Image capture apparatus and control method thereof
An image capture apparatus has an A/D converter that compares a pixel signal read out from a pixel having a photoelectric conversion element with a reference signal whose voltage changes over time, and obtains, as an A/D conversion result of the pixel signal, a digital value corresponding to a time required for a magnitude relationship between the pixel signal and the reference signal to change. The A/D converter determines a level of the pixel signal using a threshold value, makes a change rate of the voltage of the reference signal different depending on a determination result, and changes the threshold value according to a signal expansion amount of the pixel signal after A/D conversion.
1. An image capture apparatus comprising:
an imager having an A/D converter that compares a pixel signal, which is output from a pixel having a photoelectric conversion element, with a reference signal having a voltage that changes over time, and obtains, as an A/D conversion result of the pixel signal, a digital value corresponding to a time required for a magnitude relationship between the pixel signal and the reference signal to change; and
a generator that generates a high dynamic range image by composing a plurality of images obtained by sequentially shooting a same object with a reference exposure, an exposure lower than the reference exposure, and an exposure higher than the reference exposure by the imager,
wherein the A/D converter determines a level of the pixel signal using a threshold value, makes a change rate of the voltage of the reference signal different depending on a determination result, and the threshold value is changed according to respective exposures for obtaining the plurality of images.
2. The image capture apparatus according to claim 1 , wherein a magnitude of a digital gain applied to the pixel signal that has undergone A/D conversion differs depending on the change rate of the voltage of the reference signal.
3. The image capture apparatus according to claim 2 , further comprising:
an image processor which applies image processing to the pixel signal that has undergone A/D conversion,
wherein the digital gain is applied by the image processor.
4. The image capture apparatus according to claim 3 ,
wherein the image processing includes gamma correction processing, and
the digital gain is applied before the gamma correction processing.
5. A control method of an image capture apparatus having an imager that comprises an A/D converter that compares a pixel signal output from a pixel having a photoelectric conversion element with a reference signal having a voltage that changes over time, and obtains, as an A/D conversion result of the pixel signal, a digital value corresponding to a time required for a magnitude relationship between the pixel signal and the reference signal to change, the control method comprising:
obtaining a plurality of images by sequentially shooting a same object with a reference exposure, an exposure lower than the reference exposure, and an exposure higher than the reference exposure by the imager; and
generating a high dynamic range image by composting the plurality of images;
wherein the obtaining includes:
determining a level of the pixel signal using a threshold value;
making a change rate of the voltage of the reference signal different depending on a determination result; and
changing the threshold value according to respective exposures for obtaining the plurality of images.