Focus position detection device and focus position detection method

A method for detecting a focus position comprising:

• identifying, by a processor, a plurality of shift amount calculation areas included in a measurement area set on an image sensor in an imaging unit including the image sensor which generates an image and an optical system, each of the plurality of shift amount calculation areas generating a first sub-image and a second sub-image which represent a subject appearing in the shift amount calculation area, wherein a shift amount between the subject on the first sub-image and the subject on the second sub-image changes in accordance with a distance between a focus position at which the subject is brought into focus by the optical system and the image sensor;
• calculating, by the processor, for each of the plurality of shift amount calculation areas, a local shift amount of the second sub-image with respect to the first sub-image when the subject on the first sub-image and the subject on the second sub-image are most coincident with each other;
• calculating, by the processor, for each of the plurality of shift amount calculation areas, a feature quantity representing a probability distribution representing accuracy of the local shift amount;
• estimating, by the processor, for each of the plurality of shift amount calculation areas, the probability distribution on the basis of the local shift amount and the feature quantity;
• combining, by the processor, the probability distributions of the plurality of shift amount calculation areas to obtain a distribution of accuracy of the local shift amount for the measurement area;
• and
• calculating, by the processor, a representative value representing a distance between a focus position produced by the optical system and the image sensor on the basis of the distribution.

A non-transitory computer-readable recording medium having recorded thereon a computer program for focus position detection that causes a computer to execute a process comprising:

• identifying a plurality of shift amount calculation areas included in a measurement area set on an image sensor in an imaging unit including the image sensor which generates an image and an optical system, each of the plurality of shift amount calculation areas generating a first sub-image and a second sub-image which represent a subject appearing in the shift amount calculation area, wherein a shift amount between the subject on the first sub-image and the subject on the second sub-image changes in accordance with a distance between a focus position at which the subject is brought into focus by the optical system and the image sensor;
• calculating, for each of the plurality of shift amount calculation areas, a local shift amount of the second sub-image with respect to the first sub-image when the subject on the first sub-image and the subject on the second sub-image are most coincident with each other and calculating a feature quantity representing a probability distribution representing accuracy of the local shift amount;
• estimating, for each of the plurality of shift amount calculation areas, the probability distribution on the basis of the local shift amount and the feature quantity;
• combining the probability distributions of the plurality of shift amount calculation areas to obtain a distribution of accuracy of the local shift amount for the measurement area;
• and
• calculating a representative value representing a distance between a focus position produced by the optical system and the image sensor on the basis of the distribution.