Imaging apparatus, imaging method, integrated circuit, and storage medium
View Patent ↗An imaging apparatus captures a large dynamic range image of a scene including a backlit person with a blue sky background in a manner that the person's face has an appropriate luminance level without saturating the background sky. An imaging unit obtains analogue image signals through exposure control that prevents a highlight from being saturated, an A/D converter converts the analogue image signals to digital image signals, and a signal processing unit linearly increases the dynamic range of the digital image signals. The image signals with the increased dynamic range are nonlinearly compressed to have a dynamic range of 100% or less through nonlinear dynamic range compression that intensively compresses a highlight portion. The imaging apparatus with this structure first increases the dynamic range of an image and efficiently compresses the increased large dynamic range of the image.
1. An imaging apparatus, comprising:
an optical system operable to adjust an exposure light amount;
an A/D converter operable to receive an analogue signal obtained by the optical system, and convert the analogue signal that is obtained by the optical system to a digital signal;
a dynamic-range increasing unit operable to increase an output value of the digital signal with a dynamic range magnification ratio;
a control unit operable to generate control signals, one for decreasing the exposure light amount and another for increasing the dynamic range magnification ratio;
a dynamic-range compression unit operable to compress the increased value of the digital signal so as to output a value that is within a predetermined range; and
a representative value detection unit operable to detect a representative value of a predetermined portion of image data that is formed using the digital signal,
wherein the dynamic-range compression unit compresses the increased value of the digital signal in a manner that a peak value is converted to be a maximum value of the predetermined range, and the control unit generates, in accordance with the maximum value, the signal for decreasing the exposure light amount, which is a signal for adjusting the exposure light amount according to the representative value, and the signal for increasing the dynamic range magnification ratio.
2. The imaging apparatus according to claim 1 , further comprising:
a face detection processing unit operable to extract a representative value of a digital signal corresponding to a face portion of image data that is formed using the digital signal,
wherein the dynamic-range increasing unit adjusts the dynamic range magnification ratio according to the representative value.
3. The imaging apparatus according to claim 1 , wherein
the dynamic-range compression unit comprises:
a vicinity luminance detection unit operable to extract a vicinity luminance value of a digital signal corresponding to a predetermined position; and
a dynamic tone correction unit operable to convert an input value of a digital signal for a position to an output value of a digital signal for the position by using a conversion characteristic,
wherein the conversion characteristic changes an output value according to the vicinity luminance value for the digital signal.
4. The imaging apparatus according to claim 3 , wherein
the conversion characteristic changes the value of the digital signal for the position more when a value of the digital signal is close to a value of the vicinity luminance value than when the value of the digital signal is not close to the value of the vicinity luminance value.
5. The imaging apparatus according to claim 3 , wherein
when m=x, where x is the value of the digital signal corresponding to the predetermined position and m is the vicinity luminance value, the conversion characteristic expressed using a quadratic function f (x, m) satisfies:
∂ f ( x,m )/∂ x ≧( f ( x,m )/ x ).
6. The imaging apparatus according to claim 3 , wherein
the dynamic tone correction unit is a two-dimensional lookup table storing, as data, an output value that is determined by the value of the digital signal and the vicinity luminance value.
7. The imaging apparatus according to claim 6 , wherein
the control unit generates signals,
one signal for decreasing the exposure light amount, one signal for increasing the dynamic range increase ratio, and one signal for storing conversion characteristic data that is determined by the dynamic range increase ratio into the lookup table.
8. The imaging apparatus according to claim 3 , further comprising:
a range adjustment unit operable to receive the digital signal whose dynamic range has been magnified by the dynamic-range magnification unit, and convert the value of the received digital signal to a value that is within an input range of the dynamic range compression unit when the value of the received digital signal is greater than a predetermined value.
9. The imaging apparatus according to claim 3 , further comprising:
a peak adjustment unit operable to adjust the value of the digital signal in a manner that a peak value of image data that is formed using the digital signal whose dynamic range has been increased by the dynamic-range increasing unit is adjusted to a maximum value of an input range of the dynamic-range compression unit.
10. An imaging apparatus, comprising:
an optical system operable to adjust an exposure light amount;
an A/D converter operable to receive an analogue signal obtained by the optical system, and convert the analogue signal that is obtained by the optical system to a digital signal;
a dynamic-range increasing unit operable to increase an output value of the digital signal with a dynamic range magnification ratio;
a control unit operable to generate control signals, one for decreasing the exposure light amount and another for increasing the dynamic range magnification ratio;
a dynamic-range compression unit operable to compress the increased value of the digital signal so as to output a value that is within a predetermined range; and
a representative value detection unit operable to detect a representative value of a predetermined portion of image data that is formed using the digital signal,
wherein the dynamic-range compression unit compresses the increased value of the digital signal in a manner that a peak value is converted to be a maximum value of the predetermined range, and the control unit generates, in accordance with the maximum value, the signal for decreasing the exposure light amount, and the signal for increasing the dynamic range magnification ratio, which is a signal for adjusting the dynamic range magnification ratio according to the representative value.
11. An imaging method used in an imaging apparatus that includes an optical system operable to adjust an exposure light amount, and an A/D converter operable to receive an analogue signal obtained by the optical system and convert the analogue signal to a digital signal, the imaging method comprising:
(A) increasing the digital signal with a dynamic range magnification ratio;
(B) in accordance with a maximum value of image data formed by the increased digital signal, generating control signals, one for decreasing the exposure light amount and another for increasing the dynamic range magnification ratio;
(C) in accordance with the maximum value of image data formed by the increased digital signal, compressing the increased value of the digital signal so as to output a value that is within a predetermined range; and
(D) detecting a representative value of a predetermined portion of image data that is formed using the digital signal,
wherein the step (C) compresses the increased value of the digital signal in a manner that a peak value is converted to be a maximum value of the predetermined range, and the step (B) generates, in accordance with the maximum value, the signal for decreasing the exposure light amount, which is a signal for adjusting the exposure light amount according to the representative value, and the signal for increasing the dynamic range magnification ratio.
12. An non-transitory computer-readable storage medium that stores a program causing a computer to execute an imaging method according to claim 11 .
13. An integrated circuit used in an imaging apparatus that includes an optical system operable to adjust an exposure light amount, and an A/D converter operable to receive an analogue signal obtained by the optical system and convert the analogue signal to a digital signal, the integrated circuit comprising:
a dynamic-range increasing unit operable to increase the digital signal with a dynamic range magnification ratio;
a control unit operable to generate, in accordance with a maximum value of image data formed by the increased digital signal, control signals, one for decreasing the exposure light amount and another for increasing the dynamic range magnification ratio;
a dynamic-range compression unit operable to compress, in accordance with the maximum value of image data formed by the increased digital signal, the increased value of the digital signal so as to output a value that is within a predetermined range; and
a representative value detection unit operable to detect a representative value of a predetermined portion of image data that is formed using the digital signal,
wherein the dynamic-range compression unit compresses the increased value of the digital signal in a manner that a peak value is converted to be a maximum value of the predetermined range, and the control unit generates, in accordance with the maximum value, the signal for decreasing the exposure light amount, which is a signal for adjusting the exposure light amount according to the representative value, and the signal for increasing the dynamic range magnification ratio.
14. An imaging method used in an imaging apparatus that includes an optical system operable to adjust an exposure light amount, and an A/D converter operable to receive an analogue signal obtained by the optical system and convert the analogue signal to a digital signal, the imaging method comprising:
(A) increasing the digital signal with a dynamic range magnification ratio;
(B) in accordance with a maximum value of image data formed by the increased digital signal, generating control signals, one for decreasing the exposure light amount and another for increasing the dynamic range magnification ratio;
(C) in accordance with the maximum value of image data formed by the increased digital signal, compressing the increased value of the digital signal so as to output a value that is within a predetermined range; and
(D) detecting a representative value of a predetermined portion of image data that is formed using the digital signal,
wherein the step (C) compresses the increased value of the digital signal in a manner that a peak value is converted to be a maximum value of the predetermined range, and the step (B) generates, in accordance with the maximum value, the signal for decreasing the exposure light amount, and the signal for increasing the dynamic range magnification ratio, which is a signal for adjusting the dynamic range magnification ratio according to the representative value.
15. A non-transitory computer-readable storage medium that stores a program causing a computer to execute an imaging method according to claim 14 .