Inverse halftoning for multi-level halftones

An apparatus for reconstructing an image from its halftone version using information obtained from a dither matrix used to generate the halftone version, comprising:

• means for determining a bounding region defined by (xmin, xmax) for each pixel color value, based on the information obtained from the dither matrix;
• a low-pass filter for filtering the halftone version, such that for each pixel, the reconstructed color is the filtered value, if the filtered value is greater than or equal to xmin and less than or equal to xmax, the xmin value, if the filtered value is less than xmin, and the xmax value, if the filtered value is greater than xmax;
• and
• means for determining, for each pixel, whether its value for that color is to be used in an averaging process based on the distance between the bounding region of that pixel and an adjacent pixel bounding region.

A machine-readable medium having a program of instructions for directing a machine to reconstruct an image from its halftone version using information obtained from a dither matrix used to generate the halftone version, the program of instructions comprising:

• (a) instructions for determining a bounding region defined by (xmin, xmax) for each pixel location and color value, based on the information obtained from the dither matrix;
• (b) instructions for applying a low-pass filter to the halftone version, such that for each pixel, the reconstructed color is
• (b)(1) the filtered value, if the filtered value is greater than or equal to xmin and less than or equal to xmax,
• (b)(2) the xmin value, if the filtered value is less than xmin, and
• (b)(3) the xmax value, if the filtered value is greater than xmax;
• and
• (c) instructions for determining, for each pixel, whether its value for that color is to be used in an averaging process based on the distance between the bounding region of that pixel and neighborhood pixels' bounding regions.