A method of generating 3D information includes: varying the distance between the sample and an objective lens of the optical microscope at pre-determined steps, capturing an image at each pre-determined step; determining a characteristic value of each pixel in each captured image; determining, for each captured image, the greatest characteristic value across all pixels in the captured image; comparing the greatest characteristic value for each captured image to determine if a surface of the sample is present at each pre-determined step; determining a first captured image that is focused on a first surface of the sample based on the characteristic value of each pixel in each captured image; determining a second captured image that is focused on a second surface of the sample based on the characteristic value of each pixel in each captured image; and determining a first distance between the first surface and the second surface.