Image processing apparatus and image processing method

Abstract

An image processing apparatus for converting a multiple gradation image into a binary or multivalue image by use of an area gradation method according to a screen cell, which includes: a receiving unit that receives an input pixel value of each pixel of the multiple gradation image and position information on the screen cell; and an output unit that outputs an output pixel value, which is increased or decreased with an increase in the input pixel value, at a pixel position on the screen cell corresponding to the position information, according to the input pixel value and the position information received by the receiving unit.

1 . An image processing apparatus for converting a multiple gradation image into a binary or multivalue image by use of an area gradation method according to a screen cell, comprising: 
 a receiving unit that receives an input pixel value of each pixel of the multiple gradation image and position information on the screen cell; and    an output unit that outputs an output pixel value, which is increased or decreased with an increase in the input pixel value, at a pixel position on the screen cell corresponding to the position information, according to the input pixel value and the position information received by the receiving unit.    
   
   
       2 . The image processing apparatus according to  claim 1 , wherein: 
 the output unit comprises:    a lookup table in which the output pixel value corresponding to the input pixel value is stored in such a manner that the corresponding output pixel value is increased or decreased with the increase in the input pixel value, and    outputs the output pixel value by referring to the lookup table on the basis of the input pixel value and the position information received by the receiving unit.    
   
   
       3 . The image processing apparatus according to  claim 2 , wherein: 
 the lookup table stores the output pixel value corresponding to the input pixel value in such a manner that the output pixel value monotonically is increased from zero with the increase in the input pixel value, then returned to zero once and monotonically increased again.    
   
   
       4 . The image processing apparatus according to  claim 2 , wherein: 
 the lookup table stores the output pixel value corresponding to the input pixel value in such a manner that a screen line number is continuously changed with the increase in the input pixel value.    
   
   
       5 . The image processing apparatus according to  claim 2 , wherein: 
 the lookup table stores the output pixel value corresponding to the input pixel value in such a manner that an image is formed in which a screen line number is kept at a prescribed level with the increase in the input pixel value but a dot position is different.    
   
   
       6 . An image processing method which converts a multiple gradation image into a binary or multivalue image by use of an area gradation method according to a screen cell, comprising: 
 receiving an input pixel value of each pixel of the multiple gradation image and position information on the screen cell; and    outputting an output pixel value which is increased or decreased with an increase in the input pixel value at a pixel position on the screen cell corresponding to the position information, according to the received input pixel value and the position information.    
   
   
       7 . The image processing method according to  claim 6 , wherein: 
 the corresponding output pixel value which is increased and decreased with the increase in the input pixel value is previously stored at each of pixel positions of the screen cell on a lookup table in which an output pixel value corresponding to an input pixel value of each pixel of the multiple gradation image is stored; and    an output pixel value is output based on the input pixel value and the position information by referring to the lookup table.    
   
   
       8 . The image processing method according to  claim 6 , wherein: 
 the lookup table stores the output pixel value corresponding to the input pixel value in such a manner that the output pixel value is monotonically increased from zero with the increase in the input pixel value, then returned to zero once and monotonically increased again; and    a single lookup table is used to form an image having a different screen line number between a low gradation portion and a high gradation portion.    
   
   
       9 . The image processing method according to  claim 6 , wherein: 
 the lookup table stores the output pixel value corresponding to the input pixel value in such a manner that a screen line number is continuously changed with the increase in the input pixel value; and    a single lookup table is used to form the image having a screen line number continuously changing according to the increase in the input pixel value.    
   
   
       10 . The image processing method according to  claim 6 , wherein: 
 the lookup table stores the output pixel value corresponding to the input pixel value in such a manner that an image is formed in which a screen line number is kept at a prescribed level with the increase in the input pixel value but a dot position is different; and    a single lookup table is used to form the image having a screen line number kept at the prescribed level with the increase in the input pixel value but a different dot position.