Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Reexamination Certificate
1996-10-22
2001-10-09
Grant, II, Jerome (Department: 2624)
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
C358S515000
Reexamination Certificate
active
06301017
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image processing apparatus and, more particularly, to an image processing apparatus for improving quality of a multi generation copy.
2. Related Background Art
A digital copying machine is known well as an apparatus for causing a reader to read an original, converting a read image into an electrical signal, and driving a record head or a laser to form an image in accordance with this electrical signal, thereby forming a copy. This digital copying machine has features such as image processing and image editing and has been very popular.
A digital color copying apparatus is superior to an analog color copying apparatus in image quality such as color reproducibility. Because of the possibility of obtaining various types of color copies by utilizing various editing functions, the market in this field is rapidly expanding.
FIG. 2
is a block diagram showing a flow of an image signal in the above digital color copying apparatus.
Referring to
FIG. 2
, a CCD
1
outputs R (red), G (green), and B (blue) signals
2
a
,
2
b
, and
2
c
to a black offset & shading correction circuit
3
. The black offset & shading correction circuit
3
outputs shading-corrected R, G, and B signals
4
a
,
4
b
, and
4
c
to a log conversion circuit
5
. The log conversion circuit
5
outputs C (cyan), M (magenta), and Y (yellow) density signals
6
a
,
6
b
, and
6
c
to a color processing circuit
7
. The color processing circuit
7
outputs color-processed C, M, Y, and Bk (black) signals
8
a
,
8
b
,
8
c
, and
8
d
to a gamma correction circuit
9
. The gamma correction circuit
9
outputs gamma-corrected C, M, Y, and Bk signals
10
a
,
10
b
,
10
c
, and
10
d
to an edge emphasis & smoothing circuit
20
. The edge emphasis & smoothing circuit
20
outputs edge-emphasized and smoothed image signals
21
a
,
21
b
,
21
c
, and
21
d
to record heads
11
a
to
11
d
. The record heads
11
a
to
11
d
serve as cyan, magenta, yellow, and black record heads, respectively.
An original image is read by the CCD
1
and converted into electrical signals. The electrical signals are converted into the digital R, G, and B signals
2
a
,
2
b
, and
2
c
by an A/D converter (not shown). These signals are subjected to black offset processing and shading correction processing for correcting variations in the CCD
1
and an original illumination lamp (not shown) by the black offset & shading correction circuit
3
.
A standard black board and a standard white board (neither is shown) are arranged in an original reader. By using these boards, the above processing operations are performed. More specifically, the standard black board is a black board having an optical density of 2.0, and the standard white board is a white board having an optical density of 0.07. Values A and B obtained upon reading of the black and white boards are stored in units of pixels. A value X obtained upon reading of an original is converted into the following value by the black offset & shading correction circuit:
X
′
=
255
B
-
A
(
X
-
A
)
In this case, each signal is an 8-bit signal which has a maximum value of 255.
The converted R, G, and B signals are logarithmically converted into the C, M, and Y density signals
6
a
,
6
b
, and
6
c
. These signals are subjected to color correction processing in the color processing circuit
7
. Black extraction processing and masking processing are performed in this color correction processing. The black extraction processing is processing for extracting a black component from the C, M, and Y signals to improve reproducibility of black. The masking processing is processing for correcting transmission characteristics of filters within the CCD
1
and reflecting characteristics of inks C, M, Y, and Bk.
If signals input to the color processing circuit
7
are given as C, M, and Y, the black component is extracted by the following calculation in black extraction processing:
Bk
=min(
C, M, Y
)
Subsequently, color correction is performed in the masking processing as follows:
C′=a
11
C+a
12
M+a
13
Y+a
14
Bk
M′=a
21
C+a
22
M+a
23
Y+a
24
Bk
Y′=a
31
C+a
32
M+a
33
Y+a
34
Bk
Bk′=a
41
C+a
42
M+a
43
Y+a
44
Bk
The masking parameters a
11
to a
44
are set to obtain optimal color reproducibility.
The color-corrected signals (
8
a
to
8
d
) are gamma-corrected in the gamma correction circuit
9
. In the gamma correction circuit
9
, gradation characteristics of the heads
11
a
to
11
d
are corrected to obtain a linear relationship between the density signals and the print densities, and at the same time, the C, M, Y, and Bk components are balanced. When the gradation characteristics of the heads are linear, the gamma correction circuit
9
corrects the input C, M, Y, and Bk signals as follows:
C′=a
5
×C
M′=a
6
×M
Y′=a
7
×Y
Bk′=a
8
×Bk
The gamma-corrected signals
10
a
to
10
d
are subjected to edge emphasis and smoothing processing in the edge emphasis & smoothing circuit
20
. The edge emphasis and smoothing circuit
20
performs known edge emphasis and known smoothing processing in the following manner.
FIG. 3
is a detailed block diagram of the edge emphasis & smoothing circuit
20
. The edge emphasis & smoothing circuit
20
comprises a smoothing unit
22
for receiving the gamma-corrected image signal C on line
10
a
and outputting a smoothing signal on line
23
, a subtracter
24
for outputting an edge component signal on line
25
, multipliers
26
,
27
, and
28
for outputting product output signals on lines
29
,
30
, and
31
, respectively and an adder
32
for outputting an output signal C on line
21
a
as an output signal from the edge emphasis & smoothing circuit
20
.
The smoothing unit
22
averages image signals of neighboring pixels of a target pixel and outputs a smoothing signal S. If a smoothing matrix has a size of 3×3 and an image signal of a target pixel position (i,j) is given as f(i,j), the smoothing signal S is calculated as follows:
S
={fraction (1/9)}
{f
(
i−
1
,j
−1)+
f
(
i,j−
1)+
f
(
i
+1
,j
−1)+
f
(
i−
1
,j
)+
f
(
i,j
)+
f
(
i
+1
,j
)+
f
(
i
−1
,j
+1)+
f
(
i,j
+1)+
f
(
i
+1
,j
+1)}
The subtracter
24
subtracts the smoothing signal S from the signal f(i,j) of the target pixel to extract an edge component. An edge component signal E is given as follows:
E=f
(
i,j
)−S
The multipliers
26
,
27
, and
28
multiply the target pixel signal, the smoothing signal, and the edge component signal with predetermined coefficients k
1
to k
3
, respectively. The adder
32
adds the product components from the multipliers
26
,
27
, and
28
and outputs an output signal from the edge emphasis & smoothing circuit
20
.
The component coefficients k
1
, k
2
, and k
3
are determined by spatial frequency characteristics and the design concept of the copying machine. For example, when the spatial frequency characteristics of the copying machine are poor and a thin line is blurred, the smoothing signal coefficient k
2
is set to zero, and the edge component signal coefficient k
3
is increased. In order to emphasize a character original and a thin portion with good reproducibility, similar changes are performed. In order to emphasize a picture or the like of a print to obtain a good halftone image without forming a moire pattern, the coefficient k
3
is set to be small, and the coefficient k
2
is increased.
In this case, k
1
+k
2
is kept constant because the sum k
1
+k
2
represents the magnitude of the signal. If this sum is changed, an image density is changed.
The edge emphasis and the smoothing processing are performed for the remaining color signals, i.e., M, Y, and Bk by using common coefficients. The record heads
11
a
to
11
d
are driven
Suzuki Akio
Takada Yoshihiro
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Grant II Jerome
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