Patent Publication Number: US-7710500-B2

Title: Video processing apparatus and methods using selectively modified sync positions

Description:
RELATED APPLICATION 
   This application claims the benefit of Korean Patent Application No. 10-2004-0108824, filed on Dec. 20, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to video signal processing apparatus and methods and, more particularly, to apparatus and methods for synchronizing a video signal. 
   A video processing system, such as a video decoder, may include apparatus configured to perform a 3D luminance/chrominance (Y/C) separation of an input video signal.  FIG. 1  is a block diagram illustrating a conventional video signal processing apparatus  100  for performing a 3D Y/C separation. Referring to  FIG. 1 , the video signal processing apparatus  100  includes an analog/digital (A/D) converter  110 , a Y/C separator and demodulator  120 , a sync detector  130 , a field/frame memory  140 , and a re-sampler  150 . 
   The A/D converter  110  converts an input analog video signal into a digital video signal. The input analog video signal may be a composite video blank sync (CVBS) signal including a front porch signal, a horizontal sync level signal, a back porch signal, and an active video signal. The sync detector  130  detects a horizontal sync position and a vertical sync position used to define horizontal and vertical scan periods from the converted digital video signal. The field/frame memory  140  stores the detected horizontal sync positions {p i } for a plurality of fields or frames. The Y/C separator and demodulator  120  performs a 3D Y/C separation according to the detected horizontal sync positions {p i } stored in the field/frame memory  140 , extracts a luminance signal Y and a chrominance signal C from the converted digital video signal, interpolates the luminance signal Y and the chrominance signal C, and generates color signals, such as R, G, B color signals (R, G, B) or luminance (Y) and chrominance component (Cb, Cr) signals used by a display device (e.g., a liquid crystal display (LCD)). The color signals generated in the Y/C separator and demodulator  120  are re-sampled in the re-sampler  150  according to the horizontal sync positions {p i }. The re-sampled color signals may be used to generate a display on a display device. 
   When a video cassette recorder (VCR) outputs a CVBS signal, mechanical factors may cause jitter among horizontal sync positions extracted from the CVBS signal. When a TV or a digital video disk (DVD) system outputs a CVBS signal, less jitter may occur. Noise in the CVBS signal may deteriorate accuracy of the horizontal sync positions detected from the sync detector  130 . Referring to  FIG. 2 , when the re-sampler  150  re-samples the color signals generated in the Y/C separator and demodulator  120 , the screen  210  may display an unstable image due to errors in the horizontal sync positions {p i }. In particular, phase differences among the horizontal sync positions {p i } may be present, which may cause an unstable display. 
   SUMMARY OF THE INVENTION 
   Some embodiments of the present invention provide digital video signal processing apparatus that may generate a stable image by performing a 3D Y/C separation and sampling the Y/C separated color signals according to horizontal sync positions that are modified to reduce errors caused by noise. Some embodiments of the present invention also provide video signal processing methods using modified horizontal sync positions by fields or frames to reduce errors in horizontal sync position caused by noise. 
   In some embodiments of the present invention, an apparatus includes a sync position determiner configured to receive sync positions and to process (e.g., average) the received sync positions to generate modified sync positions. The apparatus further includes a sync position selector configured to selectively output the received sync positions and the modified sync positions. 
   In some embodiments, the sync position selector configured to selectively output the received sync positions and the modified sync positions responsive to differences between the modified sync positions. For example, the sync position selector may be configured to determine a minimum difference between the modified sync positions and a maximum difference between the modified sync positions and to select from the received sync positions and the modified sync positions based on the minimum and maximum differences. In further embodiments, the sync position determiner may be configured to generate a modified horizontal sync position n i  according to the formula 
               n   i     =       n     i   -   1       +       1       2   ⁢   M     +   1       ⁢       ∑     j   =     i   -   M         i   +   M       ⁢     (       p   j     -     p     j   -   1         )             ,         
wherein i is a horizontal sync position index and p j  are received sync positions corresponding to, preceding and following the modified horizontal sync position n i .
 
   According to additional embodiments of the present invention, the sync position selector may be configured to select received horizontal sync positions if a difference between the minimum and maximum differences meets a predetermined criterion. The sync position selector may select modified horizontal sync positions if the difference between the minimum and maximum differences fails to meet the predetermined criterion. 
   In some embodiments of the present invention, a video signal processing apparatus includes a sync detector configured to detect sync positions from an input video signal and a memory configured to store the detected sync positions for one or more fields. The apparatus also includes a Y/C separator and demodulator configured to perform a Y/C separation and demodulation of the input video signal according to the detected horizontal sync positions to generate a color signal. The apparatus further includes a selective sync position generator configured to receive the detected sync positions from the memory, to process the received sync positions to generate modified horizontal sync positions, and to selectively output the received sync positions and the modified sync positions. The apparatus further includes a sampler configured to sample and synchronize the color signal according to the sync positions output by the selective sync position generator. 
   The selective sync position generator may selectively output the received sync positions and the modified sync positions responsive to differences between the modified horizontal sync positions. The input video signal may include a digital video signal, and the apparatus may further include an A/D converter configured to convert an analog video signal to produce the digital video signal. The selective sync position generator may be configured to provide modified sync positions to the sampler if the input video signal is a TV or DVD output signal, and the sync position selector may be configured to provide detected sync positions to the sampler if the input video signal is a VCR output signal. 
   In some method embodiments of the present invention, sync positions are detected from a video signal. The detected sync positions are processed (e.g., averaged) to generate modified sync positions. The detected sync positions and the modified sync positions are selectively used to sample and synchronize a color signal derived from the video signal. In some embodiments, the detected sync positions and the modified sync positions are selectively used to sample and synchronize the color signal responsive to differences between the modified sync positions. 
   In further method embodiments, the detected sync positions are stored in a memory configured to store detected sync positions for one or more fields. The input video signal is Y/C separated and demodulated according to the stored detected horizontal sync positions to generate the color signal. Processing the detected sync positions to generate modified sync positions includes processing the stored sync positions, and selectively using the detected sync positions and the modified sync positions to sample and synchronize a color signal derived from the video signal includes sampling and synchronizing the color signal according sync positions selected from the stored detected sync positions and the modified sync positions. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram illustrating a conventional video signal processing apparatus; 
       FIG. 2  illustrates horizontal sync errors that may occur in conventional video signal processing; 
       FIG. 3  is a block diagram illustrating a digital video signal processing apparatus according to some embodiments of the present invention; 
       FIG. 4  is a block diagram illustrating a re-sampler that may be used in the apparatus of  FIG. 3  according to further embodiments of the present invention; 
       FIG. 5  illustrates rearrangement of horizontal syncs in accordance with some embodiments of the present invention; and 
       FIGS. 6A and 6B  illustrate reorganization of pixel signals responsive to modified horizontal syncs according to further embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
   Specific exemplary embodiments of the invention now will be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. Furthermore, “connected” or “coupled” as used herein may include wirelessly connected or coupled. 
   The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes,” “includes,” “including” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
   Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present specification and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
   It will be understood that although the terms first and second are used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, a first item could be termed a second item, and similarly, a second item may be termed a first item without departing from the teachings of the present invention. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. The symbol “/” may also used as a shorthand notation for “and/or”. 
     FIG. 3  is a block diagram illustrating a digital video signal processing apparatus  300  according to some embodiments of the present invention. The digital video signal processing apparatus  300  includes an analog/digital (A/D) converter  310 , a Y/C separator and demodulator  320 , a sync detector  330 , a field/frame memory  340 , a selective sync position generator  350 , and a re-sampler  360 . The digital video signal processing apparatus  300  is configured to detect horizontal sync positions from an input analog video signal and to generate a stabilized image from resampled color signals according to horizontal sync positions {n i } or {p i } provided by the selective sync position generator  350 . The input analog video signal may be a composite video blanking sync (CVBS) signal, which may include a front porch signal, a back porch signal, and an active video signal. 
   The A/D converter  310  converts the input analog video signal into a digital video signal and outputs the converted digital video signal to the Y/C separator and demodulator  320 , the sync detector  330 , and the field/frame memory  340 . The sync detector  330  detects a horizontal sync position p i  from the digital video signal during each horizontal scan period. The field/frame memory  340  stores detected horizontal sync positions for a plurality of fields (/frames) along with data of the digital video signal for the fields (/frames). 
   The Y/C separator and demodulator  320  perform a 3D Y/C separation based on horizontal sync positions for more than 3 fields (/frames) stored in the field/frame memory  340  and demodulates the separated signal. The Y/C separator and demodulator  320  extracts a luminance signal Y and a chrominance signal C from the digital video signal in the 3D Y/C separation process. The Y/C separator and demodulator  320  extracts the luminance signal Y and the chrominance signal C for display pixels of a current field based on horizontal sync positions corresponding to a previous field and a subsequent field and data of corresponding horizontal scan lines. The Y/C separator and demodulator  320  interpolates the luminance signal Y and the chrominance signal C and generates color signals, such as R, G, B color signals or a luminance signal Y and chrominance component signals (Cb, Cr), which may be used by a display device, such as a liquid crystal display (LCD). 
   The selective sync position generator  350  averages horizontal sync positions {p i } of a current field (/frame) stored in the field/frame memory  340  to generate modified horizontal sync positions {n i }. The selective sync position generator  350  determines whether to provide the unmodified horizontal sync positions {p i } or the modified horizontal sync positions {n i } to the re-sampler  360 . The selective sync position generator  350  selects the modified horizontal sync positions {n i } or the non-modified horizontal sync positions {p i } based on differences between the modified horizontal sync positions {n i }, which may depend on the type of system (e.g., VCR, TV, DVD) providing the input analog video signal. 
   The re-sampler  360  samples the demodulated color signals generated in the Y/C separator and demodulator  320  responsive to the modified horizontal sync positions {n i } or the non-modified horizontal sync positions {p i } provided by the sync position generator  350  and outputs synchronized color signals. The re-sampler  360  may use the current horizontal sync position p i  detected by the sync detector  330 . The color signals re-sampled in the re-sampler  350  may be used to generate a display on a display device. 
     FIG. 4  is a block diagram illustrating a selective sync position generator  350 ′ which may be used in the apparatus shown in  FIG. 3 . Referring to  FIG. 4 , the selective sync position generator  350 ′ includes a sync position determiner  351 , and a sync position selector  356  including a maximum length calculator  352 , a minimum length calculator  353 , a subtractor  354 , and a comparator  355 . The sync position determiner  351  averages a predetermined number of horizontal sync positions among the horizontal sync positions {p i } of a current field (/frame) stored in the field/frame memory  340  and generates respective modified horizontal sync positions {n i } corresponding to the respective horizontal sync positions {p i }. 
   The modified horizontal sync positions {n i } may be given by Equation 1, 
                   n   i     =       n     i   -   1       +       1       2   ⁢   M     +   1       ⁢       ∑     j   =     i   -   M         i   +   M       ⁢     (       p   j     -     p     j   -   1         )                   (   1   )               
wherein i denotes a horizontal sync position index, and p j  denotes 2M+1 input sync positions corresponding to, preceding and following the modified horizontal sync position n i . A modified horizontal sync position n i  is obtained by summing up a previous horizontal sync position n i−1  and an average 2M+1 (e.g., 240 in NTSC, 288 in PAL/SECAM) differences (p j −p j−1 ) between adjacent input horizontal sync positions p j . This may attenuate noise so that the modified horizontal sync positions {n i } modified in the position arranger  351  can be used to generate a stable image on a screen  510 , as shown in  FIG. 5 .
 
   The maximum length calculator  352  calculates a maximum difference I max  between neighboring locations of the modified horizontal sync positions {n i } generated by the sync position determiner  351  as given by Equation 2: 
                   I   max     =           max               i   =   2     ,   3   ,     …   ⁢           ⁢   N             ⁢     (       n   i     -     n     i   -   1         )               (   2   )               
The minimum length calculator  353  calculates a minimum difference I min  between neighboring locations of the modified horizontal sync positions {n i } generated by the sync position determiner  351  as given by Equation 3:
 
   
     
       
         
           
             
               
                 
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   The subtractor  354  determines a difference between the minimum difference I min  and the maximum difference I max . The comparator  355  selects the horizontal sync positions {p i } stored in the field/frame memory  340  or the horizontal sync positions {n i } generated by the sync position determiner  351  based on the difference and outputs the selected horizontal sync positions. If the difference is smaller than a threshold, the comparator  355  selects the modified horizontal sync positions {n i }. When the comparator  355  selects the modified horizontal sync positions {n i }, the comparator  355  may output a flag signal to the Y/C separator and demodulator  320  to perform the 3D Y/C separation. If the input analog video signal is output from a TV or DVD system, for example, the re-sampler  360  may synchronize and re-sample the demodulated color signals with the modified horizontal sync positions {n i }. When a CVBS signal is input from a TV or DVD system, a horizontal synchronizing frequency may have a very small short-term variation, whereas, the horizontal sync positions detected in the sync detector  330  may have an error caused by the noise. 
     FIGS. 6A and 6B  illustrate reorganization of pixel signals according to modified horizontal syncs. A modification of horizontal sync positions may reduce an error generated when re-sampled signals S pi , S pi +1, S pi +2, S pi +3 . . . S pi+1 −2, S pi+1 −1 are scanned at wrong positions of the screen  510 , as shown in  FIG. 6A . As shown in  FIG. 6B , signals S 1 , S 2 , S 3 , . . . S NS  re-sampled according to the modified horizontal sync positions {n i } are scanned at appropriate positions, which can provide a stable image. 
   Referring again to  FIG. 4 , if the difference determined by the subtractor  354  is greater than the threshold, the comparator  355  selects the horizontal sync positions {p i } stored in the field/frame memory  340 . When the comparator  355  selects the unmodified horizontal sync positions {p i }, the comparator  355  may output a flag signal to the Y/C separator and demodulator  320  not to perform the 3D Y/C separation. If the input analog video signal is output from the VCR, for example, the re-sampler  360  may synchronize and re-sample the demodulated color signals using the unmodified horizontal sync positions {p i }. When the CVBS signal is input from the VCR, mechanical errors may cause a short-term variation of the horizontal synchronizing frequency. In particular, a specific horizontal sync scanning period may cause an inconsistency in horizontal sync phase differences between fields or frames necessary for the 3D Y/C separation. In this case, the inconsistency may be resolved, and it may not be necessary to modify horizontal sync positions. 
   In the video signal processing apparatus  300 , the selective sync position generator  350  determines characteristics of horizontal sync positions {p i } stored in the field/frame memory  340  and, if the sync positions meet a predetermined criteria, which may correspond to the video signal being from a source, such as a TV or DVD system, outputs modified horizontal sync positions {n i } generated by averaging a predetermined number of input horizontal sync positions. The video signal processing apparatus may reduce horizontal sync error caused by noise, and may thereby provide a stable image. A video decoder having a 3D Y/C separation function can use an embedded field or frame memory without a separate memory upgrade. 
   It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.