Image analysis – Color image processing – Color correction
Reexamination Certificate
1999-03-31
2004-01-13
Johns, Andrew W. (Department: 2621)
Image analysis
Color image processing
Color correction
C382S118000, C382S165000, C358S518000, C358S523000
Reexamination Certificate
active
06678407
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and a device of light source discrimination, skin color correction, and color image correction, and storage medium thereof capable of being read by a computer. More to particularly, this invention relates to a method and a device of light source discrimination, skin color correction, and color image correction, and storage medium thereof capable of being read by a computer which are intended to correct color in a color image based on skin area in a color image.
DESCRIPTION OF THE PRIOR ART
When there is displayed color image inputted by a color image input device such as video camera, digital camera, and so forth to a computer screen and so forth, in many cases, color reproduction is insufficient (color representation gives a sense of incompatibility to persons). In particular, when a face of person is included in image, requirement in terms of accuracy of color reproduction is severe. By way of problem often occurs, in some cases, image is reproduced in a different color from original color because there is taken photograph under different light source such as a fluorescent light from daylight which is original light for this photograph. Formerly, there is known a computer software in order to correct such image to a natural color representation, that is known by way of a photo retouch software.
In such the software, for instance, there is an image whose green component is exceedingly increased because it is taken photograph under the fluorescent light. Concerning this image, there is implemented a conversion based on curved line as shown in
FIG. 1
, toward respective three primary color components of red (R), green (G), and blue (B) for the color image, thus an operator corrects color in accordance with his experience, while suppressing green component, and increasing red component. Consequently, RGB value (horizontal axis) of input is converted into R′G′B′ value (vertical axis) of output. Further, there is known a software enabling such empirical correction processing to be simply realized in certain degree by only an amateur.
However, the conventional image processing (color correction) implemented as described above is known content as it is by way of know-how. The operator should specify content of processing. The content of processing was determined in accordance with the know-how of the operator or the sense of the operator. There is the problem that reproducibility of color is low, because it is incapable of being unnecessary to be executed the processing with appropriate content. Concretely, there are following matters depending on those problems.
Firstly, there can not be implemented appropriate color correction in terms of the image given previously, because processing itself (operation) depends on sensitive ability of person.
Secondly, since processing itself (operation) depends on sensitive ability of person, different result occurs in every operator.
Lastly, for instance, when there is used the software in order to correct green excessive image, the result of correction is different in every operator, because the operator judges whether or not the image is green excessive image, in accordance with his sense about how much degree, and inputs the result thereof to the computer as an information.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention, in order to overcome the above mentioned problems, to provide a method and a device of light source discrimination, skin color correction, and color image correction, and a storage medium capable of being read by a computer which enable reproducibility of color to be maintained always highly regardless of difference of light source.
PRINCIPLE OF COLOR CORRECTION
There will be described the principle of color correction in the present invention. There is taken spectral reflectance (reflectance in every each wavelength &lgr;) of skin or a face to be &agr;(&lgr;). Spectral radiant intensity of a light source is taken to be S(&lgr;). Spectral sensitivity of three kinds of sensor of color image input device are taken to be r(&lgr;), g(&lgr;), b(&lgr;). At this time, there is represented outputs R, G, B, of respective sensors by formula 1.
{
R
=
∫
380
780
r
(
λ
)
β
(
λ
)
S
(
λ
)
ⅆ
λ
G
=
∫
380
780
g
(
λ
)
β
(
λ
)
S
(
λ
)
ⅆ
λ
B
=
∫
380
780
b
(
λ
)
β
(
λ
)
S
(
λ
)
ⅆ
λ
[FORMULA 1]
Here, wavelength &lgr; is a value with nm as a unit.
Radiant intensity of daylight is taken to be S
1
(&lgr;), at this time, outputs of respective sensors are (R
1
, G
1
, B
1
). Radiant intensity of a fluorescent light is taken to be S
2
(&lgr;), at this time, outputs of respective sensors are (R
2
, G
2
, B
2
). Difference between these sensor outputs brings unnatural skin color. Generally, it is incapable of being discriminated whether radiant intensity of light source is S
1
(&lgr;) or S
2
(&lgr;) only seeing an image. However, skin is taken photograph in an image, and reflectance &agr;(&lgr;) is known. When the sensor output (R, G, B) equals to (R
1
, G
1
, B
1
), it is capable of being known that a light source is daylight. Similarly, when the sensor output (R, G, B) equals to (R
2
, G
2
, B
2
), it is capable of being known that a light source is a fluorescent light. Practically, reflectance &agr;(&lgr;) of skin which is different according to a person, is not constant. It is difficult that sensor output agrees therewith completely as above. However, it is possible to estimate a light source whose possibility is high, by checking distribution of sensor output in terms of skin color of respective light sources.
According to a first aspect of the present invention, in order to achieve the above-mentioned object, there is provided a light source discrimination method which comprises the steps of calculating color distribution of skin area of a color image, comparing the color distribution calculated previously in the above calculating step with a color distribution already known of skin taken photograph under a plurality of different lighting light sources, and discriminating a lighting light source under which the color image is taken photograph, based on result of the comparison.
According to a second aspect of the present invention, there is provided a light source discrimination device which comprises a color distribution calculation means for calculating color distribution of skin area of a color image, a reference color distribution storage means for storing therein color distribution of skin taken photograph under a plurality of different lighting light sources, and a light source discrimination means for discriminating lighting light source under which the color image is taken photograph, while comparing color distribution of skin area of the color image calculated by the color distribution calculation means with color distribution of skin under a plurality of lighting lights, which is stored in the reference color distribution storage means.
According to a third aspect of the present invention, there is provided a skin color correction method which comprises the steps of calculating color distribution of skin area of a color image, comparing color distribution calculated previously at the above calculating step with color distribution already known of skin taken photograph under a plurality of different lighting light sources, and correcting color of the skin area into a skin color under prescribed lighting light source based on result of the comparison.
According to a fourth aspect of the present invention, in the third aspect, there is provided a skin color correction method, wherein correction of color of the skin area is implemented based on result of discrimination while discriminating lighting light source under which the color image i
Alavi Amir
Foley & Lardner
Johns Andrew W.
NEC Corporation
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