Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
1999-05-21
2002-05-14
Luu, Matthew (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C345S589000, C345S591000, C345S600000, C382S166000, C382S167000, C358S519000, C358S520000
Reexamination Certificate
active
06388674
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gamut mapping method usable when a color reproduction range (referred to as “color gamut” hereinunder) of an output system is different from that of an input system suitable for use to reproduce by an electronic device of one kind of a color picture data supplied from an electronic device of another kind, both the devices included in a picture input/output system such as a desk top publishing (DTP). The gamut mapping method and apparatus are suitably used in hard copying, by a printer having a small color gamut, of a color picture signal supplied from a monitor whose color gamut is large, for example.
2. Description of Related Art
Recently, with electronic devices having remarkably been innovated for lower prices and higher speeds, color desk top publishing (color DTP) network, internet network, and so forth have been prevailing and a variety of electronic devices dealing with color picture signals (referred to simply as “device” hereinunder) has been incorporated in such network systems. Thus, currently, for a printer to print out a color picture signal supplied from a monitor, for example, it is necessary to introduce the so-called device-independent color (DIC) concept that a color picture from a device of one kind is reproduced in a same color also at a device of another kind, both the devices being included in a picture input/output system.
A system to implement a DIC is generally called a “color management system (CMS)”. In the CMS, measured physical values of color signals at an input device are adjusted to those at an output device to implement a DIC. Referring now to
FIG. 1
, there is schematically illustrated the color management system (CMS) by way of example. The CMS comprises devices such as a video camera
61
, monitor
62
, printer
63
, and so forth. In this CMS, since a color signal of an input or output picture is dependent upon each of the devices, it is necessary to adjust measured physical values of a color signal at the video camera
61
or monitor
62
as an input device to those of a color signal at the printer
63
as an output device.
In the CMS shown in
FIG. 1
for example, since a color signal of a picture on the monitor
62
as an input device is an RGB color signal dependent upon the device, an input device profile (monitor profile) created using a predetermined transform formula or table is used to transform the color signal to one independent of the device and further an output device profile (printer profile) is used to transform the device-independent color signal to a one such as CMYK or the like dependent upon the printer
63
as an output device, thereby printing out the picture from the printer
63
, as shown in FIG.
2
.
Namely, when a color signal is transformed to an output color signal in the CMS, a transform formula or table called “device profile (will be referred to simply as “profile” hereinunder as the case may be) is used to transform the input color signal to a color signal in a color space independent of each device (CIE/XYZ, and so forth), thereby implementing the DIC. The “device profile” may be considered as a file of parameter groups calculated based on a relationship between a color signal (RGB, CMYK, and so forth) of a device and a color measured (XYZ, L*a*b*, CIE/L*C*h, and so forth) by a colorimeter or the like.
However, each input/output device is limited in color reproduction range (gamut), namely, in a color gamut. The color gamut varies greatly from one kind of device to another. Therefore, it has been physically difficult to reproduce a completely same color at all of the different kinds of devices, and especially, the difference in color gamut from one to another kind of device has been a great barrier against implementation of the CMS. This will further be described concerning a computer graphic (CG) monitor and an inkjet printer (referred to simply as “printer” hereinunder).
As well known, the CG monitor reproduces a color by the addition mixture of primary colors emitted from three phosphors, red (R), green (G) and blue (B). Therefore, the color gamut of the CG monitor depends upon the kinds of phosphors used in the CG monitor. On the other hand, the printer reproduces a color with inks of cyan (C), magenta (M), yellow (Y) and black (K). The color gamut of the printer varies from one to another kind of ink as well as from one to another type of paper as a picture recording medium and from one to another gradation reproducing method.
FIG. 3
shows the result of a comparison between a color gamut GMmon of the CG monitor and a color gamut GMijp of the printer, each obtained by integration in the direction of L* and plotting in a plane of a*-b*. As seen, the color gamut GMijp of the printer is smaller than the color gamut GMmon of the CG monitor. Especially, the G (green) and B (blue) gamuts are very smaller. As seen from
FIG. 3
, the peak chroma deviates in the direction of lightness also in other areas in which the color gamuts are not so much different. Therefore, when a color displayed on the CG monitor is reproduced by the printer, it is physically different for the printer to reproduce the color in the areas of a high lightness and chroma on the CG monitor.
Thus, when the color gamut of an output device is smaller than that of an input device, all the colors displayed on the input device cannot be reproduced by the output device. Therefore, in such a case, it is necessary to make some operation for compressing the color gamut of the input device into that of the output device. At this time, the color gamut of the input device have to be compressed into that of the output device while maintaining picture information (gradation, tone, and so forth) represented on the input device as much as possible. Namely, the color should be corrected to compress a color outside the color reproduction range (color gamut) into the color gamut while maintaining an input original picture information.
The operation to compress into the color gamut of the output device a color which cannot physically be reproduced is generally called “gamut compression”. Taking in consideration a case that the color gamut of the output device is larger than that of the input device, the operation to transform the color gamut of the input device to that of the output device of a different kind from the input device will be referred to as “gamut mapping”.
Since the color gamut of a printer as an output device is much smaller than that of other input device, the color reproduction depends greatly upon the method of gamut mapping in many cases. The gamut mapping is done in a common color space not dependent upon any device. It is most popular to effect the gamut mapping in a CIE/L*C*h color space matching the human visual characteristics.
The human eyes can perceive three attributes of a color, namely, lightness, chroma and hue. The aforementioned CIE/L*C*h is a color space based on these three attributes of color perceivable by the human eyes. The CIE/L*C*h is a color space derived from an L*a*b* color space by representing the latter in the font of spherical coordinates in which L* indicates the lightness, C* indicates a chroma and h indicates a hue. In the CIE/L*C*h color space, the above three attributes may be handled as independent parameters.
It is generally said that the gamut mapping should preferably be done in a two-dimensional plane of the lightness L* and chroma C* in the CIE/L*C*h space while the hue h is being maintained constant. More particularly, the gamut mapping methods include a chroma compression in which only the chroma C* is compressed while the lightness L* and hue h are being kept constant as shown in
FIG. 4
, a lightness compression in which the lightness L* is compressed in a direction of (L*, a*, b)=(50, 0, 0) while the hue h is being kept constant as shown in
FIG. 5
, and other methods. Further, for a gamut mapping by three-dimensional compression of the lightness, chroma and hue h as well, it has been proposed to weight
Ito Masahiko
Kato Naoya
Kananen, Esq. Ronald P.
Luu Matthew
Rader & Fishman & Grauer, PLLC
Sajous Wesner
Sony Corporation
LandOfFree
Gamut mapping method and apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Gamut mapping method and apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gamut mapping method and apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2849433