Image analysis – Color image processing
Reexamination Certificate
1999-03-04
2003-01-07
Grant, II, Jerome (Department: 2624)
Image analysis
Color image processing
C382S167000, C358S500000
Reexamination Certificate
active
06504950
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a terminal that has a keyboard and a display for a user to communicate with a data processing system or the like, and that adjusts the color reproduction of the screen of a display device.
The invention also relates to an input/output characteristic measurement method and an input/output characteristic calculation apparatus for obtaining the input/output characteristics, i.e., the electro-optical conversion characteristics, of a display such as a CRT display device or a liquid crystal display device.
The invention further relates to a display profile creation method and display profile creation apparatus for creating a profile relating to the color appearance of the display device.
Furthermore, the invention relates to a display calibration method and calibration apparatus that enable adjustments relating to the profile, etc. of the display device to be made in a simple manner.
The present invention further relates to a recording medium recording a program that may advantageously be used, for example, when adjusting the color appearance, etc. of a screen or when calculating the input/output characteristics of a display.
2. Description of the Related Art
With increasing prevalence of high-performance personal computers (hereinafter, personal computers may also be referred to as PCs) and the decreasing prices of image input devices such as scanners and image output devices such as color printers, the opportunities for individuals to handle color images are increasing. However, as more individuals have come to handle color images, color reproducibility is becoming a problem. That is, the problem concerns the difficulty in color matching between an original image and an image produced on a display, or between an original image and an image printed by a printer, or further between an image produced on a display and an image printed by a printer. Such a problem arises because color characteristics such as a color producing mechanism and a color gamut differ between different input/output devices.
A color management system (hereinafter sometimes referred to as the CMS) is a technique for matching color appearance between different input/output devices such as displays, scanners, color printers, etc. Using the CMS, it becomes possible to match color appearance between an image read by a scanner and an image displayed on a display and also between such an image and an image output by a color printer, and an image processing system can be constructed that does not give the user the feeling of unnaturalness about the color appearances of the various images output from different input/output devices.
In recent years, it has become common to incorporate a CMS framework at the OS level, such as ICM (Image Color Matching) 1.0 in Windows 95 and ColorSync 2.0 in the Macintosh environment. Manufacturers of input/output devices provide users with device profiles conforming to ICM 1.0 or ColorSync 2.0 so that the users can view color images without unnatural differences in color between images produced by different image output devices, for example, an image produced on a display and an image printed by a printer.
Device profiles for ICM 1.0 and ColorSync 2.0 conform to the ICC profiles proposed by the International Color Consortium (ICC). With manufacturers of input/output devices providing device profiles conforming to the ICC Profile Specification, users, in the Windows environment and the Macintosh environment alike, can obtain images free from unnaturalness in color appearance and can use various input/output devices without having to worry about differences in color appearance.
When using a CMS in a computing environment today, the ICC profiles are generally used as information holding the characteristics of input/output devices.
FIG. 51
conceptually shows the format of an ICC profile Ip.
FIG. 52
shows dump data in hexadecimal to illustrate the format of the ICC profile Ip in a specific example.
As shown in
FIGS. 51 and 52
, the ICC profile Ip consists of a fixed length 128-byte profile header Ph containing information on the profile itself and information on the target device (input/output device), a variable length tag table Tt indicating what information is stored where, and tag element data Ted of variable length containing actual information.
In the ICC profile Ip, each necessary data element is described within the tag table Tt using a 12-byte tag consisting of a 4-byte signature tag Ta, a 4-byte storage address tag Tb, and a 4-byte size tag Tc indicating the size of the data element. A 4-byte tag count tag Tn at the head of the tag table Tt contains a count of the number of tags, (n), in the tag table itself. It is therefore seen that the total number of bytes in the tag table Tt is given by 4+12n bytes. In the example of
FIG. 52
, the tag count n is 4 (that is, 00000004h (h indicating hexadecimal notation)).
To describe in further detail the contents of the first 12-byte tag labeled profileDescriptionTag PDT (see
FIG. 52
) following the 4-byte tag count tag Tn in the tag table Tt, the first four bytes (6465 7363) as the signature tag Ta indicate information (name) unique to the profile, and the next four bytes (0000 00b4) as the storage address tag Tb represent the starting address (row b and column 4) in the tag element data Ted. The last four bytes (0000 0074) as the size tag Tc show that the data size is 74h=116. The tag element data Ted having the size of 74h is also a Profile Description Tag PDT and contains information (name, etc.) unique to the profile.
The tag element data Ted specified by the next 12-byte tag labeled mediaWhitePointTag (also referred to as wtptTag) wtpt contains CIEXYZ values of white (w). The tag element data Ted specified by the next 12-byte tag labeled redColorantTag (also referred to as rXYZTag) rXYZ contains normalized CIEXYZ values of red (r). The last 12-byte tag labeled redTRCTag (also referred to as rTRCTag) rTRC stores input/output characteristic values of red (r); in the example of
FIG. 52
, values of 16 points are stored in the last 32 bytes (two bytes for each point). In the CCC profile Ip, the stored CIEXYZ values are normalized with respect to the standard illuminant of D50.
FIG. 53
shows the color gamut of a display, such as a CRT display, plotted on an u′, v′ chromaticity diagram. In
FIG. 53
, the horseshoe-shaped region containing the triangle bounding the range of reproducible colors (color gamut) indicates the limits of chromaticities distinguishable by the human eye.
FIG. 54
shows an example of CIEXYZ measurements. Further,
FIG. 55
shows an example of the gamma characteristic (electro-optical conversion characteristic) as an input/output characteristic of a display.
In the case of a display, if the CIEXYZ values (see
FIG. 54
) when the primary colors R, G, and B are at their maximum values (Rmax, Gmax, and Bmax), as shown in
FIG. 53
, and the input/output characteristic for each of the R, G, and B colors, such as shown in
FIG. 55
, are known, then a gamma coefficient value can be calculated using the gamma coefficient calculation formula (IEC 1966-3) shown in equation (1) below defined by the International Electrotechnical Commission (IEC), and the display characteristics of the display can be determined using equations (2) to (5) below which are known linear conversion equations. Here, the CIEXYZ values of the R, G, and B colors define the range of reproducible colors (color gamut), and the input/output characteristic of the display is represented by the gamma characteristic.
γ
=
1
D
(
n
∑
i
=
1
n
P
i
q
i
-
∑
i
=
1
n
P
i
∑
n
=
1
n
q
i
)
(
1
)
where
P
i
=log
10
x
i
(x
i
=input voltage)
q
i
=log
10
y
i
(y
i
=display luminance)
D
=
n
∑
i
=
1
n
P
i
2
-
(
∑
i
=
1
n
q
i
)
2
In equation (1), x
i
represents the value of input voltage and y
i
the value of displayed luminance.
x=X/
(
X+Y+Z
)&ems
Mori Masahiro
Murashita Kimitaka
Suzuki Shoji
Fujitsu Limited
Grant II Jerome
Staas & Halsey , LLP
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