The invention provides a line scan camera apparatus and a computer-implemented method for real-time virtual slide image assessment. The method comprises identifying a set of focus points on a tissue sample on a microscope slide； capturing a focus value for each focus point； calculating a best fit surface from the set of focus points； determining a distance of each focus point from the best fit surface； comparing the identified distance of each focus point from the best fit surface to a predetermined threshold distance to identify one or more outlier focus points in the set of focus points； modifying each of the identified one or more outlier focus points by changing a location of the focus point and recapturing the focus value for the new location of the focus point； determining a focal surface from the set of focus points； and moving an objective lens to follow the focal surface during a scanning process.
