Method for printing an image from a halftone binary bitmap using multiple exposures
The invention is a method for printing an image ( 10 ) from a halftone binary bitmap ( 12 ) having pixels ( 14 a- 14 g ) comprising the steps of: creating a feature location identification filter ( 16 ) for a halftone binary bitmap image; using the feature location identification filter to map pixel identifications ( 18 a- 18 g ); assigning a location specific exposure ( 20 a- 20 g ) to the mapped pixel identifications; and exposing media using the location specific exposures to create an image ( 10 ) on a printer ( 24 ).
1. A method for printing an image from a halftone binary bitmap having pixels comprising:
a) creating a feature location identification filter for said halftone binary bitmap;
b) using said feature location identification filter to map pixel identifications;
c) assigning a location specific exposure to each of said mapped pixel identifications; and
d) exposing media using said location specific exposures to create an image on a printer.
2. The method of claim 1 , wherein said feature location identification filter is a filter created by the steps comprising:
a) assigning pixels to address bits of a lookup table;
b) forming said lookup table by:
i) creating a set of all possible addresses for said pixels; and
ii) mapping said set of addresses to a feature of a halftone dot forming mapped address bits; and
c) assigning a value to each feature of said halftone dot using said mapped address bits to create an output.
3. The method of claim 2 , wherein said feature said pixel represents is selected from the group comprising: off, outside dot, single dot, edge of the dot, and inside of a dot.
4. The method of claim 3 , wherein said location specific exposure for a single dot exposure can be adjusted to be greater than the average exposure of dots in said halftone binary bitmap.
5. The method of claim 2 , wherein said lookup table is a table comprising between 3 and 25 bits.
6. The method of claim 5 , wherein said lookup table is a 25 bit table.
7. The method of claim 2 , wherein said assigned location specific exposure is greater for an edge of said halftone dot than a center of said halftone dot.
8. The method of claim 2 , wherein said location specific exposure is set by:
a) identify a screen ruling and an angle from said halftone binary bitmap;
b) for each feature starting with the smallest, compose a target;
c) print each target at different exposure levels forming a calibration output;
d) measure said calibration output for density at each of said different exposure level forming a density measurement for each different exposure level;
e) convert said density measurements to a dot-gain for each of said different exposure level;
f) calculate an equivalent percent halftone dot for each feature of said halftone dot at said screen ruling and said angle;
g) identify a desired halftone dot-gain for each of said calculated equivalent percent halftone dot; and
h) set said location specific exposure for said feature to obtain said desired halftone dot-gain.
9. The method of claim 8 , wherein said target is composed of said feature within an area to be filtered by said feature location identification filter.
10. The method of claim 1 , wherein said feature location identification filter is a lookup table created by the steps comprising:
a) creating a set of all possible addresses for said pixels; and
b) mapping said set of address to a feature of a halftone dot forming mapped pixel address bits, wherein addresses for pixels are composed of adjacent pixels, and said lookup table is adapted to provide mapped pixel identifications.
11. The method of claim 10 wherein said feature said pixel represents is selected from the group comprising: off, outside dot, single dot, edge of the dot, and inside of a dot.
12. The method of claimed 11 , wherein said location specific exposure for a single dot exposure can be adjusted to be greater than said average exposure of dots in said halftone binary bit map.
13. The method of claim 10 , wherein said assigned location specific exposure is greater for an edge of said halftone dot than a center of said halftone dot.
14. The method of claim 10 , wherein said location specific exposure is set by:
a) identify a screen ruling and an angle from said halftone binary bitmap;
b) for each feature starting with the smallest, compose a target;
c) print each target at different exposure levels forming a calibration output;
d) measure said calibration output for density at each of said different exposure level forming a density measurement for each different exposure level;
e) convert said density measurements to a dot-gain for each of said different exposure level;
f) calculate an equivalent percent halftone dot for each feature of said halftone dot at said screen ruling and said angle;
g) identify a desired halftone dot-gain for each of said calculated equivalent percent halftone dot; and
h) set said location specific exposure for said feature to obtain said desired halftone dot-gain.
15. The method of claim 14 , wherein said target is composed of said feature within an area to be filtered by said feature location identification filter.
16. The method of claim 1 , wherein said filter is composed of pixels in one direction.
17. The method of claim 1 , wherein said filter is composed of pixels in two directions.
18. The method of claim 1 , wherein said printer is a color printer.