Patent Publication Number: US-2009231486-A1

Title: Method and Device for De-Interlacing a Video Signal Having a Field of Interlaced Scan Lines

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and a device for de-interlacing a video signal, and more particularly to a method and a device for de-interlacing the video signal by individual blocks of pixels thereof. 
     2. Descriptions of the Related Art 
     It should be noted that a conventional video image is constituted, in respect of each image, by two fields, known as an even-numbered field and an odd-numbered field, which are interlaced on alternate lines. When the image is displayed, these fields are scanned successively in time on the screen, typically a cathode ray tube, with the lines of the second field of the image being scanned on the spaces left between the scanning lines of the first field. In a progressive scanning, the successive lines of a complete image are displayed sequentially. The interlaced scanning is able to double the vertical resolution while still retaining the same pass band. In addition, the interlaced scanning is able to double the frame return frequency at equal vertical resolution. Thus, the effect of flickering is well reduced by using the interlaced scanning. 
     Analog and digital video signals are generally formatted in the form of interlaced frames, known as “interlaced video”. It is necessary to de-interlace interlaced video signals for displaying in the progressive scanning mode. The progressive scanning mode is used particularly in addressable line-by-line display devices such as plasma panels, liquid crystal display (LCD), organic light-emitting diodes (OLEDs). 
     Such systems, known as “de-interlacing” systems, produce all the displayed lines of an image from only one field of the two fields of which it consists. In fact, since a field contains only one line in two lines of the image, interpolation technique is utilized to determine the content of the missing lines according to adjacent lines and where appropriate the adjacent fields. 
     Edge Line Average (ELA) technique is generally utilized to interpolate pixels for missing lines, wherein the existing adjacent lines are applied to find edge direction and interpolate pixels of the missing lines in a pixel-by-pixel basis. That is each pixel of the missing lines is interpolated along its own direction. Because it is required to compute a direction for each pixel of the missing lines to be interpolated, the ELA technique has some drawbacks, such as large computation, less stability, and inconsistency. 
     Accordingly, a de-interlacing system with less computation, better stability and consistency is desired. 
     SUMMARY OF THE INVENTION 
     One objective of this invention is to provide a method for de-interlacing a video signal having a field of interlaced scan lines. The method comprises the following steps: calculating a de-interlacing cost with respect to a plurality of target pixels according to a first block and a second block of a plurality of pixels in first and second interlaced scan lines respectively along each of a plurality of predetermined directions; determining an interpolating direction for the target pixels among the predetermined directions according to the calculated de-interlacing cost of each of the predetermined directions; and interpolating the target pixels between the first and second interlaced scan lines along the interpolating direction. 
     Another objective of this invention is to provide a device for de-interlacing a video signal having a field of interlaced scan lines. The device comprises a direction engine and an interpolator. The direction engine is configured to calculate a de-interlacing cost with respect to a plurality of target pixels according to a first block and a second block of a plurality of pixels in first and second interlaced scan lines respectively along each of a plurality of predetermined directions, and determine an interpolating direction for the target pixels among the predetermined directions according to the calculated de-interlacing cost of each of the predetermined directions. The interpolator interpolates the target pixels between the first and second interlaced scan lines along the interpolating direction. 
     To achieve these objectives, the present invention de-interlaces a field of interlaced scan lines in a block manner; that is, a block of the target pixels to be interpolated between the interlaced scan lines is computed and interpolated along one direction. Accordingly, the computation for de-interlacing the field of interlaced scan lines can be reduced and stability and consistency of de-interlaced images are improved at the same time. 
     The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in the art to well appreciate the features of the claimed invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a de-interlacing device of a first embodiment of the present invention; 
         FIG. 2   a ˜ FIG. 2   e  are schematic diagrams illustrating interpolating pixels of a de-interlace line along different predetermined directions; and 
         FIG. 3  is a flow chart of a method for de-interlacing a video signal according to a second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A first embodiment of the present invention is a de-interlacing device  1  for de-interlacing a video signal having a field of interlaced scan lines. Each interlaced scan line has a plurality of pixels. The de-interlacing device  1  is illustrated in  FIG. 1 , which comprises a receiving module  101 , a direction engine  103 , and an interpolator  105 . 
     The receiving module  101  is configured to receive the video signal  100 . The interlaced scan lines of the video signal  100  are illustrated in  FIGS. 2   a ˜ 2   e . There are only two interlaced scan lines  21 ,  23  illustrated in  FIGS. 2   a ˜ 2   e , and the interlaced scan lines will be denoted hereinafter as the first interlaced scan line  21  and the second interlaced scan line  23 . Both the first and second interlaced scan lines  21 ,  23  have a plurality of pixels. A de-interlaced line  25  having a plurality of target pixels is generated according to the first interlaced scan line  21  and the second interlaced scan line  23 , and interpolated between the first and second interlaced scan lines  21 , and  23 . 
     Before the de-interlaced line  25  is interpolated, the direction engine  103  decides a number of the pixels in a first block of the first interlaced scan line and a number of the pixels in a second block of the second interlaced scan line. The numbers of the pixels in the first block and the second block may be the same and may be different. In the embodiments of the invention described in the following, both the numbers of the pixels in the first and second blocks are set to be four. Since the de-interlacing device  1  will process in various predetermined directions, there are respective first block and second block for each of the predetermined directions, which are shown in  FIGS. 2   a ˜ 2   e.    
     Once the numbers of the pixels in the first block and second block have been decided, the direction engine  103  interpolates four pixels of the de-interlaced line  25  according to the first block and the second block along each of the predetermined direction to derive a plurality of temporary de-interlaced results. Target pixels  28  of the de-interlaced line  25  and the corresponding first block  27  and second block  29  along different predetermined directions represented by the arrows are illustrated in  FIG. 2   a ˜ FIG. 2   e.  For example, in the predetermined direction (diagonal direction at +45°∘) represented by the arrow shown in  FIG. 2   b,  the corresponding first block  27  in the first interlaced scan line  21  for the target pixels  28  includes pixels  213 ,  214 ,  215 , and  216 , and the corresponding second block  29  in the second interlaced scan line  23  includes pixels  233 ,  234 ,  235 , and  236 . It is noted that the predetermined direction is not limited to the directions shown in  FIGS. 2   a ˜ 2   e,  and designers may adjust it according to design necessity. This is known in the art and thus not further described. 
     The direction engine  103  calculates a de-interlacing cost for the target pixels  28  according to the first block  27 , and the second block  29  along each of the predetermined directions. 
     More specifically, the de-interlacing cost comprises three kinds of costs, such as a neighbor cost, an internal cost, and a continuity cost. It means that the direction engine  103  respectively computes the neighbor cost, the internal cost, and the continuity cost for the target pixels  28  according to the corresponding pixels of the first interlaced scan line  21  and the second interlaced scan line  23 , and previously interpolated pixels. The neighbor cost corresponds to pixel value differences between at least one pixel in the first interlaced scan line  21  and neighboring to the first block  27  and at least one pixel in the second interlaced scan line  23  and neighboring to the second block  29 . The internal cost corresponds to pixel value differences between pixels in the first block  27  and pixels in the second block  29 . The continuity cost is computed between at least one previously interpolated pixel neighboring to the target pixels in the de-interlaced line  25  and at least one pixel in the first interlaced scan line  21  and neighboring to the first block, and/or computed between at least one previously interpolated pixel neighboring to the target pixels in the de-interlaced line  25  and at least one pixel in the second interlaced scan line  23 . 
     A more concrete example is given here. In  FIG. 2   b,  the direction engine  103  computes square differences between each corresponding pixels in the first block  27  and the second block  29  to derive the internal cost with respect to the target pixels  28  along each of a plurality of predetermined directions. For example, the direction engine  103  computes a first square difference between the pixel  213  and the pixel  233 , a second square difference between the pixel  214  and the pixel  234 , a third square difference between the pixel  215  and the pixel  235 , and a fourth square difference between the pixel  216  and the pixel  236 . It is noted that the internal cost of this example is computed along a diagonal direction at +45°, which is represented by the arrow in  FIG. 2   b.  The internal cost with respect to the target pixels  28  along the +45°∘ diagonal direction is then derived with the direction engine  103  by summing up the first, second, third and fourth square differences. 
     The direction engine  103  then computes square differences between the pixels in the first interlaced scan line  21  and neighboring to the first block  27  and the pixels in the second interlaced scan line  23  and neighboring to the second block  29  to derive the neighbor cost with respect to the target pixel  28 . For example, the direction engine  103  computes a first square difference between the pixel  211  and the pixel  231 , a second square difference between the pixel  212  and the pixel  232 , a third square difference between the pixel  217  and the pixel  237 , and a fourth square difference between the pixel  218  and the pixel  238 . The neighbor cost with respect to the target pixels  28  along the +45°∘ diagonal direction is then derived by the direction engine  103  by summing up the computed square differences This invention is not limited by the number of the square differences which are computed to derive the neighbor cost. That is, the direction engine  103  may compute different number of the square differences for respective pixels neighboring to the first block  27  and second block  29 , e.g. 2 or 6 square differences to derive the neighbor cost. Those skilled in the art are able to realize operations and functions of embodiments considering different number of neighboring pixels to derive the neighbor cost based on the above descriptions. Therefore, the descriptions therefor are not repeated herein. 
     The direction engine  103  proceeds to compute square differences between the pixels in the first interlaced scan line  21  neighboring to the first block  27  and previously interpolated pixels neighboring to the target pixels  28  in the de-interlaced line  25 , or the pixels in the second interlaced scan line  23  neighboring to the second block  29  and previously interpolated pixels along a plurality of each of a plurality of predetermined directions to derive the continuity cost. For example, the direction engine  103  computes a first square difference between the pixel  211  and the pixel  251 , a second square difference between the pixel  212  and the pixel  252 . The direction engine  103  then sums up the square differences to derive the continuity cost with respect to the target pixels  28  along the +45°∘ diagonal direction. Alternatively, the direction engine  103  may be adapted to compute square differences between the pixels in the second interlaced scan line  23  and neighboring to the second block  29  and previously interpolated pixels neighboring to the target pixels  28  in the de-interlaced line  25 . For example, the direction engine  103  is adapted to compute a first square difference between the pixel  231  and the pixel  251  and a second square difference between the pixel  232  and the pixel  252 , and sum up the square differences to derive the continuity cost. Moreover, the direction engine  103  is capable of summing up the four square differences which are described above to derive the continuity cost. This invention is not limited by the number of the square differences which are computed to derive the continuity cost. Those skilled in the art are able to realize operations and functions of embodiments considering different number of square differences to derive the continuity cost based on the above descriptions. Therefore, the descriptions therefor are not repeated herein 
     After the costs with respect to the target pixels  28 , such as the internal cost, the neighboring cost, and the continuity costs. have been computed, the direction engine  103  sums up the neighbor cost, the internal cost and the continuity cost to derive a de-interlacing cost for the target pixels  28  along one of the predetermined directions such as the +45°∘ diagonal direction shown in  FIG. 2   b . The direction engine  103  proceeds to calculate another de-interlacing cost for the target pixels  28  along another predetermined direction. It should be appreciated by those skilled in the art that adjustment of the number and type of costs of the de-interlacing cost in accordance with desired functions is applicable within the disclosure. 
     When the de-interlacing cost for the target pixels  28  along each of the predetermined directions has been computed, the direction engine  103  derives a minimum de-interlacing cost thereamong, and accordingly determines an interpolating direction  102  corresponding to the minimum de-interlacing cost for the target pixels  28 . The interpolator  105  computes a plurality of pixels values for the target pixels  28  in the de-interlace line  25  according to the first block  27  and the second block  29  respectively in interlaced scan lines  21 ,  23  of the video signal  100  along the interpolating direction  102 . Finally, the interpolator  105  interpolates the target pixels having the computed pixel values between the first and second interlaced scan lines  21  and  23 . 
     A second embodiment of the invention provides a method for de-interlacing a video signal having a field of interlaced scan lines. Each interlaced scan line has a plurality of pixels. The method applied to a device, such as the de-interlacing device  1 , is as described in the first embodiment. The corresponding flow chart is shown in  FIG. 3 . 
     First, step  301  is executed for receiving the video signal. Step  303  is executed for deciding a number of the pixels in a first block. And Step  305  is executed for deciding a number of the pixels in a second block, wherein the number of the pixels in the first block and the number of the pixels in the second block may be the same. Step  307  is executed for calculating a de-interlacing cost with respect to a plurality of target pixels according to the first block and the second block of a plurality of pixels in first and second interlaced scan lines respectively along each of a plurality of predetermined directions. Then step  309  is executed for determining an interpolating direction for the target pixels among the predetermined directions according to the calculated de-interlacing cost of each of the predetermined directions. Step  311  is executed for interpolating the target pixels between the first and second interlaced scan lines, along the interpolating direction. 
     In addition to the steps shown in  FIG. 3 , the second embodiment is also capable of executing all the operations of the first embodiment. Those skilled in the art can understand the corresponding steps and operations of the second embodiment based on the above descriptions of the first embodiment, and thus the operations are not described in further detail. 
     According to the aforementioned descriptions, the present invention provides a new method and device for de-interlacing a field of interlaced scan lines in a block manner. That is an interpolating direction for a block of a plurality of pixels is determined, and the block of the pixels to be interpolated between the interlaced scan lines is then computed and interpolated along the interpolating direction. Accordingly, the computation for de-interlacing the field of interlaced scan lines can be reduced and stability and consistency of de-interlaced images are improved at the same time. 
     The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in the art may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.