Cytological imaging systems and methods

1. An automatic focusing method for an optical system, comprising:

performing an initial coarse focus action along a focal axis at a scan position corresponding to a point on a surface of a slide;

respectively performing a plurality of subsequent fine focus actions along a plurality of focal axes at a plurality of scan positions corresponding to different points on the slide surface, wherein the performance of each of the fine focus actions comprises determining a fine in-focus coordinate along the respective focal axis, determining an area of fine focus jurisdiction surrounding the respective point, and correlating the fine in-focus coordinate to the respective fine focus jurisdiction area; and

determining if another scan position corresponds to a point within at least one previously determined fine focus jurisdiction area.

2. The method of claim 1 , wherein each of the fine focus jurisdiction areas is generally elliptical in shape.

3. The method of claim 2 , wherein each of the fine focus jurisdiction areas has a major axis substantially parallel to a scan axis of the optical system and has a minor axis substantially parallel to an index axis of the optical system.

4. The method of claim 1 , further comprising performing another fine focus action along a focal axis at the other scan position if the other scan position does not correspond to a point within at least one previously determined fine focus jurisdiction area.

5. The method of claim 4 , further comprising determining another area of fine focus jurisdiction surrounding the other point.

6. The method of claim 1 , further comprising determining if the other scan position corresponds to a point within exactly one previously determined fine focus jurisdiction area.

7. The method of claim 6 , further comprising using the fine in-focus coordinate correlated to the exactly one previously determined fine focus jurisdiction area to define another fine in-focus coordinate along a focal axis at the other scan position if the other scan position is determined to correspond to a point within exactly one previously determined fine focus jurisdiction area.

8. The method of claim 7 , further comprising correcting the fine in-focus coordinate correlated to the exactly one previously determined fine focus jurisdiction area for tilt based on a global focal plane, wherein the corrected fine in-focus coordinate is used as the other fine in-focus coordinate.

9. The method of claim 1 , further comprising determining if the other scan position corresponds to a point within more than one previously determined fine focus jurisdiction area.

10. The method of claim 9 , further comprising using a weighted average of the fine in-focus coordinates of the more than one previously determined fine focus jurisdiction area to define another fine in-focus coordinate along a focal axis at the other scan position if the other scan position is determined to correspond to a point within more than one previously determined fine focus jurisdiction area.

11. The method of claim 10 , further comprising correcting the weighted average of the fine in-focus coordinates for tilt based on a global focal plane, wherein the corrected weighted average of the fine in-focus coordinates is used as the other in-focus coordinate at the other scan position.

12. The method of claim 1 , wherein the performance of the coarse focus action comprises determining a coarse in-focus coordinate along the focal axis.

13. The method of claim 12 , wherein the performance of each of the fine focus actions is based on the coarse in-focus coordinate.

14. The method of claim 13 , wherein the performance of each of the fine focus actions comprises estimating an in-focus coordinate along the respective focal axis as a function of the coarse in-focus coordinate.

15. The method of claim 13 , wherein the performance of each of the fine focus actions comprises estimating an in-focus coordinate along the respective focal axis based on a function of the coarse in-focus coordinate and a global focal plane.

16. The method of claim 1 , wherein the performance of the coarse focus action comprises repeatedly obtaining an image of the slide at different coordinates along the focal axis until a coarse in-focus coordinate is determined.

17. The method of claim 1 , wherein the performance of each of the fine focus actions comprises estimating a fine in-focus coordinate along the respective focal axis and obtaining images of the slide at predetermined coordinates relative to the estimated fine in-focus coordinate along the respective focal axis.

18. The method of claim 1 , wherein the performance of at least one of the coarse focus action and each fine focus action comprises:

obtaining images of the slide at a plurality of coordinates along the focal axis;

determining a plurality of focus scores for the respective coordinates; and

selecting one of the coordinates as an in-focus coordinate based on the focus scores.

19. The method of claim 1 , wherein the coordinate having a maximum focus score is the coordinate selected as the fine in-focus coordinate.

20. The method of claim 1 , wherein the slide carries a biological specimen.

21. The method of claim 1 , wherein the coarse focus action and fine focus actions are performed during a single image scan.

22. The method of claim 1 , wherein the performance of one or both of the coarse focus action and fine focus actions comprises moving an element of the optical system relative to the slide surface to coordinates along the respective focal axes.

23. The method of claim 1 , wherein the performance of the fine focus actions comprises moving an element of the optical system relative to the slide along a scan axis to the respective scan positions.