Model-based halftoning of color images

A method for displaying a color image at a second location based on a continuous tone color image at a first location, the color image generated by a display device located at a second location, the method comprising the steps of:

• (a) receiving at the second location a set of input signals representing the continuous tone image;
• (b) determining a color halftone image based on the received set of input signals, the step of determining the color halftone image including the steps of
• (1) forming past signals predictive of regions of color halftone images formed by said display device in response to applied color image signals,
• (2) modifying each of a plurality of said input signals in response to one or more past error signals, said past error signals reflecting differences between past modified input signals and said past signals predictive of regions of color halftone images, and
• (3) forming an output image signal in response to each of a plurality of said modified input signals;
• and
• (c) displaying the color halftone image with use of the plurality of output image signals.

A method of generating an array of image signals suitable for application to a display device to generate a color halftone image in response to an array of signals characterizing a color image and an array of initial image signals, said display device for generating spots at selected ones of regularly spaced positions on a display surface, said method characterized by a repeated sequence of steps, each repetition of the sequence of steps operating on an array of input signals and producing an array of output signals, said initial signals for use as said input signals on an initial pass through said sequence of steps, said output signals of said sequence of steps suitable for use as said input signals in a subsequent repetition of the sequence of steps, the method comprising the steps of:

• performing said sequence of steps, said sequence including:
• filtering a plurality of said input signals using a 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;
• filtering said first signals using an eye-model filter to produce second signals;
• forming an error signal representative of a difference between said signals characterizing a color image and said second signals;
• selectively modifying one or more of said input signals based on said error signal to produce said output signals;
• and
• repeating said sequence of steps one or more times until said output signals realize a preselected error criterion, said output signals which realize said error criterion for application to said display device.

A method for displaying a color image at a second location based on a continuous tone color image at a first location, the second location receiving a set of signals representing the continuous tone image, the color image generated by a display device located at a second location, said display device for generating spots at selected ones of regularly spaced positions on a display surface, said method characterized by a repeated sequence of steps, each repetition of the sequence of steps operating on an array of input signals and producing an array of output signals, said initial signals for use as said input signals on an initial pass through said sequence of steps, said output signals of said sequence of steps suitable for use as said input signals in a subsequent repetition of the sequence of steps, the method comprising the steps of:

• receiving at the second location the set of signals representing the continuous tone color image;
• determining a color halftone image based on the received set of signals representing the continuous tone color image, the step of determining the color halftone image including the steps of:
• filtering a plurality of input signals using a filter reflecting characteristics representatives of said display device to produce first signals representing an estimate of an output of said display device;
• filtering said first signals using an eye-model filter to produce second signals, wherein said filtering comprises forming a non-linear function of said initial or corrected image signals that generates said first signals, said function representing interaction of one or more displayed spots;
• forming an error signal representative of a difference between said signals representing the continuous tone color image and said second signals;
• selectively modifying one or more of said input signals based on said error signal to produce said output signals;
• and
• repeating said sequence of steps one or more times until said output signals realize a preselected error criterion, said output signals which realize said error criterion for application to said display device;
• and
• displaying the color halftone image with use of the plurality of output signals.

A method of color halftoning a color image, for display on a display device, said display device for generating spots at selected ones of regularly spaced positions on a display surface, the color image represented by an array of one or more input signals, the method comprising the steps of:

• generating an array of one or more signals representing at least a portion of a predicted display of a color halftone image with use of a color display model, the model representing color display distortion;
• forming an array of one or more error signals reflecting a difference between the array of signals representing at least a portion of a predicted color halftone image and an array of one or more signals reflecting said array of input signals;
• and
• determining an array of one or more signals for application to a display device based on said array of error signals;
• wherein said color display model comprises a non-linear function of signals suitable for application to said display device, which function generates said array of one or more signals and represents interaction of one or more displayed spots.