Observation system, focus position calculation method, and computer readable medium

An observation system comprising:

• an illumination device that includes a plurality of light sources provided at symmetrical positions with respect to an optical axis of an objective that condenses light from an observation object, and that selectively causes the plurality of light sources to emit light to illuminate the observation object with the illumination light from two symmetrical directions;
• an imaging device that includes the objective and that images the observation object with the light condensed by the objective;
• and
• a control unit that calculates a focus position of the imaging device based on a plurality of image groups acquired by the imaging device at observation positions different from each other in the optical axis direction of the objective, each of the plurality of image groups including a plurality of images of the observation object illuminated from the two symmetrical directions by the illumination device,
• wherein the control unit is configured to execute processes comprising:
• shift amount calculation processing of calculating a shift amount between the plurality of images in a direction orthogonal to the optical axis of the objective based on the plurality of images;
• and
• focus position calculation processing of calculating the focus position based on a plurality of shift amounts calculated in the shift amount calculation processing and corresponding to observation positions different from each other in the optical axis direction.

A focus position calculation method, the method comprising:

• calculating, by a computer, a focus position of an imaging device that images an observation object based on a plurality of image groups acquired by the imaging device at observation positions different from each other in an optical axis direction of an objective included in the imaging device, each of the plurality of image groups including a plurality of images of the observation object illuminated from directions different from each other by an illumination device that includes a plurality of light sources,
• wherein:
• the calculating comprises:
• shift amount calculation processing of calculating a shift amount between the plurality of images in a direction orthogonal to the optical axis of the objective based on the plurality of images;
• and
• focus position calculation processing of calculating the focus position based on a plurality of shift amounts calculated in the shift amount calculation processing and corresponding to observation positions different from each other in the optical axis direction,
• the shift amount calculation processing includes:
• processing of calculating a correlation between a plurality of regions, each of which is a portion of one of the plurality of images;
• and
• processing of calculating the shift amount from a positional relationship between the plurality of regions where the correlation indicates a peak,
• the shift amount calculation processing further includes processing of calculating a correlation value at the peak, and
• the focus position calculation processing includes processing of calculating the focus position based on the plurality of shift amounts and a plurality of correlation values calculated in the shift amount calculation processing and corresponding to observation positions different from each other in the optical axis direction.

A non-transitory computer-readable medium storing a program for causing a computer to execute processing comprising:

• processing of calculating a focus position of an imaging device that images an observation object based on a plurality of image groups acquired by the imaging device at observation positions different from each other in an optical axis direction of an objective included in the imaging device, each of the plurality of image groups including a plurality of images of the observation object illuminated from directions different from each other by an illumination device that includes a plurality of light sources,
• wherein:
• the processing of calculating the focus position comprises:
• shift amount calculation processing of calculating a shift amount between the plurality of images in a direction orthogonal to the optical axis of the objective based on the plurality of images;
• and
• focus position calculation processing of calculating the focus position based on a plurality of shift amounts calculated in the shift amount calculation processing and corresponding to observation positions different from each other in the optical axis direction,
• the shift amount calculation processing includes:
• processing of calculating a correlation between a plurality of regions, each of which is a portion of one of the plurality of images;
• and
• processing of calculating the shift amount from a positional relationship between the plurality of regions where the correlation indicates a peak,
• the shift amount calculation processing further includes processing of calculating a correlation value at the peak, and
• the focus position calculation processing includes processing of calculating the focus position based on the plurality of shift amounts and a plurality of correlation values calculated in the shift amount calculation processing and corresponding to observation positions different from each other in the optical axis direction.