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Method and apparatus for color conversion
| Details |
Inventors: Kanamori, Katsuhiro; Yamada, Osamu; Motomura, Hideto; Kurosawa, Toshiharu; Fumoto, Teruo;
Assignee: Matsushita Electric Industrial Co., Ltd. (Osaka, JP)
Primary Examiner: Coles, Sr.; Edward L.
Assistant Examiner: Lee; Thomas D.
Attorney, Agent or Firm: Lowe, Price, LeBlanc & Becker
The present invention relates to a method and apparatus applied to a widely-used and high-speed color conversion which is utilized in a color printer, a color display apparatus and the like, and provides a novel three-dimensional interpolation operation by use of a triangle-pole shaped interpolation unit-space. Input color signals R,G, and B are converted into lightness signal Y and chromaticity signals Cr, Cb which constitute a three-dimensional space. This three-dimensional space is dissected into rectangular parallelopipeds and is further divided into two prisms having base planes parallel to the chromaticity plane CrCb. A prism judging section 207 judges which of prisms an input color is involved in. There are provided a plurality of color conversion table memories 210.about.215 which store output values corresponding to input values constituting respective points of the prism and difference values of mutual output colors and further difference values of mutual difference values. Stored data in respective color conversion table memories 210.about.215 are weighted by lower-bit signals 205, 206 of the input color signals in multipliers 219, 220, 226, 227, and 230. Then, these data are added in adders 220, 221, 228, 229, and 231 so as to accomplish a linear interpolation using output values of six vertices which constitute the prism. |
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DETAILED DESCRIPTION In order to accomplish above purpose, the present invention provides a method and apparatus for transforming color signals which can transform an input color signal consisting of three principal color separation colors into a lightness and a chromaticity signals and, in turn, executes an interpolation operation in a space defined by these lightness and chromaticity components.
Further, the interpolation method of the present invention dissects a three-dimensional space into prisms as unit interpolation sections so as to execute a linear interpolation in respective inside spaces.
An operation of the color conversion method and its apparatus in accordance with the present invention will be discussed below.
Color spaces such as R, G, and B, which are formed by output signals from the color scanner and the like as described above, are called as "device depend colors" which are dependent on an individual color apparatus.
But, these expression are not general as an expression of colors.
Furthermore, it is hard to say that respective axes adequately reflect the human visual characteristics.
It is therefore a recent development that there is a movement to unify the color expression among various color apparatus (color display devices, various color hard copies).
This is called as "device independent colors".
It is predicted in view of various color spaces that separated spaces like CIE-Lab or YIQ defined by lightness and chromaticity components will be prospective for future use.
Furthermore, from the view point of executing a color adjustment of images, separating an input color signal into lightness and chromaticity components is advantageous in changing its color only while maintaining its gradation without being changed.
In view of these reasons, a combination of a lightness and two kinds of chromaticities such as (Y, I, Q, or Y, R-Y, B-Y) will be most appropriate for an input space of a widely-used color conversion apparatus of an interpolation type.
Therefore, as a primary measure for solving above-described problem, even if the input color signal is a three-principal-color signal consisting of a red, a green, and a blue, the input color signal is transformed into a lightness-chromaticity separation type signal before the interpolation is carried out
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Optical Systems 
