Focus detection apparatus and method, and image capturing apparatus

An image capturing apparatus comprising:

• an image sensor that includes a plurality of photoelectric conversion portions for each of a plurality of microlenses, performs photoelectric conversion on light entering via an imaging optical system to output an electric signal, and is covered with color filters of a plurality of colors;
• a focus detection apparatus comprising one or more processors and/or circuitry which functions as:
• an acquisition unit that acquires, for each color, correction values for respectively correcting first and second focus detection signals of a pair of focus detection signals of respective colors acquired from the image sensor based on color sensitivity information unique to the image sensor, the image sensor;
• a correction unit that corrects each of the first and second focus detection signals of the pair of focus detection signals of the respective colors by using the correction value;
• a generation unit that combines each of the first focus detection signals of the respective colors corrected by the correction unit, combines each of the second focus detection signals of the respective colors corrected by the correction unit, and generates a pair of combined focus detection signals including the combined first focus detection signals and the combined second focus detection signals;
• and
• a focus detection unit that detects an evaluation value indicating a focus state, based on the pair of combined focus detection signals generated by the generation unit;
• and
• a control unit that controls a focus state of the imaging optical system based on the evaluation value.

A method for focus detection using first and second focus detection signals of a pair of focus detection signals of respective colors obtained from an image sensor, the image sensor including a plurality of photoelectric conversion portions for each of a plurality of microlenses, performing photoelectric conversion on light entering via an imaging optical system to output an electric signal, and being covered with color filters of a plurality of colors, the method comprising:

• acquiring, for each color, correction values for respectively correcting the first and second focus detection signals based on color sensitivity information unique to the image sensor;
• correcting each of the first and second focus detection signals of the pair of focus detection signals of the respective colors by using the correction value;
• combining each of the first corrected focus detection signals of the respective colors, combining each of the second corrected focus detection signals of the respective colors, and generating a pair of combined focus detection signals including the combined first focus detection signals and the combined second focus detection signals;
• and
• detecting an evaluation value indicating a focus state, based on the pair of combined generated focus detection signals.