Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-11-10
2001-09-25
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S040000, C347S041000
Reexamination Certificate
active
06293643
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing apparatus that has a head, which enables at least two types of dots having different ink densities and ink weights to be recorded, and prints a multi-tone image with inks spouted from the head. The present invention also pertains to a printing method and a recording medium for realizing the above functions.
2. Description of the Related Art
Color ink jet printers that spout inks of plural colors from the respective ink spout heads are widely used as the output apparatus of the computer. The color ink jet printer prints multi-color multi-tone images processed by the computer. One proposed technique applicable for such a printing apparatus and the corresponding printing method utilizes a higher-density ink and a lower-density ink, with a view to further improving the printing quality in a highlighted area or in an area of low image density. This technique provides a higher-density ink and a lower-density ink for an identical color and controls the spout of these inks, so as to realize printing of excellent tone expression. Another proposed printing apparatus creates dots of different ink weights by the respective inks.
Another proposed technique for expressing the multi-tone creates two different types of dots having different ink densities and different ink weights, so as to vary the density per unit area in multiple stages (for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 59-201864). This technique causes each pixel to consist of four dots and varies the frequency of appearance of the higher-density dots and the lower-density dots in the pixel, in order to print an image of multiple densities.
In a printer that creates dots to record an image, the mechanical manufacturing error of the head that spouts ink and creates dots may cause banding, that is, unevenness of formation of dots, in the head-reciprocating direction or in the main scanning direction. The banding at any tone level deteriorates the picture quality. The effect is especially pronounced in the half tone area that has a relatively small number of dots. In the printer that records an image with dots, it is important to prevent such a banding for the improvement in picture quality. A variety of techniques have been proposed to cancel the banding, separately from realizing the multi-toning, which also leads to an improvement in picture quality. One example is the overlap method that forms each raster by a plurality of main scans of the head.
In the printing apparatus that can create two different types of dots having different ink densities and ink weights, however, no special attention is given to cancel the banding and improve the picture quality. This conventional printing apparatus creates the two different types of dots corresponding to the input tones of the respective pixels according to a predetermined pattern. It is not determined which one of the two types of dots is to be created for each dot unit, based on a variety of conditions for recording an image with dots.
The conventional printing apparatus makes the density per unit area for the dots of a larger ink weight generated by the light ink lower than that for the dots of a smaller ink weight generated by the dark ink, in order to realize multi-toning and improve the picture quality. The density of each pixel is expressed by a combination of these different types of dots. In this arrangement, the dots to be used depend upon only the tone values of the image data, and there is a relatively restricted degree of freedom for the section of the dots. This may cause an inadequate printing result. In general, dots of a smaller ink weight are liable to cause banding. The banding often arises at the tone level where a large number of small dots are created. The larger number of small dots may also result in exceeding the allowable quantity of ink per unit area of the paper, that is, the ink duty of the paper.
SUMMARY OF THE INVENTION
The object of the present invention is thus to provide a technique of effectively utilizing at least two different types of dots having different ink densities and different ink weights, for various purposes including prevention of banding, in a printing apparatus.
At least part of the above and the other related objects is realized by a printing apparatus that records plural types of dots on a printing medium, based on input image data, and thereby prints an image. The printing apparatus includes: a head that creates plural types of dots with respect to at least one hue by combinations of different ink densities and different ink weights, the dots including at least two types of identical-density dots having a substantially identical unit density or density per unit area and at least one type of different-density dot having a different unit density from the identical-density dots; a dot specification unit that determines creation or non-creation of a dot with respect to each pixel and which type of a dot among plural types of dots having different unit densities is to be created, according to the input image data for the pixel; a dot type selection unit that selects one of the at least two types of identical-density dots based on a predetermined selecting condition, with respect to the pixel where one of the identical-density dots is to be created; and a head driving control unit that drives the head and creates the dots determined by the dot specification unit and the dots selected by the dot type selection unit, so as to print a resulting image.
The present invention is also directed to a method of recording plural types of dots on a printing medium with a head, based on input image data, and thereby printing an image. The head that creates plural types of dots with respect to at least one hue by combinations of different ink densities and different ink weights, the dots including at least two types of identical-density dots having a substantially identical unit density or density per unit area and at least one type of different-density dot having a different unit density from the identical-density dots. The method includes the steps of: (a) determining creation or non-creation of a dot with respect to each pixel and which type of a dot among plural types of dots having different unit densities is to be created, according to the input image data for the pixel; (b) selecting one of the at least two types of identical-density dots based on a predetermined selecting condition, with respect to the pixel where one of the identical-density dots is to be created; and (c) driving the head and creating the dots determined in the step (a) and the dots selected in the step (b), so as to print a resulting image.
The printing apparatus of the present invention and the corresponding method create at least three different types of dots having different ink densities and ink weights. There are at least two types of identical-density dots having a substantially identical density per unit area, among the variety of available dots. The structure of the present invention determines creation or non-creation of a dot with respect to each pixel and which type of a dot among these plural types of dots having different unit densities is to be created, according to the tone value of input image data for the pixel. The structure also selects one of the at least two types of identical-density dots based on a predetermined selecting condition, with respect to the pixel where one of the identical-density dots is to be created. The allocation of these at least two types of identical-density dots enhances the degree of freedom for the selection of the dots. This arrangement accordingly improves the picture quality and the convenience of the user according to the selecting condition of the identical-density dots.
In the printing apparatus of the present invention, the predetermined selecting condition used in the dot type selection unit may be related to improvement in picture quality of the resulting printed image.
This arrangement effectively improves the picture
Fujimori Yukimitsu
Liu Sa
Shimada Kazumichi
Zhou Shixin
Barlow John
Do An H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
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