Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-12-06
2001-11-06
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S015000, C358S296000
Reexamination Certificate
active
06312101
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to printing digital images using a digital printer having two or more colorants that have substantially the same color, but different densities.
BACKGROUND OF THE INVENTION
In the field of digital printing, a digital printer receives digital data from a computer and places colorant on a receiver to reproduce the image. A digital printer may use a variety of different technologies to transfer colorant to the page. Some common types of digital printers include inkjet, thermal dye transfer, thermal wax, electrophotographic, and silver halide printers.
It is a common goal in the field of digital printing to continually improve the quality of the output print, particularly when printing digital images of photographs. In recent years, advances in the technology related to digital printing have provided much opportunity for improving the quality of the output, particularly in the field of inkjet printing. An inkjet printer reproduces an image by ejecting small drops of ink from a printhead containing nozzles, where the ink drops land on a receiver medium (typically paper) to form ink dots. A typical inkjet printer reproduces a color image by using a set of color inks, usually cyan, magenta, yellow, and black. Often, the dots produced by the inkjet printer are visible to the human eye, and result in an undesirable noise or “grainy” appearance to the reproduced image. Modern inkjet printers typically reproduce images using smaller ink drops than their predecessors, thus reducing the visibility of the ink dots and therefore improving the image quality. Another technique employed by some modem inkjet printers to reduce the grainy appearance of reproduced images is to use multiple inks of the same color, but different densities, such as a light cyan and a dark cyan ink. The light ink dots are less visible to the human eye than the dark ink dots, and regions of the image reproduced with the light ink will appear less grainy than if a dark ink had been used to reproduce the same region.
One problem with using multiple inks of the same color to reduce the graininess of a printed image is that the total amount of ink that is placed on the page is increased. It is commonly known in inkjet printing that poor image quality can result when too much ink is printed on the page. For example, excessive ink can cause the receiver to physically warp or deform. Too much ink can also result in ink “bleeding” , where ink flows across the surface of the receiver from one area to another, resulting in undesired image artifacts and poor image quality. In addition to the potential poor image quality that results from using excessive ink, it is also more costly to operate the printer due to the greater ink usage. It is therefore advantageous to minimize the total amount of ink used to reproduce an image.
U.S. Pat. No. 4,604,654 to Sakurada et. al., describes a printer in which a light ink is used primarily in highlight regions of the image, and a dark ink is used primarily in the shadows, with the midtones being generally reproduced with a combination of the two inks. While this arrangement does provide for reduced image noise, it completely neglects the issue of the total ink amount that gets placed on the page, and could result in the undesired image artifacts described above. U.S. Pat. No. 5,142,374 to Tajika et. al., describes an inkjet et printer in which the light and dark inks are used with different dot sizes or resolutions. This art also provides for reduced graininess of the printed image, but does not consider the amount of ink that is being placed on the page, or the negative image quality artifacts that may occur. Related art describing similar printers are described in U.S. Pat. Nos. 4,635,078, 4,672,432, and 4,727,436, but the total amount of ink that is used is ignored in all of these references.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the disadvantages of the prior art and provide a method for producing high quality images on a digital printer where multiple colorants of the same color are used.
It is another object of the present invention to produce high quality images while minimizing the total amount of colorant such as ink used and the perceived graininess of the printed image.
These objects are achieved by a method for reproducing digital images having at least one color channel containing pixels using a digital printer having a set of colorants, wherein two or more of the colorants of the set have substantially the same color but different densities, and input code values for a particular color channel are used to control colorant amounts for said two or more colorants, comprising the steps of:
a) forming a look-up table for each of the two or more colorants, said look-up table producing a colorant control signal as a function of an input code value for the particular color channel and wherein each control signal individually corresponds to a colorant;
b) addressing the look-up tables with the input code value for each pixel of the digital image to determine the colorant control signal for each of the two or more colorants; and
c) controlling the digital printer using the colorant control signal to control the colorant amount for each of the two or more colorants in the process of reproducing the digital image.
ADVANTAGES
The present invention has an advantage in that it provides for printing high quality images on a digital printer such as an inkjet printer. When an inkjet printer is used having multiple inks of the same color, the total amount of ink is minimized as well as reducing the perceived graininess of the image. Minimizing the total amount of ink used to print an image is advantageous because of the absence of image quality artifacts such as bleeding and cockling, and the reduced operating cost associated with reduced ink usage. The present invention achieves these benefits while maintaining excellent image quality by ensuring that the perceived graininess of the image is simultaneously minimized along with the ink usage.
REFERENCES:
patent: 4604654 (1986-08-01), Sakurada et al.
patent: 4635078 (1987-01-01), Sakurada et al.
patent: 4672432 (1987-06-01), Sakurada et al.
patent: 4727436 (1988-02-01), Kawamura et al.
patent: 5142374 (1992-08-01), Tajika et al.
patent: 5729259 (1998-03-01), Gotoh et al.
patent: 6014457 (2000-01-01), Kubo et al.
Digital Halftoning, by Robert Ulichney, 3rd edition (1990), MIT press, ISBN 0-262-21009-6.
International Color Consortium (ICC) Specification ICC.1:1998-09, “File Format for Color Profiles”.
Couwenhoven Douglas W.
Miller Rodney L.
Spaulding Kevin E.
Eastman Kodak Company
Le N.
Nguyen Lamson D.
Owens Raymond L.
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