Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-08-08
2001-05-01
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S251000, C358S001100
Reexamination Certificate
active
06224190
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an ink-jet recording device which records a color image by putting a plurality of ink dots on the same pixel position using multiple-ink-color heads.
BACKGROUND ART
Usually, an ink-jet recording device repeatedly moves a recording head, with a plurality of ink-ejecting nozzles arranged thereon, in the direction different from the nozzle arrangement direction to form a band of image area (band) during one movement. This repeated one-band image recording, one band for each specific amount of movement of recording medium, completes one whole image recording.
Today, there are a variety of recording media for use in the ink-jet recording device. Among these recording media, print results look much more beautiful on lustrous paper or film than on plain paper. Furthermore, the ink-jet recording device may print on cloth such as cotton or enamel. This demand will grow in future.
However, some of these media described above do not absorb ink well, and some others are easily blurred. Printing on these recording media results in an overflow of ink in a high-density print area, significantly degrading the print image quality. This degradation depends on the characteristics of the recording media. The overflow of ink also dirties some mechanical parts of the ink-jet recording device, such as a platen, sometimes affecting print operations.
The conventional solution to this problem is that the ink ejection amount is limited by a masking that is performed during the preprocessing of conversion from gray-scale images to binary (bi-level) images.
However, the prior art described above has the drawbacks described below because the correction is made on an image signal basis.
First, a popular ink-jet recording device is connected, in most cases, to a computer terminal. This computer terminal performs image processing, such as conversion to binary values, and transfers the processed result to the ink-jet recording device for recording thereon. However, an image input unit or an image processing unit which processes multi-valued signals, if built in an ink-jet recording device, would increase the cost and the processing time and, therefore, they are not standard on a popular ink-jet recording device. When an ink-jet recording device performs correction on an image signal basis, conversion from gray-scale images to binary images waists time and the recording speed is reduced. An ink-jet recording device according to the present invention makes correction, not on multi-valued signal, but on binary image data.
It is therefore an object of the present invention to prevent image quality degradation caused by a blur on the recording medium by limiting, through binary image processing, the ink ejection amount to a level at which no image degradation is caused by a blur on the recording medium.
It is another object of the present invention to reduce the change in color and to produce a good-quality color image recording even when the ink ejection amount is limited during color image recording.
DISCLOSURE OF INVENTION
An ink-jet recording method according to the present invention is an ink-jet recording method for putting a plurality of ink dots on the same pixel position using multiple-color ink heads to record a color image, the ink-jet recording method comprising the steps of:
(a) dividing a whole image area into a plurality of unit areas each composed of a predetermined plurality of pixels;
(b) for each unit area of the image to be recorded, calculating a total of ejection ink dots instructed to be printed in the unit area;
(c) checking if the calculated total of ink dots exceeds a predetermined limit value;
(d) if so, proportionally distributing the limit value to colors according to mutual ratios among numbers of ink dots of the colors to be ejected in the unit area and rounding each of distribution results to an integer to determine a number of ejection ink dots of each color in the unit area;
(e) correcting the instructed number of ink dots of each color by reducing the same based on the determined number of ejection ink dots of each color; and
(f) ejecting ink from each head into the unit area according to the corrected number of ejection ink dots.
As described above, a check is made for each unit area as to whether the total of the ink dots therein exceeds a predetermined limit value. If the total exceeds the predetermined limit value, the number of ejection ink dots of each color is reduced in such a way that the limit value is proportionally distributed among the colors according to the ratio of the number of ejection ink dots of each color in the unit area. As a result, the image quality degradation of a printed matter caused by an ink blur may be reduced by limiting the ink ejection amount in a high-density print area to a given level while keeping the change in color to a minimum.
Preferably, when reducing the number of ejection ink dots in step (e), the ejection ink dots are thinned out according to an ejection ink dot reduction priority pre-established for each pixel position in the unit area. More specifically, the priority is established so that the ejection ink dots of adjacent pixels in the unit area are not thinned out consecutively and so that thinning-out orders of adjacent pixels are different between adjacent unit areas. This prevents an uneven distribution in the image caused by thinning-out.
Preferably, an error generated by rounding the result of the proportional distribution of the limit value to the integer, in step (d), is accumulated and passed to an adjacent unit area for each area and, when an absolute value of the accumulation value becomes 1 or larger, the accumulation value is reflected on the determined number of ejection ink dots of each color in the adjacent unit area. This compensates for an error generated by rounding and substantially prevents the color from being changed.
When the total of the numbers of ejection ink dots of the colors exceeds the limit value, the number of ejection ink dots of the colors is reduced by the exceeded number of the ejection ink dots according to a predetermined color order, and, for the color whose ejection ink dots have been reduced, the number of reduced ejection ink dots is added to the error of the color in the unit area. This prevents the total of the ejection ink dots from exceeding the limit value after the numbers of ejection ink dots are rounded to integers.
An ink-jet recording device according to the present invention is an ink-jet recording device which puts a plurality of ejection ink dots on the same pixel position using multiple-color ink heads to record a color image, the ink-jet recording device comprising a plurality of heads each of which ejects ink droplets based on binary image data; a correction table which contains a number of ejection ink dots of each head limited in advance according to a combination of the numbers of ejection ink dots instructed to be ejected for respective colors in a unit area in such a way that the total number of ejection ink dots does not exceed a predetermined limit value, the unit area being composed of a predetermined plurality of pixels; an error table which contains errors which may be produced when determining the limited numbers of ejection ink dots of the colors and which are previously calculated and determined according to the combination of the numbers of ejection ink dots specified for the colors in the unit area; and a control means for controlling an ink ejection of the plurality of heads based on the corrected binary image data, wherein the control means sequentially processes a plurality of consecutive areas, one unit area at a time, during which the correction table and the error table are referenced according to the combination of ejection ink dots of colors to be ejected in the unit area based on the binary image data and the error obtained from the error table is passed sequentially to a subsequent unit area for accumulating the error for each color and wherein, for the unit area, a corrected number of ejection ink d
Sato Hitoshi
Sekiya Hideki
Takahashi Kazuyoshi
Copyer Co. Ltd.
Dellett and Walters
Nguyen Thinh
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