Focusing control under microscopic views based on regional monotones of image focal values

Generally, clarity of images or focal value (FV) varies in hill-shaped manner with respect to lens motion in a focus region. However, the FV variation in the far-off focused region is usually subjected to disturbances and the image signals may not be informative for focusing control. Therefore, challenges exist if focusing control under microscopic views for a large depth of lens displacement is needed. The challenges are primarily due to lack of a method to differentiate image FVs at far-off focused regions.