Two-dimensional display model-based halftoning

A system for printing halftone images on a printing surface in response to an array of signals characterizing a gray scale image and initial binary signals, the system comprising:

• printing means for generating spots at selected ones of regularly spaced positions on said printing surface;
• means for filtering said signals characterizing the gray scale image using a first eye-model filter reflecting characteristics of human vision to derive first signals representative of an estimate of the gray scale image as perceived by a human eye;
• means for generating output signals based on input signals, wherein said means for generating output signals may be invoked one or more times, said initial binary signals for use as said input signals on a first invocation of said means for generating output signals, said output signals for use as said input signals on a subsequent invocation, if any, of said means for generating output signals, said means for generating comprising
• means for filtering a plurality of said input signals using a two-dimensional filter reflecting characteristics representative of said printing means to produce second signals representing an estimate of an output of said printing means, wherein said means for filtering comprises means for forming a non-linear function of said input signals that generates said second signals, said function representing overlap of one or more printed spots;
• means for filtering said second signals using a second eye-model filter to produce third signals;
• means for forming an error signal representative of a difference between said first and third signals;
• means for selectively modifying one or more of said input signals responsive to said error signal to produce said output signals;
• and
• means for applying to said printing means a plurality of binary signals comprising said output signals which plurality realizes a preselected error criterion;
• wherein said printing means generates spots at said selected positions in response to said plurality of binary signals which realizes said error criterion.

A facsimile system for printing halftone images on a printing surface at a second location corresponding to a gray scale image at a first location, the facsimile system comprising:

• means for receiving at said second location an ordered sequence of gray-scale coded signals representing said gray-scale image;
• printing means for generating spots at selected ones of regularly spaced positions on said printing surface;
• means for filtering gray scale coded signals using a first eye-model filter reflecting characteristics of human vision to derive first signals representative of an estimate of the gray scale image as perceived by a human eye;
• means for generating output signals based on input signals, wherein said means for generating output signals may be invoked one or more times, said initial binary signals for use as said input signals on a first invocation of said means for generating output signals, said output signals for use as said input signals on a subsequent invocation, if any, of said means for generating output signals, said means for generating comprising
• means for filtering a plurality of said input signals using a two-dimensional filter reflecting characteristics representative of said printing means to produce second signals representing an estimate of an output of said printing means, wherein said means for filtering comprises means for forming a non-linear function of said input signals that generates said second signals, said function representing overlap of one or more printed spots;
• means for filtering said second signals using a second eye-model filter to produce third signals;
• means for forming an error signal representative of a difference between said first and third signals;
• means for selectively modifying one or more of said input signals responsive to said error signal to produce said output signals;
• and
• means for applying to said printing means a plurality of binary signals comprising said output signals which plurality realizes a preselected error criterion;
• wherein said printing means generates spots at said selected positions in response to said plurality of binary signals which realizes said error criterion.

A method for generating an array of binary signals suitable for application to a display device to generate a halftone image in response to an array of signals characterizing a gray scale image and initial binary signals, said display device for generating spots at selected ones of regularly spaced positions on a display surface, said method comprising the steps of:

• (a) performing a sequence of steps one or more times, the sequence of steps operating on input signals and generating output signals, said initial binary signals for use as said input signals on a first pass through said sequence of steps, said output signals for use as said input signals on a subsequent pass, if any, through said sequence said sequence comprising
• (i) filtering a plurality of said input signals using a two-dimensional filter reflecting characteristics representative of said display device to produce first signals representing an estimate of an output of said display device, wherein said filtering comprises forming a non-linear function of said input signals that generates said first signals, said function representing interaction of one or more displayed spots;
• (ii) filtering said first signals using an eye-model filter to produce second signals;
• (iii) forming an error signal representative of a difference between said input and second signals;
• (iv) selectively modifying one or more of said input signals responsive to said error signal to produce said output signals;
• and
• (b) selecting as the binary signals to be applied to said display device a plurality of binary signals comprising output signals which plurality realizes a preselected error criterion.

A method for communicating an image for printing comprising the steps of:

• (a) encoding the image and transmitting its encoded representation;
• (b) receiving the encoded representation of the image and decoding it to produce signals characterizing the image;
• (c) determining a halftone image based on the signals characterizing the image and initial binary signals, wherein the step of determining a halftone image includes the steps of
• (1) performing a sequence of steps one or more times, the sequence of steps operating on input signals and generating output signals, said initial binary signals for use as said input signals on a first pass through said sequence of steps, said output signals for use as said input signals on a subsequent pass, if any, through said sequence, said sequence comprising
• (A) filtering a plurality of said input signals using a two-dimensional filter reflecting characteristics representative of a printing device to produce first signals representing an estimate of an output of said printing device, said printing device for generating spots at selected ones of regularly spaced positions on a printing surface, wherein said filtering comprises forming a non-linear function of said input signals that generates said first signals, said function representing overlap of one or more printed spots;
• (B) filtering said first signals using an eye-model filter to produce second signals;
• (C) forming an error signal representative of a difference between said input and second signals;
• (D) selectively modifying one or more of said input signals responsive to said error signal to produce said output signals;
• and
• (2) selecting as the binary signals to be applied to said printing device a plurality of binary signals comprising output signals which plurality realizes a preselected error criterion;
• and
• (d) printing the halftoned image with use of the selected plurality of binary signals.