Image analysis – Color image processing
Reexamination Certificate
1999-02-05
2001-06-19
Au, Amelia M. (Department: 2623)
Image analysis
Color image processing
Reexamination Certificate
active
06249601
ABSTRACT:
This application claims priority under 35 U.S.C. §§119 and/or 365 to 98-53119 filed in Korea on Dec. 4, 1998; the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for determining the color of an illuminant and an apparatus therefor, and more particularly, to a method for determining the color of an illuminant by estimating the color of an illuminant of an input image and an apparatus therefor.
2. Description of the Related Art
Color correction is performed, considering the influence of illumination during photography in a color image inputting apparatus such as a digital camera. A white balancing function for performing color correction with respect to a channel ratio among R, G, and B channels is widely used as a representative example of color correction with respect to an illuminant Various methods for performing color correction such as white balancing have been developed. In the case of a video camera, chrominance information of an illuminant is generally obtained by photographing white paper or a white board before photography and white balancing is performed with reference to the chrominance information. Alternatively, controlling buttons corresponding to specific illuminations may be included and the button input by a user may be referred to. Alternatively, an illumination detector may be attached to a camera and information on the illumination may be obtained from a detected signal. Alternatively, the color of an illuminant may be obtained from a photographed image. However, the method of using the photo detector has problems in that the manufacturing costs increase since additional hardware is required for the camera and it is difficult to use for an image obtained by remote photography. Also, the method of using buttons has a problem in that many buttons are necessary in order to appropriately correspond to various illuminant components.
A method according to a conventional technology for solving the above problems is provided in U.S. Pat. No. 4,685,071. According to the above method, the color of a specularly reflected light is detected in a scene of an image so that the color of the light used to illuminate the scene is determined. According to this method, the color of the specularly reflected light is detected by detecting a surrounding area which includes highlight displaying varying hues and saturations on a plurality of differently colored surfaces in the scene. Also, according to the method, an image is transformed into a color signal of a chrominance coordinate in order to detect the change of a color which is independent of brightness and color boundaries on which saturation and color most severely change. Then, the color of the illuminant is detected using a data set around the boundary due to the change in saturation. In this case, in order to determine whether the boundary is due to the change in saturation or due to color, the data sets positioned on both sides of the boundary are collected and approximated to straight lines and variables determined to be colors of illuminants are collected from the paths of the intersection points of the straight lines.
However, in this method, it is not easy to collect data since the data sets are not approximated to the straight lines and further to this it is required that collection data on both sides of the boundary point, approximating the data to straight lines, and comparing and determining the data must be repeated. Therefore, such a method has disadvantage in that it takes an excessively long time to perform.
A method according to another conventional technology is provided in the U.S. Pat. No. 5,495,428. According to this method, the color of an illuminant is determined by grasping the color distribution using a histogram with respect to the entire image, obtaining a direct line which becomes a main axis in each cluster, and applying an appropriate scale factor to each direct line. While in this method it is relatively easy to secure data to be processed, it requires a large amount of calculation during the process of interpreting though.
SUMMARY OF THE INVENTION
To solve the above problem, it is an object of the present invention to provide a method for determining the color of an illuminant by which it is possible to extract stable and effective illuminant information by selectively excluding self luminous areas from an image which human visually perceives.
It is another object of the present invention to provide an apparatus for determining the color of an illuminant which utilizes the above method.
Accordingly, to achieve the first object, a method for detecting the color of an illuminant during photography of a color image having arbitrary standard color coordinates which can be transformed, comprising the steps of obtaining a mean vector value by selecting an arbitrary image and calculating an average value in each color coordinate channel with respect to the image, defining a predetermined coefficient f which is a positive integer larger than 1 and estimating a value obtained by multiplying f by the mean vector value as a temporary color of the illuminant with respect to the selected image, setting a value obtained by multiplying k by the temporarily estimated color of the illuminant as a self luminous threshold value in order to establish a self luminous area using human visual characteristics, wherein k is a predetermined coefficient which is a positive integer larger than 1, generating an image from which the self luminous area is removed by removing the self luminous area having a color coordinate value exceeding a self luminous threshold value, determining whether the difference value of the self luminous threshold value exceeds a predetermined reference value and returning to the step of calculating the mean vector value when the difference value is determined to exceed a predetermined reference value, and calculating the color of the illuminant from a chrominance value of an image average from which the self luminous area is removed and outputting the color of the illuminant when it is determined that the difference value does not exceed a predetermined reference value in the step of determining the difference value step.
In the above method, the coefficient k is determined by the steps of providing a plurality of color patches, selecting an illuminant which can be used in an image, illuminating the selected illuminant on the plurality of color patches, selecting an arbitrary patch among the plurality of color patches, increasing the RGB value of a corresponding packet until the selected patch looks like an illuminant, establishing the RGB value when the corresponding patch looks like the illuminant as an upper boundary, increasing the RGB value of the patch by a predetermined amount, reducing the RGB value of a corresponding packet until the selected patch looks like the illuminant, establishing the RGB value when the corresponding patch looks like the illuminant as a lower boundary, and determining a mean value between the upper boundary and the lower boundary as the variable k with respect to the selected illuminant.
Also, it is preferably that the above method further comprising a step of estimating illuminant color closest to the temporarily estimated illuminant color on a day light locus as the illuminant color before the step of setting the self luminous threshold value.
To achieve the first object, there is provided another method for detecting the color temperature of an illuminant during photography of an arbitrary color image, comprising the steps of obtaining an RGB mean vector value by selecting an arbitrary image and calculating a mean value in each RGB channel with respect to the image, defining a predetermined coefficient f which is a positive integer larger than 1 and estimating a value obtained by multiplying f by the RGB mean vector value as temporary color of the illuminant with respect to the selected image, setting a value obtained by multiplying k by the estimated
Kim Chang-yeong
Kim Jeong-yeop
Lee Seong-deok
Seo Yang-seok
Au Amelia M.
Burns Doane , Swecker, Mathis LLP
Samsung Electronics Co,. Ltd.
Wu Jingge
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