Abstract:
A digital image processor is provided. The digital image processor includes a deinterlacing processor that is implemented upon a digital processing unit. The deinterlacing processor is coupled to an input operable to receive an interlaced video stream, a digital memory for storing portions of the interlaced video signal, and an output operable to transmit a deinterlaced video stream. The deinterlacing processor is operable to detect the source type of the received interlaced video stream to generate the deinterlaced video stream having reduced or no motion artifacts.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Patent Provisional Application No. 60/102,946 filed on Oct. 2, 1998, and is related to U.S. patent application Ser. No. 09/167,527 filed on Oct. 6, 1998, both of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the processing of video images and, more particularly, to techniques for deinterlacing video images. 
     2. Description of the Related Art 
     All major television standards use a raster scanning technique known as “interlacing” or “interlace scanning.” Interlace scanning draws horizontal scan lines from the top of the screen to the bottom of the screen in two passes. Each pass is known as a field. In the National Television System Committee (NTSC) standard used in North America, each field takes approximately {fraction (1/60)} th  of a second to draw. 
     Interlace scanning depends on the ability of the cathode ray tube (CRT) phosphors to retain an image for a few milliseconds, in effect acting like a “memory” to retain the previous field while the newer interleaved field is being scanned. Interlace scanning provides a benefit in television systems by doubling the vertical resolution of the system without increasing broadcast bandwidth. 
     FIG. 1 shows a number of parallel horizontal scan lines  10  on a conventional television display. A first set of horizontal lines  12  is scanned in a first field period and then a second set of horizontal lines  14  is scanned in a second field period. Thus, the first field is temporarily shifted by {fraction (1/60)} th  of a second from the second field. When rapidly changing images are being displayed, an object in motion may appear to be fuzzy due to the temporal displacement between the two fields. 
     This temporal displacement typically does not create a problem on conventional television displays, primarily because the image of the “older” field quickly fades in intensity as the light output of the phosphors decays. A secondary reason is that the spatial displacement in the images caused by motion results in a fine detail that television displays do not resolve well. For these reasons, interlace scanning of motion pictures works acceptably well on conventional television displays. 
     FIG. 2 shows a set of progressively scanned horizontal lines  16 . In progressive scanning, all horizontal lines  16 , are scanned out in one vertical pass  18 , so there is no time displacement of adjacent lines as in interlace scan. Progressive scanning requires a much higher bandwidth signal. Consequently, progressive scanning is typically used for applications where improved image quality and higher resolution are required, relative to conventional television systems. Progressive scanning is widely used in computer CRTs and liquid crystal displays (LCD). 
     If a motion picture formatted for an interlaced monitor device as in FIG. 1 is to be displayed on a progressively scanned device as in FIG. 2, then it must be converted from the interlaced format to the progressive format. This format conversion is known as deinterlacing. FIG. 3 is an illustration of a deinterlace process  19  of the prior art. A first series of interlaced video fields  20  is generated by a video source (not illustrated) at {fraction (1/60)} th  second intervals. 
     In this example, each of the video fields  20  has a spatial resolution of 720 horizontal by 240 vertical pixels. Each field contains half the vertical resolution of a complete video image. The first series of video fields  20  are input to a deinterlace processor  22 , which converts the 720 by 240 interlaced format to a second series of video fields  24 . In this example, each of the second series of video fields  24  may have 720 by 480 pixels where the fields are displayed at 60 frames per second. 
     FIG. 4 is an illustration of a prior art method of deinterlace processing, which uses field combination to deinterlace an image using multiple fields. A video field  26  containing scan lines  30 , and a previous video field  28  containing scan lines  32  is fed into a field combination deinterlace processor  34 . The result is a combined frame  36  with scan lines  38  sourced from video field  26  and scan lines  40  sourced from video field  28 . When this simple deinterlacing of the prior art is performed, and a motion picture formatted for an interlace display is converted to a progressive format, a noticeable “artifact” or error arises because the image content of vertically adjacent lines is time shifted by {fraction (1/60)} th  second as noted previously. The error is most visible around the edges of objects that are in motion. 
     FIG. 5 is an illustration of a prior art method of deinterlace processing, which uses line interpolation to deinterlace an image using a single reference field. The method  42  interpolates or doubles the number of lines of one field to produce a progressive frame. A video field  44  is scanned from an image to contain a half set of lines  46 . The half set of lines  46  is deinterlaced by line interpolation in a deinterlacing interpolator  48 . 
     The resulting frame  50  will have all the lines  46  of the original video field  44 . The remaining lines  52  are created by interpolation of lines  46 . The resultant image will not have motion artifacts because all the lines in the image will be created from lines  46  that are time correlated. This alternative method  42  of deinterlacing does not produce motion artifacts, but the vertical resolution of the image is reduced by half. 
     FIG. 6 shows a deinterlaced image  54  with a stationary object  55  that is rendered without distortion. FIG. 7 shows an image  56  with the object  55 ′ in motion. The edges of object  55 ′ create artifacts  57  on the edges of the image  54  because of the aforementioned temporal shift. These artifacts  45  are introduced into the image by the conventional field combination deinterlacing method  25  of FIG.  4 . 
     Motion artifacts in deinterlaced video images will have characteristics that vary depending on the original source of the motion picture. Video cameras, such as those used for television broadcasts, update motion in each field produced so that fields at 60 Hertz (Hz) will have motion updated at 60 Hz. But motion pictures from other sources are commonly displayed as video, which requires a conversion a different type of motion picture to video. For example, movies originally shot as film must be converted to video for display on a television set. Since film is originally shot at 24 frames per second, maximum update rate for motion for a film source is 24 Hz. 
     A film source may be viewed as a series of still image frames that are displayed in series at the rate of 24 per second. Film is converted to video in a two step process. First, each of the original film frames must be converted to video fields. Secondly, the video fields must be sequenced in a way that allows them to be displayed at 60 Hz for the NTSC video standard or at 50 Hz for the phase alternation line (PAL) standard. The conversion from film to NTSC video is known as 3:2 pulldown. The conversion of film to PAL video is known as 2:2 pulldown. 
     FIG. 8 illustrates a diagram of a method  58  for converting film into video of the prior art. A film frame  60  is digitized according to a standard for digital video known at ITR-R BT.601, which specifies the number of horizontal samples per line and the number of lines per field. The film frame  60  is shown with a horizontal by vertical resolution of 720×480, which is the approximate resolution specified by ITU-R BT.601 for NTSC video. (Note: this discussion assumes that film is being converted to a digital format. This may not always be the case but the explanation of 3:2 or 2:2 pulldown applies whether or not the film is digitized.) 
     Each film frame  60  contains the fall vertical resolution of the image. Since video fields contain half the vertical resolution, each film frame will be converted into two video fields. Assuming the horizontal lines of frame  60  are numbered in sequence from top to bottom, the white bands indicate even numbered lines  62  in the original film frame and the gray bands indicate odd numbered lines  64 . When the frame is converted to fields, the even lines  62  are assembled into a first video field  66  and the odd lines  64  are assembled into a second video field  68 . The field  66  is shown as white and the field  68  is shown in gray in the figures to indicate whether they contain the even numbered lines  62  or odd numbered lines  64  of the original frame  60 . 
     The significance of the method  58  is that the video fields  66  and  68  created from the original film frame  60  are time correlated. In other words, the image contained in the film frame  60  is a “snapshot” in time; so there is no motion displacement between the even field  66  and odd field  68  that are derived from the same original film frame  60 . This is not the case with video that was originally shot with video cameras, such as those used for television. Video cameras update motion in every field, and there are no “frames.” As mentioned previously, film has 24 frames per second and NTSC video uses 60 fields per second. The ratio of 24:60 equals 2:5. This means that for every 2 frames in the film source, 5 video fields must be created. 
     FIG. 9 illustrates a prior art method  70  providing for 3:2 pulldown (converting film frames to NTSC video fields). A time sequential series of film frames  72  at 24 frames per second are converted to even and odd fields. The fields are then displayed as video fields  74  at 60 fields per second. From FIG. 9 it is illustrated that Fields  1 ,  2 , and  3  originate from Frame  1 ; Fields  4  and  5  originate from Frame  2 , and so forth. Therefore, five fields are created from two film frames in order to achieve the 24/60 ratio of film frames to video fields. 
     The fields  74  are then assembled into a series of deinterlaced frames  76  by the method  46  shown in FIG. 5, which performs deinterlacing by combining the most recent two video fields into a single frame. Fields  1  and  2  are combined to create DI Frame  1 ; Fields  2  and  3  are combined to create DI Frame  2 ; Fields  3  and  4  are combined to create DI Frame  3 , and so forth. Since Fields  1  and  2  came from the same original film frame, there will be no motion artifacts in DI Frame  1  because Fields  1  and  2  are time correlated. There will be no motion artifacts in DI Frame  2  because Fields  2  and  3  come from the same film frame and are time correlated. 
     However, DI Frame  3  is the combination of Fields  3  and  4 . Because Field  3  comes from film Frame  1  and Field  4  comes from film Frame  2 , there may be motion artifacts because the two fields come from different original film frames. The diagram in FIG. 9 shows a heavy border around the deinterlaced frames  76  that result from the combination of fields from different original film frames and may have motion artifacts. The deinterlaced frames  76  with light borders will not have artifacts. 
     FIG. 10 illustrates a prior art method  78  providing for 2:2 pulldown (converting computer rendered animation to NTSC video fields). The animation motion picture forms a series of frames  80  at a rate of 30 frames per second. The series of frames  80  is converted to video fields  82  at a rate of 60 per second. 2:2 pulldown is also used to convert film at the rate of 24 frames per second to PAL video fields at 48 fields per second. The PAL video fields are then displayed 50 fields per second. 
     FIG. 10 further illustrates that when the video fields  82  are converted by a deinterlace processor by combining the two most recent field pairs into series of frames  84 , that motion artifacts may appear in half the deinterlaced frames. DI Frames  1 ,  3 ,  5 ,  7 , and  9  are created from pairs of fields that originally come from the same frame and so will be free of artifacts, but DI Frames  2 ,  4 ,  6 , and  8  are created from fields that come from different original frames and can have artifacts. 
     The 24 frame per second series of frames  72  of FIG.  9  and the 30 frame per second series of frames  80  of FIG. 10 have a characteristic in common: they are types of motion pictures sources that have full resolution frames from which time correlated even and odd fields are derived during the conversion to video. This type of source is referred to in this document as a “progressive frame source.” 
     The purpose of a deinterlace processor is to create progressively scanned frames from a series of interlaced video fields. If the original source of the motion picture is a type that has time correlated fall resolution frames, then knowledge of this type of source will be useful to a deinterlace processor. In view for the foregoing, it is desirable for a deinterlace processor to have a method for determining the original motion picture type from the series of input video fields, so that the deinterlace processing may be optimized for the source type. 
     SUMMARY OF THE INVENTION 
     The present invention fills these needs by providing a method and apparatus for deinterlacing a video input stream by analyzing the video stream to determine if the video stream originated from a progressive scanned source. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device or a method. Several inventive embodiments of the present invention are described below. 
     In one embodiment of the present invention, a digital image processor is provided. The digital image processor includes a deinterlacing processor that is implemented upon a digital processing unit. The deinterlacing processor is coupled to an input operable to receive an interlaced video stream, a digital memory for storing portions of the interlaced video signal, and an output operable to transmit a deinterlaced video stream. The deinterlacing processor is operable to detect the source type of the received interlaced video stream to generate the deinterlaced video stream having reduced or no motion artifacts. 
     In another embodiment of the present invention, a method for deinterlacing an interlaced video stream is provided. The method includes receiving a set of video fields from an input of the interlaced video stream. The set of video fields is analyzed to determine a source type of said interlaced video stream. If the source type of the interlaced video stream contains progressive frames, then the sequencing the interlaced video stream is detected. The set of video fields is then assembled into a deinterlaced video frame with reduced or no motion artifacts using the source type and the sequencing of said interlaced video stream as a control. 
     An advantage of the present invention is that it allows for reduction of motion artifacts in video images. By identifying the type of the source motion picture, a video deinterlacer can use the information to combine frames that are time correlated. The result is a video image that is free of artifacts. 
     Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements. 
     FIG. 1 shows a number of parallel horizontal scan lines on a conventional television display. 
     FIG. 2 shows a set of progressively scanned horizontal lines in a prior art progressive scan display. 
     FIG. 3 is an illustration of a deinterlace process of the prior art. 
     FIG. 4 is an illustration of a prior art method of deinterlace processing, which uses field combination to deinterlace an image using multiple fields. 
     FIG. 5 is an illustration of a prior art method of deinterlace processing, which uses line interpolation to deinterlace an image using a single reference field. 
     FIG. 6 shows a deinterlaced image of the prior art with a stationary object. 
     FIG. 7 shows a deinterlaced image of the prior art with an object in motion, creating undesirable “artifacts.” 
     FIG. 8 illustrates a diagram of a method for converting film into video of the prior art. 
     FIG. 9 illustrates a prior art method providing for 3:2 pulldown (converting film frames to NTSC video fields). 
     FIG. 10 illustrates a prior art method providing for 2:2 pulldown (converting computer rendered animation to NTSC video fields). 
     FIG. 11 illustrates a method of combining fields into frames in a deinterlacing process in accordance with one embodiment of the present invention. 
     FIG. 12 is a block diagram of a video deinterlacer in accordance with one embodiment of the present invention. 
     FIG. 13 is a system diagram of a progressive frame detector in accordance with one embodiment of the present invention. 
     FIG. 14 is a flow diagram of the processing steps within a field-differencing module in accordance with one embodiment of the present invention. 
     FIG. 15 illustrates the operation of the frequency detection module in accordance with one embodiment of the present invention. 
     FIG. 16 is a system diagram of the PFPD module in accordance with one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A method and apparatus for detection of the original source type of motion picture of a series of video input fields is disclosed. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be understood, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. 
     FIGS. 1-10 were discussed with reference to the prior art. FIG. 11 illustrates a method  100  of combining fields into frames in a deinterlacing process in accordance with one embodiment of the present invention. A series of film frames  102  at 24 frames per second are converted to video fields  104  at 60 fields per second. The video fields are then converted to deinterlaced frames  106  by a deinterlacing process. The deinterlaced frames  106   a  are created by combining the two most recent fields into a single frame, but the deinterlaced frames  106   b  are created by combination of different video fields and distinguished by bold arrows and bold borders. 
     When Field  2  is the “current” field, then DI Frame  1  is created by combining Field  1  (the “last” field) and Field  2  (the “current” field). DI Frame  2  is created in the same way by combining Field  3  with Field  2  when Field  3  is the current field. In contrast, when Field  4  is the current field, combining Field  4  and Field  5  creates DI Frame  3 . In this case, the combination is the “current” and the “next” fields. When the field combination is done in this way, all of the deinterlaced frames  106  will be created by combining fields that originate from the same source frame. Because these combining fields originate from the same source frame, they are time correlated. Therefore, no motion artifacts exist in the deinterlaced frames  106 . 
     Combining fields into frames as shown in FIG. 11 requires identification of the type of motion picture used in the original source. First, a source must be identified to be one in which original progressive frames exist; second, the sequencing used to create fields from the frames of the original source must be determined in order to assemble video fields into frames and avoid artifacts. 
     FIG. 12 is a block diagram of a video deinterlacer  130  in accordance with one embodiment of the present invention. A digital video stream enters the deinterlacer  130  through a FIFO memory module  132  before being written into a digital memory unit  134 . The digital memory unit  134  has the capacity to store four complete video fields in a set of field buffers  134   a-d.  The incoming field is written to each of the field buffers  134   a-d  in sequence. Therefore, the first incoming video field is written to field buffer  134   a,  the second incoming video field is written to field buffer  134   b,  etc. After field buffer  134   d  is filled, the next incoming video field is written to field buffer  134   a  again. 
     During the time period in which one field of the video stream is processed, the incoming field is written to one field buffer  134 , and the three previous fields are read from the other field buffers  134 . For example, if as shown in FIG. 12, the incoming field is written to  134   a,  then field buffers  134   b-d  are being read into a set of FIFO memories  136 ,  138 , and  140 . The FIFO memories  136 ,  138  and  140  are provided to accommodate the reading and writing of the four video fields into a single physical memory unit  134 , and also to decouple the clocking domains of the incoming video, the memory unit  134 , and the subsequent deinterlace processing stages. 
     The labeling of the field buffers in  134   a-d  as “incoming,” “1st,” 2nd,” and “3rd” previous fields are from the point of view of the incoming video streams. The outputs of the three read FIFOs  136 ,  138 , and  140  are labeled Next Field, Current Field, and Last Field respectively. This labeling is from the point of view of the deinterlace processor  130  and implies that deinterlace processing imposes a delay of approximately two field time periods on the video stream. 
     The outputs of FIFOs  136 ,  138 , and  140  are synchronized so that the three fields presented to subsequent processing stages are spatially concurrent. The three fields are then presented as inputs to an inter-field progressive frame detector  142  which produces a last/next (L/N) signal  144 , a progressive frame detection (PFD) signal  146  and a stage  1  detection value (Stage1DV)  148 . The L/N signal  144  is a control signal that instructs a field assembly module  150  to assemble the Current Field with the Last Field or the Next Field, which are three sequential fields from the input video stream. 
     With the three fields, the field assembly module  150  produces a progressively formatted output frame  152 . If the Current Field is even, then the Next and Last Fields must be odd and vice versa. Therefore, the progressively formatted frame  152  output of the field assembly module  150  will always be a combination of one even and one odd field. This is important because the correct assembly of fields into progressive frames requires one even field and one odd field for input. 
     The optional intra-frame deinterlacer  153  may provide additional processing to remove artifacts that occur within the output frame  152  under certain conditions, such as when the PFD signal  146  is not asserted. If the frame detector  142  detects that the incoming video signals were originally from a source that contains progressive frames, the PFD signal  146  is asserted. Three original types of source video are detected: film at 24 frames per second, computer animations or frames rendered at 30 frames per second, and still images, in which no motion occurs in the image over a period of several fields. When the PFD signal  146  is asserted, the optional processor  153  is disabled. 
     However, if the frame detector  142  is unable to detect a progressive frame sequence from the incoming video fields, then it will set the L/N signal  144  to always assemble Current and Last fields in the field assembly module  150 . Then, the frame detector  142  de-asserts the PFD signal  146 , which informs the optional deinterlacer  153  that artifacts may be present in the output frame  152  and that further processing may be necessary to remove the artifacts and create a final progressive output frame  152 ′. 
     Detection of a progressive frame sequence requires keeping a history of the preceding fields. However, the progressive frame detector  142  can look only one field ahead. In cases where a large transition in the image occurs, it is possible for the progressive frame sequence to change because of edits in the original video source. These changes could require changes in the way frames are created from incoming fields, but it is not possible to know in advance of the arrival of the incoming fields. 
     For this reason, the progressive frame detector  142  must be capable of detecting transitions in the motion picture because transitions may indicate edits that may change the progressive field sequencing. If a transition is detected, the progressive frame detector  142  will de-assert the PFD signal  146  for the time period required to determine if the progressive frame sequence has been broken. This allows motion artifacts to be removed by the optional deinterlacer  153  during the time period in which those artifacts may be present. In cases where a progressive frame sequence is not detected and the PFD output is not asserted, the Stage1DV  148  output contains magnitude information related to the amount of motion present in the image. This information may be used in the optional deinterlacer  153  to further process the image. 
     FIG. 13 is a system diagram of a progressive frame detector  142  in accordance with one embodiment of the present invention. The frame detector  142  includes a field differencing module  154 , a frequency detection module  156 , and a progressive frame pattern detection (PFPD) module  158 . The field differencing module  154  calculates the difference between a Next Field  162  and a Last Field  160 , processes the differences into the Stage 1 DV  148 , a transition detection  3 : 2  value  166 , and a number of field difference history bits  168 . 
     The frequency detection module  156  combines a Current Field  164  and the Next Field  162  into a frame and then detects the vertical high frequencies that result from motion artifacts. Then, the frequency detection module  156  outputs a number of frequency detection history bits  170  and a transition detection  2 : 2  value  172 . Finally, the PFPD  158  takes as input the transition detection  3 : 2  value  166 , the number of field difference history bits  168 , the number of frequency detection history bits  170  and the transition detection  2 : 2  value  172  to produce the L/N signal  144  and the PFD signal  146 . 
     FIG. 14 is a flow diagram of the processing steps within the field-differencing module  154  in accordance with one embodiment of the present invention. A Next array of pixels  174  which is a subset of the Next Field  160  and a Last array of pixels  176  which is a subset of the Last Field  162  comprise the inputs to a differencer  178 . The Next and Last pixel arrays  174  and  176  can be viewed as windows moving across their respective fields. The “window” is moved from left to right and top to bottom. Each time the windows are moved, a new difference is computed. The differencer  178  generates an array of differences  180 . 
     A weighted average of the array of differences  180  is computed. The weighting is such that the difference values near the center of the array of differences have the most influence on the weighted average. The weighted average of the differences  180  is compared in an operation  183  with a programmable threshold value  181 , and values less than the threshold value are zeroed out. The result of the comparison operation  183  is output at the Stage1DV  148 , and is also input into a field difference accumulator  182  that sums the differences over the entire field to produce a field difference value  184 . The previous five field difference values are stored in a memory module  186  and are summed in an operation  188 . 
     The sum of the previous five field difference values is compared to the current field difference value in an operation  190 , and the result is the Transition  3 : 2  output signal  192 . The current field difference value  184  is compared in a threshold operation  194  with the value in a programmable field difference register  196 . The result of the threshold operation  194  is an equal field bit  198 , which is a single bit that indicates that the Next Field  160  and Last Field  162  are the same. The previous field difference bits are stored in a memory module  200  and are used in the PFPD  158  of FIG.  13 . 
     FIG. 15 illustrates the operation of the frequency detection module  156  of the present invention. Vertically adjacent pixels from the Current Field  164  and the Next Field  162  are assembled, as they would appear spatially on a display  206 . A frequency detection value is calculated in an operation  208 . This calculation is performed to detect the frequencies that are associated with deinterlaced motion artifacts. The output of the frequency detection is compared in an operation  210  with a programmable threshold value  212 , and values less than the threshold value are zeroed out. 
     The output of the operation  210  is accumulated over the entire field period in  218  to produce a field frequency detection value  220 . The field frequency detection value  220  is stored in a memory module  222  that contains the previous 5 field frequency detection values. The five previous field frequency detection values are summed in an operation  224  and the results are compared to the current frequency detection value  220  in an operation  226 . The result of this comparison in operation  226  is the Transition  2 : 2  bit  228 , which indicates that a transition has occurred in the 2:2 sequence. 
     As part of a parallel process, a first previous field detection value  230  that was stored in the memory module  222  is transferred to a multiplier  232 , and multiplied with a value stored in a programmable field frequency threshold register  234 . The result of the multiplication is compared in an operation  236  to the current field frequency detection value  220 . The result is a relative frequency difference bit  238 , which is then stored in a memory module  240 . The previous ten relative frequency difference bits  242  are output to the PFPD module  158 . 
     FIG. 16 is a system diagram of the PFPD module  158  in accordance with one embodiment of the present invention. The PFPD module  158  performs logical operations on a set of field difference history bits  244 , the frequency detection history bits  242 , the transition  3 : 2  value  192 , and the transition  2 : 2  value  228 . From the input of the field difference history bits  244 , a logical operation  246  determines the  3 : 2  pulldown detection bit by looking for patterns in which every fifth field is equal. Also, a logical operation  248  detects still images by setting the STILL bit when the most recent four field differences are zeros. The state of the L/N control signal is set by a logical operation  250 . 
     From the input of the frequency detection history bits  242 , a logical operation  252  determines a 2:2 pulldown detection bit by searching for alternating patterns of high frequency content in successive fields. Then, a logical operation  254  determines the L/N control signal for the 2:2 pulldown case. The PFD signal  146  is determined from the 3:2 pulldown detection bit, the transition  3 : 2  value  192 , the 2:2 pulldown bit, and the transition  2 : 2  value  228 . 
     Three source types of progressive frames are detected. Film converted to video using 3:2 pulldown is detected by computing the difference between pairs of even fields or pairs of odd fields and looking for the condition in which every fifth difference is zero. This condition is indicated by the 3:2 pulldown signal. 30 frame/second progressive video sources using 2:2 pulldown are detected using a frequency detection method which looks for the frequencies associated with motion artifacts in every second combined frame, indicated by the 2:2 pulldown signal. Still images are detected when the field differences are zero for several consecutive fields, indicated by the STILL signal. 
     Progressive frames are simply the logical OR of these three signals as shown by a logical OR gate  256 . However, transitions must also be taken into account. As mentioned above, a transition is a large change in the field sequence that result from edits, or dropout of the video signal. If a large change is detected, then progressive frame detection, which depends on a history of several fields, may be unreliable for the period required to establish that the progressive frame pattern has been broken. In the examples illustrated, this period consists of multiple field periods and varies depending on the type of source detected. 
     In a set of logical operation  258 , a pulse is generated under two conditions. One is that a 3:2 pulldown sequence is detected and a transition occurs; the second is a 2:2 pulldown sequence is detected and a transition is detected in the sequence. Either of these cases triggers a timer  260 , which generates a pulse of a multiple field duration, sufficient to establish that the progressive sequence has been broken. During this time, a logical AND gate  262  disables the PFD bit  146 . As mentioned previously, if the PFD bit  146  is not asserted, then the optional intra-frame deinterlace processor  153  (illustrated in FIG. 12) may remove motion artifacts during the timeout period. 
     It will therefore be appreciated that the progressive frame detecting process of the present invention provides for elimination of edge artifacts in a video image. This is accomplished by identifying the source type of the original motion picture and determining a sequencing of the input video stream if the source type uses progressive scanning. The information is then used to reassemble video fields in the deinterlacing process. The combination of these techniques provides a low-artifact, high-resolution deinterlaced image. 
     Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention. Furthermore, certain terminology has been used for the purposes of descriptive clarity, and not to limit the present invention. The embodiments and preferred features described above should be considered exemplary, with the invention being defined by the appended claims.