Color converting device

Details Color converting device Color converting device

1999-12-03

2002-10-01

Luu, Matthew (Department: 2672)

Computer graphics processing and selective visual display system

Computer graphics processing

Attributes

C345S606000

Reexamination Certificate

active

06459437

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color converting device that converts a pixel value represented in a predetermined color space into a pixel value represented in a different color space and outputs the converted pixel value.
2. Description of the Related Arts
There is a device that converts an input pixel value represented in a predetermined color space into a pixel value represented in a different color space and outputs the converted pixel value as an output pixel value. The color space in which the input pixel value is represented is referred to as an input color space and the color space in which the output pixel value is represented is referred to as an output color space hereinbelow. There have been various devices adopting various methods for converting a pixel value.
For example, there is a device that an input color space represented by RGB is converted into an output color space represented by YCbCr, as is well known as a television set. The color space processing from RGB into YCbCr can be represented by a simple conversion equation of Y=0.6G+0.3R+0.1B, Cb=Y−B, Cr=Y−R. Accordingly, a color converting device from RGB into YCbCr can be realized by an arithmetical device that processes the conversion equation.
However, there is a case where a complicate conversion process from the input color space into the output color space cannot be represented by a simple conversion equation. Example of such a case is the one for converting RGB inputted by a scanner into YMC of a printing device. The RGB is a color space according to spectrum characteristics of an optical sensor of the scanner, while the YMC is a color space according to spectrum characteristics of ink of the printing device or tone characteristics of a mesh point, so that the relationship between RGB and YMC frequently becomes a nonlinear to afford a complicate conversion equation. Therefore, a realization of a converting device by using an arithmetical device executing the conversion equation entails a problem of large-sized device or long processing period.
In order to deal with the case where the conversion from the input color space into the output color space is complicate, there has been proposed a device that stores an output pixel value corresponding to an input pixel value in a conversion table in advance and performs a processing for simply referring the Conversion table to thereby realize a color conversion.
However, such a device has a problem that a capacity of the conversion table rapidly increases as the kind of the input pixel value, i.e., the tone number increases. For example, the capacity of the conversion table is n
3
in case where the input color space is represented by n tone of each RGB.
In order to deal with the case of plenty of tone numbers of the input pixel value, there has been proposed a device in which a conversion table is divided into plural portions for storing an output pixel value only at a position of a lattice point of a subspace. If there is no lattice point corresponding to the input pixel value, a value of a lattice point in the vicinity thereof is interpolated to be used. Specifically, such a converting device comprises, as shown in
FIG. 13
, a pixel value inputting part
101
, index converting part
102
, delta converting part
103
, coefficient storing part
106
and interpolating part
108
. With respect to the lattice point positioned at the boundary of a subspace of an input color space, a corresponding output pixel value (referred to as interpolation coefficient hereinbelow) is stored in advance in the coefficient storing part
106
. Further, this device converts the input pixel value
110
into a position (index)
111
of a subspace and a position (delta signal)
112
in the subspace. An interpolation coefficient
120
corresponding to the lattice point that composes the subspace is taken out from the conversion table based upon the index, whereupon the interpolating part
108
performs an interpolation by using the interpolation coefficient
120
and the position (delta signal)
112
in the subspace for obtaining an output pixel value
123
. Such a construction can reduce the capacity of the conversion table. This type of color converting device is disclosed, for example, in Japanese Published Examined Patent Application No. Sho
58-16180.
However, the problem of increasing the number of referring times of the conversion table still exists depending upon the interpolating method. When the number of the referring lattice point is designated by G, the number of referring times to the conversion table is proportional to G. In the case of input color space of three colors such as RGB, for example, a considered case is the one in which the input color space is divided into a plurality of rectangular solids and a linear interpolation is performed by using eight lattice points composing the rectangular solids. At this time, the conversion table has to be referred to eight times for processing one input pixel value.
There has been proposed a device in which an idea is put to take out the lattice point in order to decrease the number of the referring times to the conversion table. A color converting device disclosed in Japanese Published Unexamined Patent Application No.
Hei
5
-
46750
, for example, adopts an input color space of three colors and uses a vertex of a triangular prism to which the input pixel value belongs as a lattice point. By using six vertexes of the triangular prism that is decreased in number compared with eight vertexes of the rectangular solid, the number of referring times to the conversion table per one input pixel decreases from eight times to six times.
However, there occurs a problem of increasing an interpolation error when the referring lattice point is decreased in the interpolating processing. As the interpolation error increases, the color conversion error increases, to deteriorate a performance as a color converting device.
Further, the color converting device using the conversion table has a problem of increasing the number of referring times to the conversion table when the number of colors of the input color space increases. When the number of the input color space is designated by D, the number of the referring times to the Conversion table becomes
2
D. Assuming that the vertex f D-dimensional rectangular solid is used as a lattice point, eighth reference per one pixel is required in the input color space of three colors of YMC, while sixteenth reference is required per one pixel in the input color space of four colors of YMCK.
In order to deal with the input color space of four colors, there has been proposed, for example, a device in which the input color space is limited to YMCK so that a conversion table of three colors of YMC is used and a conversion of K alone is performed like a color converting device disclosed in Japanese Published Unexamined Patent Application No. Hei 8-116456. This device can realize a color conversion with relatively high precision with less scale of the device under a condition that the generating method of K is not greatly changed between the input color space and the output color space. However, this device does not have a function of greatly changing the generating method of K in the output color space.
The conventional color converting device simplifies its converting method in order to realize a complicated conversion from the input color space into the output color space with less scale of the device. As a result, the precision of the color conversion is somewhat deteriorated, but the effect of reducing the scale of the device takes first priority.
However, high image quality is advanced with respect to an image output device such as a printing device or printer. There is a possibility that the conventional conversion precision cannot deal with these image output devices having high image quality. Therefore, it is important to avoid a technique that can be a factor to deteriorate the conversion prec

Affiliated with

Also associated with

Rating

Color converting device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Color converting device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Color converting device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2975276