Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-09-21
2001-05-01
Lee, Thomas D. (Department: 2724)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S451000, C358S451000, C358S296000, C382S237000
Reexamination Certificate
active
06226104
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique of recording a halftone image utilizing tone reproduction at each pixel.
2. Description of the Related Art
In the conventional technique of recording a halftone image, each recording pixel is recorded in a binary on/off state, and the density of an image is reproduced by a halftone dot percent (a ratio of the ON pixels). The number of tone levels reproducible by one halftone dot increases with the number of recording pixels included in the halftone dot.
In order to increase the number of tone levels reproducible by one halftone dot in the conventional technique, it is required to enhance the resolution of recording pixels, that is, to reduce the size of the recording pixels to increase the number of pixels within one halftone dot. In some recording apparatuses, however, it is difficult to enhance the resolution of recording pixels. A technique that increases the number of tone levels reproducible by one halftone dot without enhancing the resolution of recording dot has been desired.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to increase the number of tone levels reproducible by one halftone dot without enhancing the resolution of recording pixels.
The above and other objects of the present invention are attained at least partly by a method of recording a halftone image utilizing tone reproduction of each pixel. The method comprises the steps of: (a) providing a threshold pattern having threshold values that are assigned respectively to divisions of a unit block including a plurality of pixels, the divisions being obtained by dividing each pixel into M pieces, where M is an integer of at least 2; (b) comparing a given multi-tone image signal with the threshold values in the threshold pattern to thereby generate an image recording signal, the image recording signal representing tone levels of at least 3 for each pixel, the multi-tone image signal having a common value for the M divisions of the same pixel; and (c) recording each pixel in response to the image recording signal, thereby producing a halftone image. The step (b) comprises the step of: (i) comparing the threshold values assigned to the M divisions of each pixel with the multi-tone image signal to obtain M pieces of binary comparison results, and generating the image recording signal as a function of a sum of the M pieces of binary comparison results.
Since each pixel can be recorded by at least three tone levels, the method of the present invention effectively increases the number of tone levels reproducible by one halftone dot, compared with the conventional technique that records each recording pixel in a binary on/off state,.
In a preferred embodiment, each pixel is reproducible at (N+1) density levels in an image output device, where N is an integer in the range of 2 to M, wherein each value of the sum ranging from 0 to M is related to one of the (N+1) density levels, and wherein the step (i) comprises the step of converting the sum into the image recording signal representing one of the reproducible density levels for each pixel. The (N+1) reproducible density levels can be related to (N+1) pixel tone levels which are defined to be area rates obtained by converting the (N+1) reproducible density levels into equivalent area rates of recorded portion of one pixel, and wherein the integer M is selected such that values of the (N+1) pixel tone levels are substantially equal to values of m(j)/M, respectively, where j is an integer ranging from 0 to N and where m(j) are (N+1) pieces of different integers in the range of 0 to M.
Even when the reproducible density levels of the pixels are restricted to the (N+1) levels, this arrangement takes advantage of the restricted density levels and increases the tone levels of the halftone dots.
The step (c) may comprise the step of reproducing a density level of each pixel by overlaying ink droplets where volume of the ink droplets is controlled by the image recording signal. Alternatively, the step (c) may comprise the step of reproducing a density level of each pixel by exposing a recording medium with light where quantity of the light is controlled by the image recording signal.
The present invention is also directed to an apparatus for recording a halftone image utilizing tone reproduction of each pixel. The apparatus comprises: a threshold pattern memory which stores a threshold pattern having threshold values that are assigned respectively to divisions of a unit block including a plurality of pixels, the divisions being obtained by dividing each pixel into M pieces, where M is an integer of at least 2; an image recording signal generator which compares a given multi-tone image signal with the threshold values in the threshold pattern to thereby generate an image recording signal, the image recording signal representing tone levels of at least 3 for each pixel, the multi-tone image signal having a common value for the M divisions of the same pixel; and a recording unit which records each pixel in response to the image recording signal, thereby producing a halftone image. The image recording signal generator comprises a first unit which compares the threshold values assigned to the M divisions of each pixel with the multi-tone image signal to obtain M pieces of binary comparison results, and generates the image recording signal as a function of a sum of the M pieces of binary comparison results.
The present invention is further directed to a method of generating an image recording signal to record a halftone image with an image recording device that is capable of reproducing at least three density levels at each pixel. The method comprises the steps of: (a) providing a threshold pattern having threshold values that are assigned respectively to divisions of a unit block including a plurality of pixels, the divisions being obtained by dividing each pixel into M pieces, where M is an integer of at least 2; and (b) comparing a given multi-tone image signal with the threshold values in the threshold pattern to thereby generate an image recording signal, the image recording signal representing tone levels of at least 3 for each pixel, the multi-tone image signal having a common value for the M divisions of the same pixel.
The present invention is still further directed to an apparatus for generating an image recording signal to record a halftone image with an image recording device that is capable of reproducing at least three density levels at each pixel. The apparatus comprises: a threshold pattern memory which stores a threshold pattern having threshold values that are assigned respectively to divisions of a unit block including a plurality of pixels, the divisions being obtained by dividing each pixel into M pieces, where M is an integer of at least 2; and an image recording signal generator which compares a given multi-tone image signal with the threshold values in the threshold pattern to thereby generate an image recording signal, the image recording signal representing tone levels of at least 3 for each pixel, the multi-tone image signal having a common value for the M divisions of the same pixel.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.
REFERENCES:
patent: 5237650 (1993-08-01), Priem et al.
patent: 5361084 (1994-11-01), Paton et al.
patent: 5712711 (1998-01-01), Suzuki
patent: 61-189774 (1986-08-01), None
patent: 2-49592 (1990-10-01), None
patent: 7-57104 (1995-03-01), None
Hirawa Takahide
Shiomi Junichi
Dainippon Screen Mfg. Co,. Ltd.
Lee Thomas D.
McDermott & Will & Emery
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