Abstract:
An image processing apparatus converts an interlaced signal including a signal converted so as to be matched to a frame rate of an input video signal with original images arranged on a basis of a predetermined sequence as the video signal into a progressive signal. The image processing apparatus includes a field-interpolated signal generator generating a progressive field-interpolated signal by interpolating a signal at a selected position corresponding to a scanning line to be interpolated in a present field, the signal at the selected position belonging to one of a field preceding the present field and a field succeeding the present field; and a double image detector determining whether a pixel in the field-interpolated signal forms a part of a double image, and replacing a pixel in the field-interpolated signal which forms a part of a double image in the field-interpolated signal with a predetermined substitute signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims priority from Japanese Patent Application No. JP 2005-066052 filed on Mar. 9, 2005, the disclosure of which is hereby incorporated by reference herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to an apparatus and a method for image processing that are suitable for use in converting an interlaced signal including a converted signal converted into an interlaced signal by 3-2 pulldown, 2-2 pulldown or the like and resulting from an editing process into a progressive signal.  
         [0003]     Standard video signals such as an NTSC signal, a high-definition television signal and the like are interlaced signals.  FIGS. 9A, 9B , and  9 C are diagrams showing scanning line structures,  FIG. 9A  representing an interlaced signal,  FIG. 9B  representing a progressive signal, and  FIG. 9C  representing a signal obtained by converting an interlaced signal into a progressive signal by scanning line interpolation. Incidentally, the symbol of a circle (∘) in  FIG. 9  represents a scanning line, and the symbol of a cross (x) in  FIG. 9  represents an interpolated scanning line.  
         [0004]     In  FIG. 9 , a vertical direction V is the vertical direction of a screen, and a horizontal direction t is a time direction. As shown in  FIG. 9A , one frame of an interlaced signal is formed by two fields shifted from each other in the time direction and the vertical direction. On the other hand, there is no shift in the scanning line structure of a progressive signal, as shown in  FIG. 9B . In the case of the interlaced signal, an interlace disturbance such as line flicker or the like occurs when a high-frequency component in the vertical direction of an image is increased. On the other hand, the progressive signal is free from the interlace disturbance.  
         [0005]     As shown in  FIG. 9C , there is a processing method for eliminating the interlace disturbance by interpolating a scanning line in a part discretely reduced by the interlace using neighboring scanning lines, and thereby converting the interlaced signal into a progressive signal. Such a processing method is referred to as progressive conversion or double density conversion.  
         [0006]     In the case of an interlaced signal originating from normal video, scanning line interpolation for progressive conversion is performed by a motion adaptive type interpolation process. Specifically, as shown in  FIG. 10 , when an image is still, a new scanning line is formed by performing inter-field interpolation using an average value of signals PA and PB representing pixels in a previous field and a subsequent field as a signal PQ representing a new pixel denoted by a cross (x) symbol. On the other hand, when an image is moving, a new scanning line is formed by performing intra-field interpolation using an average value of signals PC and PD representing vertically adjacent pixels as the signal PQ representing a new pixel denoted by the cross (x) symbol. Thus, when an image is still, excellent quality of a converted image with little aliasing and high resolution can be obtained. However, when an image is moving, the quality of a converted image is degraded with much aliasing and low resolution.  
         [0007]     In a case where an input signal to be converted into a progressive signal includes a converted signal originating from film video which signal is converted by 3-2 pulldown, 2-2 pulldown or the like, excellent converted image quality can be obtained even when the image is moving, by employing a method different from the motion adaptive type interpolation process for the part originating from the film video. The 3-2 pulldown is a frame rate conversion as represented in  FIG. 11 . Specifically, the 3-2 pulldown is used as a method for converting progressive signals A, B, C . . . (hereinafter referred to as “frames A, B, C . . . ” as appropriate) of film video having a rate of 24 frames per second or the like into interlaced signals a, a′, a, b′, b, c′, c, c′ . . . (hereinafter referred to as “fields a, a′, a . . . ” as appropriate) of an NTSC system having a rate of 60 fields per second. Incidentally, presence or absence of “′” in  FIG. 11  indicates a difference between an odd field and an even field. On the other hand, the 2-2 pulldown is a frame rate conversion as represented in  FIG. 12 . Specifically, the 2-2 pulldown is used as a method for converting progressive signals A, B, C . . . of film video having a rate of 30 frames per second, for example, into interlaced signals a, a′, b, b′, c, c′ . . . of the NTSC system having a rate of 60 fields per second.  
         [0008]     As shown in  FIG. 11  and  FIG. 12 , the 3-2 pulldown divides an image as an originally identical frame into three or two fields, while the 2-2 pulldown divides an image as an originally identical frame into two fields. Hence, when the 3-2 pattern or the 2-2 pattern of a part converted into an interlaced signal by 3-2 pulldown or 2-2 pulldown, that is, a pulldown sequence is known, the interlaced signal can be converted into a progressive signal by performing field interpolation using an adjacent field generated from a same frame regardless of whether the image is still or moving. The field interpolation, which is different as an interpolation method from the inter-field interpolation represented in  FIG. 10  but is similar to the inter-field interpolation, generates a new scanning line by setting a signal PA in a previous field or a signal PB in a subsequent field as a signal PQ representing a new pixel. Thus, after the conversion, excellent image quality can be obtained with little aliasing and high resolution. Above described image processing apparatus and method in related art is disclosed, for example, in Japanese Patent Laid-Open No. 2004-343333.  
         [0009]     There are cases where the pulldown sequence is disrupted as a result of an editing process performed on a part originating from film video which part has been thus converted into an interlaced signal by 3-2 pulldown, 2-2 pulldown or the like. For example, when 3-2 pulldown as represented in  FIG. 11  is performed, an interlaced signal normally has a sequence such as fields a, a′, a, b′, b, c′, c, c′, d, and d′. As a result of cutting off the fields c and c′ by an editing process as shown in  FIG. 13 , the interlaced signal can have a sequence such as fields a, a′, a, b′, b, c′, d, and d′.  
         [0010]     When the interlaced signal in which the pulldown sequence is thus disrupted by an editing process is converted into a progressive signal, as a result of field interpolation being performed expecting that fields originating from the frame C such as the fields c′, c, and c′ continue, a frame as indicated by hatch lines in  FIG. 13  is generated from the field c′ and the field d before and after a boundary between the field c and the field d, as shown in  FIG. 13 . However, since the field c′ and the field d originate from different frames on a time axis, the frame generated from the field c′ and the field d is a comb-shaped image, that is, a double image, and thus image quality is greatly impaired.  
         [0011]     Incidentally, since such disruption of the sequence is caused by an editing process, the boundary between the field c′ and the field d will hereinafter be referred to as an edit point.  
         [0012]     In order to solve such a problem, a progressive conversion unit in related art compares the field c′ and the field d to be subjected to field interpolation with each other, and detects that the field next to the field c′ is the field d rather than the expected field c. However, it is difficult to find an edit point when the field c′ and the field d are similar to each other, for example, when only one part of a screen is moving. Consequently, a frame is generated from the field c′ and the field d, and thus image quality is greatly impaired.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention has been proposed in view of such an actual situation in the related art. It is desirable to provide an image processing apparatus and a method thereof that can convert even an interlaced signal including a signal converted into an interlaced signal by 3-2 pulldown, 2-2 pulldown or the like and resulting from an editing process into a progressive signal excellently without degradation in image quality.  
         [0014]     According to an embodiment of the present invention, there is provided an image processing apparatus for converting an interlaced signal into a progressive signal, the interlaced signal including a signal converted so as to be matched to a frame rate of an input video signal with original images arranged on a basis of a predetermined sequence as the video signal, the image processing apparatus including field-interpolated signal generating means for generating a progressive field-interpolated signal by interpolating a signal at a selected position corresponding to a scanning line to be interpolated in a present field, the signal at the selected position belonging to one of a field preceding the present field and a field succeeding the present field; and double image detecting means for determining whether a pixel in the field-interpolated signal forms a part of a double image, used for replacing a pixel in the field-interpolated signal which forms a part of a double image with a predetermined substitute signal.  
         [0015]     According to an embodiment of the present invention, there is provided an image processing method for converting an interlaced signal into a progressive signal, the interlaced signal including a signal converted so as to be matched to a frame rate of an input video signal with original images arranged on a basis of a predetermined sequence as the video signal, the image processing method including generating a progressive field-interpolated signal by interpolating a signal at a selected position corresponding to a scanning line to be interpolated in a present field, the signal at the selected position belonging to one of a field preceding the present field and a field succeeding the present field; determining whether a pixel in the field-interpolated signal forms a part of a double image of the field-interpolated signal; and replacing a pixel in the field-interpolated signal which forms a part of a double image in the field-interpolated signal with a predetermined substitute signal.  
         [0016]     The converted signal is a signal converted into an interlaced signal by 3-2 pulldown or 2-2 pulldown, for example.  
         [0017]     The image processing apparatus and the method thereof according to the embodiments of the present invention can convert even an interlaced signal including a signal converted into an interlaced signal by 3-2 pulldown, 2-2 pulldown or the like and resulting from a part of images of the converted signal being subjected to an editing process into a progressive signal excellently without degradation in image quality.  
         [0018]     The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a diagram showing an example of an outline of configuration of an image processing apparatus according to an embodiment;  
         [0020]      FIG. 2  is a diagram showing an example of internal configuration of a progressive conversion unit in the image processing apparatus;  
         [0021]      FIG. 3  is a diagram showing an example of internal configuration of a pulldown error detecting unit in the progressive conversion unit;  
         [0022]      FIG. 4  is a diagram showing the position of line-delayed signals;  
         [0023]      FIG. 5  is a diagram showing an example of internal configuration of a double image detecting unit in the pulldown error detecting unit;  
         [0024]      FIG. 6  is a diagram showing another example of internal configuration of a pulldown error detecting unit in the progressive conversion unit;  
         [0025]      FIG. 7  is a diagram showing an example of a binary pattern of five lines;  
         [0026]      FIG. 8  is a flowchart of assistance in explaining a process procedure of the progressive conversion unit;  
         [0027]      FIGS. 9A, 9B , and  9 C are diagrams showing various scanning line structures,  FIG. 9A  representing an interlaced signal,  FIG. 9B  representing a progressive signal, and  FIG. 9C  representing a signal obtained by converting an interlaced signal into a progressive signal by scanning line interpolation;  
         [0028]      FIG. 10  is a diagram of assistance in explaining inter-field interpolation and intra-field interpolation;  
         [0029]      FIG. 11  is a diagram of assistance in explaining 3-2 pulldown;  
         [0030]      FIG. 12  is a diagram of assistance in explaining 2-2 pulldown; and  
         [0031]      FIG. 13  is a diagram of assistance in explaining a problem when an interlaced signal converted to an interlaced signal by 3-2 pulldown and resulting from an editing process is converted into a progressive signal. 
     
    
     DETAILED DESCRIPTION  
       [0032]     A concrete embodiment to which the present invention is applied will hereinafter be described in detail with reference to the drawings. This embodiment is an application of the present invention to an image processing apparatus and a method thereof that can convert even an interlaced signal including a converted signal converted into an interlaced signal by 3-2 pulldown or 2-2 pulldown and resulting from an editing process into a progressive signal excellently without degradation in image quality.  
         [0033]      FIG. 1  shows an example of an outline of a configuration of the image processing apparatus according to the present embodiment. As shown in  FIG. 1 , the image processing apparatus  100  according to the present embodiment includes a front image processing unit  10 , a progressive conversion unit  11 , a display device driving circuit  12 , and a display device  13 .  
         [0034]     The front image processing unit  10  is supplied with a video signal from various signal sources, such for example as an NTSC signal, a PAL signal, or an HDTV signal from a BS digital tuner. Incidentally, the format of the video signal is the format of an interlaced signal such as 525i (an interlaced signal with 525 lines), 625i, 1125i, or the like.  
         [0035]     The progressive conversion unit  11  converts a 525i signal into a 525p signal (a progressive signal with 525 lines), converts a 625i signal into a 625p signal, and converts a 1125i signal into a 1125p signal. At this time, the progressive conversion unit  11  can convert even an interlaced signal including a converted signal converted into an interlaced signal by 3-2 pulldown or 2-2 pulldown and resulting from an editing process into a progressive signal excellently without degradation in image quality, as will be described later. The progressive conversion unit  11  supplies the resulting progressive signal to the display device driving circuit  12 .  
         [0036]     The display device driving circuit  12  drives the display device  13  to display the progressive signal supplied from the progressive conversion unit  11 . As the display device  13 , various display devices such as cathode-ray tubes, liquid crystal displays, plasma displays and the like can be used.  
         [0037]     Incidentally, the display device driving circuit  12  may include a resolution converting circuit for converting standard-resolution or low-resolution images into high-resolution images including a high-frequency component that is not included in the standard-resolution or low-resolution images. Such a resolution converting circuit is described in Japanese Patent Laid-Open No. Hei 7-193789 or Japanese Patent Laid-Open No. Hei 11-55630, for example.  
         [0038]      FIG. 2  shows an example of internal configuration of the above-described progressive conversion unit  11 . An interlaced signal input from the front image processing unit  10  is supplied as a present signal to a plurality of blocks in the progressive conversion unit  11 . This present signal is delayed by a time of one field to be converted into a past-1 signal by a field delay device  20 , and further delayed by a time of one field to be converted into a past-2 signal by a field delay device  21 .  
         [0039]     A motion detecting unit  22  performs motion detection using the present signal, the past-1 signal, and the past-2 signal. A motion detection determination uses a motion detection determination history indicating whether a pixel stored in a memory  23  has been moving or stood still in the past. The motion detecting unit  22  supplies a result of the motion detection to a motion adaptive type interpolation signal generating unit  24 . The motion adaptive type interpolation signal generating unit  24  performs an inter-field interpolation or an intra-field interpolation on the basis of the result of the motion detection to generate a progressive motion adaptive type interpolation signal. Specifically, when the image is still, the motion adaptive type interpolation signal generating unit  24  generates a new scanning line by performing an inter-field interpolation using an average value of pixels in a preceding field and a succeeding field for a new pixel. When the image is moving, on the other hand, the motion adaptive type interpolation signal generating unit  24  generates a new scanning line by performing an intra-field interpolation using, for the new pixel, an average value of pixels vertically adjacent to the new pixel. The motion adaptive type interpolation signal generating unit  24  supplies the generated motion adaptive type interpolation signal to an interpolation signal selecting unit  26  and a pulldown error detecting unit  28 .  
         [0040]     The pulldown detecting unit  25  detects 3-2 pulldown or 2-2 pulldown from the present signal, the past-1 signal, and the past-2 signal, and thereby detects whether a field being processed is a field originating from film video. Specifically, when the field being processed is a field of a part converted into an interlaced signal by 3-2 pulldown or 2-2 pulldown, there is always an adjacent field originating from the same frame. It is therefore possible to detect 3-2 pulldown or 2-2 pulldown by detecting a field sequence on the basis of presence or absence of inter-field movements (correlations between fields), for example. The pulldown detecting unit  25  supplies a result of the pulldown detection to the interpolation signal selecting unit  26  and the pulldown error detecting unit  28 .  
         [0041]     In addition, the pulldown detecting unit  25  has a state transition model therewithin. When detecting 3-2 pulldown or 2-2 pulldown, the pulldown detecting unit  25  makes the state transition model transition from a video picture state to a film picture state. When detecting 3-2 pulldown, for example, the pulldown detecting unit  25  makes five states corresponding to three or two fields originating from the same frame make transitions as the film picture state. By using such a state transition model, the pulldown detecting unit  25  determines the position of the field currently being processed in a sequence in which three fields and two fields alternate with each other. Incidentally, when a reset signal to be described later is supplied from the pulldown error detecting unit  28 , the pulldown detecting unit  25  returns the state transition model to the video picture state to detect 3-2 pulldown or 2-2 pulldown again even when the pulldown detecting unit  25  is making the film picture state transition.  
         [0042]     The interpolation signal selecting unit  26  determines an interpolation signal on the basis of the motion adaptive type interpolation signal, the present signal, the past-2 signal, and the result of the pulldown detection. Specifically, when the field being processed is a field of a part converted into an interlaced signal by 3-2 pulldown or 2-2 pulldown, there is always an adjacent field originating from the same frame. Thus, the interpolation signal selecting unit  26  supplies, as an interpolation signal, the signal (the present signal or the past-2 signal) of the field generated from that same frame to a double speed conversion unit  27 . When the field being processed is not a field of a part converted into an interlaced signal by 3-2 pulldown or 2-2 pulldown, the interpolation signal selecting unit  26  supplies, as an interpolation signal, the output signal of the motion adaptive type interpolation signal generating unit  24  to the double speed conversion unit  27 . The double speed conversion unit  27  converts the interpolation signal and the past-1 signal into a progressive field-interpolated signal by reading the interpolation signal and the past-1 signal in order at a speed twice that of the input signal. The double speed conversion unit  27  supplies the field-interpolated signal to the pulldown error detecting unit  28 .  
         [0043]     The progressive conversion unit in related art supplies the display device driving circuit  12  with this field-interpolated signal as it is. However, when the pulldown sequence of a part converted into an interlaced signal by 3-2 pulldown or 2-2 pulldown is disrupted, a frame generated from fields before and after an edit point is a double image, so that the quality of the image is greatly degraded.  
         [0044]     Accordingly, the progressive conversion unit  11  in the present embodiment has the pulldown error detecting unit  28  in a stage succeeding the double speed conversion unit  27 . The pulldown error detecting unit  28  evaluates the field-interpolated signal. When detecting a double image error, the pulldown error detecting unit  28  replaces the field-interpolated signal with the motion adaptive type interpolation signal. In particular, the pulldown error detecting unit  28  detects a double image error on the basis of surrounding pixel information in pixel units. When detecting a double image error, the pulldown error detecting unit  28  replaces the field-interpolated signal with the motion adaptive type interpolation signal in a pixel unit. When the number of pixels judged to be a double image error reaches a predetermined threshold value, the pulldown error detecting unit  28  selects the motion adaptive type interpolation signal for all of subsequent pixels or lines. Incidentally, this double image detection is performed only when the pulldown detecting unit  25  determines that the field being processed is a field of a part converted into an interlaced signal by 3-2 pulldown or 2-2 pulldown and when the interpolation signal selecting unit  26  uses the present signal or the past-2 signal as pixels to be interpolated.  
         [0045]      FIG. 3  shows an example of internal configuration of the pulldown error detecting unit  28 . The field-interpolated signal supplied from the double speed conversion unit  27  is delayed by a time corresponding to one line by a line delay device  30 . The field-interpolated signal is further delayed by a time corresponding to one line by each of line delay devices  31 ,  32 , and  33 . Finally, signals A, B, C, D, and E are obtained. Positional relation between the signals A, B, C, D, and E are as shown in  FIG. 4 . Incidentally, a dotted line in the figure represents a scanning line generated by field interpolation, and a straight line in the figure represents a scanning line of the input signal as it is.  
         [0046]     When a part converted into an interlaced signal by 3-2 pulldown or 2-2 pulldown is subjected to progressive conversion, lines adjacent to each other after the progressive conversion should have a strong correlation because the adjacent lines originally formed the same frame (original image). On the other hand, when a pulldown sequence is disrupted by an editing process and a frame is generated by two fields originating from different frames (original images), lines vertically adjacent to each other at the time of the interlaced signal, that is, alternate lines at the time of the progressive signal should have a stronger correlation than the lines vertically adjacent to each other at the time of the progressive signal. The pulldown error detecting unit  28  having the configuration of  FIG. 3  determines whether a double image has occurred using this correlation difference.  
         [0047]     Difference absolute value calculating units  34  to  37  calculate the absolute value of a difference in pixel data between adjacent lines. Specifically, the difference absolute value calculating unit  34  calculates the absolute value of a difference between the signal A and the signal B. The difference absolute value calculating unit  35  calculates the absolute value of a difference between the signal B and the signal C. Similarly, the difference absolute value calculating unit  36  calculates the absolute value of a difference between the signal C and the signal D. The difference absolute value calculating unit  37  calculates the absolute value of a difference between the signal D and the signal E. A one-line difference absolute value average calculating unit  38  calculates an average value of the difference absolute values calculated by the difference absolute value calculating units  34  to  37 . The one-line difference absolute value average calculating unit  38  supplies the average value to a flip-flop (FF)  39 . When supplied with the average values of one-line difference absolute values for five neighboring pixels by flip-flops  39  to  42 , a neighborhood average calculating unit  43  calculates an average value for the five neighboring pixels. The neighborhood average calculating unit  43  supplies this average value to a double image detecting unit  53 .  
         [0048]     Meanwhile, difference absolute value calculating units  44  to  46  calculate the absolute value of a difference in pixel data between alternate lines. Specifically, the difference absolute value calculating unit  44  calculates the absolute value of a difference between the signal A and the signal C. The difference absolute value calculating unit  45  calculates the absolute value of a difference between the signal B and the signal D. The difference absolute value calculating unit  46  calculates the absolute value of a difference between the signal C and the signal E. A two-line difference absolute value average calculating unit  47  calculates an average value of the difference absolute values calculated by the difference absolute value calculating units  44  to  46 . The two-line difference absolute value average calculating unit  47  supplies the average value to a flip-flop  48 . When supplied with the average values of two-line difference absolute values for five neighboring pixels by flip-flops  48  to  51 , a neighborhood average calculating unit  52  calculates an average value for the five neighboring pixels. The neighborhood average calculating unit  52  supplies this average value to the double image detecting unit  53 .  
         [0049]     The double image detecting unit  53  compares the average value supplied from the neighborhood average calculating unit  43  with the average value supplied from the neighborhood average calculating unit  52 . When the latter is smaller, that is, when correlation between alternate lines is stronger, the double image detecting unit  53  determines that a double image error has occurred, and supplies a signal indicating that a double image error has occurred to an output selecting unit  55 . In addition, the double image detecting unit  53  counts pixels judged to be a double image error. When a count value has reached a predetermined threshold value, the double image detecting unit  53  supplies a signal indicating that the count value has reached the predetermined threshold value to the output selecting unit  55 , and supplies a reset signal as described above to the pulldown detecting unit  25 . Incidentally, the double image detecting unit  53  resets the count value in the V-period of the image.  
         [0050]      FIG. 5  shows an example of internal configuration of the double image detecting unit  53 . A double image determining unit  60  compares the average value supplied from the neighborhood average calculating unit  43  with the average value supplied from the neighborhood average calculating unit  52 . When the latter is smaller, that is, when correlation between alternate lines is stronger, the double image determining unit  60  determines that a double image error has occurred, and supplies a signal indicating that a double image error has occurred to a counter  61  and an OR circuit  64 . The counter  61  counts the number of pixels judged to be a double image error, and supplies a count value to a comparing unit  62 . The comparing unit  62  supplies a result of comparison of the present count value with a predetermined threshold value to a latch circuit  63 . When the count value has reached the predetermined threshold value, a signal indicating that the count value has reached the predetermined threshold value is supplied from the latch circuit  63  to the OR circuit  64 . In addition, when the count value has reached the predetermined threshold value, there is a strong possibility that the pulldown sequence is disrupted. Thus, in order to reset the state transition model of the pulldown detecting unit  25 , the above-described reset signal is supplied from the latch circuit  63  to the pulldown detecting unit  25 . The OR circuit  64  supplies a signal as a logical sum of the signal supplied from the double image determining unit  60  and the signal supplied from the latch circuit  63  to the output selecting unit  55 . Incidentally, the counter  61 , the comparing unit  62 , and the latch circuit  63  are reset in the V-period of the image.  
         [0051]     Returning to  FIG. 3 , the output selecting unit  55  is supplied with the motion adaptive type interpolation signal delayed by a time corresponding to two lines by a two-line delay device  54 , the signal C, and the result of the pulldown detection. When a signal indicating that a double image error has occurred is supplied from the double image detecting unit  53  to the output selecting unit  55 , the output selecting unit  55  replaces a pixel in the signal C (field-interpolated signal) with a pixel at the same position in the motion adaptive type interpolation signal, and outputs the result, thereby avoiding the occurrence of a double image error. In addition, when a signal indicating that the count value has reached the predetermined threshold value is supplied from the double image detecting unit  53  to the output selecting unit  55 , the output selecting unit  55  is fixed to select the motion adaptive type interpolation signal for all of subsequent pixels or lines, thereby avoiding the occurrence of a double image error. Incidentally, this fixation is cancelled when the pulldown detecting unit  25  detects 3-2 pulldown or 2-2 pulldown again after being reset, and supplies a result of pulldown detection to the output selecting unit  55 .  
         [0052]      FIG. 6  shows another example of internal configuration of the pulldown error detecting unit  28 . As in  FIG. 3 , the field-interpolated signal supplied from the double speed conversion unit  27  is delayed by a time corresponding to one line by a line delay device  70 . The field-interpolated signal is further delayed by a time corresponding to one line by each of line delay devices  71 ,  72 , and  73 . Finally, signals A, B, C, D, and E are obtained.  
         [0053]     An average value calculating unit  74  calculates an average value of the signals A, B, C, D, and E. A binarizing unit  75  converts the signals A, B, C, D, and E into binary signals A′, B′, C′, D′, and E′. Specifically, when pixel data is larger than the average value of the signals A, B, C, D, and E, the binarizing unit  75  converts the pixel data to “1”, for example. When the pixel data is smaller than the average value of the signals A, B, C, D, and E, the binarizing unit  75  converts the pixel data to “0”, for example. A double image detecting unit  76  determines that a double image error has occurred when a binary pattern of five lines matches a predetermined pattern.  
         [0054]      FIG. 7  shows an example of a binary pattern of five lines. When a binary pattern of five lines matches a pattern (1, 0, 1, 0, 1) or (0, 1, 0, 1, 0) as shown in  FIG. 7 , that is, when correlation between alternate lines is stronger, the double image detecting unit  76  determines that there is a double image error, and supplies the determination result to a flip-flop  77 . When supplied with results of double image determination for five neighboring pixels on the same scanning line by flip-flops  77  to  80 , a neighborhood comprehensive double image detection unit  81  comprehensively determines whether a double image error has occurred from the determination results for the five neighboring pixels. When the neighborhood comprehensive double image detection unit  81  determines that a double image error has occurred, the neighborhood comprehensive double image detection unit  81  supplies a signal indicating that a double image error has occurred to an output selecting unit  83 . For example, the neighborhood comprehensive double image detection unit  81  determines that a double image error has occurred when all the binary patterns of the five neighboring pixels match the above-described double image pattern. In addition, the neighborhood comprehensive double image detection unit  81  counts pixels judged to be a double image error. When a count value has reached a predetermined threshold value, the neighborhood comprehensive double image detection unit  81  supplies a signal indicating that the count value has reached the predetermined threshold value to the output selecting unit  83 , and supplies a reset signal as described above to the pulldown detecting unit  25 . Incidentally, the neighborhood comprehensive double image detection unit  81  resets the count value in the V-period of the image.  
         [0055]     The output selecting unit  83  is supplied with the motion adaptive type interpolation signal delayed by a time corresponding to two lines by a two-line delay device  82 , the signal C, and the result of the pulldown detection. When a signal indicating that a double image error has occurred is supplied from the neighborhood comprehensive double image detection unit  81  to the output selecting unit  83 , the output selecting unit  83  replaces a pixel in the signal C (field-interpolated signal) with a pixel at the same position in the motion adaptive type interpolation signal, and outputs the result, thereby avoiding the occurrence of a double image error. In addition, when a signal indicating that the count value has reached the predetermined threshold value is supplied from the neighborhood comprehensive double image detection unit  81  to the output selecting unit  83 , the output selecting unit  83  is fixed to select the motion adaptive type interpolation signal for all of subsequent pixels or lines, thereby avoiding the occurrence of a double image error. Incidentally, this fixation is cancelled when the pulldown detecting unit  25  detects 3-2 pulldown or 2-2 pulldown again after being reset, and supplies a result of pulldown detection to the output selecting unit  83 .  
         [0056]     A process procedure of the above-described progressive conversion unit  11  will be described below with reference to a flowchart of  FIG. 8 . In first step S 1 , a video signal is input for each field. In step S 2 , whether a field being processed is a field originating from film video is determined by detecting 3-2 pulldown or 2-2 pulldown. When 3-2 pulldown or 2-2 pulldown is not detected, the field originates from normal video. Therefore, in step S 3 , the video signal is converted into a progressive signal by a motion adaptive type interpolation process. The process then proceeds to step S 13 . When 3-2 pulldown or 2-2 pulldown is detected, on the other hand, the field originates from film video. Therefore, in step S 4 , the video signal is converted into a progressive signal by a field interpolation process. The process then proceeds to step S 5 .  
         [0057]     In step S 5 , whether a double image error has occurred is detected in a pixel unit. In step S 6 , whether a double image error has occurred is determined. When it is determined in step S 6  that a double image error has occurred, the process proceeds to step S 7 . When it is determined in step S 6  that no double image error has occurred, the process proceeds to step S 10 .  
         [0058]     In step S 7 , the count value of the counter is incremented. In step S 8 , whether the count value has reached a predetermined threshold value is determined. When the count value has not reached the predetermined threshold value, the pixel is replaced with a pixel at the same position in a motion adaptive type interpolation signal in step S 9 . The process proceeds to step S 10 . In step S 10 , whether there is a next pixel is determined. When there is a next pixel, the process proceeds to the next pixel in step S 11 , and then returns to step S 5 . When there is not a next pixel, the process proceeds to step S 13 . When the count value has reached the predetermined threshold value in step S 8 , on the other hand, the pixel is replaced with a pixel at the same position in the motion adaptive type interpolation signal, and the motion adaptive type interpolation signal is selected for all of subsequent pixels or lines in step S 12 . Further, the state transition model of the pulldown detecting unit  25  is reset. The process proceeds to step S 13 .  
         [0059]     In step S 13 , whether there is a next field is determined. When there is a next field, the counter is reset in step S 14 . The process then returns to step S 1 . When there is not a next field, the process is ended.  
         [0060]     As described above, when an interlaced signal including a converted signal converted into an interlaced signal by 3-2 pulldown or 2-2 pulldown and resulting from an editing process is converted into a progressive signal, the progressive conversion unit  11  in the present embodiment generates a field-interpolated signal and a motion adaptive type interpolation signal, detects a double image error in the field-interpolated signal in a pixel unit, replaces a pixel judged to be a double image error with a pixel at the same position in the motion adaptive type interpolation signal, and selects the motion adaptive type interpolation signal for subsequent pixels or lines when the number of pixels judged to be a double image error has reached a predetermined threshold value. It is thereby possible to avoid the double image error that greatly degrades image quality, and generate the progressive signal of higher quality.  
         [0061]     It is to be noted that the present invention is not limited to only the foregoing embodiment, and is of course susceptible of various modifications without departing from the spirit of the present invention.  
         [0062]     For example, while the foregoing embodiment performs double image error detection using information of five vertical lines and five horizontal pixels, the present invention is not limited to this, and the number of lines and the number of pixels may be increased or decreased.  
         [0063]     In addition, while in the foregoing embodiment, description has been made of a case where a frame rate is 60 fields per second, the present invention is not limited to this, and is widely applicable to signals with desired frame rates based on various formats, such as a PAL signal displayed at a frame rate of 50 fields per second.  
         [0064]     Further, the present invention is widely applicable to signals with a frame rate changed by arranging pictures of original images on the basis of a predetermined sequence other than 3-2 pulldown or 2-2 pulldown.  
         [0065]     Further, description has been made of an embodiment in which a field-interpolated signal is replaced with a motion adaptive type interpolation signal when the pulldown detecting unit  25  detects a double image error. However, the present invention is not limited to this. For example, the field-interpolated signal may be replaced with a signal obtained simply by intra-field interpolation. Thus, the present invention is widely applicable to cases where the field-interpolated signal is replaced with another signal for remedying a double image.  
         [0066]     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.