Image processing apparatus, image processing method and information recording medium

• US 20030020974A1
• Filed: 06/07/2002
• Published: 01/30/2003
• Est. Priority Date: 06/11/2001
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Matsushima, Yuki
• Granted Patent: US 7,251,056 B2
• Time in Patent Office: Days
• US Class Current: 358/521
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 2207/20008 Globally adaptive
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement
• CPC Class Codes: G06T 7/194 involving foreground-background segmentation
• CPC Class Codes: H04N 1/4074 using histograms

Abstract

A subject area extracting unit extracts a main-subject area from the color image data; a correction amount calculating unit calculates a gradation correction amount based on the information on the thus-extracted main-subject area; a control zone extracting unit extracts a predetermined control zone from a brightness zone to which the main-subject area does not belongs; a determining unit determines whether or not the gradation correction amount on the control zone should be controlled, according to a predetermined control requirement; and a control unit controls the gradation correction amount according to the determination result of the determination unit.

Claims

1. An image processing apparatus having a function of correcting a gradation of color image data, comprising:

a subject area extracting unit extracting a main-subject area from the color image data;

a correction amount calculating unit calculating a gradation correction amount based on the information on the thus-extracted main subject area;

a control zone extracting unit extracting a predetermined control zone from a brightness zone to which the main-subject area does not belong;

a determining unit determining whether or not the gradation correction amount on the control zone should be controlled, according to a predetermined control requirement; and

a control unit controlling the gradation correction amount according to the determination result of said determination unit.

2. The image processing apparatus as claimed in claim 1, wherein a brightness zone brighter than a brightness zone of the main-subject area is determined as the control zone.

3. The image processing apparatus as claimed in claim 1, wherein a brightness zone darker than a brightness zone of the main-subject area is determined as the control zone.

4. The image processing apparatus as claimed in claim 1, wherein the predetermined control requirement comprises providing at least one of upper limit or lower limit on the tangent inclination of a gradation correction curve.

5. The image processing apparatus as claimed in claim 4, wherein the predetermined control requirement on the gradation correction curve is determined according to a scene in which the relevant image data obtained.

6. The image processing apparatus as claimed in claim 5, wherein the lower limit on the tangent inclination of the gradation correction curve is set lower in a backlight scene than in a night flash-light photography scene.

7. The image processing apparatus as claimed in claim 4, wherein the predetermined control requirement on the gradation correction curve is determined according to an image outputting device to be applied.

8. The image processing apparatus as claimed in claim 7, wherein the lower limit on the tangent inclination of the gradation correction curve is set lower for the image outputting device having a higher gradation reproducibility.

9. The image processing apparatus as claimed in claim 4, wherein the predetermined control requirement on the gradation correction curve is determined according to a feature of the image data to be processed.

10. The image processing apparatus as claimed in claim 1, wherein the gradation correction amount is determined by using a statistics value obtained from a component representing brightness of the main-subject area.

26. An image output apparatus comprising;

an image output-control unit comprising the image processing apparatus claimed in claim 1;

and

an image forming unit outputting the image data having undergone the gradation correction processing by said image output control unit.

27. The image output apparatus as claimed in claim 26, wherein a saturation evaluation criterion on the saturation determining unit of the image processing apparatus is determined according to the image forming unit applied.

28. The image output apparatus as claimed in claim 27, wherein a saturation allowance criterion on the saturation determining unit of the image processing apparatus is determined according to the image forming unit applied.

11. An image processing method comprising the steps of:

a) extracting a main-subject area from color image data;

b) calculating a gradation correction amount based on brightness information of the main-subject area;

c) calculating a gradation correction curve according to the gradation correction amount calculated in the step b);

d) extracting a control zone from a brightness zone not of the main-subject area;

e) determining whether or not the gradation correction amount on the control area is proper;

f) calculating a new gradation correction curve using a predetermined control requirement, when it is determined in the step e) that the gradation correction amount on the control area is not proper;

g) performing gradation correction processing on the color image data by using the thus-obtained gradation correction curve.

12. A computer-readable information recording medium storing therein a software program for causing a computer to perform the respective steps claimed in claim 11.

13. An image processing apparatus comprising:

a control area extracting unit extracting a candidate area as a control area on which gradation crush becomes conspicuous when gradation correction is performed on input image data; and

a gradation correction adjustment unit updating a gradation correction curve using information on the control area.

14. The image processing apparatus as claimed in claim 13, wherein said gradation correction adjustment unit comprises:

a saturation determining unit evaluating a saturation occurring when the gradation correction is performed on the image data belonging to the control area by using the gradation correction curve; and

an updating unit updating the gradation correction curve into a new gradation correction curve when the saturation is not permitted by said situation determining unit.

15. The image processing apparatus as claimed in claim 14, wherein said saturation determining unit determines a pixel of the control areas as of saturation when at least one of the components thereof exceeds a reference value, and thus, determines whether or not conspicuousness on the saturation can be permitted.

16. The image processing apparatus as claimed in claim 14, wherein said saturation determining unit determines a pixel of the control areas as of saturation when at least one of the components thereof exceeds a reference value, and determines that the saturation is permitted when a saturation degree calculated by using the area of a thus-obtained saturation area with respect to the area of the control area is smaller than a predetermined threshold.

17. The image processing apparatus as claimed in claim 14, wherein said saturation determining unit determines a pixel of the control areas as of saturation when at least one of the components thereof exceeds a reference value, and determines that the saturation is permitted when a saturation degree calculated by using the area of a thus-obtained saturation area with respect to the whole area of the relevant image is smaller than a predetermined threshold.

18. The image processing apparatus as claimed in claim 14, wherein said saturation determining unit determines a pixel of the control areas as of saturation when at least one of the components thereof exceeds a reference value, and determines that the saturation is permitted when a saturation degree calculated according to a concentration degree of at least one of the control area and saturation area is smaller than a predetermined threshold.

19. The image processing apparatus as claimed in claim 14, wherein said updating unit updates the gradation correction curve by reducing the degree of gradation correction.

20. The image processing apparatus as claimed in claim 14, wherein said updating unit updates the gradation correction curve by increasing the degree of gradation correction.

21. The image processing apparatus as claimed in claim 13, wherein said control area extracting unit extracting an area belonging to the brightest level out of a plurality of levels obtained through classification of the relevant image data with respect to the brightness.

22. The image processing apparatus as claimed in claim 21, wherein said control area extracting unit determines an area having a luminance more than a predetermined value, and also, having a chroma less than a predetermined value, as not belonging to the control area.

23. The image processing apparatus as claimed in claim 21, wherein said control area extracting unit determines an area of an edge or in the vicinity of an edge as not belonging to the control area.

24. The image processing apparatus as claimed in claim 21, wherein said control area extracting unit determines an area having a chroma component more than a predetermined value as not belonging to the control area.

25. The image processing apparatus as claimed in claim 14, wherein said gradation correction adjustment unit comprises a control area updating unit which updates the control area when the saturation is not permitted.

29. An image processing method comprising the steps of:

a) extracting a candidate area as a control area on which gradation crush becomes conspicuous when gradation correction is performed on input image data;

b) updating a gradation correction curve using information on the control area; and

c) performing gradation correction by using the thus-updated gradation correction curve.

30. The image processing apparatus as claimed in claim 29, further comprising the steps of:

c) evaluating a saturation occurring after the gradation correction is performed on the image data belonging to the control area by using the gradation correction curve; and

d) updating the gradation correction curve into a new gradation correction curve when the saturation is not permitted in said step c).

31. A computer-readable information recording medium storing therein a software program for causing a computer to perform the image processing method claimed in claim 29.

32. An image processing apparatus comprising:

a color range setting unit setting a color range for a background area of input color image data by using information on a background candidate area having a high possibility of belonging to the background area; and

a background extracting unit extracting the background area from the input color image data by using the color range set by said color range setting unit.

33. The image processing apparatus as claimed in claim 32, wherein

said color range setting unit sets a size of the color range for the background area according to a spread degree of color component in the background candidate area.

34. The image processing apparatus as claimed in claim 32, wherein

said color range setting unit sets the color range for the background area by using an average value and a standard deviation value concerning a color component of the background candidate area.

35. The image processing apparatus as claimed in claim 32, wherein:

the background candidate area of a night photographic scene image is determined as corresponding to the darkest level out of a plurality of levels obtained from classification of the input image data with respect to the brightness.

36. The image processing apparatus as claimed in claim 32, wherein:

the background candidate area of a backlight or half-backlight scene image is determined as corresponding to the brightest level out of a plurality of levels obtained from classification of the input image data with respect to the brightness.

37. The image processing apparatus as claimed in claim 32, wherein:

said color range setting unit sets a color range for background area in a division area by using information of a background candidate area having a high possibility of belonging to the background area existing in the division area.

38. The image processing apparatus as claimed in claim 32, wherein:

said color range setting unit sets a color range for background area in a target division area by using information of a peripheral division area present in the vicinity of the target division area and having background color range information when no background candidate area exists in the target division area.

39. An image processing method comprising the steps of:

a) setting a color range for a background area of input color image data by using information on a background candidate area having a high possibility of belonging to the background area; and

b) extracting the background area from the input color image data by using the color range set by said color range setting unit.

40. A computer-readable information recording medium storing therein a software program for causing a computer to perform the steps of:

a) setting a color range for a background area of input color image data by using information on a background candidate area having a high possibility of belonging to the background area; and

b) extracting the background area from the input color image data by using the color range set by said color range setting unit.