Raster image processor with printhead profile compensation for a multi level digital printing machine

• US 9,053,410 B2
• Filed: 11/06/2014
• Issued: 06/09/2015
• Est. Priority Date: 01/29/2014
• Status: Active Grant

• Current Assignee: Rampage LLC
• Original Assignee: Scaleabilities LLC
• Inventors: Bogart, Mitchell J.
• Primary Examiner(s): Rudolph, Vincent
• Assistant Examiner(s): BURLESON, MICHAEL L
• Application Number:
  US14/534,587
• Publication Number:
  US 20150062659A1
• Time in Patent Office: 215 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G06K 15/1873 Increasing spatial resolution; Anti-aliasing
• CPC Class Codes: G06K 15/1881 Halftoning halftoning of still images in general H04N1/405, H04N1/52
• CPC Class Codes: H04N 1/4057 the pattern being a mixture of differently sized sub-patterns, e.g. spots having only a few different diameters multi-toning H04N1/40087

Abstract

A system and method of calibration, screening, and compensation is presented for multiple gray-level digital presses. Unequal quantization of the input range is employed with compensated overlapping of sub-ranges. Multiple instances of bi-level screening algorithms, tone modification functions, and a recombination algorithm are employed to produce calibrated screening on individual tone ranges. The method works with any bi-level screening algorithm and devices with any number of gray-levels. Quality imaging results from high detail, high tonal accuracy, low screening noise, and lack of printed artifacts. Dynamic re-calibration is facilitated. The elimination of the constraint of evenly spaced gray-levels also has advantages of cost and yield for both print head fabricators as well as digital press manufacturers. Multiple implementations of the system and method are given for both hardware and software embodiments of the invention.

Claims

1. A method of generating a screened multi-bit data output file for a digital printing machine having the ability to print on a page a first printable tone level, a second printable tone level, and a third printable tone level, from an unscreened raster data file specifying a continuous tone value for a first colorant for each printable position of the page, the method comprising the steps of:

(a) creating first and second tonal sub-ranges corresponding to the first and second printable tone levels, respectively, for the first colorant;

each of said first and second tonal sub-ranges comprising beginning and ending boundary tone values defining first and second tone range spans and a first transition tone value to be both said ending boundary tone value of said first tonal sub-range and said beginning boundary tone value of said second tonal sub-range;

(b) shifting the position of said first transition tone value so that said first tone range span is different from said second tone range span;

(c) producing a modified output tone value for said first and second tonal sub-ranges by first and second tone modification functions, respectively; and

(d) producing a single multi-bit output value corresponding to the first colorant for each printable position on the page by using said modified output tone values of said first and second tone modification functions as inputs to at least one bi-level half-toning algorithm.

2. The method of claim 1, wherein step (a) further comprises the step of producing a third tonal sub-range corresponding to the third printable tone level;

said third tonal sub-range comprising beginning and ending boundary tone values defining a third tone range span and a second transition tone value to be both said ending boundary tone value of said second tonal sub-range and said beginning boundary tone value of the said third tonal sub-range.

3. The method of claim 2, wherein step (b) comprises the further step of shifting the position of said second transition tone value so that said third tone range span is different from said second tone range span.

4. The method of claim 3, wherein step (b) further comprises the step of setting said first transition tone value based on the optical density of the first and second printable tone levels.

5. The method of claim 4, wherein step (b) further comprises the step of setting said second transition tone value based on the optical density of the second and third printable tone levels.

6. The method of claim 5, wherein step (d) comprises the further step of producing a single multi-bit output value indicative of the first colorant for each printable position on the page by using said modified output tone values from said first, second, and third tone modification functions as inputs to at least one bi-level half-toning algorithm.

7. The method of claim 6, wherein step (c) comprises the steps of:

assigning said modified output tone value for said first tone modification function to be zero if said input tone value of said first tone modification function is less than said beginning tone value of said first sub-range;

assigning said modified output tone value for said first tone modification function to be 100% if said input tone value of said first tone modification function is greater than said ending tone value of said first sub-range; and

assigning said modified output tone value for said first tone modification function to be given by a linear interpolation formula defined by;

output tone value=((input_tone_value−

starting_tone_value)*100)/(ending_tone_value−

starting_tone_value)) if said input tone value of said first tone modification function is greater than or equal to said starting tone value of said first sub-range and said input tone value of said first tone modification function is less than or equal to said ending tone value of said first sub-range.

8. The method of claim 7, wherein step (c) comprises the steps of:

assigning said modified output tone value for said second tone modification function to be zero if said input tone value of said second tone modification function is less than said beginning tone value of said second sub-range;

assigning said modified output tone value for said second tone modification function to be 100% if said input tone value of said second tone modification function is greater than said ending tone value of said second sub-range; and

assigning said modified output tone value for said second tone modification function to be given by a linear interpolation formula defined by;

output tone value=((input_tone_value−

starting_tone_value)*100)/(ending_tone_value−

starting_tone_value)) if said input tone value of said second tone modification function is greater than or equal to said starting tone value of said second sub-range and said input tone value of said second tone modification function is less than or equal to said ending tone value of said second sub-range.

9. The method of claim 8, wherein step (c) comprises the steps of:

assigning said modified output tone value for said third tone modification function to be zero if said input tone value of said third tone modification function is less than said beginning tone value of said third sub-range;

assigning said modified output tone value for said third tone modification function to be 100% if said input tone value of said third tone modification function is greater than said ending tone value of said third sub-range; and

assigning said modified output tone value for said third tone modification function to be given by a linear interpolation formula defined by;

output tone value=((input_tone_value−

starting_tone_value)*100)/(ending_tone_value−

starting_tone_value)) if said input tone value of said third tone modification function is greater than or equal to said starting tone value of said third sub-range and said input tone value of said third tone modification function is less than or equal to said ending tone value of said third sub-range.

10. A raster image processor for producing a screened multi-bit data output file for a digital printing machine capable of printing on a page a first printable tone level, a second printable tone level, and a third printable tone level, from an unscreened raster data file specifying a continuous tone value for a first colorant for each printable X-Y position of the page, the raster image processor comprising:

a computing device;

a memory device connected with said computer device;

a screening module comprising;

a tone sub-range module configured to create first, second, and third tonal sub-ranges corresponding to the first, second, and third printable tone levels, respectively, for the first colorant;

each of said first, second, and third tonal sub-ranges comprising beginning and ending boundary tone values defining first, second, and third tone range spans and a first transition tone value to be the value of both said ending boundary tone value of said first tonal sub-range and said beginning boundary tone value of said second tonal sub-range and a second transition tone value to be the value of both said ending boundary tone value of said second tonal sub-range and said beginning boundary tone value of said third tonal sub-range;

a shifting module configured to shift the position of said first and second transition tone values so that said first tone range span is different from said second tone range span and said third tone range span;

a pixel processing module comprising a tone modification sub-module configured to produce a modified output tone value for said first, second, and third tonal sub-ranges by first, second, and third tone modification functions, respectively;

wherein said pixel processing module further comprises an output sub-module configured to produce a single multi-bit output value corresponding to the first colorant for each printable position on the page by using said modified output tone values from said first, second, and third tone modification functions as inputs to at least one bi-level half-toning algorithm.

11. The system of claim 10, wherein said tone sub-range module comprises a first set of instructions stored on said memory device to produce said first, second, and third tonal sub-ranges.

12. The system of claim 11, wherein said shifting module comprises a first set of instructions stored on said memory device to set said first and second transition tone values based on the optical strength of the first, second, and third printable tone levels.

13. The system of claim 12, wherein said first set of instructions of said shifting module comprises a set of instructions to set said first and second transition tone values based upon the optical density of the first, second, and third printable tone levels for the first colorant.

14. The system of claim 13, wherein said first set of instructions of said shifting module comprises a set of instructions to set said first and second transition tone values using said highest measured optical density of the first, second, and third printable tone levels, for the first colorant, as the Dmax value used in a Murray-Davies Equation.

15. The system of claim 14, wherein said tone modification sub-module comprises a first set of instructions stored on said memory device to produce said first, second, and third tone modification functions for said first, second, and third tonal sub-ranges, respectively.

16. The system of claim 15, wherein said tone modification sub-module comprises a second set of instructions stored on said memory device to assign said modified output tone value for said first tone modification function to be zero if said input tone value of said first tone modification function is less than said beginning tone value of said first tonal sub-range;

a third set of instructions stored on said memory device to assign said output tone value for said first tone modification function to be 100% if said input tone value of said first tone modification function is greater than said ending tone value of said first tonal sub-range; and

a fourth set of instructions stored on said memory device to assign said output tone value for said first tone modification function to be given by a linear interpolation formula defined by;

output tone value=((input_tone_value−

starting_tone_value)*100)/(ending_tone_value−

starting_tone_value)) if said input tone value of said first tone modification function is greater than or equal to said starting tone value of said first tonal sub-range and said input tone value of said first tone modification function is less than or equal to said ending tone value of said first tonal sub-range.

17. The system of claim 16, wherein said tone modification sub-module comprises a fifth set of instructions stored on said memory device to assign said modified output tone value for said second tone modification function to be zero if said input tone value of said second tone modification function is less than said beginning tone value of said second tonal sub-range;

a sixth set of instructions stored on said memory device to assign said output tone value for said first tone modification function to be 100% if said input tone value of said second tone modification function is greater than said ending tone value of said second tonal sub-range; and

a seventh set of instructions stored on said memory device to assign said output tone value for said second tone modification function to be given by a linear interpolation formula defined by;

output tone value=((input_tone_value−

starting_tone_value)*100)/(ending_tone_value−

starting_tone_value)) if said input tone value of said second tone modification function is greater than or equal to said starting tone value of said second tonal sub-range and said input tone value of said second tone modification function is less than or equal to said ending tone value of said second tonal sub-range.

18. The system of claim 17, wherein said tone modification sub-module comprises an eighth set of instructions stored on said memory device to assign said modified output tone value for said third tone modification function to be zero if said input tone value of said third tone modification function is less than said beginning tone value of said third tonal sub-range;

a ninth set of instructions stored on said memory device to assign said output tone value for said third tone modification function to be 100% if said input tone value of said second tone modification function is greater than said ending tone value of said third tonal sub-range; and

a tenth set of instructions stored on said memory device to assign said output tone value for said third tone modification function to be given by a linear interpolation formula defined by;

output tone value=((input_tone_value−

starting_tone_value)*100)/(ending_tone_value−

starting_tone_value)) if said input tone value of said third tone modification function is greater than or equal to said beginning tone value of said third tonal sub-range and said input tone value of said third tone modification function is less than or equal to said ending tone value of said third tonal sub-range.