Apparatus and method for compensating for pixel distortion in reproduction of hologram data

Abstract

An apparatus for compensating for pixel distortion while reproducing hologram data includes an extraction unit, a determination and calculation unit, a table, and a compensation unit. The extraction unit extracts a reproduced data image from a reproduced image frame including the reproduced data image and borders. The determination and calculation unit determines position values of edges of the extracted reproduced data image, and calculates average magnification error values of pixels within line data from position values of start and end point pixels thereof, which are based on the determined position values of the edges. The table stores misalignment compensation values for the pixels within the line data, wherein the misalignment compensation values correspond to predetermined references for average magnification error values. The compensation unit compensates for pixel positions in the extracted reproduced data image using the misalignment compensation values that correspond to the calculated average magnification error values.

What is claimed is: 
     
       1. A method of using a pixel compensation apparatus to compensate for pixel distortion while reproducing hologram data, which is recorded in a storage medium as an interference pattern that is obtained through interference of reference light with signal light that is modulated in accordance with the data, the method comprising the steps of:
 reading an image frame from said storage medium to obtain a reproduced image frame;   said pixel compensation apparatus extracting a reproduced data image from said reproduced image frame including the reproduced data image and borders;   said pixel compensation apparatus determining position values of edges of the extracted reproduced data image;   said pixel compensation apparatus determining position values of start and end point pixels of line data based on the determined position values of the edges;   said pixel compensation apparatus calculating average magnification error values of pixels within the line data based on the determined position values of the start and end point pixels, wherein the average magnification error values represent a ratio of a difference between a size of the extracted reproduced data image and an actual data size to the actual data size; and   said pixel compensation apparatus compensating for pixel positions in the extracted reproduced data image using predetermined misalignment compensation values for the pixels that correspond to the calculated average magnification error values,   wherein the calculated average magnification error values include an x-directional average magnification error value and an y-directional average magnification error value,   wherein the step of calculating the average magnification error values includes the steps of:   calculating an x-directional magnification error value X mag error and a y-directional magnification error value Y mag error using the following Equations; and
   X mag error=(x2−x1)−X data size
 
   Y mag error=(y3−y1)−Y data size
 
   calculating the degree of x-directional misalignment per pixel x and the degree of y-directional misalignment per pixel y using the following Equations,
   x=X mag error/X data size 
   y=mag error/Y data size, and 
   wherein X data size is an actual data size in the x direction, X1 is the position value of the start point pixel in the x direction, x2 is the position value of the end point pixel in the x direction, Y data size is an actual data size in the y direction, y1 is the position value of the start point pixel in the y direction, and y3 is the position value of the end point pixel in the y direction.   
     
     
       2. The method of  claim 1 , further comprising the step of differentiating data sections, which determine compensation directions of the pixel positions, based on the position values of the start or end point pixels and the calculated average magnification error values,
 wherein the respective pixel positions are compensated for in accordance with the compensation directions of the differentiated data sections.   
     
     
       3. The method of  claim 1 , wherein the predetermined misalignment compensation values for the pixels are values that are set to correspond to each of predetermined references for average magnification error values, and are stored in a table. 
     
     
       4. A method of using a pixel compensation apparatus to compensate for pixel distortion while reproducing hologram data, which is recorded in a storage medium as an interference pattern that is obtained through interference of reference light with signal light that is modulated in accordance with the data, the method comprising the steps of:
 reading an image frame from said storage medium to obtain a reproduced image frame;   said pixel compensation apparatus extracting a reproduced data image and alignment marks inserted into predetermined positions from said reproduced image frame including the reproduced data image and borders;   said pixel compensation apparatus detecting degrees of misalignments of pixels within the reproduced data image using the extracted alignment marks, and calculating misalignment correction values based on the detection results;   said pixel compensation apparatus correcting pixel positions of the reproduced data image based on the calculated misalignment correction values, determining position values of edges of the reproduced data image the pixel positions of which are corrected, and determining position values of start and end point pixels of line data based on the determined position values of the edges;   said pixel compensation apparatus calculating average magnification error values of pixels based on the determined position values of the start and end point pixels, wherein the average magnification error values represent a ratio of a difference between a size of the extracted reproduced data image and an actual data size to the actual data size; and   said pixel compensation apparatus compensating for pixel positions in the extracted reproduced data image using predetermined misalignment compensation values for the pixels that correspond to the calculated average magnification error values,   wherein the calculated average magnification error values include an x-directional average magnification error value and a y-directional average magnification error value,   wherein the step of calculating the average magnification error values includes the steps of:   calculating an x-directional magnification error value X mag error and a y-directional magnification error value Y mag error using the following Equations; and
   X mag error=(x2−x1)−X data size
 
   Y mag error=(y3−y1)−Y data size
 
   calculating the degree of x-directional misalignment per pixel x and the degree of y-directional misalignment per pixel y using the following Equations,
   x=X mag error/X data size 
   y=Y mag error/Y data size, and 
   wherein X data size is an actual data size in the x direction, x1 is the position value of the start point pixel in the x direction, x2 is the position value of the end point pixel in the x direction, Y data size is an actual data size in the y direction, y1 is the position value of the start point pixel in the y direction, and y3 is the position value of the end point pixel in the y direction.   
     
     
       5. The method of  claim 4 , further comprising the step of differentiating data sections, which determine compensation directions of the pixel positions, based on the calculated average magnification error values,
 wherein the pixel positions are compensated for in accordance with the compensation directions of the differentiated data sections.   
     
     
       6. The method of  claim 4 , wherein the calculated average magnification error values include an x-directional average magnification error value and a y-directional average magnification error value. 
     
     
       7. The method of  claim 4 , wherein the alignment marks are formed at the predetermined positions in a boundary region between the borders and the reproduced data image. 
     
     
       8. The method of  claim 4 , wherein the alignment marks are formed at the predetermined positions in the borders. 
     
     
       9. The method of  claim 4 , wherein each of the alignment marks has a 4×4 block size and a shape in which 2×2 on/off sub-blocks are alternately arranged. 
     
     
       10. A method of using a pixel compensation apparatus to compensate for pixel distortion while reproducing hologram data, which is recorded in a storage medium as an interference pattern that is obtained through interference of reference light with signal light that is modulated in accordance with the data, the method comprising the steps of:
 reading an image frame from said storage medium to obtain a reproduced image frame;   said pixel compensation apparatus extracting a reproduced data image and a plurality of alignment marks inserted into predetermined positions from a reproduced image frame including the reproduced data image, borders and the plurality of alignment marks;   said pixel compensation apparatus dividing the extracted reproduced data image into a plurality of sub-image blocks based on the plurality of extracted alignment marks;   said pixel compensation apparatus determining position values of edges of each of the sub-image blocks;   said pixel compensation apparatus determining position values of start and end point pixels of line data based on the determined position values of the edges;   said pixel compensation apparatus calculating average magnification error values of pixels within the respective sub-image blocks, based on the determined position values of the start and end point pixels, wherein the average magnification error values represent a ratio of a difference between a size of the sub-image block and an actual data size to the actual data; and   said pixel compensation apparatus compensating for pixel positions in the sub-image blocks using predetermined misalignment compensation values for the pixels that correspond to the calculated average magnification error values,   wherein the calculated average magnification error values include an x-directional average magnification error value and a y-directional average magnification error value,   wherein the step of calculating the average magnification error values includes the steps of:   calculating an x-directional magnification error value X mag error and a y-directional magnification error value Y mag error using the following Equations; and
   X mag error=(x2−x1)−X data size
 
   Y mag error=(y3−y1)−Y data size
 
   calculating the degree of x-directional misalignment per pixel x and the degree of y-directional misalignment per pixel y using the following Equations,
   x=X mag error/X data size 
   y=Y mag error/Y data size, and 
   wherein X data size is an actual data size in the x direction, X1 is the position value of the start point pixel in the x direction, x2 is the position value of the end point pixel in the x direction, Y data size is an actual data size in the y direction, y1 is the position value of the start point pixel in the y direction, and y3 is the position value of the end point pixel in the y direction.   
     
     
       11. The method of  claim 10 , further comprising the step of differentiating data sections, which determine compensation directions of the pixel positions within the respective sub-image blocks, based on the position values of the start or end point pixels and the calculated average magnification error values,
 wherein the pixel positions are compensated for in accordance with the compensation directions of the differentiated data sections.   
     
     
       12. The method of  claim 11 , wherein each of the compensation directions with respect to each of the data sections is changed whenever a value, which is obtained by accumulating the calculated average magnification error values on the position value of the start or end point pixel, reaches 0.5×n, wherein n is an integer. 
     
     
       13. The method of  claim 11 , wherein the predetermined misalignment compensation values for the pixels are values that are set to correspond to each of predetermined references for average magnification error values, and are stored in a table. 
     
     
       14. The method of  claim 10 , wherein the alignment marks are formed at the predetermined positions in a boundary region between the borders and the reproduced data image at predetermined intervals. 
     
     
       15. The method of  claim 10 , wherein the alignment marks are formed at the predetermined positions in the borders at predetermined intervals. 
     
     
       16. The method of  claim 10 , wherein each of the alignment marks has a 4×4 block size and a shape in which 2×2 on/off sub-blocks are alternately arranged. 
     
     
       17. A method of reading data recorded as a holographic image on an optical storage medium, comprising:
 reading an image frame from the optical storage medium;   obtaining a reproduced data image having pixels and at least one alignment mark using a 1:1 pixel matching operation;   determining at least one misalignment correction value based on the at least one alignment mark;   producing an aligned data image by aligning the pixels of the reproduced data image from a start point of origin according to the at least one misalignment correction value;   determining one or more average values associated with magnification error based on the at least one misalignment correction value;   selecting a number of blocks on the aligned data image based on the one or more average values;   mapping the one or more average values to one or more misalignment compensation values; and   compensating pixels for each block based on the one or more misalignment compensation values.    
     
     
       18. The method of claim 17, wherein the blocks are selected using points on the aligned data image where a fraction part of accumulation of the at least one misalignment correction value for the pixels in at least one direction becomes a predetermined value.  
     
     
       19. The method of claim 18, wherein the fraction part of accumulation of misalignment correction value for the pixels in respective vertical and horizontal directions becomes a predetermined value.  
     
     
       20. The method of claim 18, wherein the predetermined value is one of half a pixel and a pixel.  
     
     
       21. The method of claim 17, further comprising determining a direction of compensating the pixels.  
     
     
       22. The method of claim 20, wherein determining the direction of compensating the pixels comprises:
 dividing the aligned data image into three data sections starting from the start point of origin; and assigning different compensation directions to adjacent sections.    
     
     
       23. The method of claim 17, wherein said determining at least one misalignment correction value comprises determining a vertical (x) and a horizontal (y) misalignment correction value.  
     
     
       24. The method of claim 22, wherein determining a vertical (x) and a horizontal (y) misalignment correction value comprises:
 detecting a misalignment based on amounts of light in pixels in vicinity of off-pixels or on-pixels in the at least one alignment marks; and   calculating the vertical (x) and the horizontal (y) misalignment correction value based on detecting the misalignment.    
     
     
       25. The method of claim 22, wherein determining one or more average values associated with magnification error comprises ascertaining a vertical (X) and the horizontal (Y) average magnification error per pixel value based on the vertical (x) and a horizontal (y) misalignment correction value.  
     
     
       26. The method of claim 24, wherein ascertaining a vertical (X) and a horizontal (Y) average magnification error per pixel value comprises:
 calculating a vertical magnification error value and a horizontal magnification error value based on position values of start and end point pixels; and   calculating a degree of a vertical misalignment per pixel based on the vertical magnification error value and a degree of a horizontal misalignment per pixel based on the horizontal magnification error value.    
     
     
       27. The method of claim 17, wherein the mapping between the one or more average magnification error per pixel values and the one or more misalignment compensation values is provided in a lookup table.  
     
     
       28. A method of reading data recorded as a holographic image on an optical storage medium, comprising:
 reading an image frame from the optical storage medium to obtain a reproduced image frame, and at least two alignment marks;   photoelectrically converting the image frame using a 1:1 pixel matching operation, to obtain a reproduced data image, a border and at least two alignment marks provided in the image frame:   determining a vertical (x) and a horizontal (y) misalignment correction value based on the alignment marks and aligning the pixels of the reproduced data image from a start point of origin and the misalignment correction value, to obtain an aligned data image;   ascertaining a vertical (X) and a horizontal (Y) average magnification error per pixel value based on the respective misalignment correction values and selecting a number of blocks on the aligned data image based on the average magnification error per pixel values;   mapping the X and Y average magnification error per pixel values to a misalignment compensation value and performing pixel compensation for each block using the respective misalignment compensation value.