Halftone proofing with inkjet printers
View Patent ↗Techniques are described for preparing halftone bitmap images for printing on inkjet printers. The techniques may involve exclusive use of low-density inks to reproduce highlight colors and means for reducing the amount of ink applied to the page within “solid” areas while maintaining complete coverage of these areas. The techniques may rely on the high addressability and larger ink palette of recent inkjet printers. For example, some inkjet printers offer seven ink channels: low and high density inks for the cyan, magenta, and black channels, and a single high-density yellow ink. In one embodiment, halftone dots within a bitmap image are separated into perimeter data and core data. The perimeter data is then associated with a low-density ink channel and the core data is associated with a high-density ink channel.
1. A method for preparing a bitmap image for an inkjet printer comprising:
separating a halftone dot within the bitmap image into perimeter data and core data;
associating the perimeter data with a low-density ink channel; and
associating the core data with a high-density ink channel.
2. The method of claim 1 , wherein separating the halftone dot into perimeter data and core data comprises eroding the halftone dot to determine the core data and eliminating the core data from the halftone dot to determine the perimeter data.
3. The method of claim 1 , further comprising applying threshold array screening to the core data to reduce a volume of ink used during printing of the bitmap image.
4. The method of claim 3 , wherein applying threshold array screening to the core data comprises reducing a number of core data pixels to be printed within the halftone dot and determining an order in which the core data pixels are printed.
5. The method of claim 4 , wherein determining the order in which the core data pixels are printed comprises comparing an input pixel value and a threshold value, and eliminating pixels that are below the threshold value.
6. The method of claim 5 , wherein reducing the number of core data pixels to be printed comprises applying a fractional value to the input pixel value.
7. The method of claim 4 , wherein the order in which the core data pixels are printed produces dispersed dot growth.
8. The method of claim 7 , wherein the dispersed dot growth comprises one of a periodic and a pseudo-random placement of the core data pixels.
9. The method of claim 8 , wherein the pseudo-random placement of the core data pixels is produced by application of precomputed stochastic threshold screening to the core data.
10. The method of claim 4 , wherein applying threshold array screening comprises specifying a subset of the core data pixels to be associated with the low-density ink channel.
11. The method of claim 1 , further comprising applying a bitmap thinning filter to the perimeter data to control the placement of ink during printing.
12. The method of claim 11 , wherein applying the bitmap thinning filter to the perimeter data comprises reducing a number of perimeter data pixels to be printed within the halftone dot.
13. The method of claim 12 , wherein reducing the number of perimeter data pixels comprises applying a thinning glyph to replace a pattern of three adjacent set pixels by a pattern with a middle pixel not set.
14. The method of claim 11 , further comprising associating a subset of the core data with the low-density ink channel and applying the bitmap thinning filter to the subset of the core data.
15. The method of claim 14 , wherein associating the subset of the core data with the low-density ink channel comprises combining the subset of the core data with the perimeter data.
16. The method of claim 1 , wherein the low-density ink channel includes one of a low-density cyan channel, a low-density magenta channel, and a low-density black channel.
17. The method of claim 1 , wherein the high-density ink channel includes one of a cyan channel, a yellow channel, a magenta channel, and a black channel.
18. The method of claim 1 , further comprising resizing the bitmap image to a resolution of the inkjet printer.
19. The method of claim 18 , wherein resizing the bitmap image comprises applying a resizing kernel with a stop-band attenuation that substantially reduces moiré in the bitmap image.
20. The method of claim 19 , wherein the resizing kernel comprises a bicubic kernel.
21. A computer-readable medium comprising instructions to cause a programmable processor to:
separate a halftone dot within a bitmap image into perimeter data and core data;
associate the perimeter data with a low-density ink channel; and
associate the core data with a high-density ink channel.
22. The computer-readable medium of claim 21 , wherein the instructions cause the programmable processor to separate the halftone dot into perimeter data and core data cause the programmable processor to erode the halftone dot to determine the core data and eliminate the core data from the halftone dot to determine the perimeter data.
23. The computer-readable medium of claim 21 , wherein the instructions cause the programmable processor to apply threshold array screening to the core data to reduce a volume of ink used during printing.
24. The computer-readable medium of claim 21 , wherein the instructions cause the programmable processor to apply a bitmap thinning filter to the perimeter data to control the placement of ink during printing.
25. The computer-readable medium of claim 24 , wherein the instructions cause the programmable processor to associate a subset of the core data with the low-density ink channel and apply the bitmap thinning filter to the subset of the core data.
26. The computer-readable medium of claim 25 , wherein the instructions cause the programmable processor to associate the subset of the core data with the low-density ink channel cause the programmable processor to combine the subset of the core data with the perimeter data.
27. The computer-readable medium of claim 21 , wherein the instructions cause the programmable processor to resize the bitmap image to a resolution of the inkjet printer.
28. A system comprising a processor that prepares a bitmap image for an inkjet printer by separating a halftone dot within the bitmap image into perimeter data and core data, associating the perimeter data with a low-density ink channel, and associating the core data with a high-density ink channel.
29. The system of claim 28 , further comprising an inkjet printer that prints the bitmap image based on the perimeter data associated with the low-density ink channel and the core data associated with the high-density ink channel.
30. The system of claim 28 , wherein the inkjet printer includes seven ink channels including cyan, yellow, magenta, black, low-density cyan, low-density magenta, and low-density black.
31. The system of claim 28 , wherein the processor erodes the halftone dot to determine the core data and eliminates the core data from the halftone dot to determine the perimeter data.
32. The system of claim 28 , wherein the processor applies threshold array screening to the core data to reduce a volume of ink used during printing of the bitmap image.
33. The system of claim 28 , wherein the low-density ink channel includes one of a low-density cyan channel, a low-density magenta channel, and a low-density black channel, and the high-density ink channel includes one of a high-density cyan channel, a high-density yellow channel, a high-density magenta channel, and a high-density black channel.