| 摘要 |
<p>A method and apparatus for gradation reproduction of continuous tone images having a determination criterion for reliably setting suitable threshold values ensuring continuity at the halftone gradation are disclosed, the apparatus has an adder 6 for adding a corrected error to input image data, a 3-valuing section 7 for 3-valuing corrected data by using two sets of threshold values, an error computation section 8 for computing an error between corrected data and 3-value data, an error diffusing section 9 for spreading an error to unprocessed neighbor pixels according to weight coefficients, an error memory 10 for storing spread errors with respect to each pixel, and a threshold look-up table 11 which is referred to when the magnitude and the interval of the two sets of threshold values. The interval of threshold values is determined so that the amplitude of the corrected data according to rising and falling variations in the corrected error spikes outward beyond the threshold values at a halftone gradation, thereby preventing generation of a transient region where the amplitude of the corrected data becomes excessively small at the halftone gradation of the corrected data. <IMAGE></p> |
