Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
1997-12-24
2002-10-01
Ho, Tuan (Department: 2612)
Television
Camera, system and detail
Combined image signal generator and general image signal...
C348S231900
Reexamination Certificate
active
06459449
ABSTRACT:
This application claims the benefit of Japanese Patent Application No. 08-357917, filed in Japan on Dec. 28, 1996, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color reproduction correction device and method for an imaging apparatus, and more particularly to a technique wherein images of an object acquired by means of a color-image imaging device, such as a television camera or the like, can accurately be reproduced in accordance with the colors as seen by the operator of the imaging apparatus even if the light source used for illumination of the object varies.
2. Discussion of the Related Art
The human eye generally sees a white surface of an object as white regardless of the type of illumination involved. This property of the human eye is referred to as visual adaptation. In a color-image imaging apparatus, such as a television camera or the like, an adjustment is made in order to reproduce the visual adaptation of the human eye so that the output signals of the three primary colors used in imaging are the same when a white object is imaged regardless of the illumination. This technique is called white balance processing.
However, the three primary colors, red (R), green (G), and blue (B), used in imaging do not necessarily have the same characteristics as those exhibited by the human eye. Furthermore, the physical characteristics of the reference white color of the display devices displaying the results of the imaging differ from the illumination actually used in the imaging process. Because of these factors, colors other than achromatic colors may appear different from the colors of the actual object when the results of the imaging are viewed by means of a display device. In cases where the viewers have no knowledge of the colors at the imaging site, as in broadcasts, no problems exists as long as the colors match the colors in the memory of the viewers. However, when the colors themselves are critical, as in printed documents, or when the imaging is required to illicit a feeling of actual presence the difference between the object image and the displayed image colors requires improvement.
A linear matrix method is a conventional method employed to improve the color reproduction of color-image imaging devices, such as television cameras, used for broadcasting and similar applications. For example, in conventional television cameras, in which three types of color signals are produced, i.e., red (R), green (G), and blue (B), corrected red, green, and blue signals are obtained via a matrix circuit that mixes the signals with each other. These corrected signals are then subjected to signal processing, thus producing a video signal for television use.
However, procedures for determining the constants employed in matrices used for color reproduction correction have not always been firmly established. Historically the constants were selected by trial and error until visually pleasing results were obtained. Accordingly, linear matrix constants, which produce optimal results in cases wherein the light source used to illuminate the imaging object varies, have not been obtained. Therefore, linear matrix circuits are not used in most cases. Alternatively, color tones are adjusted by adjusting the hue and amount of color on the basis of visual determinations made by broadcast technicians using an imaging monitor.
In devices, such as home-use video cameras, video signals are obtained predominantly from a single imaging element utilizing three types of color filters that are applied to each pixel. However, since there are limits to the spectral characteristics of the filters, which can be mounted on the imaging element, the color reproduction is generally poor. Correction in those devices is generally accomplished by adjusting the hue and amount of color so that color tones, which are close to skin color (for which the eye has a high color discrimination sensitivity), will be favorable under the illumination most frequently used. Generally, variations in the illumination light source is handled only by white balance processing that adjusts the levels of the red, green, and blue, generally referred to as (RGB) signals so that the color white seen by the eyes is imaged as white.
Furthermore, a common problem associated with the respective devices described above is that there is no attempt to reproduce the appearance of colors according to the illumination used. The color reproduction is selected on the basis of whether the finished image is appealing to the viewer's eye. Therefore, the atmosphere and/or feeling generated by the actual illumination is ignored. This problem occurs because no method has been established for determining correction matrices that takes into consideration the fact that since the reference white color of the television monitor of a display device does not necessarily coincide with the white color of the actual illuminating light that illuminates the imaging object. The reference white color displayed “as is” may differ from the color viewed directly by a live observer. Accordingly, it is necessary to investigate color reproduction by determining if imaging is performed under illumination from a white incandescent lamp or under outdoor sunlight, which heretofore has been ignored.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a color reproduction correction device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. An object of the present invention is to allow color reproduction correction, by means of a simple construction of a color reproduction correction device and method for an imaging apparatus, in which correction is accomplished by determining color reproduction correction matrices so that colors seen by the operator of the imaging apparatus can be accurately reproduced by a display device even if the light source used for illumination of the object varies.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a color reproduction correction device for an imaging apparatus obtains color signals, with a plurality of spectral characteristics, by imaging an object and obtaining a color image. The color image is obtained by subjecting the color signals to signal processing, wherein the reproduction correction device includes a light source inferring device, which infers the type of illuminating light source being used, and a memory device, which stores, for each of a plurality of predetermined light sources, constants for correction matrix operations. The constants are determined so that the mean values of the absolute values of the distances between values obtained by converting the positions on a uniform color space of each of a plurality of colors of the object to be imaged illuminated by the respective light sources into the respective corresponding positions on the uniform color space in the case of white light from the reference light source of a display device that uses as reference white light a light source that may not coincide with the white light of the light source used for the illumination taking into consideration the adaptive effect of the eyes; the positions on the uniform color space of colors corresponding to the respective colors of the object to be imaged that are obtained when output signals produced by applying correction matrix operations to the color signals of the imaging device imaging the object are displayed by means of the display device, are minimized, thus insuring that t
Ho Tuan
Morgan & Lewis & Bockius, LLP
Nikon Corporation
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