Abstract:
Certain embodiments of the invention disclose a method and system for processing in a non-line locked system. The phase relationship between the sub-carrier signal on consecutive video lines in a video comb filter is determined by synchronizing the two video lines. The synchronization is achieved by aligning the color bursts signals in each of the two video lines. The phase error between the two video lines is determined through the use of a correlation operation. The phase error between consecutive video lines is used to automatically adjust the delay lines used by the video comb filter. The line delay adjustment is provided by changing the values of a variable integer delay and a fractional integer delay. Line delay adjustments reduce the artifacts that occur in the separation of luma and chroma components of a composite video signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE  
       [0001]     This application makes reference to, claims priority to, and claims the benefit of U.S. Provisional Application Ser. No. 60/542,413, entitled “Data Combing in a Non-Line Locked System,” filed on Feb. 6, 2004.  
         [0002]     This application makes reference to U.S. application Ser. No. ______ (Attorney Docket No. 15504US02) filed on Jun. 24, 2004.  
         [0003]     The above stated applications are hereby incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0004]     Certain embodiments of the invention relate to processing of video signals. More specifically, certain embodiments of the invention relate to a method and system for combing in a non-line locked system.  
       BACKGROUND OF THE INVENTION  
       [0005]     In video processing, the luma (Y) and chroma (C) signal components are modulated together in order to generate a composite video signal. Integrating the luma and chroma video elements into a composite video stream facilitates video signal processing since only a single composite video stream is broadcasted. Once a composite signal is received, the luma and chroma signal components must be separated in order for the video signal to be processed and displayed.  
         [0006]     A comb filter may be utilized for separating the chroma and luma video signal components. For example, a television set may be adapted to receive a composite video input, such as a composite video with burst and syncs (CVBS) input, for example, but the chroma and luma video components have to be separated before the television can display the received video signal.  
         [0007]      FIG. 1A  is a diagram illustrating the generation of a conventional composite video signal. Referring to  FIG. 1A , adding the chroma signal component  102  and the luma signal component  104  produces a composite video signal  106 . The luma signal component  104  may or may not increase in amplitude in a stair step fashion. The chroma signal component  102  may comprise a color difference component U modulated by, for example, a sine signal with a 3.58 MHz frequency and a color difference component V modulated by, for example, a cosine signal with a 3.58 MHz frequency. The modulated signals may be selected so that they provide quadrature modulation between the U and V color difference components. The modulation frequency corresponds to the frequency of a color sub-carrier signal. The luma signal component  104  increases in amplitude in a stair step fashion. The composite video signal  106  may be used in, for example, NTSC and PAL video standards.  
         [0008]      FIG. 1B  is a graphical diagram illustrating modulated chroma signals in contiguous composite video frames. The modulated chroma component is modulated at such a frequency that every line of video is phase-shifted by 180 degrees from the previous video line. Referring to  FIG. 1B , the current video line in the “current frame” is phase-shifted by 180 degrees from the previous video line in the “current frame” as well as from the next video line in the “current frame.” Similarly, the current video line in the “previous frame” is phase-shifted by 180 degrees from the previous video line in the “previous frame” as well as from the next video line in the “previous frame.” In addition, since video field have a frequency rate of 59.94 Hz, there is a 180-degree phase shift between two adjacent frames, for example, the “current frame” and the “previous frame.” Correspondingly, the current video line in the “current frame” is 180 degrees phase-shifted from the current video line in the “previous frame.” 
         [0009]     In conventional video processing, there are three ways to separate the luma and chroma video components—by utilizing a notch filter, by combing vertically or by combing temporally. During separation of the luma and chroma components, there are three bandwidth directions that may incur losses in the separation process and in the separated signal. Depending on the combing method that is utilized, the separated signal may have reduced vertical bandwidth, horizontal bandwidth, and/or temporal bandwidth.  
         [0010]     The first way to separate the luma and chroma video components is by utilizing a notch filter. Since the components in a chroma signal are modulated at 3.58 MHz, a notch filter that is set at 3.58 MHz may be utilized. The notch filter, however, reduces the horizontal bandwidth in the output video signal. A comb filter delays a prior horizontally scanned line in order to compare it with a currently scanned line horizontal line. Combing vertically may also be utilized to separate the luma and chroma video components. Combing vertically may be achieved in three different ways—the current video line may be combed with the previous and the next video line, the current video line may be combed with the video line just before it, or the current video line may be combed with the video line just after it. The vertical combing is performed spatially, i.e., only within one field at a time and without any temporal combing. During combing in the “current frame,” for example, if the current video line is added to the previous video line, the chroma content cancels out and two times the luma content is obtained. On the other hand, if the previous video line is subtracted from the current video line, the luma content cancels out and two times the chroma content is obtained. In this way, luma and chroma content may be separated from the composite video signal for further processing. Comb filters provide better separation than notch filters because they suppress cross-color and cross-luma artifacts. In addition, vertical combing results in a reduced vertical bandwidth.  
         [0011]     A third way to comb a composite signal is to comb temporally. Combing temporally comprises combing between two adjacent frames, for example, the “current frame” and the “previous frame”. Further, temporal combing is characterized by a reduced temporal bandwidth. The luma and chroma components may be separated by utilizing the same addition and subtraction methodology between a current video line and a previous video line, which is employed by vertical combing.  
         [0012]     While 2-D comb filters are adapted to process successive scan lines for a single field of a video frame, 3-D comb filters are adapted to process scan lines that are taken from successive video frames. In general, for 3-D comb filtering, if there is motion between the successive video frames, a 3-D comb filter must revert to 2-D comb filtering. Motion includes color changes and image movement between frames. Accordingly, the 3-D comb filter is required to buffer at least one successive frame in order to determine whether there is motion between the buffered frames. In instances where there is color changes or image movements between the buffered frames, the corresponding Y/C components for the buffered frames will be different and the results of combing would be incorrect.  
         [0013]     Before using comb filters to separate the luma and chroma video components, it may be necessary to process the video lines to ensure that the time length of each video line is the same. Changes in the timing of video lines produces errors in the luma and chroma separation because the corresponding addition and subtraction operations may not produce the necessary signal cancellation. While certain error in luma and chroma separation is generally accepted, timing variations may increase the error well above the level that the video system is capable of tolerating.  
         [0014]     An ideal line locked system ensures that there are always a constant number of samples per scan video line regardless of whether the timing changes. During combing, conventional line locked systems may still produce artifacts. For example, some conventional line locked 2-D combing systems produce artifacts while combing multiple video lines in the same field. Similarly, some conventional line locked frame combing systems produce artifacts while temporally combing multiple video lines separated by one or more frames. Also, some conventional line locked 3-D combing systems produce artifacts while combing multiple video lines in the same field and multiple video lines separated by one or more frames. These artifacts generally result from variations occurring in the scanned video lines.  
         [0015]     An ideal NTSC signal that conforms perfectly to the NTSC standard has a video line length of 63.55 μs. When this ideal NTSC signal is sampled at exactly 27 MHz, there are exactly 1716 samples per video line, for example, corresponding to approximately 37.04 ns of video line length for each sample. In a digital system, a constant delay, which may be an integer delay or integer plus a factional delay, may be constructed. The NTSC standard allows certain tolerable variations of the line length of up to about 0.001%. Notwithstanding, there are a number of devices which generate signals outside of the standard tolerable range for the video line length. VCRs, for example, may generate video line lengths that vary by ±5000 parts per million or ±317 ns. Assuming an ideal clock of frequency of 27 MHz, the variation in the video line length from an ideal line length of 63.55 us may require a system with a non-constant delay. Even if an incoming signal is always ideal, any variation in the frequency of the sampling clock may also require a non-constant delay. Variations in the frequency of the sampling clock may be due to factors such as temperature, voltage and/or printed circuit board (PCB) variations. Line locking circuits may be utilized to overcome these variations in the line length of the incoming signal and in the variations in the frequency of the sampling clock.  
         [0016]     A line locked system utilizes a phase-locked loop (PLL) type mechanism, which measures the length of each incoming video line to sub-sample accuracy and adjusts the frequency of the sampling clock such that there are always 1716 samples per line. For example, if the line is shorter than 63.55 us, then the sampling frequency is increased. A line locking system creates a signal after sampling that is always a constant length. This allows the use of an easily implemented constant delay for video signal combing. However, line locked systems may need to maintain different clock domains in a single integrated circuit (IC) in order to provide the appropriate sampling frequency to the incoming signal and also provide the appropriate clock signal to the processing circuitry. Multiple clock domains are difficult to implement on an IC because of clock signal distribution requirements.  
         [0017]     Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.  
       BRIEF SUMMARY OF THE INVENTION  
       [0018]     Certain embodiments of the invention may be found in a method and system for video line processing in a non-line locked system. Certain aspects of the method may comprise synchronizing a first video line and a second video line to be used in a vertical or temporal comb filter. The first video line and the second video line may be consecutive video lines in the same video frame or they may be corresponding video lines in consecutive video frames. The video line synchronization may be based on an alignment of a color burst signal in each of the video lines.  
         [0019]     After synchronization, a phase relationship may be determined between the first video line and the second video line. The phase relationship may be a phase error between a sub-carrier signal in the color burst signal of the first video line and a sub-carrier signal in the color burst signal of the second video line. The phase error may be determined by using a correlation operation or by using another digital phase error technique.  
         [0020]     A line delay adjustment to the vertical or temporal comb filter may be generated from the phase relationship between the two video lines. The adjustment may be applied to the line delay by a variable integer delay and a variable fractional delay. The variable integer delay and the variable fractional delay may be applied to the same line delay or they may be applied to different line delays depending on system or design requirements.  
         [0021]     Another embodiment of the invention may provide a machine-readable storage, having stored thereon, a computer program having at least one code section for executable by a machine, thereby causing the machine to perform the steps as described above for a method and system for processing in a non-line locked system.  
         [0022]     Certain aspects of the system may comprise a phase measurement and delay adjustment processor (PMDAP). The PMDAP may comprise a video line phase measurer and a line delay adjuster. The video line phase measurer synchronizes a first video line and a second video line to be used in a vertical or temporal comb filter. The first video line and the second video line may be consecutive video lines in the same video frame or they may be corresponding video lines in consecutive video frames. The video line synchronization by the video line phase measurer may be based on an alignment of a color burst signal in each of the video lines.  
         [0023]     After synchronization, a phase relationship between the first video line and the second video line may be determined by the video line phase measurer. The phase relationship may be a phase error between a sub-carrier signal in the color burst signal of the first video line and a sub-carrier signal in the color burst signal of the second video line. The phase error may be determined by the video line phase measurer or by a processor through the use of a correlation operation or by using another digital phase error calculation technique.  
         [0024]     The line delay adjuster may adjust or modify a line delay in a vertical or a temporal comb filter by generating the appropriate delay from the phase relationship between the two video lines determined by the video line phase measurer. The adjustment may be applied by the line delay adjuster to the line delay by changing the values in a variable integer delay and a variable fractional delay. The variable integer delay may be generated from data that resides in a delay memory, for example, random access memory (RAM). The variable fractional delay may be generated by a digital filter block, for example, a polyphase filter. The variable integer delay and the variable fractional delay may be applied by the line delay adjuster to the same line delay or they may be applied to different line delays depending on system and/or design requirements. The processor may be used to control the operation of the PMDAP, the video line phase measurer, the line delay adjuster, and to modify the contents of the delay memory and the digital filter.  
         [0025]     These and other advantages, aspects and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.  
     
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS  
       [0026]      FIG. 1A  is a graphical diagram illustrating the generation of a conventional composite video signal.  
         [0027]      FIG. 1B  is a graphical diagram illustrating modulated chroma signals in contiguous composite video frames.  
         [0028]      FIG. 2  is a diagram illustrating an exemplary phase measurement and delay adjustment processor that may be utilized for video line processing in a non-line locked system, in accordance with an embodiment of the present invention.  
         [0029]      FIG. 3A  illustrates exemplary variable integer and variable fractional delays that may be utilized for video line processing in a non-line locking system, in accordance with an embodiment of the present invention.  
         [0030]      FIG. 3B  illustrates exemplary variable integer and variable fractional delays that may be utilized for video line processing in a non-line locking system, in accordance with an embodiment of the present invention.  
         [0031]      FIG. 4  is a flow chart of exemplary steps that may be utilized for video line processing in a non-line locked system, in accordance with an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]     Certain embodiments of the invention may be found in a method and system for video line processing in a non-line locked system. Certain aspects of the method may comprise synchronizing a first video line and a second video line to be used in a vertical or temporal comb filter. The first video line and the second video line may be consecutive video lines in the same video frame or they may be corresponding video lines in consecutive video frames. The video line synchronization may be based on an alignment of a color burst signal in each of the video lines.  
         [0033]     After synchronization, a phase relationship may be determined between the first video line and the second video line. The phase relationship may be a phase error between a sub-carrier signal in the color burst signal of the first video line and a sub-carrier signal in the color burst signal of the second video line. The phase error may be determined by using a correlation operation or by using another digital phase error technique.  
         [0034]     A line delay adjustment to the vertical or temporal comb filter may be generated from the phase relationship between the two video lines. The adjustment may be applied to the line delay by a variable integer delay and a variable fractional delay. The variable integer delay and the variable fractional delay may be applied to the same line delay or they may be applied to different line delays depending on system or design requirements.  
         [0035]      FIG. 2  is a diagram illustrating an exemplary phase measurement and delay adjustment processor that may be utilized for video line processing in a non-line locked system, in accordance with an embodiment of the present invention. Referring to  FIG. 2 , a non-line locked system  200  for video line processing may comprise a phase measurement and delay adjustment processor (PMDAP)  204 , a processor  202 , and delay elements  214 . The PMDAP  204  may comprise a video line phase measurer  210  and a line delay adjuster  212 . The delay elements  214  may comprise at least one delay memory  206 , at least one digital filter  208 , or at least one delay memory  206  and at least one digital filter  208 . The PMDAP  204  may be coupled to delay elements  214 , or to processor  202  and delay elements  214 .  
         [0036]     The video line phase measurer  210  may be used to select the point of alignment for video line synchronization, to determine the phase relationship between video lines, and/or to communicate and transfer data and instructions with other hardware resources in the video system. The line delay adjuster  212  may be used to determine the line delay, to determine the amount of delay to be provided by the variable integer delay and/or the amount to be provided by the variable fractional delay, and/or to communicate and transfer data and instructions with other hardware resources in the video system.  
         [0037]     The processor  202  may be used by the PMDAP  202  to select the point of alignment for video line synchronization, to determine the phase relationship between video lines, to determine the line delay, to determine the amount of delay to be provided by the variable integer delay and/or the amount to be provided by the variable fractional delay. The processor  202  may also be used to transfer data and instructions to/from PMDAP  204  and to update or modify the contents of delay memory  206  and digital filter  208 . Delay memory  206  may be RAM, embedded memory, registers, look-up tables, and/or other on-chip memory elements. The delay memory  206  may be used to provide variable integer delays and/or variable fractional delays. The digital filter  208  may be used to provide variable integer delays and/or variable fractional delays. The digital filter  208  may be, for example, a polyphase digital filter bank. The polyphase digital filter may provide a desired delay of Δ=UM samples, where L and M are integers and L&lt;M, by first upsampling by M, delaying by L samples, and then downsampling by M.  
         [0038]     The application of the appropriate variable integer delay and/or variable fractional delay by PMDAP  204  allows the non-line locked system  200  to perform vertical or temporal video line combing REMOVE (with fewer color artifacts than a line locked) system and without the need of a phase-locked loop (PLL).  
         [0039]      FIG. 3A  illustrates exemplary variable integer and variable fractional delays that may be utilized for video line processing in a non-line locking system, in accordance with an embodiment of the present invention. Referring to  FIG. 3A , the exemplary non-line locking system comprises variable integer delays  302 ,  304 , variable fractional delays  308 ,  310 , a phase measurement and delay adjustment processor (PMDAP)  306 , line delays  312 ,  314 , and  316 . The variable integer delays  302 ,  304  and the variable fractional delays  308 ,  310  may be adjusted by PMDAP  306 . The variable integer delays  302 ,  304  and the variable fractional delays  308 ,  310  may be hardware resources, delay memories  206 , and/or digital filters  208 . The PMDAP  306  may be used to select the point of alignment for video line synchronization, to determine the phase relationship between video lines, to determine the line delay, to determine the amount of delay to be provided by the variable integer delay and/or the amount to be provided by the variable fractional delay, and/or to communicate and transfer data and instructions with other hardware resources. Line delays  312 ,  314 , and  316  may be added or subtracted to provide video line processing and determine the luma and chroma values.  
         [0040]     In determining the amount of delay to be provided by variable integer delay and/or the amount to be provided by variable fractional delay in  FIG. 3A , the PMDAP  306  may consider the configuration and placement of variable integer delays  302 ,  304  and variable fractional delays  308 ,  310 .  
         [0041]      FIG. 3B  illustrates exemplary variable integer and variable fractional delays that may be utilized for video line processing in a non-line locking system, in accordance with an embodiment of the present invention. Referring to  FIG. 3B , a different embodiment of the variable integer delay and the variable fractional delay are provided by variable integer-fractional delays  318 ,  320 . For example, variable integer-fractional delays  318  may provide the functionality of variable integer delays  302  and variable fractional delays  308 . Similarly, variable integer-fractional delays  320  may provide the functionality of variable integer delays  304  and variable fractional delays  310 . Variable integer-fractional delays  318 ,  320  may be hardware resources, delay memories  206 , and/or digital filters  208 . Line delays  312 ,  314 , and  316  may be added or subtracted to provide video line processing and determine the luma and chroma values.  
         [0042]      FIG. 4  is a flow chart of exemplary steps that may be utilized for video line processing in a non-line locked system, in accordance with an embodiment of the present invention. Referring to  FIG. 4 , after start step  402 , the non-line locked system  200  may receive in step  404  a first video line for processing in processing flow  400 . The first video line received by the non-line locked system  200  may be processed or combed with a previous video line, with a next video line, or with both the previous video line and the next video line. The previous video line and the next video line may be from the same video frame or may be from video frames that are prior to and that follow the current frame respectively. When adding video lines to determine the chroma value, when two or more video lines are being added, it may be necessary to apply appropriate weighting factors to each video line being added to determine the correct chroma value. Similarly, when subtracting video lines to determine the luma value, when two or more video lines are being subtracted, it may be necessary to apply an appropriate weighting factor to each video line being subtracted to determine the correct luma value. Determination of the luma value and the chroma value may take place in PMDAP  204  or in processor  202 .  
         [0043]     In step  406 , a second video line may be received by non-line locked system  200 . The first video line received is the previous video line to the second video line received. The second video line may be processed or combed with the first video line, with the next video line, or with both the first video line and the next video line. The second video line and the first video line may be from the same video frame or may be from different video frames.  
         [0044]     In step  408 , the video line phase measurer  210  in the PMDAP  204  may select a signal within the video line to use as an alignment point for synchronizing the first video line and the second video line. In general, each line of video may comprise a horizontal sync signal, a color burst signal, and an active video signal. In an embodiment of the invention, the color burst signal may be selected for alignment and synchronization of the video lines. The burst signal may be a brief signal of, for example, eight to ten samples of a color sub-carrier inserted by an NTSC encoder onto the back porch of a composite video signal. The NTSC encoder inserts color bursts to enable a decoder to regenerate the continuous-wave color sub-carrier. When the relationship between the length of a video line and the number of samples is violated, for example, in some VCRs, fewer artifacts are created when determining the luma and chroma values by aligning the color burst signal, in accordance with the various embodiments of the invention, than when the actual line length is used. Once selection of the alignment point is completed, the video lines are synchronized based on the selected alignment point in step  410 .  
         [0045]     In step  412 , a phase relationship may be determined by video line phase measurer  210  from the synchronized video lines. The phase relationship may be a phase difference or phase error where, for example, one of the video lines may be used as a reference and the phase of the other is measured in relation to the phase of the reference. The phase error may be determined by the video line phase measurer  210  or the processor  202  by applying a digital correlation operation between the video lines or by applying one of a plurality of digital phase detection operations.  
         [0046]     In step  414 , the delay to be applied to line delays  312 ,  314 , and  316  may be determined by line delay adjuster  212  from the phase relationship determined in step  412 . The delay in each line delay may correspond to the difference in time length between the first video line and the second video line. In step  416 , the variable integer delays  302 ,  304  may be determined from the delay in step  414 . In step  418 , the variable fractional delays  308 ,  310  may be determined from the delay in step  414 . The variable integer-fractional delays  318 ,  320  may be determined from the delay in step  414 .  
         [0047]     The determination of the delay provided by the variable integer delays  302 ,  304 , variable fractional delays  308 ,  310 , and variable integer-fractional delay  318 ,  320  may depend on the resolution provided by the non-line locked system  200 . As illustration, an exemplary video line of 63.55 μs in length may have 1716 samples, or 37 ns length per sample, while variable integer delays  302 ,  304  may provide 11 bits of resolution, or  2048  delay steps of 31 ns each. In this illustrative example, the variable integer delays  302 ,  304  may provide a delay that is approximately the length of one video line sample. Similarly, variable fractional delays  308 ,  310  may provide 5 bits of resolution for each delay step provided by variable integer delays  302 ,  304 , or  32  steps of approximately Ins each. The finer resolution of the variable fractional delays  308 ,  310  may provide a video line delay that is approximately 1/32 nd  of one video line sample. In another embodiment of the invention, the delay provided by variable integer delays  302 ,  304  may be fixed and the adjustment provided by line delay adjuster  212  may be carried out entirely by variable fractional delays  308 ,  310 . In another embodiment of the invention, the variable integer-fractional delays  318 ,  320  may provide both the coarser delay resolution of variable integer delays  302 ,  304  and the finer resolution of variable fractional delays  308 ,  310 . In this case, for example, the coarser delay may be fixed and the adjustment provided by line delay adjuster  212  may be carried out entirely by the finer resolution in variable integer-fractional delays  318 ,  320 .  
         [0048]     In step  420 , the line delay adjuster  212  applies the variable integer delays  302 ,  304 , the variable fractional delays  308 ,  310 , and the variable integer-fractional delays  318 ,  320  to line delays  312 ,  314 , and  316 . In step  422 , the video lines may be used to calculate the luma and chroma values because line delays  312 ,  314 , and  316  have been adjusted to compensate for the difference in time length between the first video line and the second video line. Once this calculation is completed, the non-line locked system  200  returns to start step  202  where it may receive a next video line. When the next video line is received, non-line locked system  200  may start processing flow  400  again with the second video line and the next video line.  
         [0049]     Accordingly, the present invention may be realized in hardware, software, or a combination of hardware and software. The present invention may be realized in a centralized fashion in at least one computer system, or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system or other apparatus adapted for carrying out the methods described herein is suited. A typical combination of hardware and software may be a general-purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods described herein.  
         [0050]     The present invention may also be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which when loaded in a computer system is able to carry out these methods. Computer program in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: a) conversion to another language, code or notation; b) reproduction in a different material form.  
         [0051]     While the present invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from its scope. Therefore, it is intended that the present invention not be limited to the particular embodiment disclosed, but that the present invention will include all embodiments falling within the scope of the appended claims.