Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-02-02
2001-10-16
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C347S040000, C347S043000
Reexamination Certificate
active
06302508
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing apparatus that creates dots to print an image on a printing medium. More specifically the invention pertains to a printing apparatus that enables a plurality of dots to be formed in each pixel, so as to ensure three or more levels of density expression with regard to each pixel.
2. Description of the Related Art
A variety of printers have been used widely as the output apparatus of the computer to print images in a multi-color, multi-tone expression. One of such printers is an ink jet printer that forms dots with several color inks ejected from a plurality of nozzles provided on a print head and thereby records an image. The ink jet printer generally allows expression of only two levels, that is, the dot on level and the dot off level, with regard to each pixel. The ink jet printer accordingly prints an image after the halftone processing that expresses the various tones of original image data by a distribution of dots.
Multilevel printers that enable tone expression of three or greater levels have been proposed as the technique of ensuring the rich tone expression. Examples of such multilevel printers include a printer that enables at most N dots (where N is an integer of not less than 2) to be created in each pixel, in order to ensure expression of multiple tones. This prior art multilevel printer enables expression of (N+1) levels including creation of no dots, thereby attaining the high quality printing with smooth tone expression. In this multilevel printer, an increase in maximum number N of dots created in each pixel extends the range of possible tone expression. Compared with the printer that varies the quantity of ink or the density of ink, this multilevel printer readily attains the tone expression in a wider range.
In the prior art multilevel printer, the increase in maximum number N of dots created in each pixel lowers the printing speed. Namely it is required to lower the speed of the main scan in the case where N dots are created consecutively in each pixel. It is alternatively required to increase the number of passes of the main scan in the case where N dots are created in each pixel by plural passes of the main scan. In either case, the printing speed is lowered. In the prior art multilevel printer that enables at most N dots to be created in each pixel, the maximum number N of dots created in each pixel is determined by taking into account the conflicting factors, that is, the improved picture quality with smooth tone expression and the sufficient printing speed.
In the prior art multilevel printer, there has been no discussion on the positions of dots formed in each pixel. It is thus possible to further improve the picture quality by taking into account the dot forming positions. This is true not only in the ink jet-type multilevel printers but in any multilevel printers that enable a plurality of dots to be created in each pixel.
SUMMARY OF THE INVENTION
The object of the present invention is thus to improve the picture quality in a printing apparatus that enables a plurality of dots to be formed in each pixel.
At least part of the above and the other related objects is actualized by a printing apparatus that forms dots in respective pixels with a print head in response to a driving signal, while scanning the print head relative to one axis of a printing medium forward and backward, thereby printing a resulting image on the printing medium. The printing apparatus includes a drive unit that outputs the driving signal to the print head in the course of forward and backward passes of the scan of the print head and enables at most N dots to be created in each pixel in each pass of the scan, where N is an integer of not less than 2, according to a predetermined dot formation pattern, which has been set by taking into account a deviation of the center of gravity of all dots to be created in each pixel from the center of gravity of the pixel.
In the printing apparatus of the present invention, the number of dots to be created in each pixel varies from 0 to N, in order to enable tone expression of (N+1) levels in each pixel. The printing apparatus of the present invention creates the respective dots according to the predetermined dot formation pattern, which has been set by taking into account the deviation of the center of gravity of all the dots to be created in each pixel from the center of gravity of the pixel. This technique desirably improves the picture quality of the resulting printed image.
The following describes the effects of dot forming positions on the picture quality, prior to the details of the technique of the present invention. In the printer that consecutively forms dots in each pixel while scanning the print head in each pass of the main scan, the position of the center of gravity of each dot is shifted in the main scanning direction. When the maximum number of dots created in each pixel is successively increased, the center of gravity of all the dots formed in each pixel is gradually shifted in the main scanning direction according to the maximum number of dots created in each pixel. A large maximum number N of dots created in each pixel causes the center of gravity of dots to be shifted by a large quantity. Like in the case of misalignment of dot forming positions, the shift of the center of gravity of dots by a large quantity causes the unevenness of density between adjoining pixels or the roughness, thereby lowering the picture quality of the resulting printed image.
The printer that consecutively forms dots in each pixel while scanning the print head in each pass of the main scan has just been proposed recently, and there has been no study on the effects of the dot forming positions on the picture quality. The inventors of the present invention have noted the relationship between the dot forming positions and the picture quality, and found that the picture quality is readily improved by taking into account the dot forming positions.
The technique of the present invention sets the dot formation pattern by taking into account the deviation of the position of the center of gravity of dots formed in each pixel from the position of the center of gravity of the pixel. By way of example, the dot formation pattern is set to cause a variation in deviation of the center of gravity of dots formed in each pixel from the center of gravity of the pixel, which is based on a variation in maximum number N of dots created in each pixel, to be within a specific range that does not affect the picture quality. This arrangement of the present invention effectively prevents the unevenness of density and the roughness due to the positional shift of the center of gravity of dots, thereby attaining the high quality printing. The technique of the present invention readily improves the picture quality of the resulting printed image without changing the hardware configuration of the prior art multilevel printer but only with changing the settings of the dot formation pattern.
The term ‘center of gravity’ in the specification hereof represents the center of gravity in an area occupied by one or a plurality of dots or by a pixel. In the printing apparatus having a print head that enables formation of variable area dots, the center of gravity of the respective dots may not be positioned symmetrically in the main scanning direction in each pixel. The expression ‘at most N dots to be created in each pixel in each pass of the scan’ means that at most N dots can be created in each pixel by a single pass of the main scan. The at most N dots may be formed in each pixel by either one of the forward pass and the backward pass of the scan of the print head. Alternatively the at most N dots may be formed in each pixel respectively by the forward pass and the backward pass of the scan.
In the printing apparatus of the present invention, any geometrically defined ‘center’ may replace the ‘center of gravity’. One example of the geometrically defined center is at a specific posi
Asauchi Noboru
Fujimori Yukimitsu
Otsuki Koichi
Le N.
Nguyen Lamson D.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
LandOfFree
Printing apparatus, method of printing, and recording medium does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Printing apparatus, method of printing, and recording medium, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Printing apparatus, method of printing, and recording medium will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2593306