Typewriting machines – Carriage or carriage-moving or movement-regulating mechanism – Carriage-feed mechanism
Utility Patent
1997-12-31
2001-01-02
Hilten, John S. (Department: 2854)
Typewriting machines
Carriage or carriage-moving or movement-regulating mechanism
Carriage-feed mechanism
C400S120020, C400S615200
Utility Patent
active
06168329
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a color printing apparatus, and more particularly to a color printing apparatus for printing a color print image composed of a dot matrix.
2. Description of the Related Art
In a color printing apparatus of the type mentioned above, a plurality of primary colors, for example, yellow, cyan, and magenta are superimposed on each dot in a color print image to realize a desired color for each dot, thus providing for a variety of color print images. Moreover, it has been a general tendency to add black to the three colors to print images using four primary colors in order to realize more attractive color print images in additional consideration of brightness or the like, and also in order to print particularly solid black portions in images.
On the other hand, for achieving required improvements in printing speed and print quality (print resolution and so on), there have been widely used color printing apparatus which perform printing in two directions, i.e., a going direction and a returning direction of reciprocal movements of a printing head in directions orthogonal to a feeding direction of a printing medium.
In the bi-directional printing, however, when a vertical straight line L is to be printed on a printing medium T, for example, as illustrated in
FIG. 1B
, i.e., in the same direction as a feeding direction of the printing medium T (a PF direction indicated in FIG.
1
A), mechanical variations or the like of stopping positions of a printing head at left and right limits (CR direction) and stepping feed of the printing medium T cause the straight line L to be jaggy. Particularly, in an image which has a high contrast color with respect to a background color of the printing medium T, the contour of the image appears clearly due to the high contrast, so that displaced dots, if any, printed on the printing medium T become more prominent.
It should be noted herein that while the term “contrast” may refer only to the degree of difference in brightness (bright and shade) or luminance in a particular technical field, the term “contrast” in this disclosure is used to have its essential meaning, i.e., the meaning of “comparison (for demonstrating a difference), or the difference indicated thereby.” Thus, the term “contrast” in the following description includes not only the meaning of a difference in brightness or the like but also the meaning of a difference in color (hue and saturation, see FIG.
2
), reflectivity, lustre (brightness), contrast, and so on, and refers to the degree of such difference, particularly to the degree of visual difference (identity). For example, the “contrast” represents a concept which generally includes visually contrastable differences such as a black image on a white printing medium T, cyan with red, a low saturation color with a high saturation color, a low lustrous image with a highly lustrous image, and so on. Moreover, it is assumed that a high contrast color includes not only a distinctive contrast colors (such as red with respect to cyan) but also a color which provides a visually prominent contour to some degree in comparison with other colors in a printed image, such as colors having a similar tendency (for example, a color prevalently including a hue such as blue, green and so on with respect to red).
For printing a character image (or a sequence of characters) such as a letter, a symbol, a figure, or the like on a predetermined background image, while the background image may be rough to some degree as long as a general impression is understandable, the character image must be clearly identifiable, so that any deviations of dots printed as a character image are more prominent. Moreover, a high contrast color is often used for distinctly printing a character image in contrast with a background image, in which case deviated dots, if any, become further prominent.
It will be understood from the foregoing that the bi-directional printing requires a high accuracy in its position control in a variety of cases as mentioned above in comparison with a uni-directional printing (see Laid-open Japanese Patent Application Nos. 62-279957, 63-280671, and so on). More specifically, the bi-directional printing requires a complicated position control for absorbing a deviation due to variations in moving conditions depending on a moving direction, in addition to a zero point correction at the left and right limits of a print available region.
OBJECTS AND SUMMARY OF THE INVENTION
In view of the problems mentioned above, it is an object of the present invention to provide a color printing apparatus which is capable of solving the problems of the prior art as mentioned above, and specifically, which is capable of realizing an attractive color print at a high printing speed with a relatively simple position control.
To solve the above object, according to a first aspect of the present invention, there is provided a color printing apparatus comprising printing means for printing a color print image composed of a dot matrix on a printing medium, feeding means for feeding the printing medium, reciprocal moving means for reciprocally moving the printing means in directions orthogonal to a direction in which the printing medium is fed, and control means for instructing the printing means to perform printing in a plurality of colors to each dot of the color print image so as to selectively conduct uni-directional printing and/or bi-directional printing in the reciprocal movements of the printing means, wherein the control means instructs the printing means to conduct the uni-directional printing for a high contrast color with respect to a background color of the printing medium within the plurality of colors, and to conduct the bi-directional printing for the remaining colors.
The color printing apparatus prints a high contrast color with respect to the color of a printing medium in one of two directions orthogonal to a direction in which the printing medium is fed, so that moving conditions for the printing means in a printing operation can be made identical for all dots to be printed. Stated another way, since positional deviations due to a difference in moving direction or the like in the bi-directional printing can be prevented, horizontal deviations are less likely to occur even when a straight line or the like is drawn. Also, since the printing in other colors is controlled by a bi-directional printing scheme similar to the prior art, it is possible to meet requirements to printing speed, printing quality, and so on. In addition, since these colors have a relatively low contrast, deviations are less prominent even if occurring in an image. The color printing apparatus therefore provides for high speed printing and highly attractive print images with a relatively simple position control similar to that used in a uni-directional printing scheme.
Preferably, in the color printing apparatus, the print image includes a character image and a background image, and the control means instructs the printing means to print the high contrast color for the character image and to print one of the remaining colors for the background image.
In the color printing apparatus, a print image may have a character image and a background image, wherein the character image is printed using a high contrast color, while the background image is printed using one of the remaining colors, so that the character image can be clearly and distinctively printed on the background image. Also, since the character image is printed in accordance with a uni-directional printing control, it is possible to prevent positional deviations due to a difference in moving direction or the like in the bi-directional printing.
According to a second aspect of the present invention, there is provided a color printing apparatus comprising printing means for printing a color print image composed of a dot matrix on a printing medium, feeding means for feeding the printing medium, reciprocal moving means for reciprocally mov
Hilten John S.
Hogan & Hartson LLP
Seiko Epson Corporation
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