Real-time autofocus scanning

A method for focusing a digital scanning apparatus that comprises an objective lens, at least one sensor positioned in the optical path of the objective lens to sense a field of view of the objective lens, and at least one processor, the method comprising, by the at least one processor of the digital scanning apparatus:

• for each of a plurality of reference regions along a line representing a maximum length across a sample,
• scanning the reference region to acquire a buffer of reference image data,
• based on the buffer of reference image data, determining a true-Z value that represents a distance between the objective lens and the sample that provides best focus for the reference region, and
• storing the true-Z value, determined for the reference region, in association with a location on the sample;
• and,
• for each of a plurality of regions of the sample to be scanned,
• determining a predicted-Z value for the region based on a stored true-Z value that is associated with a location that is nearest to the location of the region than any other location that is associated with any stored true-Z value,
• at a start of scanning the region, adjusting a distance between the objective lens and the sample based on the predicted-Z value,
• scanning the region to acquire a buffer of image data, and,
• after scanning the region,
• based on the buffer of image data, determining a true-Z value that represents a distance between the objective lens and the sample that provides best focus for the region, and
• storing the true-Z value, determined for the region, in association with a location on the sample.