Image Processing Device, Image Processing Method, Image Processing Program Product, and Image-Capturing Device

• US 20080253650A1
• Filed: 06/19/2006
• Published: 10/16/2008
• Est. Priority Date: 06/20/2005
• Status: Active Grant

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Kuniba, Hideyasu
• Granted Patent: US 8,103,119 B2
• Time in Patent Office: Days
• US Class Current: 382/167
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement
• CPC Class Codes: H04N 1/407 Control or modification of tonal gradation or of extreme levels, e.g. background level

Abstract

An image processing device includes: a parameter calculation unit that obtains a plurality of values based on a plurality of different conversion parameters for a pixel in image data; a weighting unit that performs predetermined weighting on the plurality of values obtained by the parameter calculation unit; and a gradation correction unit that performs gradation correction of the image data based on a result of the weighting by the weighting unit.

Claims

1. An image processing device comprising:

a parameter calculation unit that obtains a plurality of values based on a plurality of different conversion parameters for a pixel in image data;

a weighting unit that performs predetermined weighting on the plurality of values obtained by the parameter calculation unit; and

a gradation correction unit that performs gradation correction of the image data based on a result of the weighting by the weighting unit.

2. An image processing device according to claim 1, wherein:

the parameter calculation unit obtains the plurality of values based on a plurality of gradation conversions having different characteristics for the pixel in the image data.

3. An image processing device according to claim 1, wherein:

the gradation correction unit includes a gain coefficient calculation unit that calculates a gain coefficient of a pixel based on the result of the weighting by the weighting unit, and performs the gradation correction of the image data according to the gain coefficient calculated by the gain coefficient calculation unit.

4. An image processing device according to claim 1, wherein:

the weighting unit performs the predetermined weighting according to brightness of neighborhood pixels neighboring the pixel.

5. An image processing device according to claim 4, further comprising:

an exposure correction value acquiring unit that acquires an exposure correction value set upon capturing an image corresponding to the image data; and

a brightness correcting unit that corrects brightness of the neighborhood pixels neighboring the pixel based on a result of the acquiring by the exposure correction value acquiring unit, wherein;

the parameter calculation unit obtains the plurality of values based on image data corrected by the brightness correcting unit.

6. An image processing device according to claim 2, further comprising:

a selection unit that selects two gradation conversions out of the plurality of gradation conversions that are three or more types of gradation conversions according to brightness of an image, wherein;

the parameter calculation unit obtains the plurality of values with a brightness value of a pixel using each of the two gradation conversions selected by the selection unit.

7. An image processing device according to claim 6, wherein:

the plurality of gradation conversions include a first gradation conversion having a characteristic represented by a curve that is monotonically increasing and concave upward in at least a part thereof, a second gradation conversion having a characteristic represented by a curve that is monotonically increasing and concave upward in at least a part thereof and having the characteristic in which a change of an output value for an input is smaller that the first gradation conversion, and a third gradation conversion having a characteristic represented by a curve that is montonically increasing and concave downward in at least a part thereof.

8. An image processing device according to claim 7, wherein:

when an average luminance within a predetermined range of the image data is less than a predetermined value, the selection unit selects the first gradation conversion and the second gradation conversion.

9. An image processing device according to claim 7, wherein:

when an average luminance within a predetermined range of the image data is equal to or more than a predetermined value, the selection unit selects the first gradation conversion of the second gradation conversion, and the third gradation conversion.

10. An image processing device according to claim 3, wherein:

when the image data are expressed in a primary color system expression, the gain coefficient calculation unit calculates a gain coefficient for performing gradation correction, based on one color component included in the image data, of another color component.

11. An image processing device according to claim 3, wherein:

when the image data are expressed in a luminance and chrominance expression, the gain coefficient calculation unit calculates a gain coefficient for performing gradation correction of a luminance of each pixel in the image data based on a luminance of the image data.

12. An image processing device according to claim 11, further comprising:

a chrominance data correction unit that corrects chrominance data of each pixel according to the gain coefficient for each pixel obtained by the gain coefficient calculation unit.

13. An image processing device according to claim 1, wherein:

the plurality of values are a plurality of gain coefficients.

14. An image processing device according to claim 4, further comprising:

a reduced image generation unit that generates reduced image data of a reduced image based on the image data;

a smoothing unit that performs smoothing processing of the reduced image data; and

a neighborhood calculation unit that obtains the brightness of the neighborhood pixels based on the reduced image data having undergone the smoothing processing.

27. An image processing method according to claim 13, wherein:

the plurality of values are a plurality of gain coefficients.

15. An image processing method comprising:

a parameter calculating step that obtains a plurality of values based on a plurality of different conversion parameters for a pixel in image data;

a weighting step that performs predetermined weighting on the plurality of values obtained in the parameter calculating step; and

a gradation correction step that performs gradation correction of the image data based on a result of the weighting in the weighting step.

16. An image processing method according to claim 15, wherein:

the parameter calculation step obtains the plurality of values based on a plurality of gradation conversions having different characteristics for the pixel in the image data.

17. An image processing method according to claim 15, wherein:

the gradation correction step includes a gain coefficient calculation step that calculates a gain coefficient of a pixel based on the result of the weighting by the weighting step, and performs the gradation correction of the image data according to the gain coefficient calculated by the gain coefficient calculation step.

18. An image processing method according to claim 15, wherein:

the weighting step performs the predetermined weighting according to brightness of neighborhood pixels neighboring the pixel.

19. An image processing method according to claim 18, further comprising:

an exposure correction value acquiring step that acquires an exposure correction value set upon capturing an image corresponding to the image data; and

a brightness correction step that corrects brightness of the neighborhood pixels neighboring the pixel based on a result of the exposure correction value acquiring step, wherein;

the parameter calculation step obtains the plurality of values based on image data corrected by the brightness correction step.

20. An image processing method according to claim 16, further comprising:

a selection step that selects two gradation conversions from three or more types of gradation conversions according to brightness of an image, wherein;

the parameter calculation step obtains the plurality of values from with a brightness value of the pixel using each of the two gradation conversions selected in the selection step.

21. An image processing method according to claim 20, wherein:

the plurality of gradation conversions include a first gradation conversion having a characteristic represented by a curve that is monotonically increasing and concave upward in at least a part thereof, a second gradation conversion having a characteristic represented by a curve that is monotonically increasing and concave upward in at least a part thereof and having the characteristic in which a change of an output value for an input is smaller than the first gradation conversion, and a third gradation conversion having a characteristic represented by a curve that is monotonically increasing and concave downward in at lest a part thereof.

22. An image processing method according to claim 21, wherein:

when an average luminance within a predetermined range of the image data is less that a predetermined value, the selection step selects the first gradation conversion and the second gradation conversion.

23. An image processing method according to claim 21, wherein:

when an average luminance within a predetermined value, the selection step selects the first gradation conversion or the second gradation conversion, and the third gradation conversion.

24. An image processing method according to claim 17, wherein:

when the image data are expressed in a primary color system expression, the gain coefficient calculation step calculates a gain coefficient for performing gradation correction, based on one color component included in the image data, of another color component.

25. An image processing method according to claim 17, wherein:

when the image data are expressed in a luminance and chrominance expression, the gain coefficient calculation step calculates a gain coefficient for performing gradation correction of a luminance of each pixel in the image data based on a luminance of the image data.

26. An image processing method according to claim 25, further comprising:

a chrominance data correction step that corrects chrominance data of each pixel according to the gain coefficient for each pixel obtained by the gain coefficient calculation step.

28. An image processing method according to claim 18, further comprising:

a reduced image generation step that generates reduced image data of a reduced image based on the image data;

a smoothing step that performs smoothing processing of the reduced image data; and

a neighborhood calculation step that obtains the brightness of the neighborhood pixels based on the reduced image data having undergone the smoothing processing.

30. A computer-readable computer program product comprising:

an image processing program for causing a computer to execute an image processing method according to claim 15.

31. An image-capturing device comprising:

an image sensor that captures an image; and

an image processing unit that executes an image processing program constituting a computer program product according to claim 30 to perform gradation correction of image data corresponding to the image captured by the image sensor.

29. An image processing method comprising:

acquiring an image including a plurality of pixels;

obtaining a plurality of values corresponding to a plurality of different characteristics based on a value indicating a luminance of a target pixel;

obtaining brightness of a vicinity of the target pixel;

obtaining a weighted average of the obtained plurality of values based on the brightness of the vicinity of the target pixel; and

performing gradation correction of the target pixel based on the value indicating the luminance of the target pixel and the obtained weighted average.