Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1999-03-02
2002-10-08
Lee, Thomas D. (Department: 2724)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S001900, C358S001400
Reexamination Certificate
active
06462836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a double-tone printer in which an image is printed in light color ink and dark color ink which are overlapped with each other, and more particularly to a double-tone printer such as a digital stencil printer for professional use which prints a high quality black-and-white image and a method of making a density correction curve for use in a density correction processing of a digital image with double-tone printing.
2. Description of the Related Art
For example, a digital stencil printer has been widely used because of its high printing speed and low cost. In the digital stencil printer, a stencil master is made by bringing a thermal head, provided with an array of heater elements which are selectively heated according to an image to be printed, into contact with a heat-sensitive master material so that the parts of the heat-sensitive master material brought into contact with the heated heater elements are perforated and become ink-permeable and form picture elements.
In the digital stencil printer, gradation is controlled by controlling the density of the dots (picture elements). Accordingly, in a low density region, grain coarseness appears in the image due to a low dot density. Further since it is hard to uniform the size and shape of the dots, rough impression appears in a low density region and an intermediate density region.
As a method of printing a high quality black-and-white image, there has been a method known as double-tone printing. In the double-tone printing, two kinds of stencil masters are made on the basis of an original and printing is effected by use of the stencil masters with light color ink and dark color ink which are similar in hue. The light color ink is generally gray ink and the dark color ink is generally black ink. In this system, to faithfully reproduce the gradation of the original is important, and gradation of an intermediate density region to a high density region which has been hard to reproduce in conventional black-and-white printing can be expressed and depth of an image can be obtained. (See, for instance, “All of Scanner”: Nihon Gijutsu Insatu Kyoukai, from P78 on.) It is expected that when the technique of double-tone printing is applied to the digital stencil printing, appearance of grain coarseness in a low density region and appearance of rough impression in an intermediate density region can be suppressed.
As methods of making two kinds of stencil masters in the double-tone printing, there have been known those in which a plate making camera or a scanner is used and the two kinds of stencil masters are made by use of different tone curves.
However, since the two different tone curves are empirically set by a printer operator, the steps of making stencil masters and trial printing must be repeated until a desired density of the image is obtained.
To the contrast, there are methods in which the density obtained when the light color ink image and the dark color ink image are overlapped is theoretically obtained without actually effecting printing. For example, there has been known a method in which Neugebauer equation (Neugebauer, H. E.: Z. wiss. Phot., 34(4)(1937), p.73), an equation obtained by combining the proportions of areas of the respective color inks with mean additive blending, is used and the print density for given proportions of areas of the respective color inks is obtained.
However, in this method, there are enormous number of combinations of proportions of the color ink areas for a given print density. Accordingly, it is impossible to determine the tone curves for the respective inks on the basis of a target print density by use of Neugebauer equation. That is, there are many solutions for the equation unless one of the tone curves is determined.
Accordingly, conventionally, the proportion of the area of gray ink ag and the proportion of the area of black ink ak are related to each other to satisfy the following formula (1)
ag=K·ak
(1)
wherein K represents a value depending on a target reflectance, so that only one solution is obtained.
When the technique of the known double-tone printing is applied to the digital stencil printing as it is, the advantages of the stencil printing that the printing speed is high and printing cost is low are sacrificed due to the fact that the steps of making stencil masters and trial printing must be repeated though the quality of the printed matter is improved.
When the aforesaid formula (1) is used, the problem of the printing time and the printing cost is overcome to some extent. However this approach is disadvantageous in that since both the light color ink (gray ink) and the dark color ink (black ink) must be constantly used according to the formula (1), black ink must be included in a predetermined proportion of area even in a low density region and accordingly the picture element density is still low in such a low density region, whereby grain coarseness cannot be sufficiently removed.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a double-tone printer in which a print density suitable for suppressing appearance of grain coarseness in a low density region and appearance of rough impression in an intermediate density region can be quickly determined without repetition of trial printings and a high quality printing can be easily effected.
Another object of the present invention is to provide a method of making density correction curves for double-tone printing rationally in a routinized manner.
In accordance with a first aspect of the present invention, there is provided a double-tone printer comprising, as shown in
FIG. 1
, an image input means which inputs an image signal made up of a series of image signal components each representing a picture element on an original,
a stencil master making signal producing means which converts the image signal into a density signal made up of a series of density signal components each representing a print density of a picture element according to a density correction curve for a light color and makes a stencil master making signal for the light color by binary-coding the density signal components and which converts the image signal into a density signal made up of a series of density signal components each representing a print density of a picture element according to a density correction curve for a dark color and makes a stencil master making signal for the dark color by binary-coding the density signal components,
a stencil master making means which makes a light color stencil master and a dark color stencil master respectively on the basis of the stencil master making signal for the light color and the stencil master making signal for the dark color, and
a printing means which prints the images of the respective stencil masters on a printing paper in light color ink and dark color ink so that the printed images in the respective color inks overlap each other,
wherein the improvement comprises that
the density correction curve for the light color gives a print density which increases with increase in the value of the image signal component in a lower range where the values of the image signal components are lower than a threshold value and is fixed at a maximum value in a higher range where the values of the image signal components are not lower than the threshold value, and
the density correction curve for the dark color gives a print density which is fixed at a minimum value in the lower range and increases with increase in the value of the image signal component in the higher range.
In the printer with this arrangement, out of the image obtained from the stencil master making signal for the light color, the region which can be expressed by the light color ink is printed solely in the light color ink and the region which cannot be expressed solely by the light color ink is printed in both the light color ink and the dark color ink.
Further when the den
Hashimoto Koichi
Sato Hisako
Brinich Stephen
Lee Thomas D.
Peabody LLP Nixon
Riso Kagaku Corporation
Studebaker Donald R.
LandOfFree
Double-tone printer and method of making density correction... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Double-tone printer and method of making density correction..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Double-tone printer and method of making density correction... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2982157