically referred to as a 3:2 pull-down or a “telecine.” The 3:2 pull-down process is a process that converts two 24 Hz frames into five 60 Hz fields, producing three fields repeatedly from the first frame and two fields from the second frame. 
     Meanwhile, 30-frame-per-second progressive format images are typically used for advertisement broadcasts, music videos, or the like, for which a 2:2 pull-down, similar to the 3:2 pull-down, is used. That is, the 2:2 pull-down refers to a process for converting 30-frame progressive format film into 60-field interlace format images. 
       FIG. 1  illustrates the 2:2 pull-down. In  FIG. 1 , images produced in the 30-frame-per-second progressive format are converted into the 60 Hz interlace format by dividing each frame into two fields. For example, a Frame  1  is converted into two fields T 1  and B 1 , and a Frame  2  into two fields T 2  and B 2 , and so on. 
     However, as it has become more necessary to exchange data among devices using different scan modes as the use of image display devices employing the progressive scan mode increases, an interlaced-to-progressive conversion (IPC) method becomes necessary to convert the interlace scan mode into the progressive scan mode. During such an IPC process, if it is known that a currently input image is a 2:2 pull-down-converted image, a complete progressive format image before the 2:2 pull-down can be easily obtained merely by combining interlace format fields. Accordingly, before implementing the IPC method, it becomes necessary to detect whether a field to be interpolated is for a previously 2:2 pull-down converted image. 
     Conventional systems mainly use the 3:2 pull-down, and conventional technologies have been disclosed, especially, in U.S. Pat. No. 5,398,071 entitled “Film To Video Format Detection For Digital Television” for methods for detecting such 3:2 pull-down format images. However, few or no technologies have been known to detect 2:2 pull-down format images through a relatively simple structure. Therefore, an image signal format detection apparatus and method is desired to detect the 2:2 pull-down format through a relatively simple structure. 
     SUMMARY OF THE INVENTION 
     The present invention has been devised to solve the above and/or other problems, so it is an aspect of the present invention to provide an image format detection apparatus and method capable of detecting whether an image was previously generated by a 2:2 pull-down image format, through a relatively simple structure. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     To achieve the above and/or other aspects of the present invention, there is provided an image signal format detection apparatus, including a first summed absolute difference (SAD) value calculation unit to calculate, from a previous field, a current field, and a next field of an image signal with time-consecutive fields, a first SAD value with reference to pixel values of the current field and the previous field, a second SAD value calculation unit to calculate a second SAD value with reference to pixel values of the current field and the next field, a pattern generation unit to generate a detection pattern based on a result of a comparison of the first and the second SAD values, and a pattern analysis unit to store the detection pattern, compare the stored detection pattern with a predetermined verification pattern, and determine whether the image signal is an image signal generated by a 2:2 pull-down. 
     To achieve the above and/or other aspects of the present invention, there is provided a deinterlacing apparatus for converting an interlace scan mode image signal into a progressive scan mode image signal, including the above format detection unit, a 2:2 pull-down compensation unit, and an interlace-to-progressive conversion unit, wherein the input image to the deinterlacing apparatus is selectively deinterlaced by the deinterlacing apparatus based either on the 2:2 pull-down compensation unit or the interlace-to-progressive conversion unit based on an output of the format detection unit. 
     To achieve the above and/or other aspects of the present invention, there is provided an image signal format detection method, calculating, from a previous field, a current field, and a next field of a time-consecutive image signal, a first summed absolute difference (SAD) value with reference to pixel values of the current field and the previous field, calculating a second SAD value with reference to pixel values of the current field and the next field, generating a detection pattern based on a result of a comparison of the first and second SAD values, and storing the detection pattern, comparing the stored detection pattern with a predetermined verification pattern, and determining whether the image signal is an image signal generated by a 2:2 pull-down. 
     To achieve the above and/or other aspects of the present invention, there is provided a deinterlacing method for converting an interlace scan mode image signal into a progressive scan mode image signal, including outputting a deinterlaced image signal selectively based on interpolation values from either a 2:2 pull-down compensation operation or an interlace-to progressive conversion operation based on the above image signal format detection method. 
     To achieve the above and/or other aspects of the present invention, there is provided a deinterlacing apparatus for converting an interlace scan mode image signal into a progressive scan mode image signal, including a format detection unit to detect a format of an input image based on a comparison of summed absolute difference values between fields of the input image, a 2:2 pull-down compensation unit, and an interlace-to-progressive conversion unit, wherein the input image to the deinterlacing apparatus is selectively deinterlaced by the deinterlacing apparatus based either on the 2:2 pull-down compensation unit or the interlace-to-progressive conversion unit based on an output of the format detection unit. 
     The comparison of the summed absolute difference values between fields of the input image can be based on a comparison of the result of the following two equations: 
                       Q     i   =   0       M   -   1       ⁢     Q     j   =   0       N   -   1       ⁢              f     n   -   1       ⁡     (     i   ,   j     )       -       f   n     ⁡     (     i   ,   j     )                ;   and                   Q     i   =   0       M   -   1       ⁢     Q     j   =   0       N   -   1       ⁢              f   n     ⁡     (     i   ,   j     )       -       f     n   +   1       ⁡     (     i   ,   j     )                ,               
wherein f n−1 (i,j) denotes a value of a pixel at row i and column j in a previous field, f n (i,j) denotes a value of a pixel at row i and column j in a current field, and f n+1 (i,j) denotes a value of a pixel at row i and column j in a next field, with M−1 and N−1 denoting maximum values of i and j, respectively, for an image of M×N size.
 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects and advantages of the present invention will become and more readily appreciated from the following description of the embodiments taken in conjunction with the accompanying drawings in which: 
         FIG. 1  illustrates a conventional 2:2 pull-down-method; 
         FIG. 2  illustrates an image signal format detection apparatus, according to an embodiment of the present invention; 
         FIG. 3  is a flow chart of an operation of an image signal format detection apparatus, according to an embodiment of the present invention; 
         FIG. 4  illustrates a process for generating a detection pattern, according to an embodiment of the present invention; and 
         FIG. 5  illustrates an exemplary deinterlacing apparatus, using an image signal format detection apparatus, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
       FIG. 2  is a block diagram illustrating an image signal format detection apparatus, according to an embodiment of the present invention. The image signal format detection apparatus includes first and second summed absolute difference (SAD) value calculation units  100  and  110 , a pattern generation unit  120 , and a pattern analysis unit  130 . The pattern generation unit  120  includes a SAD comparator  123  and a multiplexer  125 , and the pattern analysis unit  130  includes a pattern buffer  133 , a pattern storage  135 , and a pattern detector  137 . 
     The first and second SAD value calculation units  100  and  110  input an image signal formed with plural fields, consecutive in time. At this time, a currently input field is referred to as a current field, and fields ahead of and behind the current field are referred to as a previous field and a next field, respectively. The first SAD value calculation unit  100  calculates a first SAD value with reference to pixel values of the current field and the previous field. The second SAD value calculation unit  110  calculates a second SAD value with reference to pixel values of the current field and the next field. 
     The pattern generation unit  120  compares the first and second SAD values calculated in the first and second SAD value calculation units  100  and  110 , and generates a detection pattern based on a result of the comparison. The pattern analysis unit  130  stores the detection pattern generated by the pattern generation unit  120 , compares a predetermined pre-stored verification pattern with a series of stored detection patterns, and decides whether the inputted image signal is a 2:2 pull-down format image generated by a 2:2 pull-down. A stored detection pattern may similarly be generated by sequentially incorporating the output of the comparison, of the first and second SAD values, in a single pattern, e.g., a series. 
       FIG. 3  is a flow chart of operations of an image signal format detection apparatus, according to an embodiment of the present invention. Referring to the flow chart of  FIG. 3 , first, the first SAD value calculation unit  100  calculates a first SAD value with reference to pixel values of a previous field and a current field (S 200 ). Further, the second SAD value calculation unit  110  calculates a second SAD value with reference to pixel values of the current field and a next field (S 205 ). At this time, the first and second SAD value calculation units  100  and  110  calculate the first and second SAD values by the following equations: 
                     First   ⁢           ⁢   SAD   ⁢           ⁢   value     =       Q     i   =   0       M   -   1       ⁢     Q     j   =   0       N   -   1       ⁢              f     n   -   1       ⁡     (     i   ,   j     )       -       f   n     ⁡     (     i   ,   j     )                              Second   ⁢           ⁢   SAD   ⁢           ⁢   value     =       Q     i   =   0       M   -   1       ⁢     Q     j   =   0       N   -   1       ⁢              f   n     ⁡     (     i   ,   j     )       -       f     n   +   1       ⁡     (     i   ,   j     )                            
f n−1 (i,j) denotes a value of a pixel at row i and column j in a previous field, f n (i,j) denotes a value of a pixel at row i and column j in a current field, and f n+1 (i,j) denotes a value of a pixel at row i and column j in a next field. Further, M−1 and N−1 denote maximum values of i and j, respectively, that is, for an image of M×N size.
 
     The SAD comparator  123  of the pattern generation unit  120  compares the magnitudes of the first and second SAD values calculated in the first and second SAD value calculation units  100  and  110  respectively (S 210 ), and generates a detection result according to a result of the comparison (S 215 ). The comparison of the first and second SAD values is carried out in the SAD comparator  123  of the pattern generation unit  120 . The multiplexer  125 , in the pattern generation unit  120 , receives values of “1” and “0”, respectively, and outputs either the input value of “1” or the value of “0” according to the controls of the SAD comparator  123 . The value output from multiplexer  125  becomes a detection pattern. 
       FIG. 4  illustrates a process for generating a detection pattern, according to an embodiment of the present invention. Referring to  FIG. 4 , 30 Hz progressive format images  300 ,  310 , and  320  are divided into two fields  301  and  302 ,  311  and  312 , and  321  and  322 , respectively, by a 2:2 pull-down. In this example, if a reference numeral  302  is a current field, a reference numeral  302 - 1  becomes a first SAD value calculated with reference to a previous field and the current field, and a reference numeral  302 - 2  becomes a second SAD value calculated with reference to the current field and a next field. Further, if a value “a” denotes the first SAD value and a value “b” denotes the second SAD value, the value a is smaller than the value b (a&lt;b) since the previous field  301  and the current field  302  are fields divided from the same frame  300  and the current field  302  and the next field  311  are fields generated from different frames  300  and  301 . With the multiplexer  125  outputting the value of “1” when a&gt;b and the multiplexer  125  outputting the value of “0” when a&lt;b, in the above example, the output value of the multiplexer  125  will be “0”. 
     If the above process is carried out with respect to the fields  302 ,  311 ,  312 , and  321 , the values output from the multiplexer  125  become the series “. . . 0101 . . . ”. Likewise, when the image is a 2:2 pull-down format image, the multiplexer  125  will repeatedly output values of “0” and “1.” 
     The detection patterns output from the multiplexer  125  are stored in a pattern buffer  133 . Accordingly, a value stored in the pattern buffer  133  becomes “. . . 0101 . . . ” of certain length. 
     A detection pattern series of “. . . 0101 . . . ” stored in the pattern buffer  133  is compared with a verification pattern stored in the pattern storage  135  (S 225 ). The verification pattern stored in the pattern storage  135  is a pattern, for example, “. . . 0101 . . . ”, of certain repetition period, based on the 2:2 pull-down. 
     It is then determined whether the series of “. . . 0101 . . . ” of the detection pattern stored in the pattern buffer  133  matches with a verification pattern, for example, “. . . 0101 . . . ”, stored in the pattern storage  135  (S 230 ). 
     If the detection pattern, stored in the pattern buffer  133 , matches with the verification pattern stored in the pattern storage  135 , a 2:2 pull-down mode signal is generated (S 230  and S 235 ). Conversely, if the patterns do not match, it is decided that the detection pattern is not a 2:2 pull-down format image. 
     Through the above process, it can be determined whether an input field is a 2:2 pull-down format field produced by the 2:2 pull-down. Such an image signal format detection apparatus can, accordingly, be applied to an IPC process and the like. 
       FIG. 5  illustrates an exemplary deinterlacing apparatus using an image signal format detection apparatus, according to an embodiment of the present invention. A deinterlacing apparatus refers to an apparatus for converting an interlace scan mode image signal into a progressive scan mode image signal. The interlacing apparatus shown in  FIG. 5  includes a format detection unit  400 , a 2:2 pull-down compensation unit  410 , an IPC unit  420 , and a multiplexer  430 . 
     The format detection unit  400 , through one of the above processes, e.g., described in  FIG. 3  and  FIG. 4 , detects whether an input image field is a field produced by a 2:2 poll-down. The 2:2 pull-down compensation unit  410  assumes that the input image is a 2:2 pull-down image, and outputs interpolation values based on that assumption. The IPC unit  420  outputs interpolated values by using an appropriate interpolation method such as motion-compensated interpolation method or the like. The multiplexer  430  outputs, as final interpolation values, interpolation values of either the 2:2 pull-down compensation unit  410  or the IPC unit  420 , by a 2:2 pull-down mode signal output from the format detection unit  400 . Accordingly, if the input image is a 2:2 pull-down image, values interpolated by the 2:2 pull-down compensation unit  410  are used. Otherwise, the interpolation values outputted from the IPC unit  420  are used, thereby enabling good quality images to be effectively obtained. 
     As described above, the present invention can detect whether an input image is an image produced by a 2:2 pull-down, based on SAD values between fields. Further, the image signal format detection apparatus and method according to the present invention can be easily implemented due to a relatively simple structure. Such image signal format detection apparatuses and methods can be applied to interlaced-to-progressive conversion (IPC) methods or the like, enabling good quality images to be effectively obtained. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.