Abstract:
An image processing method and its associated image processing circuit for processing an image based on a sequential couleur avec memoire (SECAM) system are provided. The image includes a first pixel, a second pixel and a third pixel, which are successively arranged in a same vertical line and are respectively corresponding to a first image signal and a second image signal and a third image signal. The image processing method includes steps of calculating a chroma signal via a vertical filtering process according to the first image signal, the second image signal and the third image signal; calculating a chroma angular frequency via a frequency modulation process according to the chroma signal; and generating a chromaticity according to the chroma angular frequency.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This patent application is based on Taiwan, R.O.C. patent application No. 98102071 filed on Jan. 20, 2009. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to an image processing method and an image processing circuit, and more particularly, to an image processing method and an image processing circuit based on a sequential couleur avec memoire (SECAM) system. 
       BACKGROUND OF THE INVENTION 
       [0003]    A composite video baseband signal (CVBS), a widely used analog video signal, is generated by mixing a luma signal and a chroma signal of an image. Three classifications of specifications associated with the CVBS are the National Television System Committee (NTSC) specification, the Phase Alternating Line (PAL) specification, and the SECAM specification. 
         [0004]      FIG. 1  shows a waveform diagram of the CVBS. A synchronization prompt signal  10  is used for marking a start point of each of horizontal scan lines. A sinusoidal color burst signal  12  provides a reference signal associated with chromaticity. A staircase wave after the color bust signal  12  represents a luma signal of an image signal. For example, in  FIG. 1 , V MAX  may correspond to a luminosity having a grayscale value 255, and V MIN  may correspond to a luminosity having a grayscale value 0. 
         [0005]    In the SECAM specification, a chroma signal is represented by a sinusoid added to a luma signal, such as the sinusoid signal added to the luma signal illustrated in  FIG. 1 . A chromaticity (color) is calculated by comparing angular frequencies of the chroma signal and a carrier burst signal. 
         [0006]      FIG. 2  is an image processing circuit for decoding chroma components of a SECAM signal of the prior art. An image processing circuit  1  comprises a receiving unit  13 , a filter unit  11 , a frequency demodulation module  14  and a chroma converting unit  16 . The filter unit  11  is coupled to the receiving unit  13 , the frequency demodulation module  14  is coupled to the filter unit  11 , and the chroma converting unit  16  is coupled to the frequency demodulation module  14 . 
         [0007]    The receiving unit  13  receives images encoded according to the SECAM specification. An images signal of one certain image among the received images is represented by S (S=Y+Sin [(ω c +Δω)*t+φ 1 ]), where Y is a luma signal, Sin [(ω c +Δω)*t+φ 1 ] represents a chroma signal, ω c  is a carrier angular frequency of the SECAM system, Δω is an angular frequency difference between an oscillator angular frequency and a carrier angular frequency of the image signal, and φ 1  is a phase. Since the chroma signal based on the SECAM system is encoded via a frequency modulation approach, Δω may correspond to a chromaticity. 
         [0008]    The filter unit  11  mainly filters out luma components (the luma signal) from the image signal, and comprises a band-pass filter (not shown) and a cloche filter (not shown). Only chroma components (the chroma signal) remain in the image signal after the image signal is filtered, and the filtered chroma signal is then processed by the frequency demodulation module  14  to calculate Δω. After that, the chroma converting unit  16  generates a chromaticity (color) corresponding to Δω. The processes of the frequency demodulation module  14  and the chroma converting unit  16  are known to a person having ordinary skill in the art, and thus shall not be discussed for brevity. 
         [0009]    In the SECAM system, a chroma signal of an image oscillates at a carrier angular frequency, which is 4.25 MHz or 4.41 MHz. When a luma signal illustrated in  FIG. 3A  oscillates at an angular frequency close to the carrier angular frequency, the luma signal cannot be filtered out via an image processing method of the prior art for the reason that high frequency components of the luma signal is taken into consideration in a frequency demodulation calculation of the chroma signal. Therefore, in the frequency demodulation calculation of the image processing method, regular oscillation of the luma signal corresponds to a chromaticity (color), thus resulting in abnormal color blocks in a grayscale multi-burst pattern.  FIG. 3B  is a schematic diagram of resulting abnormal color blocks in a multi-burst pattern, in which various black blocks are arranged at an interval and color blocks  20  are formed. 
         [0010]    Therefore, a main object of an image processing method and an image processing circuit according to an embodiment of the present invention is to prevent formation of abnormal color blocks in a multi-burst pattern. 
       SUMMARY OF THE INVENTION 
       [0011]    It is an objective of the invention to provide an image processing method for processing an image based on the SECAM system to address the problem of formation of abnormal color blocks in a multi-burst pattern. 
         [0012]    According to an embodiment, the image comprises a plurality of pixels at least comprising a first pixel, a second pixel and a third pixel, which are successively arranged and respectively corresponding to a first image signal, a second image signal and a third image signal. The image processing method comprises steps below. 
         [0013]    In Step (a), a first chroma signal is generated via a vertical filtering process according to the first image signal, the second image signal and the third image signal. In Step (b), a first chroma angular frequency is calculated via a frequency demodulation process according to the first chroma signal. In Step (c), a first chromaticity is calculated according to the first chroma angular frequency. 
         [0014]    In addition, by implementing the image processing method of the present invention, an accurate color of a received image is calculated according to a color distribution. 
         [0015]    In Step (d), a target image signal is selected from the first, second and third image signals, and a filtering process is performed on the target image signal to calculate a second chroma signal. In Step (e), a second chroma angular frequency is calculated via the frequency demodulation process according to the second chroma signal. In Step (f), a second chromaticity is obtained according to the second chroma angular frequency. 
         [0016]    In Step (g), a representative chromaticity is calculated by adding two products of the first chromaticity from Step (c) multiplied by a first weight and the second chromaticity from Step (f) multiplied by a second weight. A proportion between the first and second weights is properly adjusted according to the color distribution of the received image. The present invention simultaneously applies the image processing method of the prior art and the foregoing image processing method, and thus the color distribution of an original image is more appropriately processed according to the image processing method of the present invention. 
         [0017]    It is another objective of the invention to provide an image processing circuit for processing an image based on the SECAM system to address the problem of formation of abnormal color blocks in a multi-burst pattern. 
         [0018]    According to an embodiment, an image processing circuit according to the present invention comprises a receiving unit, a vertical filter module, a frequency demodulation module and a chroma converting unit. The vertical filter module is coupled to the receiving unit, the frequency demodulation module is coupled to the vertical filter module, and the chroma converting unit is coupled to the frequency demodulation module. 
         [0019]    The receiving unit is for receiving the image comprising a plurality of pixel at least comprising a first pixel, a second pixel and a third pixel, which are successively arranged in a same vertical line and are respectively corresponding to a first image signal, a second image signal and a third image signal. 
         [0020]    The vertical filter module generates a first chroma signal according to the first image signal, the second image signal and the third image signal. 
         [0021]    The frequency demodulation module calculates a first chroma angular frequency according to the first chroma signal. The chroma converting unit calculates a first chromaticity according to the first chroma angular frequency. 
         [0022]    In conclusion, an image processing circuit and image processing method according to the present invention, via a vertical filtering process, are capable of effectively removing luma components oscillating at an angular frequency close to a carrier angular frequency such that the luma components are not brought into a subsequent frequency demodulation process. Therefore, the problem of formation of abnormal color blocks in a multi-burst pattern is effectively solved according to the present invention. In addition, the image processing method of the prior art and the image processing method according to the present invention are integrated via a chromaticity weight approach, in which a weight proportion is dynamically adjusted to even more appropriately process a color distribution of an image. 
         [0023]    The advantages and spirit related to the present invention can be further understood via the following detailed description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a waveform diagram of a common CVBS. 
           [0025]      FIG. 2  is a block diagram of an image processing circuit of the prior art. 
           [0026]      FIG. 3A  is a waveform diagram of a CVBS in a multi-burst pattern. 
           [0027]      FIG. 3B  shows an image displayed after being processed by the image processing circuit of the prior art as illustrated in  FIG. 3A . 
           [0028]      FIG. 4  is a block diagram of an image processing circuit in accordance with a first embodiment of the present invention. 
           [0029]      FIG. 5  is a schematic diagram of a color distribution in accordance with an embodiment of the present invention. 
           [0030]      FIG. 6  a schematic diagram of a color distribution in accordance with another embodiment of the present invention. 
           [0031]      FIG. 7A  is a block diagram of an image processing circuit in accordance with a second embodiment of the present invention. 
           [0032]      FIG. 7B  is a spectrum of an image signal in accordance with another embodiment of the present invention. 
           [0033]      FIG. 8  is a block diagram of an image processing circuit in accordance with a third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0034]    In order to gain a better understanding of embodiments of the present invention, five main parts are described below a first part discusses a two-dimensional (2D) image processing method according to the present invention; a second part discusses the basis of how the 2D image processing method is capable of solving the problem of formation of abnormal color blocks in a multi-burst pattern; a third part discusses problems of the second 2D image processing method; a fourth part discusses how to define a weight of a chromaticity; and a fifth part discusses how to define a weight of a luminosity. 
         [0035]    According to an image processing method of the prior art, a single pixel is processed to calculate a chromaticity. However, according to an image processing method of the present invention, at least three pixels successively arranged in a same vertical line are processed to calculate a chromaticity. Therefore, in the following description, the image processing method of the prior art is called a one-dimensional method, and the image processing method according to the present invention is called a 2D image processing method. 
         [0036]    The first part of discussing the 2D image processing method according to the present invention shall be described below. 
         [0037]      FIG. 4  shows a block diagram of an image processing circuit  3  in accordance with a first embodiment of the present invention. The image processing circuit implementing the 2D image processing method according to the present invention comprises a receiving unit  30 , a vertical filter module  32 , a frequency demodulation module  34  and a chroma converting unit  36 . The vertical filter module  32  coupled to the receiving unit  30  filters out luma components of an image signal to retain a chroma signal. The frequency demodulation module  34  coupled to the vertical filter module  32  demodulates a chroma angular frequency of the chroma signal. The chroma converting unit  36  coupled to the frequency demodulation module  34  converts the chroma angular frequency to a chromaticity. 
         [0038]    The receiving unit  30  receives an image encoded according to the SECAM specification. The image at least comprises three pixels, which are successively arranged in a same vertical line and respectively corresponding to a first image signal S 1 , a second image signal S 2  and a third image signal S 3 . The vertical filter module  32  calculates a chroma signal according to the first image signal S 1 , the second image signal S 2  and the third image signal S 3 . The frequency demodulation module  34  calculates a chroma angular frequency according to the chroma signal, and the chroma converting unit  36  finds a first chromaticity V 1  corresponding to the chroma angular frequency. 
         [0039]    The vertical filter module  32  comprises a first multiplication unit  320  and an addition unit  322 . The first multiplication unit  320  respectively multiplies the first image signal S 1 , the second image signal S 2  and the third image signal S 3  by a first multiple, a second multiple and a third multiple. A sum of the first multiple, the second multiple and the third multiple is zero. 
         [0040]    The addition unit  322  coupled to the first multiplication unit  320  adds up the multiplied first image signal, the multiplied second image signal and the multiplied third image signal. Since the sum of the first multiple, the second multiple and the third multiple is zero, a sum of the luma components is zero, thus filtering a chroma signal of the image signal. 
         [0041]    A signal based on the SECAM system has characteristics below. The signal comprises three successively, vertically arranged pixels, which respectively correspond to three image signals. Among the three image signals, a difference π is present between a phase of one pixel and those of the other two pixels (supposing that the three pixels have the same luminosity and chromaticity). In order to better understand the foregoing description, a process flow of the vertical filter module  32  shall be discussed for example. The first image signal S 1 , the second image signal S 2  and the third image signal S 3 , corresponding to the three pixels successively arranged in the vertical line, are represented by: 
         [0000]        S   1   =Y +Sin [(ω c +Δω)* t+φ   1 ], 
         [0000]        S   2   =Y +Sin [(ω c +Δω)* t+φ   1 ], 
         [0000]        S   3   =Y +Sin [(ω c +Δω)* t+φ   1 +π]. 
         [0042]    The first multiplication unit  320  respectively multiplies S 1 , S 2  and S 3  by the first multiple N 1 , the second multiple N 2  and the third multiple N 3  to obtain three products to be added up by the addition unit  322 , where a sum of N 1 , N 2  and N 3  is zero. The sum added up by the addition unit  322  is represented by: 
         [0000]        N   1   *S   1   +N   2   *S   2   +N   3   *S   3   =Y *( N   1   +N   2   +N   3 )+ N   1 *Sin [(ω c +Δω)* t+φ   1   ]+N   2 *Sin [(ω c +Δω)* t+φ   1   ]+N   3 *Sin [(ω c +Δω) t+φ   1   +π]=Y ( N   1   +N   2   +N   3 )+( N   1   +N   2   +N   3 )Sin [(ω c +Δω)* t+φ   1 ], 
         [0043]    where the first item Y*(N 1 +N 2 +N 3 ) is equal to zero, meaning that the luma components are filtered out, whereas the other item (N 1 +N 2 −N 3 )Sin [(ω c +Δω)*t+φ 1 ] is not equal to zero, meaning that the chroma signal is retained. Therefore, the vertical filter module  32  filters to effectively retain the chroma signal in the image signal, and the chroma signal is called a first chroma signal in the following description. 
         [0044]    The first chroma signal filtered from the vertical filter module  32  is transmitted to the frequency demodulation module  34  for demodulating a first chroma angular frequency (Δω) of the first chroma signal. Operation principle of the frequency demodulation module  34  is identical to that of the frequency demodulation module  14  and shall not be further disclosed for brevity. 
         [0045]    It is to be noted that, on the basis of continuous variation in a phase angle, an absolute value of Δω is no more than π (180 degrees), such that a difference between two phrases corresponding to two pixels lies between π to −π. In other words, 2π is to be subtracted from the difference greater than π, and 2π is to be added to the difference smaller than −π. 
         [0046]    The foregoing description discloses the image processing circuit and the image processing method applied by the image processing circuit according to the present invention. Next, the reason why abnormal color blocks in a multi-bursting pattern are resulted from using the one-dimensional image processing method but not from the 2D image processing method according to the present invention shall be described below. 
         [0047]    The second part discusses how the problem of formation of abnormal color blocks in a multi-burst pattern by using the 2D image processing method is solved. 
         [0048]    For example, in a black and white multi-burst pattern, a target image signal S′ is: 
         [0000]        S′=Y +Sin [(ω c )* t],    
         [0049]    For that the black and white multi-burst patter does not contain other colors, the chroma angular frequency Δω representing chroma is zero and Y representing luma components varies at a predetermined frequency in the multi-burst pattern. In this embodiment, the luma components oscillate at an angular frequency ω c +ω close to the carrier angular frequency ω c , where δω represents a small angular frequency difference. 
         [0050]    Generally, the luma components being low-frequency have frequencies much lower than the carrier angular frequency ω c , in a way that a conventional filter unit  11  illustrated in  FIG. 2  is capable of filtering out the luma components by filtering in conjunction with a predetermined frequency range. However, when the oscillating angular frequencies of the luma components get too close to the carrier angular frequency ω c , the conventional filter unit  11  illustrated in  FIG. 2  becomes unable to effectively filter out the luma components. That is, the luma components oscillating at the predetermined oscillating angular frequency are mistaken for chroma components, which shall create abnormal color blocks in the black and white multi-burst pattern as illustrated in  FIG. 3B . 
         [0051]    With respect to the multi-burst pattern, the vertical filter module  32  of the image processing circuit  3  applies characteristics of the SECAM system to filter luma components rather than applying the frequency filter approach. Therefore, the image processing circuit according to the present invention is capable of effectively processing oscillating luma components so that abnormal color blocks in a black and white multi-burst pattern are not formed after decoding. 
         [0052]    The third part discusses problems of the 2D image processing method. The image processing image method may generate undesirable results when implementing the image processing circuit  3  illustrated in  FIG. 4  in two situations: (a) cross-chroma areas and (b) a non-uniform color distribution, both of which shall be described below. 
         [0053]    The situation (a) is to be discussed with reference to  FIG. 5 . In the foregoing 2D image processing method, it is a prerequisite that three pixels successively arranged in a vertical line oscillate at a same frequency. However, in the situation (a) of cross-chroma areas, an edge of the area intercepts the three successive pixels, and thus one of the pixels has an angular oscillating frequency different from those of the other two pixels. 
         [0054]    For example, the second pixel and the third pixel, from the three successively arranged pixels, are located in different chroma areas. Accordingly, image signals S 1 ′, S 2 ′ and S 3 ′ of the first, second and third pixels are respectively represented by: 
         [0000]        S   1   ′=Y +Sin [(ω c +Δω 1 )* t+φ   1 ], 
         [0000]        S   2   ′=Y +Sin [(ω c +Δω 1 )* t+φ   1 ], 
         [0000]        S   3   ′=Y +Sin [(ω c +Δω 2 )* t+φ   1 +π], 
         [0000]    where Δω 2  is not equal to Δω 1 . 
         [0055]    The vertical filter module  32  calculates and generates an item Sin [(ω c +Δω 1 )*t]+Sin [(ω c +Δω 2 )*t], which is equal to signals having oscillating frequencies ω c +Δω 1  and ω c +Δω 2 . Moreover, the chromaticity calculated by the frequency demodulation module  34  and the chroma converting unit  36  illustrated in  FIG. 4  is a result of mixing colors corresponding to Δω 1  and Δω 2  but not colors corresponding to Δω 1  or Δω 2 . That is, in the situation (a) of cross-chroma areas, a color different from two adjacent chroma areas is decoded and a color block is formed at the edge of chroma areas as illustrated in  FIG. 5 .  FIG. 5  shows an abnormal color block  22  being formed at the edge between two adjacent chroma areas having different chromaticities. 
         [0056]    Referring to  FIG. 6 , the situation (b) of a non-uniform color distribution is to be discussed. According to the foregoing 2D image processing method, it is a prerequisite that, among three image signals corresponding to three successively arranged pixels, a difference π is present between a phase of one pixel and those of the other two pixels, which is a characteristic of the SECAM system. However, when a front-end of a horizontal scan line has a non-uniform color distribution such as a color distribution at the left part shown in  FIG. 6 , an additional phase difference is created. For example, images signals S 1 ″, S 2 ″ and S 3 ″ respectively corresponding to first, second and third horizontal scan line are represented by: 
         [0000]        S   1   ″=Y +Sin [(ω c +Δω)* t+φ   1 ], 
         [0000]        S   2   ″=Y +Sin [(ω c +Δω)* t+φ   2 ], 
         [0000]        S   3   ″=Y +Sin [(ω c +Δω)* t+φ   3 +π], 
         [0057]    where +π is a phase difference defined in the SECAM specification, and φ 1 , φ 2  and φ 3  are phase differences resulting from the non-uniform color distribution at the front-end. 
         [0058]    Therefore, the phase differences of the image signals corresponding to the successively arranged pixels are not simply equal to the difference π. Suppose that a phase difference between φ 1 , φ 2  and φ 3 +π is zero. The phase difference is transmitted to the vertical filter module  32  illustrated in  FIG. 4  to output a result of zero regarded as a signal represented by Sin [(ω c +(−ω c ))*t]. That is, an absolute value of the chroma angular frequency is equal to the carrier angular frequency; however, the chroma frequency is in fact not equal to the carrier frequency. According to a SECAM check table of chroma frequencies and chromaticities (colors), Δω=−ω c  corresponds to crimson. In conclusion, referring to  FIG. 6 , unexpected colors may be calculated and rendered according to the 2D image processing method.  FIG. 6  shows horizontally adjacent chroma areas with different chromaticities, and colors of the left side are non-uniformly distributed, such that abnormal blocks  24  result at the adjoining edge of the horizontally adjacent chroma areas. 
         [0059]    The fourth part discusses defining a weight of a chromaticity. In order to solve image processing problems encountered in the situation (a) and the situation (b), an approach of involving weights is defined. More particularly, referring to  FIG. 7A , a same image is processed via a 2D image processing method (i.e., using a vertical filter module  52 , a frequency demodulation module  54  and a chroma converting unit  58 ) to obtain a first chromaticity, and via a one-dimensional image processing method (i.e., using a band-pass filter unit  51 , a frequency demodulation module  54  and a chroma converting unit  58 ) to obtain a second chromaticity. After that, the first chromaticity and the second chromaticity are respectively multiplied by a first weight and a second weight to calculate a representative chromaticity. By adjusting the first weight and the second weight, importance of the first chromaticity and the second chromaticity is defined. Accordingly, the image processing method according to an embodiment of the present invention may be applied to different color display situations, thereby rendering better application flexibility to the image processing method according to the invention. 
         [0060]    Referring to  FIG. 7A , an image processing circuit  5  comprises a chroma weight module  56  coupled to the chroma converting unit  58 . The chroma weight module  56  respectively multiplies a first chromaticity V 1  and a second chromaticity V 2  by the first weight and the second weight to calculate a representative chromaticity V 0 . 
         [0061]    The chroma weight module  56  comprises a first defining unit  560 , a second defining unit  562  and a third defining unit  564 . A chromaticity is weighted with respect to different situations, and a detailed flow thereof shall be described below. 
         [0062]    According to the description of a non-uniform color distribution in the abovementioned third part, an angular frequency difference between a first chroma angular frequency calculated in the 2D image processing method and a carrier angular frequency based on the SECAM system may be rather large, and thus the first defining unit  560  properly reduces the first weight and increases the second weight for such situation. That is, when the angular frequency difference between the first chroma angular frequency and the carrier angular frequency based on the SECAM system is rather large, an undesirable effect may be resulted according to the 2D image processing method. Therefore, the 2D image processing method according to an embodiment of the present invention is incorporated with the one-dimensional image processing method to gain a better effect. 
         [0063]    According to the foregoing description, the first defining unit  560  determines whether the first chroma angular frequency is greater than a predetermined threshold. When the answer is yes, the first weight is defined as being smaller than the second weight; otherwise, the first weight is defined as being greater than the second weight. 
         [0064]    An image received by a receiving unit  50  further comprises a fourth pixel and a fifth pixel. Further, in a vertical direction, the fourth pixel, the first pixel, the second pixel, the third pixel, and the fifth pixel, successively arranged downwards, respectively corresponds to a fourth image signal, the first image signal, the second image signal, the third image signal and a fifth image signal. The vertical filter module  52 , the frequency demodulation module  54  and the chroma converting unit  58  calculates a third chromaticity V 3  according to the fourth, the first and the second image signals, and calculates a fourth chromaticity V 4  according to the second, the third and the fifth image signals. 
         [0065]    The image processing circuit  5  further comprises a chroma edge detecting module  55  coupled to the chroma converting unit  58 . The chroma edge detecting module  55  calculates a chroma edge intensity (i.e., chromaticity difference) according to the third chromaticity V 3 , the first chromaticity V 1  and the fourth chromaticity V 4 , which are outputted by the chroma converting unit  58 . 
         [0066]    The second defining unit  562  of the chroma weight module  56  coupled to the chroma edge detecting module  55  defines the first and second weights for calculating the representative chromaticity V 0  according to the chroma edge intensity outputted by the chroma edge detecting module  55 . 
         [0067]    Logically, when a chroma edge is present between the first pixel, the second pixel and the third pixel, it means a significant difference exists between two chromaticities among the first chromaticity V 1 , the third chromaticity V 3  and the fourth chromaticity V 4 . Therefore, according to the present invention, the chroma edge intensity (chromaticity difference) is used for determining whether an edge of a chroma area is present. The calculation of the chroma edge intensity is described below. 
         [0068]    The chroma edge detecting module  55  comprises a first subtraction unit  550 , and a first determining unit  552  coupled to the first subtraction unit  550 . The first subtraction unit  550  subtracts the first chromaticity V 1  from the third chromaticity V 3  to calculate a first chromaticity difference, and subtracts the first chromaticity V 1  from the fourth chromaticity V 4  to calculate a second chromaticity difference. The first determining unit  552  determines whether an absolute value of the first chromaticity difference is greater than that of the second chromaticity difference. When the answer is yes, the first determining unit  552  defines the chroma edge intensity as the absolute value of the first chromaticity difference. When the answer is no, the first determining unit  552  defines the chroma edge intensity as the absolute value of the second chromaticity difference. 
         [0069]    When two vertically arranged pixels arranged belong to different chroma areas, a difference may exist between chromaticities corresponding to the pixels. Therefore, the second defining unit  562  identifies whether the pixels are located at a cross-chroma area according to the chroma edge intensity. Accordingly, the second defining unit  562  defines the first weight and the second weight according to the chroma edge intensity (chromaticity difference). For example, when the chroma edge intensity is the absolute value of the first chromaticity difference and is greater than a predetermined threshold, it is rather possible that a chroma area edge exists between the first pixel and the third pixel. Therefore, the first chromaticity V 1  calculated according to the 2D image processing method is given a lower weight. 
         [0070]    In addition to identifying the chroma edge, a luma edge is also taken into consideration according to the present invention. 
         [0071]    Referring to  FIG. 7A , the image processing circuit  5  further comprises a first notch filter unit  53  coupled to the receiving unit  50 , and a luma edge detecting module  57  coupled to the first notch filter unit  53 . The first notch filter unit  53  processes the first image signal, the second image signal and the third image signal to calculate a first luminosity Y 1  corresponding to the first pixel, a second luminosity Y 2  corresponding to the second pixel, and a third luminosity Y 3  corresponding to the third pixel. Referring to  FIG. 7B , a curve  62  and a curve  64  respectively represent luma components and chroma components of image signals, a dashed line  66  indicates that the first notch filter unit  53  retains most of low frequency signals (i.e., the luma components) and filters outs signals within a frequency range whose center is a carrier angular frequency ω c  (i.e., the chroma components). 
         [0072]    The luma edge detecting module  57  calculates a luma edge intensity according to the first luminosity Y 1 , the second luminosity Y 2  and the third luminosity Y 3 , which are outputted by the first notch filter unit  53 . 
         [0073]    The chroma weight module  56  comprising the third defining unit  564  is coupled to the luma edge detecting module  57 . The third defining unit  564  defines the first and second weights for calculating the representative chromaticity V 0 . 
         [0074]    The luma edge detecting module  57  calculates the luma edge intensity via a second subtraction unit  570  and a second determining unit  572  coupled to the second subtraction unit  570 . The second subtraction unit  570  subtracts the second luminosity Y 2  from the first luminosity Y 1  to calculate a first luminosity difference, and subtracts the second luminosity Y 2  from the third luminosity Y 3  to calculate a second luminosity difference. 
         [0075]    The second determining unit  572  determines whether an absolute value of the first luminosity difference is greater than that of the second luminosity difference. When the answer is yes, the second determining unit  572  defines the luma edge intensity as the absolute value of the first luminosity difference. When the answer is no, the second determining unit  572  defines the luma edge intensity as the absolute value of the second luminosity difference. 
         [0076]    When two vertically arranged pixels belong to different luma areas, a difference may exist between luminosities corresponding to the pixels. Therefore, the third defining unit  564  identifies whether a cross-luma area is present according to the luma edge intensity. For example, when the luma edge intensity is the absolute value of the first luminosity difference and is greater than a predetermined threshold, it is rather possible that a luma area edge exists between the first pixel and the third pixel. Therefore, the first chromaticity V 1  calculated according to the 2D image processing method is given a lower weight. 
         [0077]    The fifth part discusses how to define a weight of a luminosity. Reference may also be made to the above-mentioned description of calculating a chromaticity and defining a weight of a chromaticity. With respect to a notch filtering process for filtering luma components, a similar weight conception may be used for defining a filtering frequency range. 
         [0078]    In order to gain better a luma performance, an image processing circuit  7  is provided according to the present invention. Referring to  FIG. 8 , the image processing circuit  7  comprises a second notch filter unit  75 , a third notch filter unit  77  and a luma weight module  76 . The second notch filter unit  75  and the third notch filter unit  77  are coupled to a receiving unit  70 , and the luma weight module  76  is coupled to the second notch filter unit  75  and the third notch filter unit  77 . 
         [0079]    The receiving unit  70  receives an image based on the SECAM specification. The image comprises a plurality of pixels at least comprising vertically, successively arranged a first pixel, a second pixel and a third pixel respectively corresponding to a first image signal, a second image signal and a third image signal. 
         [0080]    The second notch filter unit  75  and the third notch filter unit  77  regard one image signal from the first, the second and the third image signals as a target image signal, and process the target image signal respectively by using a first frequency range and a second frequency range, so as to respectively calculate a fourth luminosity Y 4  and a fifth luminosity Y 5 , where the second frequency range covers the first frequency range and is greater than the first frequency range. 
         [0081]    The luma weight module  76  adds up two products of multiplying the fourth luminosity Y 4  by a third weight and multiplying the fifth luminosity Y 5  by a fourth weight to calculate a representative luminosity Y 0  corresponding to the target image signal. The luma weight module  76  obtains chromaticities via a one-dimensional image processing method and a 2D image processing method to define the third and fourth weights, and a detailed process flow thereof shall be described below. 
         [0082]    The image processing circuit  7  further comprises a chroma converting unit  79 , and a third subtraction unit  78  coupled to the chroma converting unit  79 . The third subtraction unit  78  subtracts the second chromaticity V 2  from the first chromaticity V 1  outputted by the chroma converting unit  79  to calculate a chromaticity difference. 
         [0083]    The luma weight module  76 , comprising a fourth defining unit  760  and being coupled to the third subtraction unit  78 , defines the third weight and the fourth weight according to an absolute value of the chromaticity difference outputted by the third subtraction unit  78 . For greater absolute values of the chromaticity difference, a narrower frequency range is applied so that the third weight is defined as being greater than the fourth weight; for smaller absolute values of the chromaticity difference, a wider frequency range is applied so that the third weight is defined as being smaller than the fourth weight. 
         [0084]    In conclusion, as disclosed in the foregoing first part and the second part, abnormal color blocks, formed in a multi-burst pattern from applying a one-dimensional image processing method (corresponding to the image processing circuit  1  illustrated in  FIG. 2 ) of the prior art, are avoided via a vertical filter calculation using a 2D image processing method (corresponding to the image processing circuit  3  illustrated in  FIG. 3 ) according to an embodiment of the present invention. 
         [0085]    As disclosed in the foregoing third part and the fourth part, by defining weights, an image processing circuit such as the image processing circuit  5  illustrated in  FIG. 7A  properly gives a weight proportion to a first chromaticity and a second chromaticity, which are respectively calculated via the 2D image processing method according to an embodiment of the present invention and a conventional one-dimensional image method. Therefore, for different color distribution situations, a reliable chromaticity is generated according to the present invention. 
         [0086]    As disclosed in the foregoing fifth part, an image processing circuit such as the image processing circuit  7  illustrated in  FIG. 8  determines a current color distribution according to a difference of a first chromaticity and a second chromaticity, so as to properly define a filtering frequency range for filtering luma components in a notch filtering process. Therefore, in situations of different color distributions, an image processing circuit according to an embodiment of the present invention is capable of effectively separating chroma and luma components. 
         [0087]    While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not to be limited to the above embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.