Image analysis – Color image processing
Reexamination Certificate
1999-10-20
2003-05-06
Patel, Jayanti K. (Department: 2625)
Image analysis
Color image processing
C382S166000, C382S167000, C358S519000, C358S521000, C345S590000
Reexamination Certificate
active
06560356
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a color gamut compression device and method therefor which is applied to color inside a color gamut of an information-input apparatus. The color gamut compression device compresses the color gamut by converting color outside a color gamut due to an information-output apparatus into color inside a color gamut due to an information-output apparatus.
BACKGROUND OF THE INVENTION
Information apparatus such as displays, printers and scanners which process color image data have a range of color which may be input or output which is characteristic to that information apparatus. That is to say, such apparatus have a color gamut. A color gamut in information-output apparatus such as displays and printers may contain a color gamut of an information-input apparatus such as a scanner or a display. In such a case, it is possible to express the color of the image from the information-input apparatus without change in the information-output apparatus. However when a section of a color gamut in an information-output apparatus is not contained in the color gamut of an information-input apparatus, a source color inside a color gamut in the information-input apparatus can not be expressed by color outside the color gamut in the information-output apparatus without change by the information-output apparatus. Thus color which is outside the color gamut of the information-output apparatus is output after conversion to a color inside a color gamut of the information-output apparatus. That is to say, when a color gamut of an information-output apparatus is not coextensive with a color gamut of an information-input apparatus, color gamut compression processing is required.
FIG. 1
to
FIG. 4
explain a conventional color gamut compression method such as disclosed for example in JP-A-9-98298.
The color gamut compression method shown in
FIG. 1
is a saturation method. In a saturation method, with respect to color inside a color gamut of an information-input apparatus, color which is outside the color gamut of the information-output apparatus is converted to color inside a color gamut of the information-output apparatus by converting only saturation and without converting the brightness.
The color gamut compression method shown in
FIG. 2
is a brightness compression method. In a brightness compression method, with respect to color inside a color gamut of an information-input apparatus, source color which is outside the color gamut of the information-output apparatus is converted to a target color inside a color gamut of the information-output apparatus by converting only brightness and without converting saturation. When a color with the same saturation as the color in the information-input apparatus is not present in the color gamut of the information-output apparatus, that is to say, when the source color of the information-input apparatus is positioned in the section of the curved line in the figure, the source color of the information-input apparatus is converted to the same fixed color of the information-output apparatus.
The color gamut compression method shown in
FIG. 3
is a color difference minimization method. In a color difference minimization method, color outside the color gamut of the information-output apparatus with respect to a color inside a color gamut of an information-input apparatus is converted to a color with the smallest color difference from the color in the information-input device. Thus color in the information-input device on the curved line in the figure is all converted to the same color.
Color gamut compression processing can be performed by use of the above method. However it is possible that if employed in a saturation compression method. The tonal range in the high saturation regions will be improved to an extent, the overall effect will be an image without color definition. Although there is almost no reduction of saturation in a brightness compression method. The color in high brightness regions is converted to low brightness color and the color in low brightness region is converted to high brightness color. Thus brightness after conversion increases with increases in saturation. Furthermore since color conversion is executed in a color difference minimization method in order to minimize color differences, an image which is comparatively close to the image of the information-input apparatus is obtained by the information-output apparatus. However the section on the curved line in
FIG. 3
is converted to the same color.
In this way, when using color conversion in the above method, there is a possibility that an unnatural image will be output by the information-output apparatus. A conventional color gamut compression method is proposed for example in JP-A-9-98298 as shown in FIG.
4
. In this color gamut compression method, a boundary is formed by a first straight line and a second straight line. The first straight line passes through a first fixed point which has a maximum L_th brightness of a color which has a maximum saturation C_max in a color gamut of an information output device and a second point on a non-saturated axis and which has a minimum brightness L_min in an information output device. The second straight line is formed by a line passing through the first point and a third point on a non-saturated axis and which has a maximum brightness L_max in an information output device. A color gamut outside the information output device with respect to the color gamut of the information input device is divided into low brightness regions
42
and high saturation regions
43
. Color in the high brightness region
41
is compressed towards the second point. Color in the low brightness region
42
is compressed towards the third point and color in the high saturation region
43
is compressed towards the first point.
With respect to the color gamut of the information-input apparatus, regions outside the color gamut of the information-output apparatus are divided into a high brightness region
41
, a low brightness region
42
and a high saturation region
43
. The color of the high brightness region
41
is compressed towards the second point, the color of the low brightness region
42
is compressed towards the third point and the color of the high saturation region
43
is compressed towards the first point.
Apart from the above method, a device for executing color gamut compression processing is proposed in JP-A-7-236069 and JP-A-9-130622 and a device for executing image processing is proposed in JP-A-7-21356.
However as the conventional color gamut compression method is arranged as discussed above it is necessary to determine, with respect to color inside a color gamut of the information-input apparatus whether color outside the color gamut of the information-output apparatus is positioned in any of the high brightness region
41
, the low brightness region
42
or the high saturation region
43
and whether to convert such color into color in a compression direction which depends on the region. Therefore the problem has arisen that such a calculation for such a conversion is complicated. Furthermore the problem has arisen that viewpoint of the image after conversion is altered in response to the position of the first point discussed above.
The present invention is proposed to solve the above problems and has the object of providing a color gamut compression device and color gamut compression method which executes the color gamut compression processing by converting source color of an information-input apparatus to a target color inside a color gamut of the information-output apparatus while maintaining the continuity of the color. The conversion is performed by a simple calculation which does not entail a determination of the region in which the color of the information-input apparatus is positioned. Such regions originate in the division of regions outside the color gamut of the information-output apparatus. Color in the information-input apparatus which is not in the color gamut of the information-output
Saito Masayuki
Sato Tsuneo
Takahashi Mariko
Bayat Ali
Birch & Stewart Kolasch & Birch, LLP
Mitsubishi Denki & Kabushiki Kaisha
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