Patent ID: 7999980

Claim:
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 corresponding position information on the screen cell; and an output unit that has a lookup table storing a plurality of output pixel values corresponding to a plurality of input pixel values in such a manner that an image is formed in which an output pixel value is increased or decreased with an increase in the corresponding input pixel value, and a screen line number is kept at a prescribed level with the increase in the corresponding input pixel value but a dot position is different, and that outputs the output pixel value at a pixel position on the screen cell corresponding to the position information by referring to the lookup table, according to the corresponding input pixel value and the corresponding input pixel position information received by the receiving unit, wherein when the plurality of input pixel values are mid-range gradation values, the plurality of output pixel values increases monotonically across a range of grayscale image values from zero to a maximum value, maintains the maximum value for a first predetermined number of input pixel values, decreases monotonically across the range of grayscale image values from the maximum value to zero, maintains zero for a second predetermined number of input pixel values, and again increases monotonically across the range of grayscale image values from zero to the the maximum value, and the first predetermined number of input pixel values is at least one and the second predetermined number of pixel values is at least one.