Image processing method and apparatus

• US 6,504,952 B1
• Filed: 03/17/1999
• Issued: 01/07/2003
• Est. Priority Date: 03/17/1998
• Status: Expired due to Term

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Film Co Limited (Fujifilm Holdings Corporation)
• Inventors: Takemoto, Fumito, Takemura, Kazuhiko
• Primary Examiner(s): Lee, Thomas D.
• Assistant Examiner(s): BRINICH, STEPHEN M
• Application Number:
  US09/271,283
• Time in Patent Office: 1,392 Days
• Field of Search: 382/167, 382/162, 358/516, 358/501, 358/504, 358/515, 358/518, 358/520, 358/523, 358/530
• US Class Current: 382/167
• CPC Class Codes: H04N 1/6002 Corrections within particular colour systems
• CPC Class Codes: H04N 1/6077 Colour balance, e.g. colour cast correction

Abstract

Tristimulus values of each of pixels in an image, which is represented by an image signal, are transformed into chromaticity values, and mean values of the chromaticity values having been calculated with respect to the pixels in the image are calculated. The mean values of the chromaticity values are transformed into physiological primary colors. The thus obtained physiological primary colors are regarded as the white of a photographing illuminant, under which a photographing operation was carried out. The chromaticity values are transformed such that the thus obtained physiological primary colors may coincide with the physiological primary colors of a reference photographing illuminant. The chromaticity values, which have been obtained from the transformation, are then transformed into RGB color signals. The thus obtained RGB color signals are subjected to image processing and then used for reproducing a visible image.

Claims

1. An image processing method, comprising the steps of:

i) transforming R, G, and B colors of each of pixels in an image, which is represented by an image signal having been acquired with an image sensing operation, into chromaticity values,

ii) calculating chromaticity mean values, which are mean values of the chromaticity values having been obtained with respect to the pixels in the image,

iii) transforming said chromaticity mean values into tristimulus values in accordance with physiological primary colors, and

iv) regarding said tristimulus values in accordance with physiological primary colors as the white of a photographing illuminant, under which said image signal was acquired, and transforming said image signal such that said tristimulus values may coincide with chromaticity values of a white point of a reference photographing illuminant, a processed image signal being thereby obtained.

2. An image processing method as defined in claim 1 wherein, as the differences between said tristimulus values in accordance with physiological primary colors and said chromaticity values of the white point of said reference photographing illuminant become large, the degree of said coincidence is kept to be low.

3. An image processing method as defined in claim 1 or 2 wherein said chromaticity mean values are calculated as weighted mean values in accordance with a reciprocal of a distance of said chromaticity values from a CIE daylight locus or a black body locus.

4. An image processing method as defined in claim 1 or 2 wherein the white point of said reference photographing illuminant is set in accordance with the white point of said photographing illuminant such that the white point of said reference photographing illuminant may have values falling within a predetermined range.

5. An image processing method as defined in claim 1 or 2 wherein said processed image signal is transformed even further in accordance with reproduction target values of a reproducing apparatus, which reproduces a visible image from said processed image signal.

9. An image processing method as defined in claim 4 or 5 wherein the white point of said reference photographing illuminant is set in accordance with the white point of said photographing illuminant such that the white point of said reference photographing illuminant may have values falling within a predetermined range.

6. An image processing method, comprising the steps of:

i) transforming R, G, and B colors of each of pixels in an image, which is represented by an image signal having been acquired with an image sensing operation, into chromaticity values,

ii) calculating chromaticity mean values, which are mean values of the chromaticity values having been obtained with respect to the pixels in the image,

iii) transforming said chromaticity mean values into RGB tristimulus values, and

iv) regarding said RGB tristimulus values as the white of a photographing illuminant, under which said image signal was acquired, and transforming said image signal such that said RGB tristimulus values may coincide with chromaticity values of a white point of a reference photographing illuminant, a processed image signal being thereby obtained.

7. An image processing method as defined in claim 6 wherein, as the differences between said RGB tristimulus values and said chromaticity values of the white point of said reference photographing illuminant become large, the degree of said coincidence is kept to be low.

8. An image processing method as defined in claim 6 or 7 wherein said chromaticity mean values are calculated as weighted mean values in accordance with a reciprocal of a distance of said chromaticity values from a CIE daylight locus or a black body locus.

10. An image processing method as defined in claim 6 or 7 wherein said processed image signal is transformed even further in accordance with reproduction target values of a reproducing apparatus, which reproduces a visible image from said processed image signal.

11. An image processing apparatus, comprising:

i) a chromaticity value transformation means for transforming R, G, and B colors of each of pixels in an image, which is represented by an image signal having been acquired with an image sensing operation, into chromaticity values,

ii) a chromaticity mean value calculating means for calculating chromaticity mean values, which are mean values of the chromaticity values having been obtained with respect to the pixels in the image,

iii) a tristimulus value transformation means for transforming said chromaticity mean values into tristimulus values in accordance with physiological primary colors, and

iv) a chromatic adaptation transformation means for regarding said tristimulus values in accordance with physiological primary colors as the white of a photographing illuminant, under which said image signal was acquired, and transforming said image signal such that said tristimulus values may coincide with chromaticity values of a white point of a reference photographing illuminant, a processed image signal being thereby obtained.

12. An image processing apparatus as defined in claim 11 wherein said chromatic adaptation transformation means operates such that, as the differences between said tristimulus values in accordance with physiological primary colors and said chromaticity values of the white point of said reference photographing illuminant become large, the degree of said coincidence may be kept to be low.

13. An image processing apparatus as defined in claim 11 or 12 wherein said chromaticity mean value calculating means calculates said chromaticity mean values as weighted mean values in accordance with a reciprocal of a distance of said chromaticity values from a CIE daylight locus or a black body locus.

14. An image processing apparatus as defined in claim 11 or 12 further comprising means for setting the white point of said reference photographing illuminant in accordance with the white point of said photographing illuminant such that the white point of said reference photographing illuminant may have values falling within a predetermined range.

15. An image processing apparatus as defined in claim 11 or 12 further comprising an output transformation means for transforming said processed image signal in accordance with reproduction target values of a reproducing apparatus, which reproduces a visible image from said processed image signal.

16. An image processing apparatus, comprising:

i) a chromaticity value transformation means for transforming R, G, and B colors of each of pixels in an image, which is represented by an image signal having been acquired with an image sensing operation, into chromaticity values,

ii) a chromaticity mean value calculating means for calculating chromaticity mean values, which are mean values of the chromaticity values having been obtained with respect to the pixels in the image,

iii) a tristimulus value transformation means for transforming said chromaticity mean values into RGB tristimulus values, and

iv) a chromatic adaptation transformation means for regarding said RGB tristimulus values as the white of a photographing illuminant, under which said image signal was acquired, and transforming said image signal such that said RGB tristimulus values may coincide with chromaticity values of a white point of a reference photographing illuminant, a processed image signal being thereby obtained.

17. An image processing apparatus as defined in claim 16 wherein said chromatic adaptation transformation means operates such that, as the differences between said RGB tristimulus values and said chromaticity values of the white point of said reference photographing illuminant become large, the degree of said coincidence may be kept to be low.

18. An image processing apparatus as defined in claim 16 or 17 wherein said chromaticity mean value calculating means calculates said chromaticity mean values as weighted mean values in accordance with a reciprocal of a distance of said chromaticity values from a CIE daylight locus or a black body locus.

19. An image processing apparatus as defined in claim 16 or 17 further comprising means for setting the white point of said reference photographing illuminant in accordance with the white point of said photographing illuminant such that the white point of said reference photographing illuminant may have values falling within a predetermined range.

20. An image processing apparatus as defined in claim 16 or 17 further comprising an output transformation means for transforming said processed image signal in accordance with reproduction target values of a reproducing apparatus, which reproduces a visible image from said processed image signal.

21. A recording medium, on which a program has been recorded and from which a computer is capable of reading said program, said program causing the computer to execute:

i) a procedure for transforming R, G, and B colors of each of pixels in an image, which is represented by an image signal having been acquired with an image sensing operation, into chromaticity values,

ii) a procedure for calculating chromaticity mean values, which are mean values of the chromaticity values having been obtained with respect to the pixels in the image,

iii) a procedure for transforming said chromaticity mean values into tristimulus values in accordance with physiological primary colors, and

iv) a procedure for regarding said tristimulus values in accordance with physiological primary colors as the white of a photographing illuminant, under which said image signal was acquired, and transforming said image signal such that said tristimulus values may coincide with chromaticity values of a white point of a reference photographing illuminant, a processed image signal being thereby obtained.

22. A recording medium as defined in claim 21 wherein, in the procedure for obtaining said processed image signal, as the differences between said tristimulus values in accordance with physiological primary colors and said chromaticity values of the white point of said reference photographing illuminant become large, the degree of said coincidence is kept to be low.

23. A recording medium as defined in claim 21 or 22 wherein, in the procedure for calculating said chromaticity mean values, said chromaticity mean values are calculated as weighted mean values in accordance with a reciprocal of a distance of said chromaticity values from a CIE daylight locus or a black body locus.

24. A recording medium as defined in claim 21 or 22 wherein said program further comprises a procedure for setting the white point of said reference photographing illuminant in accordance with the white point of said photographing illuminant such that the white point of said reference photographing illuminant may have values falling within a predetermined range.

25. A recording medium as defined in claim 21 or 22 wherein said program further comprises a procedure for transforming said processed image signal in accordance with reproduction target values of a reproducing apparatus, which reproduces a visible image from said processed image signal.

26. A recording medium, on which a program has been recorded and from which a computer is capable of reading said program, said program causing the computer to execute:

i) a procedure for transforming R, G, and B colors of each of pixels in an image, which is represented by an image signal having been acquired with an image sensing operation, into chromaticity values,

ii) a procedure for calculating chromaticity mean values, which are mean values of the chromaticity values having been obtained with respect to the pixels in the image,

iii) a procedure for transforming said chromaticity mean values into RGB tristimulus values, and

iv) a procedure for regarding said RGB tristimulus values as the white of a photographing illuminant, under which said image signal was acquired, and transforming said image signal such that said RGB tristimulus values may coincide with chromaticity values of a white point of a reference photographing illuminant, a processed image signal being thereby obtained.

27. A recording medium as defined in claim 26 wherein, in the procedure for obtaining said processed image signal, as the differences between said RGB tristimulus values and said chromaticity values of the white point of said reference photographing illuminant become large, the degree of said coincidence is kept to be low.

28. A recording medium as defined in claim 26 or 27 wherein, in the procedure for calculating said chromaticity mean values, said chromaticity mean values are calculated as weighted mean values in accordance with a reciprocal of a distance of said chromaticity values from a CIE daylight locus or a black body locus.

29. A recording medium as defined in claim 26 or 27 wherein said program further comprises a procedure for setting the white point of said reference photographing illuminant in accordance with the white point of said photographing illuminant such that the white point of said reference photographing illuminant may have values falling within a predetermined range.

30. A recording medium as defined in claim 26 or 27 wherein said program further comprises a procedure for transforming said processed image signal in accordance with reproduction target values of a reproducing apparatus, which reproduces a visible image from said processed image signal.

31. An image sensing system, comprising:

i) an image sensing means for detecting an object image with an image sensing operation and thereby obtaining an image signal, which represents the object image,

ii) an image processing apparatus comprising;

a) a chromaticity value transformation means for transforming R, G, and B colors of each of pixels in an image, which is represented by an image signal having been acquired with an image sensing operation, into chromaticity values,

b) a chromaticity mean value calculating means for calculating chromaticity mean values, which are mean values of the chromaticity values having been obtained with respect to the pixels in the image,

c) a tristimulus value transformation means for transforming said chromaticity mean values into tristimulus values in accordance with physiological primary colors, and

d) a chromatic adaptation transformation means for regarding said tristimulus values in accordance with physiological primary colors as the white of a photographing illuminant, under which said image signal was acquired, and transforming said image signal such that said tristimulus values may coincide with chromaticity values of a white point of a reference photographing illuminant, a processed image signal being thereby obtained,

wherein the image processing apparatus carries out image processing on the image signal and thereby obtains a processed image signal, and

iii) a recording means for recording said processed image signal, which has been obtained from the image processing carried out by said image processing apparatus, on a recording medium.

32. An image sensing system, comprising:

i) an image sensing means for detecting an object image with an image sensing operation and thereby obtaining an image signal, which represents the object image,

ii) an image processing apparatus comprising;

a) a chromaticity value transformation means for transforming R, G, and B colors of each of pixels in an image, which is represented by an image signal having been acquired with an image sensing operation, into chromaticity values,

b) a chromaticity mean value calculating means for calculating chromaticity mean values, which are mean values of the chromaticity values having been obtained with respect to the pixels in the image,

c) a tristimulus value transformation means for transforming said chromaticity mean values into RGB tristimulus values, and

d) a chromatic adaptation transformation means for regarding said RGB tristimulus values as the white of a photographing illuminant, under which said image signal was acquired, and transforming said image signal such that said RGB tristimulus values may coincide with chromaticity values of a white point of a reference photographing illuminant, a processed image signal being thereby obtained,

wherein the image processing apparatus carries out image processing on the image signal and thereby obtains a processed image signal, and

iii) a recording means for recording said processed image signal, which has been obtained from the image processing carried out by said image processing apparatus, on a recording medium.

33. An image reproducing system for reproducing a visible image from an image signal, comprising:

i) an input means for receiving the image signal,

ii) an image processing apparatus comprising;

a) a chromaticity value transformation means for transforming R, G, and B colors of each of pixels in an image, which is represented by an image signal having been acquired with an image sensing operation, into chromaticity values,

b) a chromaticity mean value calculating means for calculating chromaticity mean values, which are mean values of the chromaticity values having been obtained with respect to the pixels in the image,

c) a tristimulus value transformation means for transforming said chromaticity mean values into tristimulus values in accordance with physiological primary colors, and

d) a chromatic adaptation transformation means for regarding said tristimulus values in accordance with physiological primary colors as the white of a photographing illuminant, under which said image signal was acquired, and transforming said image signal such that said tristimulus values may coincide with chromaticity values of a white point of a reference photographing illuminant, a processed image signal being thereby obtained,

wherein the image processing apparatus carries out image processing on the image signal having been received from said input means and thereby obtains a processed image signal, and

iii) a reproducing means for reproducing the visible image from said processed image signal, which has been obtained from the image processing carried out by said image processing apparatus.

34. An image reproducing system for reproducing a visible image from an image signal, comprising:

i) an input means for receiving the image signal,

ii) an image processing apparatus comprising;

a) a chromaticity value transformation means for transforming R, G, and B colors of each of pixels in an image, which is represented by an image signal having been acquired with an image sensing operation, into chromaticity values,

b) a chromaticity mean value calculating means for calculating chromaticity mean values, which are mean values of the chromaticity values having been obtained with respect to the pixels in the image,

c) a tristimulus value transformation means for transforming said chromaticity mean values into RGB tristimulus values, and

d) a chromatic adaptation transformation means for regarding said RGB tristimulus values as the white of a photographing illuminant, under which said image signal was acquired, and transforming said image signal such that said RGB tristimulus values may coincide with chromaticity values of a white point of a reference photographing illuminant, a processed image signal being thereby obtained,

wherein the image processing apparatus carries out image processing on the image signal having been received from said input means and thereby obtains a processed image signal, and

iii) a reproducing means for reproducing the visible image from said processed image signal, which has been obtained from the image processing carried out by said image processing apparatus.