A method (and system) for using information contained within the scanned image to create, in an automated (or semi-automated) process, an accurate data grid. The process has steps: enhance the image; locate blocks of spots; and find each individual spot in each of the blocks. Preferably, the method makes use of image filtering using a "Principal Frequency Filter" based on a mathematical determination of major periodic elements in the image to eliminate noisy, non-periodic signals, and of smoothed intensity profiles of the filtered image data. Here, the term Principal Frequency Filter is used to indicate an image-enhancing filter based upon a mathematical operation which identifies the major periodic components of the image.