Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
1999-08-09
2002-11-12
Razavi, Michael (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C348S179000, C382S167000, C358S518000
Reexamination Certificate
active
06480202
ABSTRACT:
TECHNICAL FIELD
This invention relates to an apparatus and a method for processing images and a system and a method for transmitting and receiving images as well as a providing medium that are particularly adapted to carry out color signal processing operations that may vary as a function of individual image display apparatus in order to coordinate the colors of images to be displayed there so as to eliminate apparatus-dependency of the colors of images.
BACKGROUND ART
As a result of the rapid spread of DTP (desk top publishing) and the Internet in recent years, color images are manipulated more often than ever on the display screens of CRT (cathode ray tube) displays and liquid crystal displays.
For example, operations of drawing pictures by means of painting tools are being replaced by those of drawing computer graphics by means of personal computers. Consumers place orders by seeing images of products displayed on the display screen as electronic advertisements that are transmitted by way of the Internet.
In any of such cases, it is necessary that the colors of the original picture (which may be a picture drawn by an artist or a photographic picture) and those of the facsimile image of the picture output by an apparatus (which may be the monitor screen of a display apparatus or a color printer) agree with each other.
Thus, it is highly desirable that, for a same picture, the image displayed on the display screen of a personal computer and the image output by a printer appear same in terms of their colors.
In the case of an electronic advertisement, if the image of an article (e.g., a jacket or a painting) displayed on the display screen of the personal computer of a consumer appears differently from the actual commodity, a trouble may arise between the commodity provider and the consumer when the consumer buys the commodity.
Thus, it is necessary to provide an arrangement in which a picture appears exactly the same on all the image display apparatus displaying an image of the picture particularly in terms of colors.
A system referred to as CMS (color management system) is known for correcting the differences of colors of images of the same picture among different image display apparatus displaying it.
FIG. 1
of the accompanying drawings schematically illustrate a CMS. Referring to
FIG. 1
, with a CMS, the color signals of a picture input through an input device (e.g., camera
1
, scanner
2
, monitor
3
) are converted into common color space signals (e.g., CIE/XYZ, CIE/L*a*b*) that are not dependent on the characteristics of the device and then output through an output device (e.g., monitor
3
, printer
4
).
A conversion formula or a conversion table that is referred to as “profile” and specific to each device is used when converting a signal into that of a common color space. For examples, the color signals of a picture taken by camera
1
are converted into common color space signals by the profile specific to the camera
1
. To output the signals through monitor
3
, the common color space signals are then converted into color signals that reflect the characteristics of the monitor
3
by the profile specific to the monitor
3
and an image of the picture formed by the obtained color signals will be displayed on the monitor.
Such a profile is determined by means of the signal values input to the device and the color values (XYZ values or L*a*b* values) obtained by observing the colors of the image output according to the signal values typically through a calorimeter.
FIG. 2
of the accompanying drawings a chart showing the flow of data when the image on the monitor
3
is output to printer
4
. Referring to
FIG. 2
, the image on the monitor
10
is converted into signals of a common color space by the profile specific to the monitor
3
(monitor profile
20
). In other words, the image data (RGB data) of the monitor
3
are converted respectively into corresponding quantities of light by means of TRCs (tone reproduction curve, which will be described hereinafter) generated by TRC generator section
20
-
1
. The quantities of light for RGB reflect the colors of the image viewed by the user on the monitor
3
.
The data (on the quantities of light for RGB) generated by the TRC generator section
20
-
1
are then processed for conversion using a matrix representing the linear relationship between the quantities of light output to the monitor
3
and the CIE/XYZ values (or L*a*b* values) to obtain a series of values (CIE/XYZ values or L*a*b* values), which are then output as common color space signals
30
.
The common color space signals
30
obtained by the monitor profile are then processed for conversion by the profile specific to the printer
4
(printer profile
40
) to reflect the printing characteristics of the printer
4
and the obtained color signals for the printer, or CMY
50
, are printed and output.
Apparatus of a same type can show disparity, if slightly, in the characteristics depending on individual apparatus. Then, the profile is preferably calibrated for each apparatus.
The profiles of the monitors marketed by a same manufacturer can be calibrated typically by means of a monitor calibration tool or characterization tool provided by the manufacturer.
The monitor profile
20
is prepared by such a tool.
FIG. 3
of the accompanying drawings is a flow chart of the operation of preparing a monitor profile. Referring to
FIG. 3
, firstly in Step S
1
, TRCs (g-curves) representing the non-linear relationship between the RGB data to be input to the monitor and the quantities of light of RBG of the monitor is prepared. Such TRCs can be obtained by observing the XYZ3-stimulus values of more than ten tones (e.g., 16 tones) sampled at regular intervals from the full range of tones (e.g., 256 tones) for each of the primary colors of red (R), green (G) and blue (B) of the RGB data (or RGBW data) and applying them to the g equation out of equations (1) shown below by non-linear regression (a TRC is obtained by linear interpolation or a conversion table if the number of samples is large).
r
=
X
r
X
r
,
m
a
x
=
{
K
r
,
gain
(
dr
2
N
-
1
)
+
K
r
,
offset
}
γ
r
g
=
Y
g
Y
g
,
m
a
x
=
{
K
g
,
gain
(
d
g
2
N
-
1
)
+
K
g
,
offset
}
γ
g
b
=
Z
b
Z
b
,
m
a
x
=
{
K
b
,
gain
(
db
2
N
-
1
)
+
K
b
,
offset
}
γ
b
(
1
)
In the above equations (1), variables dr, dg and db respectively represent the input signal values for red, green and blue and variable N represent the number of bits of each input signal. Coefficient k
gain
represents the gain of each of the colors (e.g., k
r.gain
represents the gain of red) and coefficient k
offset
represent the offset of each of the colors (e.g., k
r.offset
represents the offset of red). Additionally, variables X
r
, Y
g
and Z
b
respectively represent the 3-stimulus values of the three colors and variable X
r.max
, Y
g.max
and Z
b.max
respectively represent the 3-stimulus values of the three colors when the input signal values are maximal. Thus, variables r, g and b are obtained by normalizing X
r
, Y
g
and Z
b
respectively by the maximum values X
r.max
, Y
g.max
and Z
b.max
to take a value between 0 and 1.
FIG. 4
is a flow chart illustrating the operation of preparing a TRC corresponding to an input digital signal for red in Step S
1
of FIG.
3
. Referring to FIG.
4
, in Step S
21
, XYZ
r
values (including maximum value XYZ
r.max
) are observed for the sampled several tones from the input signal corresponding to red. Then, in Step S
22
, the input signal values dr are normalized by dividing them by 2
N
−1 and, in Step S
23
, the output brightness values are normalized by dividing X
r
values by the maximum value X
r.max
. In Step S
24
, a process of non-linear interpolation is conducted by means of equations (1). Finally, in Step S
25
, the values of coefficients k
r.offset
, k
r.gain
and &ggr;
r
are determined. Note that operations of preparing TRCs corresponding to input
Deguchi Tatsuya
Kato Naoya
Razavi Michael
Savit Glenn F.
Yang Ryan R
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