Abstract:
An apparatus and method for a three-dimensional luminance/chrominance (Y/C) seperation comb filter bank. The method and system consider the effect of motions in the temporal domain as the effect of edges in the spatial domain. The method and system apply a temporal filter to the section rule of edge location detection in the spatial domain. With this applications, the three-dimension comb filter bank can separate Y and C from each other freely without motion consideration. The method and system do not simply exploit the topology in the pixel phases. Rather, the method and system consider the Y/C comb filter to operate from the spectral viewpoint. Temporal filtering function is increased to better utilize the memory buffers of the three-dimensional filter. In so doing, balanced usage among the horizontal, vertical and temporal filter functions is achieved using the method and system.

Description:
FIELD OF THE INVENTION 
     The invention relates to separation of luminance (Y) and chrominance (C) in a TV composite signal, particularly to Y/C separation for a TV composite signal using a comb filter bank. 
     BACKGROUND 
     A typical color TV decoder receives a composite TV signal as input. Using a comb filter, the color decoder separates Luminance (Y) and Chrominance (C) from the input signal. Next, the comb filter applies the band-pass filtering for the C signal and the band-stop filtering for the Y signal. Thirdly, the C signal is de-modulated back to the base-band region. Fourthly, a low-pass filter band-limits both the de-modulated C signal and the Y signal. Lastly, the band-limited Y and C signals are converted to Red, Green, and Blue outputs. 
     The composite signal allocates Y and C in the three-dimensional spectral positions in a three-dimensional spectral space. When represented in a one-dimensional or a two-dimensional subspace of the three-dimensional spectral space, the spectrum of Y and C overlap with each other. As such, one-dimensional and two-dimensional comb filters cannot separate Y and C completely. Rather, only three-dimensional comb filters can separate Y and C from a digitized composite image sequence completely. Moreover, as a genuine nonlinear characteristic of an image, edges inside image make difficult any Y/C comb filtering for completely separating Y from C or C from Y in a composite TV signal. Even worse, in an image sequence or video, motions inside image exist in a speed to any directions. Therefore, without perfect motion estimation for the motion of edges in addition to the motion of an ordinary object, the complete Y/C separation cannot be achieved by a one-dimensional or two-dimensional linear comb filter. 
     However, few real three-dimensional Y/C comb filters are available for a digital color decoder. Even a conventional three-dimensional comb filter operates mostly for the condition of motionless image sequences. It does not fully take advantage of the strong points of three-dimensional comb filters. 
     For example, most of video signal includes lots of motion contents, but a conventional three-dimensional comb filter function merely two-dimensional comb filter in the spatial domain. Specifically, conventional three-dimensional comb filters simply apply to the conditions of motionless parts in video by a go-no-go decision, wherein the temporal filter function of these three-dimensional filters is not selected in most case. Therefore, a conventional three-dimensional comb filter typically operates merely as a two-dimensional comb filter. For that reason, the conventional three-dimensional comb filter is ineffective when filtering complex motion video content. As another example, memory buffers are necessary to store data for performing the temporal filtering of a conventional three-dimensional filter. However, by operating merely as a two-dimensional comb filter most of the time, the conventional three-dimensional filter rarely use these precious memory buffers. 
     BRIEF SUMMARY OF THE INVENTION 
     A method for separating luminance (Y) and chrominance (C) of a composite television digital signal is provided. The method includes analyzing said composite signal to search for one of a plurality of pre-defined motions; in response to a pre-defined motion being detected, filtering the spectral energy of said detected pre-defined motion by a one-dimensional temporal comb filter selected from a filer bank; in response to no pre-defined motion being detected, analyzing said signal by searching for an edge in a three-dimensional sample space of said signal, wherein said sample space is spanned by a horizontal axis, a vertical axis and a temporal axis, and wherein said edge represents a motion encoded in said signal; in response to said edge being detected, selecting a filter of said filter bank in accordance with the orientation of said edge to filter the spectral energy of said motion; and in response to no edge being detected, selecting a three-dimensional spatial-temporal comb filter of said filter bank. 
     A method for separating luminance (Y) and chrominance (C) of a composite TV digital signal is provided. The method includes searching for motion encoded in said signal, wherein a motion is represented as an edge in a three-dimensional sample space of said signal, said sample space spanned by a horizontal axis, a vertical axis and a temporal axis; in response to detecting a first motion that matches one of a plurality of pre-defined motions, select a one-dimensional temporal filter of a filter bank to filter spectral energy corresponding to a first edge that represents said first motion in said sample space; and in response to detecting a second motion that is different from any of said n pre-defined motions, selecting a filter of said filter bank to filter spectral energy corresponding to a second edge, said filter selected according to the orientation of said second edge in said sample space. 
     A method for separating luminance (Y) and chrominance (C) from a composite TV digital signal is provided. The method includes searching for a plurality of pre-defined motion cases, said plurality of pre-defined motion cases comprises the motionless case; in response to finding at least one of said pre-defined motion cases, performing Y/C separation of said composite TV digital signal by selecting a one-dimensional (1D) temporal comb filter from a filter bank, said filter bank comprises a plurality of 1D temporal comb filters in one-to-one correspondence with said plurality of pre-defined motion cases; in response to finding none of said pre-defined uniform motion cases, performing Y/C separation of said composite TV digital signal by selecting according to a selection method a filter from the portion of said filter bank that comprises a 1D horizontal (H) comb filter, a 1D vertical (V) comb filter, a two-dimensional (2D) horizontal-vertical (HV) comb filter, a 2D horizontal-temporal (HT) comb filter, a 2D vertical-temporal (VT) comb filter, a 3D horizontal-vertical-temporal (HVT) comb filter. 
     A filter bank for a TV composite signal is provided. The filter bank includes an one-dimensional (1D) temporal comb filter adapted to perform Y/C separation for a motionless image; a plurality of 1D temporal comb filters adapted to perform Y/C separation by limiting spectral energy associated with an image motion detected having a pre-defined uniform velocity; and a plurality of two-dimensional (2D) comb filters. The 2D comb filters include a 2D spatial (HV) comb filter adapted to limit spectral energy along horizontal and vertical frequency axes of a 3D spectral space of said signal; a 2D spatial-temporal (HT) comb filter adapted to limit spectral energy along horizontal and temporal frequency axes of said 3D spectral space, and a 2D spatial-temporal (VT) comb filter adapted to limit spectral energy along vertical and temporal frequency axes of said 3D spectral space. The filter bank includes a three-dimensional (3D) spatial-temporal (HVT) comb filter adapted to limit spectral energy along horizontal, vertical and temporal frequency axes of said 3D spectral space. 
     A color TV decoder for a TV composite signal is provided. The color decoder includes a motion detection unit adapted to detect any of a plurality of pre-defined velocities from a set of gray level differences; and a filter bank coupled to said motion detection unit. The filter bank includes a one dimensional (1D) temporal comb filter adapted to filter a motionless image detected by said motion detection unit; a first plurality of 1D temporal comb filters adapted to filter an image motion detected by said motion detection unit as having a velocity that is equal to one of the said plurality of pre-defined velocities; a second plurality of 1D comb filters adapted to limit spectral energy along one of the three frequency axes of spectral space; a third plurality of two-dimensional (2D) comb filters adapted to filter an image by limiting spectral energy along two of said three frequency axes; and a three-dimensional (3D) comb filter adapted to filter an image by limiting spectral energy along all of said three frequency axes. 
     A filter bank for filtering a TV composite signal is provided. The filter bank includes a two-dimensional (2D) spatial horizontal-vertical (HV) comb filter adapted to be activated to filter spectral energy associated with a first edge in a two-dimensional sample space spanned by a horizontal axis and a vertical axis; a 2D spatial-temporal (T) comb filter adapted to be activated to filter spectral energy associated with a horizontal motion, wherein said horizontal motion is represented as a second edge in a two-dimensional sample space spanned by said horizontal axis and a temporal axis; and a 2D spatial-temporal (VT) comb filter adapted to be activated to filter spectral energy associated with a vertical motion, wherein said vertical motion is represented as a third edge in a two-dimensional sample space spanned by said vertical axis and said temporal axis; and a three-dimensional (3D) spatial-temporal (HVT) comb filter adapted to be activated to filter spectral energy associated with a motion that cannot be properly filtered with said above filters. 
     A filter bank for filtering a TV composite signal is provided. The filter bank includes a first filter set comprising k one-dimensional (1D) temporal comb filters, wherein a filter from said first filter set is adapted to be selected to filter said signal in a first stage of processing said signal, wherein said k&gt;1; a second filter set comprising a 1D horizontal (H) comb filter and a 1D vertical (V) comb filter, wherein a filter from said second filter set is adapted to be selected to filter said signal in a second stage of processing said signal if no filter is selected in said first stage; a third filter set comprising a two-dimensional (2D) horizontal-vertical (HV) comb filter, a 2D horizontal-temporal (HT) comb filter and a 2D vertical-temporal (VT) filter, wherein a filter from said third filter set is adapted to be selected to filter said signal in a third stage of processing said signal if no filter is selected in said second stage; and a fourth filter set comprising a three-dimensional (3D) horizontal-vertical-temporal (HVT) comb filter, wherein said 3D (HVT) comb filter is selected to filter said signal in a fourth stage of processing said signal if no filter is selected in said third stage, and wherein the orientation of an edge in a three-dimensional sample space of said signal is used for filter selection. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     The accompanying drawings which are incorporated in and form a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention: 
     FIG. 1 depicts the content of a three-dimensional comb filter bank in accordance with one embodiment of the invention. 
     FIG. 2 is a flow chart that outlines steps of a method for selecting a filter from a filter bank in accordance with one embodiment of the invention. 
     FIGS. 3A-D show a current processing field and its previous and next fields in accordance with one embodiment of the invention. 
     FIG. 3A shows a pre-defined neighborhood centered around a processing pixel of a current processing field in accordance with one embodiment of the invention. 
     FIG. 3B shows a sequence of fields having a current processing field and its previous and next fields in accordance with one embodiment of the invention. 
     FIG. 3C shows pixel labels in a current processing field and its previous and next fields in accordance with one embodiment of the invention. 
     FIG. 3D shows thirteen motions that are pre-defined with reference to a current processing field and its previous and next fields in accordance with one embodiment of the invention. 
     FIG. 4 is a flow chart that outlines steps of a method for selecting a one-dimensional temporal filter from a filter bank in accordance with one embodiment of the invention. 
     FIG. 5 is a flow chart that outlines steps of a method for selecting a filter from a filter bank according to the orientation of an edge in a sample space in accordance with one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     Reference is made in detail to the preferred embodiments of the invention. While the invention is described in conjunction with the preferred embodiments, the invention is not intended to be limited by these preferred embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the invention, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, as is obvious to one ordinarily skilled in the art, the invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so that aspects of the invention will not be obscured. 
     Referring now to FIG. 1, the content of a three-dimensional comb filter bank  100  is depicted in accordance with one embodiment of the invention. The filter bank  100  comprises these constituent filters: 
     a one-dimensional horizontal comb filter  151 ; 
     a one-dimensional vertical comb filter  152 ; 
     a two-dimensional spatial comb filter  153 ; 
     a two-dimensional horizontal-temporal comb filter  161 ; 
     a two-dimensional vertical-temporal comb filter  162 ; 
     a three-dimensional spatial-temporal comb filter  163 ; and 
     thirteen one-dimensional temporal comb filters  101 - 113 . 
     Filter bank  100  is adaptive to the detection of edge locations and motion speeds. The band limitation of the filters ( 101 - 113 ,  151 - 153  and  161 - 163 ) in filter bank  100  is based on a three-dimensional spectral space that is spanned by a horizontal frequency axis, a vertical frequency axis, and a temporal frequency axis (also known respectively as a line frequency axis, a pixel frequency axis and a field frequency axis). The spectrum energy of a TV composite signal is represented using this three-dimensional spectral space. Y/C separation is performed by filtering the spectrum energy with a filter selected from filter bank  100 . The TV composite signal itself is sampled within a three-dimensional sample space spanned by a horizontal axis, a vertical axis and a temporal axis. The sample space is the dual space of the spectral space. 
     For the spatial filters, filter bank  100  comprises two one-dimensional comb filters  151 - 152  and one two-dimensional spatial comb filter  153 . Specifically, filter  151  is adapted to filter spectrum energy of a TV composite signal along the horizontal frequency axis. Filter  152  is adapted to filter spectrum energy of a TV composite signal along the vertical frequency axis. Filter  153  is adapted to filter spectrum energy of a TV composite signal in the plane spanned by the horizontal and vertical frequency axes. 
     In the present embodiment, each of filters  151 - 152  is a 3-tab filter having filter coefficients specified as: [−1, 0, 2, 0, −1]/4. Filter  153  is a two-dimensional filter having coefficients specified as:          [         0       0           -   1     /   8         0       0               -   1     /   8         0         4   /   8         0           -   1     /   8             0       0           -   1     /   8         0       0         ]     .                          
     However, as understood herein, each of filters  151 - 152  need not be implemented with the coefficients specified above. For example, in another embodiment, each of filters  151 - 152  is implemented as a n-tab filter wherein n is greater than 3. Also, filter  153  need not be implemented with the specified coefficients. For example, in yet another embodiment, rather than the 3×5 matrix of filter coefficients shown above, a j×k matrix is used to specify the filter coefficients of filter  153 , wherein j&gt;3 and k&gt;5. 
     For the spatial-temporal filters, filter bank  100  comprises two two-dimensional comb filters  161 - 162  and one three-dimensional spatial-temporal comb filter  163 . Specifically, filter  161  is adapted to filter spectrum energy of a TV composite signal in the plane spanned by the horizontal and temporal frequency axes. Filter  162  is adapted to filter spectrum energy of a TV composite signal in the plane spanned by the vertical and temporal frequency axes. Filter  163  is adapted to filter spectrum energy of a TV composite signal along all three frequency axes (horizontal, vertical and temporal frequency axes). 
     In the present embodiment, each of filters  161 - 162  is a two-dimensional filter having coefficients specified as:          [         0       0           -   1     /   8         0       0               -   1     /   8         0         4   /   8         0           -   1     /   8             0       0           -   1     /   8         0       0         ]     .                          
     However, filters  161 - 162  need not be implemented as such. For example, in yet another embodiment, rather than the 3×5 matrix of filter coefficients shown above, a j×k matrix is used to specify the filter coefficients of filter  153 , wherein j&gt;3 and k&gt;5. 
     Also, in the present embodiment, filter  163  is a three-dimensional filter having coefficients specified as:              [         0       0       0       0       0           0       0           -   1     /   12         0       0           0       0       0       0       0         ]               at                 time     =     -   2       ;               [         0       0       0       0       0           0       0       0       0       0           0       0       0       0       0         ]               at                 time     =     -   1       ;               [         0       0           -   1     /   12         0       0               -   1     /   12         0         6   /   12         0           -   1     /   12             0       0           -   1     /   12         0       0         ]               at                 time     =   0     ;               [         0       0       0       0       0           0       0       0       0       0           0       0       0       0       0         ]               at                 time     =   1     ;   and               [         0       0       0       0       0           0       0           -   1     /   12         0       0           0       0       0       0       0         ]             at                 time     =   2.                                
     However, as understood herein, filter  163  need not be implemented with the filter coefficients shown with the five 3×5 matrices above. For example, in another embodiment of the invention, a filter is implemented having its filter coefficients specified with h j×k matrices, wherein h&gt;5, j&gt;3 and k&gt;5. 
     For the temporal filters, filter bank  100  comprises thirteen filters that are one-dimensional temporal comb filters  101 - 113 . Each of filters  101 - 113  is adapted to filter a TV composite signal whose image is moving along one of 13 pre-defined directions with respect to a processing pixel. The details to these pre-defined directions will be described with reference to FIGS. 3A-D. 
     In the present embodiment, a one-dimensional comb filer is implemented with a 2-tab filter whose filter coefficients are specified as [1, −1]/2. However, as understood herein, a one-dimensional comb filter need not be restricted to a filter having these coefficients. For example, in an alternative embodiment, a one-dimensional comb filter having different filter coefficients is implemented. 
     In contrast to a single temporal filter of a conventional three-dimensional comb filter, multiple temporal filters (thirteen temporal filters  101 - 113 ) are implemented for the temporal filter function in filter bank  100  in the present embodiment. As such, the effectiveness of filter bank  100  as a three-dimensional comb filter is increased. Specifically, filter bank  100  operates according to a selection method for selecting a filter from filter bank  100 . In so doing, the usage among the horizontal, vertical, and temporal filter functions is more balanced when compared to the conventional three-dimensional comb filter. 
     Moreover, in contrast to a conventional three-dimensional comb filter, Y/C comb filters of filter bank  100  do not simply exploit the topology in the pixel phases. Rather, these Y/C comb filters of filter bank  100  also works from a spectral viewpoint. Specifically, from a statistical viewpoint, the sudden gray-level changes in the edges have the same prediction effect of the sudden gray-level changes by the motions. As such, the effect of motions in the temporal domain can be considered to have the same effect of edges in the spatial domain. More specifically, when represented in the three-dimensional sample space, a motion encoded in a composite signal appears as an edge in the three-dimensional sample space. Therefore, filter bank  100  applies a temporal comb filter to the process of detecting edge location in the spatial domain. With this application from the spectral viewpoint, three-dimensional comb filter bank  100  can separate Y and C from each other freely without motion consideration. 
     Referring still to FIG. 1, in processing a motionless object case, the filter  151 ,  152 , and  153  will be selected by the edge locations in the sample space. On the other hand, in processing a motion object case, the filter  161 ,  162 ,  163 , and  101 - 113  will be selected by the motion speeds by a selection method to be outlined with FIG.  2 . 
     The filter selection method uses priority levels and threshold values to make a go-no-go decision. The priority levels are: 
     highest priority level filters: filters  101 - 113 ; 
     high priority level filters: filter  151 , filter  152 ; 
     low priority level filters: filter  161 , filter  162 , filter  153 ; and 
     lowest priority level filters: filter  163 . 
     In addition, the priority levels can be associated with four processing stages of the selection method. Filters  101 - 113  are associated with the first stage; filters  151 - 152  are associated with the second stage; filters  153  and  161 - 162  are associated with the third stage; and filter  163  is associated with the fourth stage. 
     Specifically, in the first processing stage, the selection method checks if one of filters  101 - 113  can be selected to perform Y/C separation for an image to be filtered. The selection method enters the second processing stage if none of filters  101 - 113  is selected to perform Y/C separation for the image. In the second processing stage, the selection method checks if one of filters  151 - 152  can be selected to perform Y/C separation for the image. The selection method enters the third processing stage if none of filters  151 - 152  is selected to perform Y/C separation for the image. In the third processing stage, the selection method checks if one of filters  161 - 162  and  153  can be selected to perform Y/C separation for the image. The selection method enters the fourth stage if none of filters  161 - 162  and  153  is selected to perform Y/C separation for the image. 
     In view of FIG. 1, FIGS. 2,  4  and  5  introduce various stages of implementing the selection method for selecting a filter from filter bank  100  in accordance with one embodiment of the invention. FIG. 2 outlines the steps of the selection method. Then, FIGS. 4-5 provide the details of the outlined steps. Specifically, FIG. 2 shows the relationship among the various stages of the selection method. FIG. 4 shows the first stage of the selection method. FIG. 5 shows the second, third and fourth stages of the selection method. 
     Referring now to FIG. 2, a flow chart  200  is shown outlining steps of a method for selecting a filter from filter bank  100  in accordance with one embodiment of the invention. The selected filter is then used to separate the Y signal and the C signal from a TV composite signal. 
     The first processing stage of the selection method comprises steps  210 ,  212  and  218 . 
     In step  210 , the filter selection method starts by matching pixels between the next field of a current processing field and the previous field of the current processing field. The matching operation involves two pre-defined pixel neighborhoods of the same size. Specifically, a first pre-defined pixel neighborhood of the next field is compared to a second pre-defined pixel neighborhood of the previous field. A pixel in the first neighborhood has a corresponding pixel in the second neighborhood. Gray level of a pixel in the first pixel neighborhood is compared to gray level of the corresponding pixel in the second pixel neighborhood. (Further details of the matching operation will be described in relation to FIG. 4.) 
     In query step  212 , the result of the matching operation is used to decide the next operating step. If at least one gray level match exists, then step  218  is performed. If no matched gray levels exist, then step  220  is performed. 
     In step  218 , a one-dimensional temporal comb filter from filter bank  100  is selected to perform Y/C separation. Specifically, the temporal comb filter is selected from among temporal filters  101 - 113 . The selected temporal filter is specifically adapted to filter a uniform velocity motion as indicated by the matched gray levels. 
     The second processing stage of the selection method comprises steps  220 ,  222  and  228 . If an edge in the sample space is detected along the horizontal, the vertical, or the temporal axes, then a filter is selected according to the orientation of the edge. 
     In step  220 , in the current processing field, operation is performed for detecting edge locations in the spatial domain (the sample space) horizontally or vertically with the four adjacent pixel samples. (Further details of the detecting operation will be described in relation to FIG. 5.) 
     In query step  222 , a check is performed to see if such horizontal or vertical edge location is detected in the sample space. If such horizontal or vertical edge location is detected, then step  228  is performed. Otherwise, if no such horizontal or vertical edge location is detected, then step  230  is performed. 
     In step  228 , a one-dimensional comb filter is selected from filter bank  100  to perform Y/C separation. Specifically, the one-dimensional horizontal comb filter  161  is selected if the detected edge horizontal. The one-dimensional vertical comb filter  162  is selected if the detected edge is vertical. A one-dimensional temporal comb filter is selected if motion is detected is along the temporal axis of the sample space. 
     The third stage of the selection method comprises steps  230 ,  232  and  238 . If an edge in the sample space is detected along a direction diagonal to the horizontal, the vertical or the temporal axes, then a filter is selected according to the orientation of the edge. 
     In step  230 , operation is performed for detecting diagonal edges. (Further details of the diagonal edge detection will be described in relation to FIG. 5.) 
     In query step  232 , a check is performed to see if any diagonal edge is detected. If such diagonal edge is detected, then step  238  is performed. If no such diagonal edge is detected, then step  240  is performed. 
     In step  238 , a two-dimensional comb filter is selected from filter bank  100  to perform Y/C separation. Specifically, the spectral energy is bounded by the three two-dimensional filters. As such, a horizontal-vertical comb filter, a horizontal-temporal comb filter, or a vertical-temporal comb filter is selected. 
     The fourth stage of the selection method comprises step  240 . 
     In step  240 , three-dimensional comb filter  163  is selected from filter bank  100  to perform Y/C separation. Specifically, three-dimensional spatial-temporal comb filter  163  is selected because it can limit the spectral energy in any directions. On the other hand, none of the other filters work well due to edges in fast motion, 
     By using the above filter selection method outlined, the present embodiment increases the effectiveness of three-dimensional comb filters and achieves a balanced usage among the horizontal, vertical, and temporal filter functions. 
     Referring now to FIGS. 3A-D, three 5 by 5 pixel neighborhoods ( 371 - 373 ) are shown respectively in three consecutive fields ( 391 - 393 ) from a TV composite signal in accordance with one embodiment of the invention. These pixel neighborhoods ( 371 - 373 ) will be used to support the following discussion regarding the details of the first processing stage of the selection method. 
     Referring now to FIG. 3A, a neighborhood  372  centered about a processing pixel  399  in a current processing field  392  is shown in accordance with one embodiment of the invention. Neighborhood  372  is pre-defined to be a window of 5 pixels by 5 pixels wherein 13 pixels out of the 25 pixels in neighborhood  372  are of the same phase. To indicate these 13 pixels as having the same phase, these 13 pixels are depicted as dark dots. 
     Referring now to FIG. 3B, a sequence of fields is shown having current processing field  392  together with its previous (past) field  391  and next (future) field  393 . As shown, each of fields  391 - 393  has a pre-defined neighborhood entered about a pixel. Pre-defined neighborhood  371  in field  391  is of the same size (5 pixels by 5 pixels) as neighborhood  372 . Also, pre-defined neighborhood  371  is centered about a pixel  391  having the same coordinates as processing pixel  392 . Similarly, pre-defined neighborhood  373  in field  393  is of the same size as neighborhood  372 . Also, pre-defined neighborhood  373  is centered about a pixel  393  having the same coordinates as processing pixel  392 . 
     Referring now to FIG. 3C, labeling schemes of pre-defined neighborhoods  371  and  373  are shown in accordance with one embodiment of the invention. The labeling scheme of pre-defined neighborhood  371  starts with x[ 1 ] from the upper-left corner and ends with x[ 13 ] at the lower-right corner of pre-defined neighborhood  371 . On the other hand, the labeling scheme of pre-defined neighborhood  373  starts from x[ 1 ] at the lower-right corner and ends with x[ 13 ] at the upper-left corner of the pre-defined neighborhood  373 . 
     Referring now to FIG. 3D, several of 13 uniform motions  301 - 313  are depicted in accordance with one embodiment of the invention. Specifically, in order not to obscure the entire FIG. 3D, only uniform motions  302 ,  303 ,  307  and  313  are depicted in FIG.  3 D. As shown, uniform motion  302  refers to a motion traveling from pixel position x[ 2 ] in previous field  391  to pixel position x[ 2 ] in next field  393 . Similarly, for any n from { 301 - 313 }, uniform motion n refers to a motion traveling from pixel position x[n−300] in previous field  391  to pixel position x[n−300] in next field  393 . For example, uniform motion  309  refers to a motion traveling from pixel position x[ 9 ] in previous field  391  to pixel position x[ 9 ] in next field  393 . 
     Uniform motions  301 ,  303 ,  311  and  313  have the same speed in the four directions shown. Uniform motions  301  and  313  have opposite velocities. Uniform motions  303  and  311  have opposite velocities. Specifically, uniform motion  301  refers to the motion of going from pixel x[ 1 ] of neighborhood  371  to pixel x[ 1 ] of neighborhood  373 . Uniform motion  303  refers to the motion of going from pixel x[ 3 ] of neighborhood  371  to pixel x[ 3 ] of neighborhood  373 . Uniform motion  311  refers to the motion of going from pixel x[ 11 ] of neighborhood  371  to pixel x[ 11 ] of neighborhood  373 . Uniform motion  313  refers to the motion of going from pixel x[ 13 ] of neighborhood  371  to pixel x[ 13 ] of neighborhood  373 . 
     Uniform motions  302 ,  306 ,  308  and  312  have the same speed in the four directions shown. Uniform motions  302  and  312  have opposite velocities. Uniform motions  306  and  308  have opposite velocities. Specifically, uniform motion  302  refers to the motion of going from pixel x[ 2 ] of neighborhood  371  to pixel x[ 2 ] of neighborhood  373 . Uniform motion  306  refers to the motion of going from pixel x[ 6 ] of neighborhood  371  to pixel x[ 6 ] of neighborhood  373 . Uniform motion  308  refers to the motion of going from pixel x[ 8 ] of neighborhood  371  to pixel x[ 8 ] of neighborhood  373 . Uniform motion  312  refers to the motion of going from pixel x[ 12 ] of neighborhood  371  to pixel x[ 12 ] of neighborhood  373 . 
     Uniform motions  304 ,  305 ,  309  and  310  have the same speed in the four directions shown. Uniform motions  304  and  310  have opposite velocities. Uniform motions  305  and  309  have opposite velocities. Specifically, uniform motion  304  refers to the motion of going from pixel x[ 4 ] of neighborhood  371  to pixel x[ 4 ] of neighborhood  373 . Uniform motion  305  refers to the motion of going from pixel x[ 5 ] of neighborhood  371  to pixel x[ 5 ] of neighborhood  373 . Uniform motion  309  refers to the motion of going from pixel x[ 09 ] of neighborhood  371  to pixel x[ 09 ] of neighborhood  373 . Uniform motion  310  refers to the motion of going from pixel x[ 10 ] of neighborhood  371  to pixel x[ 10 ] of neighborhood  373 . 
     Uniform motion  307  has zero speed. As such it is also considered as a uniform motion. 
     Referring now to FIG. 4 in view of FIGS. 3A-D, a flow chart  400  is shown providing the details of the first processing stage of the selection method (steps  210 ,  212  and  218  in flow chart  200  shown in FIG. 2) in accordance with one embodiment of the invention. Specifically, flow chart  400  is shown outlining steps for matching pixels between previous field  391  and next field  393 . 
     In step  410 , pixels between next field  393  and previous field  391  are matched and paired up. The matching operation involves two pre-defined pixel neighborhoods ( 371  and  373 ) of the same size. Specifically, pre-defined pixel neighborhood  371  is compared to pre-defined pixel neighborhood  373 . For example, a pixel labeled x[ 1 ] in neighborhood  371  is paired with a pixel that is labeled x[ 1 ] in neighborhood  373 . Gray level of pixel x[ 1 ] in pixel neighborhood  371  is compared to gray level of the corresponding x[ 1 ] pixel in pixel neighborhood  373 . Similarly, a pixel labeled x[ 2 ] in neighborhood  371  is paired with a pixel that is labeled x[ 2 ] in neighborhood  373 . Gray level of pixel x[ 2 ] in neighborhood  371  is compared to gray level of the corresponding x[ 2 ] label in neighborhood  373 . Similar label matching is also performed for pixels that are labeled x[ 3 ] to x[ 13 ]. 
     In step  420 , measurement is performed to obtain d[ 7 ], which is the gray level difference between pixel x[ 7 ] of neighborhood  371  and pixel x[ 7 ] of neighborhood  373 . If d[ 7 ] is zero, then uniform motion  301  is indicated. 
     In query step  423 , a check is made to see if d[ 7 ] is zero. If d[ 7 ] is zero, then step  425  is performed. Otherwise, step  430  is performed. 
     In step  425 , one-dimensional temporal comb filter  107  is selected from filter bank  100  to perform Y/C separation. Specifically, if d[ 7 ] is zero, then the uniform motion of zero velocity is indicated. As such, filter  107  is selected because it is specifically adapted to filter this zero velocity uniform motion (uniform motion  307  shown in FIG.  3 D). 
     In step  430 , measurements are performed to obtain d[ 2 ], d[ 6 ], d[ 8 ] and d[ 12 ], which are gray level differences. As shown, the gray level measurements are limited to the horizontal and the vertical directions of pixel x[ 7 ]. Specifically, d[ 2 ] is the gray level difference between pixel x[ 2 ] of neighborhood  371  and pixel x[ 2 ] of neighborhood  373 . If d[ 2 ] is zero, then uniform motion  302  is indicated. d[ 6 ] is the gray level difference between pixel x[ 6 ] of neighborhood  371  and pixel x[ 6 ] of neighborhood  373 . If d[ 6 ] is zero, then uniform motion  306  is indicated. d[ 8 ] is the gray level difference between pixel x[ 8 ] of neighborhood  371  and pixel x[ 8 ] of neighborhood  373 . If d[ 8 ] is zero, then uniform motion  308  is indicated. d[ 12 ] is the gray level difference between pixel x[ 12 ] of neighborhood  371  and pixel x[ 12 ] of neighborhood  373 . If d[ 12 ] is zero, then uniform motion  312  is indicated. 
     In query step  433 , a check is made to see if at least one of d[ 2 ], d[ 6 ], d[ 8 ] and d[ 12 ] is zero. If affirmative, then step  435  is performed. Otherwise, step  440  is performed. 
     In step  435 , one-dimensional temporal filter  102  is selected from filter bank  100  to perform Y/C separation if d[ 2 ] is zero. Specifically, filter  102  is specifically adapted to filter uniform motion  302 . Similarly, one-dimensional temporal filter  106  is selected from filter bank  100  to perform Y/C separation if d[ 6 ] is zero. Specifically, filter  106  is specifically adapted to filter uniform motion  306 . Similarly, one-dimensional temporal filter  108  is selected from filter bank  100  to perform Y/C separation if d[ 8 ] is zero. Specifically, filter  108  is specifically adapted to filter uniform motion  308 . Similarly, one-dimensional temporal filter  112  is selected from filter bank  100  to perform Y/C separation if d[ 12 ] is zero. Specifically, filter  112  is specifically adapted to filter uniform motion  312 . 
     In step  440 , measurements are performed to obtain d[ 4 ], d[ 5 ], d[ 9 ] and d[ 10 ], which are gray level differences. As shown, the gray level measurements are limited to the diagonal directions of pixel x[ 7 ]. Specifically, d[ 4 ] is the gray level difference between pixel x[ 4 ] of neighborhood  371  and pixel x[ 4 ] of neighborhood  373 . If d[ 4 ] is zero, then uniform motion  304  is indicated. d[ 5 ] is the gray level difference between pixel x[ 5 ] of neighborhood  371  and pixel x[ 5 ] of neighborhood  373 . If d[ 5 ] is zero, then uniform motion  305  is indicated. d[ 9 ] is the gray level difference between pixel x[ 9 ] of neighborhood  371  and pixel x[ 9 ] of neighborhood  373 . If d[ 10 ] is zero, then uniform motion  310  is indicated. d[ 10 ] is the gray level difference between pixel x[ 10 ] of neighborhood  371  and pixel x[ 10 ] of neighborhood  373 . If d[ 10 ] is zero, then uniform motion  310  is indicated. 
     Continuing with step  440 , measurements are also performed to obtain d[ 1 ], d[ 3 ], d[ 11 ] and d[ 13 ], which are gray level differences. As shown, the gray level measurements are limited to the diagonal directions of pixel x[ 7 ]. Specifically, d[ 1 ] is the gray level difference between pixel x[ 1 ] of neighborhood  371  and pixel x[ 1 ] of neighborhood  373 . If d[ 1 ] is zero, then uniform motion  301  is indicated. d[ 3 ] is the gray level difference between pixel x[ 3 ] of neighborhood  371  and pixel x[ 3 ] of neighborhood  373 . If d[ 3 ] is zero, then uniform motion  303  is indicated. d[ 11 ] is the gray level difference between pixel x[ 11 ] of neighborhood  371  and pixel x[ 11 ] of neighborhood  373 . If d[ 11 ] is zero, then uniform motion  311  is indicated. d[ 13 ] is the gray level difference between pixel x[ 13 ] of neighborhood  371  and pixel x[ 13 ] of neighborhood  373 . If d[ 13 ] is zero, then uniform motion  313  is indicated. 
     In query step  443 , a check is made to see if at least one of d[ 4 ], d[ 5 ], d[ 9 ], d[ 10 ] d[ 1 ], d[ 3 ], d[ 11 ] and d[ 13 ] is zero. If affirmative, then step  445  is performed. If affirmative, then step  455  is performed. Otherwise, none of uniform motions  301 - 313  is considered to occur. As such, step  220  of flow chart  200  (see FIG. 2) is performed. 
     In step  445 , one-dimensional temporal filter  104  is selected from filter bank  100  to perform Y/C separation if d[ 4 ] is zero. Specifically, filter  104  is specifically adapted to filter uniform motion  304 . Similarly, one-dimensional temporal filter  105  is selected from filter bank  100  to perform Y/C separation if d[ 5 ] is zero. Specifically, filter  105  is specifically adapted to filter uniform motion  305 . Similarly, one-dimensional temporal filter  109  is selected from filter bank  100  to perform Y/C separation if d[ 9 ] is zero. Specifically, filter  109  is specifically adapted to filter uniform motion  309 . Similarly, one-dimensional temporal filter  110  is selected from filter bank  100  to perform Y/C separation if d[ 10 ] is zero. Specifically, filter  110  is specifically adapted to filter uniform motion  310 . 
     Continuing with step  445 , one-dimensional temporal filter  101  is selected from filter bank  100  to perform Y/C separation if d[ 1 ] is zero. Specifically, filter  101  is specifically adapted to filter uniform motion  301 . Similarly, one-dimensional temporal filter  103  is selected from filter bank  100  to perform Y/C separation if d[ 3 ] is zero. Specifically, filter  103  is specifically adapted to filter uniform motion  303 . Similarly, one-dimensional temporal filter  111  is selected from filter bank  100  to perform Y/C separation if d[ 11 ] is zero. Specifically, filter  111  is specifically adapted to filter uniform motion  311 . Similarly, one-dimensional temporal filter  113  is selected from filter bank  100  to perform Y/C separation if d[ 13 ] is zero. Specifically, filter  113  is specifically adapted to filter uniform motion  313 . 
     Referring now to FIG. 5, a flow chart  500  is shown providing details of the second, third and fourth stages of the selection method in accordance with one embodiment of the invention. Flow chart  500  outlines steps for selecting a filter from filter bank  100  if none of uniform motions  301 - 313  is detected in the first processing stage of the selection method. A filter is selected according to the orientation of an edge in the three-dimensional sample space spanned by a horizontal axis, a vertical axis and a temporal axis. A motion can be represented as an edge in the sample space. 
     Specifically, in the current processing field, operation is performed to detect edge locations in the spatial domain (the sample space) horizontally or vertically with the four adjacent samples of the processing pixel. Then, edge detection is performed to calculate the C energy in the high frequency to the horizontal and the vertical direction respectively. The smaller amount of a direction in the spectral domain means that an edge locates in the direction in the spatial domain. That is, in the current processing field, operation is performed to detect edge locations in the spatial domain horizontally or vertically with the four adjacent samples of the processing pixel. 
     Continuing with FIG. 5, steps  530 ,  540 ,  541 - 543 , and  551 - 553  belong to the first processing stage of the filter selection method. 
     In step  530 , three gray level differences dH, dV and dT are generated. Specifically, dH of a processing pixel is the gray level difference between the right-side pixel of the processing pixel and the left-side pixel of the processing pixel. .dV of the processing pixel is the gray level difference between the upper pixel of the processing pixel and the lower pixel of the processing pixel. .dT of the processing pixel is the gray level difference between pixel x[ 7 ] of neighborhood  371  and pixel x[ 7 ] of neighborhood  373 . 
     In query step  540 , a search is made to find min(dH, dV, dT), the minimum of dH, dV and dT. If dH is min(dH, dV, dT), then query step  541  is performed. If dV is min(dH, dV, dT), then query step  542  is performed. If dT is min(dH, dV, dT), then query step  543  is performed. If dH is less than dT and equal to dV, then step . . . . Is performed. If dH is less than dV and equal to dT, then step . . . is performed. If dV is less than dH and equal to dT, then step . . . is performed. 
     In query step  541 , a check is made to see if dH is less than a pre-defined threshold value. If affirmative, then step  551  is performed. Otherwise, query step  561  is performed. 
     In query step  542 , a check is made to see if dV is less than a pre-defined threshold value. If affirmative, then step  552  is performed. Otherwise, query step  562  is performed. 
     In query step  543 , a check is made to see if dT is less than a pre-defined threshold value. If affirmative, then step  553  is performed. Otherwise, query step  563  is performed. 
     In step  551 , one-dimensional horizontal comb filter  151  is selected from filter bank  100  to perform Y/C separation. 
     In step  552 , one-dimensional vertical comb filter  152  is selected from filter bank  100  to perform Y/C separation. 
     In step  553 , a one-dimensional temporal comb filter is selected from filter bank  100  to perform Y/C separation. Specifically, this filter is specified with three filter coefficients. Thus, this filter is different from each of two-tab filters  101 - 113 . 
     Steps  561 - 563 ,  571 - 573  and  581 - 583  belong to the third processing stage of the filter selection method. For the diagonal edge detection, the spectral energy is bounded by the three two-dimensional filters; that is, a horizontal-vertical, a horizontal-temporal, and a vertical-temporal filter. The selection depends on the relative lengths of the spectral band in the directions. On the two shorter lengths in the directions among the three directions, an adequate two-dimensional filter bounds the spectral energy. The spectral limitation has the same effects as the diagonal edge detection in the directions. Therefore, the spectral limitation by the three two-dimensional filters can detect diagonal edges. 
     In query step  561 , a check is made to see if min(dV, dT) is less than a predefined threshold value. If affirmative, then step  571  is performed. Otherwise, step  590  is performed. 
     In query step  562 , a check is made to see if min(dH, dT) is less than a pre-defined threshold value. If affirmative, then step  572  is performed. Otherwise, step  590  is performed. 
     In query step  563 , a check is made to see if min(dH, dV) is less than a pre-defined threshold value. If affirmative, then step  573  is performed. Otherwise, step  590  is performed. 
     In query step  571 , a search is made to find min(dV, dT), the minimum of dV and dT. If dV is min(dV,dT), then step  583  is performed. If dT is min(dV, dT), then query step  581  is performed. If dV is equal to dT, then step  581  is performed. 
     In query step  572 , a search is made to find min(dH, dT), the minimum of dH and dT. If dH is min(dH,dT), then query step  583  is performed. If dT is min(dH, dT), then query step  582  is performed. If dH is equal to dT, then step  582  is performed. 
     In query step  573 , a search is made to find min(dH, dV), the minimum of dH and dV. If dH is min(dH,dV), then query step  581  is performed. If dV is min(dH, dV), then query step  582  is performed. If dH is equal to dV, then step  581  is performed. 
     In step  581 , two-dimensional horizontal-temporal comb filter  161  is selected from filter bank  100  to perform Y/C separation. 
     In step  582 , two-dimensional horizontal-vertical comb filter  153  is selected from filter bank  100  to perform Y/C separation. 
     In step  583 , two-dimensional vertical-temporal comb filter  162  is selected from filter bank  100  to perform Y/C separation. 
     Step  590  belongs to the fourth processing stage of the filter selection method. Specifically, if none of the previous ways works due to edges in fast motion, then for the last choice, the three-dimensional spatial-temporal filter can limit the spectral energy in any directions. The situation can happen in the case of fast moving edges. The edges have a high spatial frequency and the moving objects have a high temporal frequency. Therefore, the fast moving edges have a high three-dimensional spatial-temporal frequency. That makes the Y/C separation works difficult because the high frequency terms of the Y are likely to overlap with those of the C. Fortunately fast moving objects can be hardly seen in details with human eyes. Therefore, one solution for the case of fast moving edges is acceptable that a three-dimensional spatial-temporal filter limits spectral bands to all directions. 
     In step  590 , three-dimensional spatial-temporal filter  1 ** is selected from filter bank  100  to perform Y/C separation. 
     As understood herein, the high frequency term in the Y energy can overlap with the modulated C energy. Therefore, the above method to detect edge locations depends on the frequency characteristic of a band-pass filter. That is why the band-pass filter has 5-tap coefficients instead of ordinary 3-tap ones. The frequency characteristic of a 5-tap band-pass filter is considerably sharp to pick up the C energy only. Then, with the C energy the edge location detection is more accurate. However, the edge location detection is limited to the horizontal and the vertical direction only. 
     The foregoing descriptions of specific embodiments of the invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to explain the principles and the application of the invention, thereby enabling others skilled in the art to utilize the invention in its various embodiments and modifications according to the particular purpose contemplated. The scope of the invention is intended to be defined by the claims appended hereto and their equivalents.