1. A method for creating an image of at least a portion of a three-dimensional biological specimen, said method comprising the steps of: a) obtaining a stack of images said stack comprising a plurality of slices of said portion of said specimen, each of said plurality of slices comprising an image of said specimen obtained from a different focal distance, each of said slices comprising a plurality of pixels; b) performing an erosion on said plurality of slices; c) performing at least one of a closing and a dilation on said plurality of slices; d) calculating the sharpness values of said plurality of pixels in said plurality of slices in said stack; and e) comparing the sharpness values for pixels in specific locations on the second slice in a stack and all slices obtained after said second slice with pixels corresponding to said locations in slices whose sharpness values have been previously calculated.