Image sensing apparatus and image processing method

• US 20070182830A1
• Filed: 01/29/2007
• Published: 08/09/2007
• Est. Priority Date: 01/31/2006
• Status: Active Grant

• Current Assignee: Konica Minolta Holdings Incorporated (Konica Minolta Inc.)
• Original Assignee: Konica Minolta Holdings Incorporated (Konica Minolta Inc.)
• Inventors: Takayama, Jun, Kamon, Koichi, Katagiri, Tetsuya
• Granted Patent: US 7,843,493 B2
• Time in Patent Office: Days
• US Class Current: 348/222.100
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene

Abstract

An image sensing apparatus includes: an image sensing section for sensing an image of a subject; a detector for detecting a luminance of the subject; a compressor for compressing a dynamic range of the subject image; and a controller for controlling a compression characteristic to be used in compressing the dynamic range based on a detection result of the detector.

Claims

1. An image sensing apparatus comprising:

an image sensing section for sensing an image of a subject;

a detector for detecting a luminance of the subject;

a compressor for compressing a dynamic range of the subject image; and

a controller for controlling a compression characteristic to be used in compressing the dynamic range based on a detection result of the detector.

2. The image sensing apparatus according to claim 1, wherein

the detector detects the luminance in a plurality of areas concerning the subject image, and

the controller controls the compression characteristic based on a maximal value and a minimal value of the detected subject luminance in the plurality of areas.

3. The image sensing apparatus according to claim 2, wherein

in the case where there exist a first difference value and a second difference value smaller than the first difference value, as a difference value between the maximal value and the minimal value, the controller controls the compression characteristic in such a manner that a compression ratio set for the second difference value is larger than a compression ratio set for the first difference value.

4. The image sensing apparatus according to claim 1, wherein

the detector detects the luminance in at least two areas concerning the subject image, and

the controller controls the compression characteristic based on a discrimination result as to whether the detected subject luminance in one of the two areas is larger or smaller than that in the other one of the two areas.

5. The image sensing apparatus according to claim 4, wherein

the one of the two areas is a main subject area corresponding to a central area of the subject image, and the other one of the two areas is a background area corresponding to an area other than the central area of the subject image, and

the controller controls the compression characteristic in such a manner that a first compression ratio, a second compression ratio, and a third compression ratio satisfy the following relationship:

the first compression ratio<

the third compression ratio<

the second compression ratio,

the first compression ratio being used in the case where a first different value obtained by subtracting a background luminance in the background area from a main subject luminance in the main subject area is equal to or larger than zero,

the second compression ratio being used in the case where a second different value obtained by subtracting the background luminance from the main subject luminance is equal to or smaller than a predetermined negative threshold value, and

the third compression ratio being used in the case where a third difference value obtained by subtracting the background luminance from the main subject luminance is smaller than zero and is larger than the threshold value.

6. The image sensing apparatus according to claim 1, wherein

the image sensing section includes an image sensor having a photoelectric conversion characteristic with a linear characteristic where an electric signal is linearly converted commensurate with an incident light amount for output, and a logarithmic characteristic where the electric signal is logarithmically converted commensurate with the incident light amount for output, the image sensor being operative to obtain a linear-logarithmic image by a sensing operation thereof.

7. The image sensing apparatus according to claim 6, further comprising:

a characteristic converter for converting the linear-logarithmic image into a linear image having the linear characteristic over the entirety of the photoelectric conversion characteristic;

an image creator for creating, based on the linear image, a plurality of images having different contrasts in accordance with the detected luminance in each of a plurality of areas concerning the subject image;

an image divider for dividing the each of the plurality of images into a plurality of block images; and

an image synthesizer for selecting the block image having a maximal contrast from the block images at positions corresponding to each other among the plurality of images with respect to each of the block images for synthesis of the selected block images.

10. The image sensing apparatus according to claim 1, further comprising:

a processor for performing a dodging process concerning the dynamic range compression with respect to the subject image;

a parameter setter for setting a first parameter concerning the dodging process to control the compression characteristic;

a converter for performing a gradation conversion process with respect to the subject image; and

a gradation characteristic setter for setting a gradation conversion characteristic concerning the gradation conversion process, wherein

the gradation characteristic setter determines the gradation conversion characteristic based on the first parameter, and

the converter performs the gradation conversion process based on the gradation conversion characteristic.

11. The image sensing apparatus according to claim 10, wherein

the processor performs the dodging process by compressing an illumination component extracted from the subject image, and generating a new image based on the compressed illumination component and a reflectance component extracted from the subject image, and

the gradation characteristic setter determines the gradation conversion characteristic based on the first parameter representing a degree of compression in a luminance range where the illumination component is to be compressed.

12. The image sensing apparatus according to claim 11, wherein

the gradation conversion setter determines the gradation conversion characteristic based on information, as the first parameter, relating to a first luminance level corresponding to a predetermined compression start level in the luminance range where the illumination component is to be compressed, and a second luminance level higher than the compression start level.

13. The image sensing apparatus according to claim 12, wherein

the first luminance level is a luminance level equal to or larger than a main subject luminance corresponding to a predetermined luminance value of a main subject image, and

in the case where the first luminance level is defined as an input value for the gradation conversion process, the gradation characteristic setter determines the gradation conversion characteristic in such a manner that an output value for the gradation conversion process with respect to the gradation conversion input value is set to a small value if the degree of compression of the illumination component is large, and that the gradation conversion output value with respect to the gradation conversion input value is set to a large value if the degree of compression of the illumination component is small.

14. The image sensing apparatus according to claim 10, wherein

in the case where a proper output value for the gradation conversion process concerning a main subject image is set to I0′

, the gradation characteristic setter determines, when an input value for the gradation conversion process concerning a main subject luminance is I0, the gradation conversion characteristic that enables to convert I0 to I0′

.

15. The image sensing apparatus according to claim 1, further comprising:

a processor for performing a dodging process concerning the dynamic range compression with respect to the subject image;

a parameter setter for setting a first parameter concerning the dodging process to control the compression characteristic;

a sharpness corrector for performing a sharpness correction process with respect to the subject image; and

a correction amount setter for setting a sharpness correction amount concerning the sharpness correction process, wherein

the correction amount setter determines the sharpness correction amount based on the first parameter, and

the sharpness corrector performs the sharpness correction process based on the sharpness correction amount.

16. The image sensing apparatus according to claim 15, wherein

the dodging process is realized by performing a computation process locally with respect to a plurality of image areas obtained by dividing the subject image, and

the first parameter is a size of each of the image areas to which the local computation process is to be performed.

17. The image sensing apparatus according to claim 15, wherein

the processor performs the dodging process by compressing an illumination component extracted from the subject image, and generating a new image based on the compressed illumination component and a reflectance component extracted from the subject image, and

the first parameter is a size of a filter for extracting the illumination component from the subject image, and

the correction amount setter determines the sharpness correction amount based on the size of the filter.

18. The image sensing apparatus according to claim 15, wherein

the dodging process is realized by performing a contrast correction process locally with respect to a plurality of image areas obtained by dividing the subject image, and

the first parameter is a size of each of the image areas to which the local contrast correction process is to be performed.

19. The image sensing apparatus according to claim 16, wherein

the correction amount setter changes a frequency characteristic for edge extraction to be used by the sharpness corrector in accordance with the sharpness correction amount determined based on the size of the each of the image areas to which the local computation process is to be performed.

20. The image sensing apparatus according to claim 16, wherein

the correction amount setter changes an edge emphasis amount to be used by the sharpness corrector in accordance with the sharpness correction amount determined based on the size of the each of the image areas to which the local computation process is to be performed.

8. An image sensing system comprising:

an image sensing apparatus for sensing an image of a subject; and

an information processor for performing a predetermined computation process, wherein

the image sensing apparatus and/or the image processor includes a detector for detecting a luminance of the subject, and

the information processor includes a compressor for compressing a dynamic range of the subject image, and a controller for controlling a compression characteristic to be used in compressing the dynamic range based on a detection result of the detector.

9. An image sensing method comprising:

an image sensing step of sensing an image of a subject;

a detecting step of detecting a luminance of the subject in a plurality of areas concerning the subject image;

a calculating step of calculating a compression characteristic to be used in compressing a dynamic range of the subject image based on a detection result obtained in the detecting step; and

a compressing step of compressing the dynamic range of the subject image using the compression characteristic.