A method and system of determining a sub-pixel point position of a marker point in an image. Embodiments of the invention allow a marker point sub-pixel localization module executable by an electronic processing unit to obtain an image, including a marker point, and to derive both a background corrected marker point profile and a background and baseline corrected marker point profile. Additionally, embodiments of the invention allow defining of a sub-pixel position of the marker point as a center of a peak of the background corrected marker point profile. Thus, embodiments of the invention allow for rapidly detecting and localizing external markers placed on a patient in projection images.
