Image pickup apparatus with reduced flicker and automatic level adjusting method of the same
An image pickup apparatus includes a solid-state imaging device, an accumulating section, first and second imaging parameter setting sections, a calculating section, a flicker detecting section, and a switching section. The accumulating section calculates a projection output value of a predetermined line in a frame. The calculating section calculates inter-frame variations of the projection output values, and calculates a flicker index from the variations of a predetermined number of frames. The flicker detecting section detects the flicker from the index, and controls the switching section in response to the detection result of the flicker, so that the switching section selects either the setting signals from the first imaging parameter setting section or the setting signals from the second imaging parameter setting section. Thus, the charge storage time of the solid-state imaging device is set at either an integer multiple of 1/100 second or an integer multiple of 1/120 second in response to the frequency (50 Hz or 60 Hz) of a power supply of the fluorescent lighting. The image pickup apparatus can solve a problem of a conventional apparatus in that it is difficult for the conventional apparatus to suppress the flicker in regions where the frequency of the power supply differ from each other.
1. An image pickup apparatus comprising:
a solid-state imaging device for generating an image signal by carrying out photoelectric conversion of individual pixels at different timings;
an amplifier for amplifying the image signal; and
an automatic level adjusting section for regulating a level of the image signal at a specified level by automatically controlling a charge storage time of said solid-state imaging device and a gain of said amplifier,
wherein said automatic level adjusting section comprises:
a first setting section for setting the charge storage time of said solid-state imaging device at an integer multiple of half a reciprocal of a frequency of a first power supply;
a second setting section for setting the charge storage time of said solid-state imaging device at an integer multiple of half a reciprocal of a frequency of a second power supply;
a switching section for selecting one of said first setting section and said second setting section to set the charge storage time of said solid-state imaging device;
an accumulating section for accumulating a plurality of pixel values of a predetermined line in a frame;
an index calculating section for calculating inter-frame variations of accumulation values obtained by said accumulating section, and for calculating an index for detecting the flicker from the inter-frame variations of a predetermined number of frames; and
a flicker detecting section for detecting flicker in response to the index of said index calculating section, and for controlling said switching section in response to the detecting of the flicker.
2. The image pickup apparatus according to claim 1 , wherein
said first setting section sets the charge storage time of said solid-state imaging device at an integer multiple of 1/100 second, and
said second setting section sets the charge storage time of said solid-state imaging device at an integer multiple of 1/120 of a second.
3. The image pickup apparatus according to claim 1 , wherein said index calculating section calculates the index by accumulating the variations of accumulation values of individual frames over a predetermined number of frames over which accumulation values are obtained by said accumulating section.
4. The image pickup apparatus according to claim 3 , wherein said flicker detecting section compares the index obtained when said first setting section is in operation with the index obtained when said second setting section is in operation, and controls said switching section in response to a result of the comparison.
5. The image pickup apparatus according to claim 3 , wherein said flicker detecting section compares the index obtained when one of said first setting section and said second setting section is in operation with a predetermined threshold value, and controls said switching section in response to a result of the comparison.
6. The image pickup apparatus according to claim 1 , wherein said index calculating section comprises:
a plurality of memories for storing indices calculated from accumulation values obtained by said accumulating section over a predetermined number of frames;
a sum calculating section for calculating a sum of the indices of the predetermined number of frames; and
a maximum differential calculating section for calculating a difference between a maximum value and a minimum value of the indices of the predetermined number of frames.
7. The image pickup apparatus according to claim 1 , further comprising a threshold value setting section for setting a predetermined threshold value to be supplied to said flicker detecting section in response to the image signal captured by said solid-state imaging device, wherein said flicker detecting section detects the flicker by comparing the index with the threshold value.
8. The image pickup apparatus according to claim 7 , wherein said threshold value setting section comprises a look-up table, and sets the threshold value corresponding to the image signal by referring to the look-up table.
9. The image pickup apparatus according to any one of claim 1 , further comprising a masking section for masking a control signal supplied from said flicker detecting section to said switching section to halt the switching operation of said switching section.
10. The image pickup apparatus according to claim 9 , wherein said masking section masks the control signal to said switching section in response to an accumulation value obtained by said accumulating section, the accumulation value being obtained by accumulating the pixel values over all or part of a frame of the image signal captured by said solid-state imaging device.
11. The image pickup apparatus according to claim 9 , wherein said masking section masks the control signal to said switching section in response to the charge storage time of said solid-state imaging device.
12. The image pickup apparatus according to claim 9 , wherein said masking section masks the control signal to said switching section in response to a gain of said amplifier.
13. An automatic level adjusting method applied to an image pickup apparatus including a solid-state imaging device for generating an image signal by carrying out photoelectric conversion of individual pixels at different timings, and an amplifier for amplifying the image signal, said automatic level adjusting method regulating a level of the image signal at a specified level by automatically controlling a charge storage time of said solid-state imaging device and a gain of said amplifier, and said automatic level adjusting method comprising the steps of:
accumulating a plurality of pixel values of a predetermined line in a frame;
calculating inter-frame variations of accumulation values, and calculating an index for detecting flicker from the inter-frame variations of a predetermined number of frames;
detecting the flicker in response to the index; and
setting, in response to the detecting of the flicker, the charge storage time of said solid-state imaging device at one of an integer multiple of half a reciprocal of a frequency of a first power supply and an integer multiple of half a reciprocal of a frequency of a second power supply.