Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1999-12-22
2004-06-08
Lee, Thomas D. (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S003200
Reexamination Certificate
active
06747759
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to density control.
2. Related Background Art
FIG. 9
is a sectional view showing the structure of a multicolor image forming apparatus. This prior art will be described below with reference to FIG.
9
.
Latent images of different colors formed on an image carrier
100
by an internal semiconductor laser
204
of an optical unit
101
are developed into visual images by color toners of Y (yellow), M (magenta), C (cyan), and K (black) supplied from color developing devices Dy, Dm, and Dc, and Dk. These developed images are transferred onto the outer surface of a transfer belt
102
a plurality of times of rotation to form a multicolor image. That is, a high voltage is applied to the transfer belt
102
to transfer the toners onto the transfer belt
102
.
A recording sheet
105
supplied from a paper supply unit
103
or a paper supply tray
104
is conveyed through a paper conveyance path, and the multicolor image is again transferred from the transfer belt
102
onto this recording sheet
105
. After that, the recording sheet
105
is conveyed by conveyor rollers
106
, fixed by a fixing unit
107
, and delivered to a paper delivery tray
108
or a paper delivery unit
109
.
Each color developing device has rotary support shafts on its two ends and is held in a developing device mechanism
110
so as to be rotatable on these rotary support shafts. The developing device mechanism
110
performs rotation control to select one of these color developing devices.
A cleaning unit
111
removes toner from the surface of the transfer belt
102
. A waste toner unit
112
contains waste toner from the image carrier
100
. A density sensor
113
senses the density of a toner image.
FIG. 10
is a block diagram showing an image data processing system of the multicolor image forming apparatus shown in FIG.
10
.
A &ggr;-conversion table
201
performs &ggr; conversion for image data VIN[
7
..
0
]. A dither conversion table
202
performs dither processing for this image data VIN[
7
..
0
]. A PWM circuit
208
modulates the pulse width of the image data VIN[
7
..
0
], thereby turning on and off the semiconductor laser
204
and printing the data.
The dither conversion table
202
expresses a gradation image by using a density matrix which is a set of a plurality of multilevel image dots. This dither conversion table
202
is composed of, e.g., an SRAM which converts the image data VIN[
7
..
0
] on the basis of dither matrix position information from a sub-scanning counter
205
and a main-scanning counter
206
.
FIG. 11
is a view for explaining the way the dither conversion table
202
performs dither conversion. That is,
FIG. 11
shows the relationship between the image data VIN[
7
..
0
], a conversion output VB[
7
..
0
] from the dither conversion table
202
, and a print example obtained by pulse width modulation by the PWM circuit
203
.
Even when a plurality of pixels collectively express the density, the relationship between the image data and the actual printing density is nonlinear, as shown in FIG.
12
A. Hence, as shown in
FIG. 12B
, a halftone correction curve is derived by calculations to linearly correct the characteristic curve. This is the &ggr; conversion by the &ggr;-conversion table
201
. As an example, the &ggr;-conversion table
201
is so set as to perform data conversion as shown in FIG.
13
. This data conversion improves the linearity of the gradation of an image.
In the above prior art, to perform correction as shown in
FIG. 12B
, the &ggr;-conversion table
201
is set as shown in
FIG. 13
to perform data conversion, thereby performing halftone density correction.
Referring to
FIG. 13
, however, when VIN[
7
..
0
] is 80h to 84h, the conversion output VB[
7
..
0
] has the same value 72h. As is evident from this fact, data conversion (8 bits/8 bits conversion) is done by the image data bit width, so bit missing takes place. This reduces the number of gradation and forms a pseudo contour in a printed image.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to be able to obtain a high-quality halftone image by preventing bit missing when &ggr; conversion for dither matrix conversion is performed.
To achieve the above object, there is provided an image processing apparatus comprising a gradation converting unit for executing a gradation conversion process for input image data, and a dither converting unit for converting the gradation conversion processed image data into a plurality of image data by using a dither matrix, wherein the gradation conversion processed image data has the number of conversion errors due to the gradation conversion smaller than the number of gradation expressible by the dither matrix.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.
REFERENCES:
patent: 4858023 (1989-08-01), Tada
patent: 5374996 (1994-12-01), Eguchi et al.
patent: 5469267 (1995-11-01), Wang
patent: 5550647 (1996-08-01), Koike
patent: 5732151 (1998-03-01), Moon et al.
patent: 5854882 (1998-12-01), Wang
patent: 6014462 (2000-01-01), Yamakawa
Brinich Stephen
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Lee Thomas D.
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