Method and apparatus generating a bitmap

Abstract

A method of generating a bitmap representative of an original image. The method comprises (1) scanning the original image to generate a greyscale pixel map; (2) interpolating and rotating the greyscale pixel map to generate a higher resolution greyscale pixel map; and (3) converting the higher resolution greyscale pixel map into the bitmap. The greyscale pixel map is converted into the bitmap by (i) ranking each greyscale pixel value against the greyscale pixel values of a neighbourhood of adjacent pixel locations; (ii) determining a desired number of black binary pixels (B_Pc) in the neighbourhood; (iii) comparing the rank of the greyscale pixel with the desired number of black binary pixels; and (iv) assigning a black binary pixel value to the pixel location when the comparison carried out in step (iii) satisfies a predetermined condition.

We claim:  
     
         1 . A method of generating a bitmap representative of an original image, said bitmap comprising a plurality of white/black binary pixel values each having a respective pixel location, the method comprising 
 (1) scanning said original image to generate a greyscale pixel map, said greyscale pixel map comprising a plurality of greyscale pixel values each having a respective pixel location; and    (2) converting said greyscale pixel map into said bitmap by 
 (i) ranking each said plurality of greyscale pixel values against the greyscale pixel values of a neighbourhood of adjacent pixel locations;  
 (ii) determining a desired number of black binary pixels (B_Pc) in said neighbourhood;  
 (iii) comparing said rank of each of said plurality of greyscale pixel values with said desired number of black binary pixels; and  
 (iv) assigning a black binary pixel value to said pixel location when the comparison carried out in step (iii) satisfies a predetermined condition.  
   
     
     
         2 . A method according to  claim 1  wherein step (ii) comprises summing said greyscale pixel value of each pixel in said neighbourhood to generate a sum (TD) and determining said desired number (B_Pc) from said sum (TD) in accordance with a predetermined algorithm.  
     
     
         3 . A method according to  claim 2  wherein said desired number (B_Pc) is determined in step (ii) by inputting said sum (TD) into a look-up table, wherein said look-up table is programmed with said predetermined algorithm.  
     
     
         4 . A method according to  claim 2  further comprising calibrating said predetermined algorithm by 
 (a) providing a calibration strip comprising one or more patches each having a known required density (R_D X );  
 (b) generating a zero calibration bitmap representative of said calibration strip by a method according to claim  1 ;  
 (c) comparing said zero calibration bitmap with said required density R_D X ; and  
 (d) calibrating said algorithm in accordance with said comparison in step (c).  
 
     
     
         5 . Apparatus for generating a bitmap representative of an original image, said bitmap comprising a plurality of white/black binary pixel values each having a respective pixel location, the apparatus comprising 
 (1) means for scanning said original image to generate a greyscale pixel map, said greyscale pixel map comprising a plurality of greyscale pixel values each having a respective pixel location; and    (2) means for converting said greyscale pixel map into said bitmap by 
 (i) ranking each of said plurality of greyscale pixel values against the greyscale pixel values of a neighbourhood of adjacent pixel locations;  
 (ii) determining a desired number of black binary pixels in said neighbourhood;  
 (iii) comparing said rank of each of said plurality of greyscale pixel values with said desired number of black binary pixels; and  
 (iv) assigning a black binary pixel value to said pixel location when said comparison carried out in step (iii) satisfies a predetermined condition.  
   
     
     
         6 . A method of generating a bitmap representative of an original image, the method comprising 
 (1) scanning said original image to generate a greyscale pixel map comprising a plurality of greyscale pixel values by; 
 (i) directing a light beam onto said original image whereby said light beam is modulated by said original image to generate a modulated light beam;  
 (ii) causing relative scanning movement between said light beam and said original image;  
 (iii) detecting said modulated light beam to generate a picture signal; and  
 (iv) generating said plurality of greyscale pixel values from the picture signal;  
   (2) interpolating said greyscale pixel map to generate a higher resolution greyscale pixel map; and    (3) converting said higher resolution greyscale pixel map into said bitmap.    
     
     
         7 . A method according to  claim 6  wherein said interpolation comprises 4-point interpolation.  
     
     
         8 . A method according to  claim 6  further comprising rotating said greyscale pixel map.  
     
     
         9 . Apparatus for generating a bitmap representative of an original image, the apparatus comprising 
 (1) an input scanner for scanning said original image to generate a greyscale pixel map comprising a plurality of greyscale pixel values, said input scanner comprising; 
 (i) means for directing a light beam onto said original image whereby the light beam is modulated by said original image to generate a modulated light beam;  
 (ii) means for causing relative scanning movement between said light beam and said original image;  
 (iii) a detector for detecting said modulated light beam to generate a picture signal; and  
 (iv) means for generating said plurality of greyscale pixel values from said picture signal;  
   (2) means for interpolating said greyscale pixel map to generate a higher resolution greyscale pixel map; and    (3) means for converting said higher resolution greyscale pixel map into said bitmap.    
     
     
         10 . A method of producing an output image from a plurality of colour separations comprising 
 (1) scanning each colour separation to generate a respective plurality of greyscale pixel maps;    (2) rotating one or more of said greyscale pixel maps to correct any misregistration between said colour separations;    (3) converting each greyscale pixel map into a respective bitmap; and    (4) producing said output image by superimposing said bitmaps.    
     
     
         11 . A method according to  claim 10  further comprising detecting a plurality of registration marks in each greyscale pixel map; determining a rotation value from the locations of said detected registration marks; and rotating one or more of said greyscale pixel maps by said rotation value.  
     
     
         12 . A method according to  claim 10  further comprising interpolating said greyscale pixel maps to generate a plurality of higher resolution greyscale pixel maps, and producing said bitmaps from said higher resolution greyscale pixel maps.  
     
     
         13 . Apparatus for producing an output image from a plurality of colour separations comprising 
 (1) means for scanning each colour separation to generate a respective plurality of greyscale pixel maps;    (2) means for rotating one or more of said greyscale pixel maps to correct any misregistration between said colour separations;    (3) means for converting each greyscale pixel map into a respective bitmap; and    (4) means for producing said output image by superimposing said bitmaps.    
     
     
         14 . Apparatus according to  claim 13  further comprising means for detecting a plurality of registration marks in each greyscale pixel map; means for determining a rotation value from the locations of said detected registration marks; and means for rotating one or more of said greyscale pixel maps by said rotation value.