Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
2000-01-20
2002-08-20
Razavi, Michael (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C345S590000, C345S601000, C345S603000
Reexamination Certificate
active
06437792
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image processing apparatus and method, adapted to reduce, when the color gamut of an output device is different from that of an input device, the color gamut of a color signal outside the output device color gamut to provide a color near to that in the input device. Also, the present invention relates to a color gamut conversion creating apparatus and method, adapted to create a color gamut conversion table for use to reduce a color gamut. Also, the present invention relates to a recording medium having recorded therein an image processing program in accordance with which a color gamut is reduced. Also, the present invention relates to a recording medium having recorded therein an color gamut conversion table creating program in accordance with which a color gamut conversion table for use to reduce a color gamut is created.
2. Description of the Related Art
These days, devices dealing with color image data are provided at lower and lower prices while their processing speeds have been higher and higher. In these situations, there has rapidly been in common use a variety of systems dealing with color images such as systems for transmitting and receiving color image data via networks such as Internet and the like, color desktop publishing systems for editing data including color images, etc.
There have been proposed various types of devices dealing with color images. However, many of them differ in color gamut they can cover (range of color reproduction) from one to another. Simple transfer of a color image between such devices of different types will result in reproduction of the color image in different colors from the original ones. Suppose for example that an image displayed on a monitor is printed out as a hard copy by a printer. In this case, if a color gamut the monitor covers is different from a one the printer covers, the color of an image printed out as a hard copy by the printer will be different from that of the image displayed on the monitor as the case may be.
As various systems dealing with color images have become popular, it has been demanded to attain a so-called device-independent color concept intended to reproduce a color image in the same colors at different types of devices included in the systems. The system to implement the device-independent color is generally called “color management system”. As typical examples of this color management system, there are already available Colorsync included in Mac OS, ICM in Windows 98 and the like.
Referring now to
FIG. 1
, there is schematically illustrated the concept of the color management system in which physical colorimetric values of color signals in input and output devices are combined to implement a device-independent color. More particularly, as shown in
FIG. 1
, a color signal from an input device (such as video camera
61
, scanner
62
, monitor
63
or the like) is converted to a color signal in a device-independent color space (CIE/XYZ, CIE/L*a*b* or the like) on the basis of a device profile in which a color gamut conversion formula or color gamut conversion table is defined for each of the input devices. For an output device (monitor
63
, printer
64
or the like) to output the color signal, the latter is converted to a color signal in a color space corresponding to the device on the basis of a device profile in which a color gamut conversion formula or color gamut conversion table is defined for each of the output devices.
Thus in the color management system, for conversion of an input device color signal to an output device color signal, a device-independent color is implemented by converting once the input device color signal to a color signal in a device-independent color space on the basis of a device profile. The “device profile” is a file in which a color gamut conversion formula or color gamut conversion table is defined. In other words, it is a file having stored therein a group of parameters calculated from relations between device color signals (RGB, CMYK or the like) and chromatic values (XYZ, L*a*b* or the like) measured by a colorimeter or the like.
Even if the color management system is applied, however, it is physically impossible for all the devices to reproduce the completely same because each of the devices has only a limited color gamut (range of color reproduction) which greatly differs from one device to another. That is to say, such differences in color gamut between all the devices are a barrier against implementation of the color management system.
The above difference in color gamut will further be described herebelow concerning a CRT monitor and printer. Normally, the CRT monitor reproduces a color by additive mixture of three color stimuli, namely, red (R), green (G) and blue (B), emitted from their respective phosphors on a face plate. Thus, the color gamut of the CRT monitor depends upon the types of the phosphors used on the face plate. On the other hand, the printer uses three color inks, namely, cyan (C), magenta (M) and yellow (Y) (or four color inks including black (K) in addition to the three color inks) to reproduce a color. That is, the color gamut of the printer depends upon the types of inks used therein. Further, the printer color gamut varies depending upon the type of a paper as an image recording medium, the gradation reproducing method, etc.
FIG. 2
shows a typical color gamut of CRT monitor and a typical color gamut of printer, integrated in the direction of L* and plotted in a plane a*-b*. Normally, the CRT monitor and printer color gamuts are different from each other as shown in FIG.
2
. As seen from
FIG. 2
, the color gamut of the printer color is generally smaller than that of the CRT monitor, and especially in the green and blue color gamuts, the printer color gamut is extremely smaller than the CRT monitor color gamut.
FIG. 3
shows the typical color gamut of CRT monitor and that of printer, plotted in a plane C*-L*. Since the peak of the chroma C* in the CRT monitor color gamut is away from that of the chroma C* in the printer color gamut in the direction of lightness L* as shown in
FIG. 3
, it is physically impossible for the printer to reproduce a color in an area of a high lightness and chroma displayed on the CRT monitor even in the domain of a hue in which there is not so large a difference between the CRT monitor and printer as in FIG.
2
.
If the output device color gamut is smaller than the input device color gamut as in the above, the output device cannot reproduce all colors at the input device and the colors have to be processed in such a manner that they fall within the output device color gamut. For this purpose, all the colors have to be processed to fall within the output device color gamut while image information (gradation, tint, etc.) presented at the input device are being maintained. This process is generally called “color gamut reduction”. Especially, many printers are rather narrower in color gamut than other devices. So, for a printer to print out an, the color reproducibility often depends upon which color gamut reduction technique is employed.
It is most common that a color gamut is reduced in a common color space independent of any device, especially in a color space suitable for human visual sensation (for example, CIE/L*C*h color space). More particularly, a color gamut may be reduced after an input color signal is converted to a device-independent color signal as shown in FIG.
4
. Otherwise, as shown in
FIG. 5
, when a device profile is created, a color gamut conversion formula or a color gamut conversion table may be defined taking also a color gamut reduction in consideration, and a color gamut reduction may be effected simultaneously with converting a color signal on the basis of the device profile.
Next, the color gamut reduction will further be described below:
The human color vision has three attributes including a lightness, chroma and hue. Generally, the color gamut reduction is effected in a color space based on t
Ito Masahiko
Kato Naoya
Frommer Willia S.
Frommer & Lawrence & Haug LLP
Havan Thu-Thao
Razavi Michael
Sony Corporation
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