Image capturing device which corrects a target luminance, based on which an exposure condition is determined
An image having the image quality desired by a photographer is provided by minimizing overexposure or underexposure, making the dynamic range wide, and specifying an optimum brightness level for a main subject. An image capturing device includes a subject detecting unit which detects a main subject in an image obtained before actual photographing; a subject luminance information acquiring unit which obtains luminance information; a luminance distribution calculating unit which calculates a luminance distribution of each of multiple areas; a target luminance calculating unit which determines a target luminance; a target luminance correcting unit which corrects the target luminance; and an exposure condition determining unit which determines an exposure condition for the actual photographing, in which the target luminance correcting unit includes a criterial range determining unit which determines the criterial range; and a correction amount determining unit which determines a correction amount by using the difference between the target luminance and the luminance of the main subject.
1. An image capturing device comprising:
a subject detecting unit which detects a main subject in an image obtained before actual photographing, from an image signal of the image;
a subject luminance information acquiring unit which obtains luminance information on the main subject from the image signal;
a luminance distribution calculating unit which calculates a luminance distribution of each of multiple areas in the image;
a target luminance calculating unit which determines a target luminance, related to exposure, based on the luminance distribution;
a target luminance correcting unit which corrects the target luminance when a difference between the target luminance and the luminance of the main subject does not fall in a criterial range; and
an exposure condition determining unit which determines an exposure condition for the actual photographing based on the target luminance or a corrected target luminance when the target luminance correcting unit has corrected the target luminance,
wherein the target luminance correcting unit comprises:
a criterial range determining unit which determines the criterial range; and
a correction amount determining unit which determines a correction amount by using the difference between the target luminance and the luminance of the main subject,
wherein the image capturing device has a first setting mode in which a local gradation conversion process is applied to a pixel of interest of the image based on the image signal of a local area around the pixel of interest, and a second setting mode in which the local gradation conversion process is not applied, and
wherein the criterial range determining unit determines the criterial range according to a setting mode that is used.
2. An image capturing device according to claim 1 , wherein an absolute value of a lower threshold of the criterial range is larger than an absolute value of an upper threshold of the criterial range.
3. An image capturing device according to claim 1 , wherein the criterial range determining unit determines the criterial range according to a sensitivity setting of an image pickup device.
4. An image capturing device according to claim 1 , wherein:
the subject detecting unit comprises an area ratio calculating unit which calculates an area ratio of the main subject; and
the criterial range determining unit determines the criterial range according to the area ratio.
5. An image capturing device according to claim 1 , wherein:
the subject detecting unit comprises a face detecting Unit which detects a face; and
the criterial range determining unit determines the criterial range according to a detection result of the face detecting unit.
6. An image capturing device according to claim 1 , wherein:
the subject detecting unit comprises a face detecting unit which detects a face; and
the correction amount determining unit determines the correction amount according to a detection result of the face detecting unit.
7. An image capturing device according to claim 1 , further comprising an image processing unit which performs at least one of a first gradation conversion process in which a uniform gradation conversion process is applied to each pixel in the image according to a uniform gradation conversion characteristic curve, and a second gradation conversion process in which the local gradation conversion process is applied to the image.
8. An image capturing device according to claim 1 , wherein the criterial range determining unit sets the criterial range wider when the local gradation conversion process is applied than when the local gradation conversion process is not applied.
9. An image capturing device according to claim 7 , wherein the image processing unit comprises:
a combining unit which combines a first image serving as a result obtained through the uniform gradation conversion process and a second image serving as a result obtained through the local gradation conversion process, at a predetermined compositing ratio; and
a parameter selecting unit which sets at least one of a gradation conversion characteristic curve used for the uniform gradation conversion process and the predetermined compositing ratio such that the luminance of the subject falls in a predetermined luminance range.
10. An image capturing device according to claim 1 , wherein the image signal is obtained after the local gradation conversion process is applied to an output signal of an image pickup device.
11. An image capturing device according to claim 10 , wherein the target luminance correcting unit corrects the target luminance according to the difference between the luminance of a subject area in the image and the target luminance.
12. An image capturing device comprising:
a luminance distribution calculating unit which calculates a luminance distribution of multiple areas in an image obtained before actual photographing, from parts corresponding to the multiple areas, of an image signal of the image;
a target luminance calculating unit which determines a target luminance, related to exposure, based on the luminance distribution;
a subject detecting unit which detects a main subject in the image from the image signal;
a subject luminance information acquiring unit which obtains luminance information on the main subject from the image signal;
an image processing unit which applies a local gradation conversion process to a pixel of interest of the image based on the image signal of a local area around the pixel of interest;
a luminance evaluation value calculating unit which calculates a luminance evaluation value of the main subject by using an image signal obtained through the local gradation conversion process;
a target luminance correcting unit which corrects, when the difference between the luminance evaluation value and the target luminance does not fall in a predetermined range, the target luminance such that the difference falls in the predetermined range; and
an exposure condition determining unit which determines an exposure condition for actual photographing based on the corrected target luminance,
wherein the image capturing device has a first setting mode in which the local gradation conversion process is applied, and a second setting mode in which the local gradation conversion process is not applied, and
wherein the predetermined range is determined according to a setting mode that is used.