IMAGING APPARATUS, IMAGING METHOD, STORAGE MEDIUM STORING PROGRAM, AND INTEGRATED CIRCUIT
An imaging apparatus reduces flicker occurring under fluorescent lamp illumination in real time and also effectively reduces noise of a captured image generated by low-sensitive pixel areas fixed on an imaging surface. The imaging apparatus obtains a first image signal including no flicker element and a second image signal including a flicker element for each frame, and calculates a gain correction coefficient for eliminating the flicker element in the second image signal based on the first and second image signals, eliminates the flicker element from the second image signal based on the gain correction coefficient, and combines the first and second image signals to generate an image signal from which the flicker element has been eliminated. The imaging apparatus also effectively reduces noise of a captured image generated by low-sensitive pixel areas fixed on an imaging surface by changing the charge accumulation time of pixels depending on each frame.
1 . An imaging apparatus, comprising:
an imaging unit including an image sensor having a first group of pixels and a second group of pixels that are driven independently of each other;
a charge accumulation time setting unit that sets, for an image that is formed by the imaging unit, a first charge accumulation time with which no flicker element is generated due to a power supply frequency of illumination and a second charge accumulation time different from the first charge accumulation time;
a switch unit that switches, for every frame, a charge accumulation time for the first group of pixels and a charge accumulation time for the second group of pixels between the first charge accumulation time and the second charge accumulation time;
a drive unit that drives the pixels included in the first group and the pixels included in the second group with the first charge accumulation time and the second charge accumulation time that are switched for every frame by the switch unit;
a signal switching unit that outputs an image signal obtained with the first charge accumulation time by the imaging unit as a first image signal, and outputs an image signal obtained with the second charge accumulation time by the imaging unit as a second image signal;
a first gain correction unit that performs gain correction to adjust a signal level of the first image signal to a signal level of the second image signal;
a gain calculation unit that calculates a gain correction coefficient for correcting a flicker element included in the second image signal based on the first image signal and the second image signal;
a second gain correction unit that corrects a flicker element included in the second image signal based on the gain correction coefficient; and
a signal combining unit that combines the second image signal corrected by the second gain correction unit and the first image signal subjected to gain correction performed by the first gain correction unit in an arrangement identical to an arrangement of the first group of pixels and the second group of pixels in the image sensor.
2 . The imaging apparatus according to claim 1 ,
wherein the gain calculation unit calculates an average value A of signal levels in every horizontal line of a first image that is formed using the first image signal, and an average value B of signal levels in every horizontal line of a second image that is formed using the second image signal, and calculates a ratio C of the horizontal line average values as C=A/B as the gain correction coefficient, and
the second gain correction unit corrects the second image signal by multiplying the second image signal by the ratio C of the horizontal line average values calculated by the gain calculation unit.
3 . The imaging apparatus according to claim 1 ,
wherein the imaging unit includes the image sensor in which the pixels included in the first group and the pixels included in the second group are arranged adjacent to each another in vertical and horizontal directions on an imaging surface of the image sensor.
4 . The imaging apparatus according to claim 1 ,
wherein the imaging unit includes the image sensor in which the pixels included in the first group and the pixels included in the second group are arranged adjacent to each another in a vertical direction on an imaging surface of the image sensor.
5 . The imaging apparatus according to claim 1 ,
wherein the imaging unit includes the image sensor in which the pixels included in the first group and the pixels included in the second group are arranged adjacent to each another in a horizontal direction on an imaging surface of the image sensor.
6 . The imaging apparatus according to claim 1 ,
wherein the charge accumulation time setting unit sets the first charge accumulation time at n/100 second, where n is a natural number, when the power supply frequency of illumination is 50 Hz, and sets the first charge accumulation time at n/120 second, where n is a natural number, when the power supply frequency of illumination is 60 Hz.
7 . An imaging method that is used in an imaging apparatus including an imaging unit whose image sensor has a first group of pixels and a second group of pixels that are driven independently of each other, the method comprising:
setting, for an image that is formed by the imaging unit, a first charge accumulation time with which no flicker element is generated due to a power supply frequency of illumination and a second charge accumulation time different from the first charge accumulation time;
switching, for every frame, a charge accumulation time for the first group of pixels and a charge accumulation time for the second group of pixels between the first charge accumulation time and the second charge accumulation time;
driving the pixels included in the first group and the pixels included in the second group with the first charge accumulation time and the second charge accumulation time that are switched for every frame in the switch step;
outputting an image signal obtained with the first charge accumulation time by the imaging unit as a first image signal, and outputting an image signal obtained with the second charge accumulation time by the imaging unit as a second image signal;
performing gain correction to adjust a signal level of the first image signal to a signal level of the second image signal;
calculating a gain correction coefficient for correcting a flicker element included in the second image signal based on the first image signal and the second image signal;
correcting a flicker element included in the second image signal based on the gain correction coefficient; and
combining the second image signal corrected in the second gain correction step and the first image signal subjected to gain correction performed in the first gain correction step in an arrangement identical to an arrangement of the first group of pixels and the second group of pixels in the image sensor.
8 . A storage medium storing a computer-readable program that is used in an imaging apparatus including an imaging unit whose image sensor has a first group of pixels and a second group of pixels that are driven independently of each other, the program enabling a computer to function as:
a charge accumulation time setting unit that sets, for an image that is formed by the imaging unit, a first charge accumulation time with which no flicker element is generated due to a power supply frequency of illumination and a second charge accumulation time different from the first charge accumulation time;
a switch unit that switches, for every frame, a charge accumulation time for the first group of pixels and a charge accumulation time for the second group of pixels between the first charge accumulation time and the second charge accumulation time;
a drive unit that drives the pixels included in the first group and the pixels included in the second group with the first charge accumulation time and the second charge accumulation time that are switched for every frame by the switch unit;
a signal switching unit that outputs an image signal obtained with the first charge accumulation time by the imaging unit as a first image signal, and outputs an image signal obtained with the second charge accumulation time by the imaging unit as a second image signal;
a first gain correction unit that performs gain correction to adjust a signal level of the first image signal to a signal level of the second image signal;
a gain calculation unit that calculates a gain correction coefficient for correcting a flicker element included in the second image signal based on the first image signal and the second image signal;
a second gain correction unit that corrects a flicker element included in the second image signal based on the gain correction coefficient; and
a signal combining unit that combines the second image signal corrected by the second gain correction unit and the first image signal subjected to gain correction performed by the first gain correction unit in an arrangement identical to an arrangement of the first group of pixels and the second group of pixels in the image sensor.
9 . An integrated circuit, comprising:
an imaging unit including an image sensor having a first group of pixels and a second group of pixels that are driven independently of each other;
a charge accumulation time setting unit that sets, for an image that is formed by the imaging unit, a first charge accumulation time with which no flicker element is generated due to a power supply frequency of illumination and a second charge accumulation time different from the first charge accumulation time;
a switch unit that switches, for every frame, a charge accumulation time for the first group of pixels and a charge accumulation time for the second group of pixels between the first charge accumulation time and the second charge accumulation time;
a drive unit that drives the pixels included in the first group and the pixels included in the second group with the first charge accumulation time and the second charge accumulation time that are switched for every frame by the switch unit;
a signal switching unit that outputs an image signal obtained with the first charge accumulation time by the imaging unit as a first image signal, and outputs an image signal obtained with the second charge accumulation time by the imaging unit as a second image signal;
a first gain correction unit that performs gain correction to adjust a signal level of the first image signal to a signal level of the second image signal;
a gain calculation unit that calculates a gain correction coefficient for correcting a flicker element included in the second image signal based on the first image signal and the second image signal;
a second gain correction unit that corrects a flicker element included in the second image signal based on the gain correction coefficient; and
a signal combining unit that combines the second image signal corrected by the second gain correction unit and the first image signal subjected to gain correction performed by the first gain correction unit in an arrangement identical to an arrangement of the first group of pixels and the second group of pixels in the image sensor.
10 . An integrated circuit that is used in an imaging apparatus including an imaging unit whose image sensor has a first group of pixels and a second group of pixels that are driven independently of each other, the integrated circuit comprising:
a charge accumulation time setting unit that sets, for an image that is formed by the imaging unit, a first charge accumulation time with which no flicker element is generated due to a power supply frequency of illumination and a second charge accumulation time different from the first charge accumulation time;
a switch unit that switches, for every frame, a charge accumulation time for the first group of pixels and a charge accumulation time for the second group of pixels between the first charge accumulation time and the second charge accumulation time;
a drive unit that drives the pixels included in the first group and the pixels included in the second group with the first charge accumulation time and the second charge accumulation time that are switched for every frame by the switch unit;
a signal switching unit that outputs an image signal obtained with the first charge accumulation time by the imaging unit as a first image signal, and outputs an image signal obtained with the second charge accumulation time by the imaging unit as a second image signal;
a first gain correction unit that performs gain correction to adjust a signal level of the first image signal to a signal level of the second image signal;
a gain calculation unit that calculates a gain correction coefficient for correcting a flicker element included in the second image signal based on the first image signal and the second image signal;
a second gain correction unit that corrects a flicker element included in the second image signal based on the gain correction coefficient; and
a signal combining unit that combines the second image signal corrected by the second gain correction unit and the first image signal subjected to gain correction performed by the first gain correction unit in an arrangement identical to an arrangement of the first group of pixels and the second group of pixels in the image sensor.