Method for identification of candidate points as possible characteristic points of a calibration pattern within an image of the calibration pattern , the method comprising the steps of - determining spots within a filtered image derived from the image of the calibration pattern , with a spot being defined as a coherent set of pixels of the filtered image having pixel values exceeding a threshold, - for each determined spot calculating a central point of the determined spot, and - identifying as candidate points all calculated central points. wherein the step of determining the spots comprises scanning the filtered image one pixel of the filtered image after another, wherein, if a scanned pixel has a pixel value exceeding the threshold, the scanning is paused and a spot contour tracing is executed starting with the last scanned pixel as current pixel and the second last pixel as previous pixel, the spot contour tracing comprising as a tracing step the steps of - logging the current pixel as a contour pixel, - for neighboring pixels adjacent to the current pixel, evaluating the condition, whether both the neighboring pixel has a pixel value exceeding the threshold and another neighboring pixel, which immediately precedes this neighboring pixel with respect to a sense of rotation around the current pixel, has a pixel value not exceeding the threshold, - selecting from all neighboring pixels, for which the condition is fulfilled, the neighboring pixel farthest from the previous pixel with respect to said sense of rotation, and - defining the current pixel as previous pixel and defining the selected neighboring pixel as current pixel; the spot contour tracing further comprising the steps of - repeating the tracing step until the current pixel is again equal to the last scanned pixel, - determining the spot as the set of pixels comprising the logged contour pixels and the pixels surrounded by the logged contour pixels. - determining spots within a filtered image derived from the image of the calibration pattern , with a spot being defined as a coherent set of pixels of the filtered image having pixel values exceeding a threshold, - for each determined spot calculating a central point of the determined spot, and - identifying as candidate points all calculated central points. wherein the step of determining the spots comprises scanning the filtered image one pixel of the filtered image after another, wherein, if a scanned pixel has a pixel value exceeding the threshold, the scanning is paused and a spot contour tracing is executed starting with the last scanned pixel as current pixel and the second last pixel as previous pixel, the spot contour tracing comprising as a tracing step the steps of - logging the current pixel as a contour pixel, - for neighboring pixels adjacent to the current pixel, evaluating the condition, whether both the neighboring pixel has a pixel value exceeding the threshold and another neighboring pixel, which immediately precedes this neighboring pixel with respect to a sense of rotation around the current pixel, has a pixel value not exceeding the threshold, - selecting from all neighboring pixels, for which the condition is fulfilled, the neighboring pixel farthest from the previous pixel with respect to said sense of rotation, and - defining the current pixel as previous pixel and defining the selected neighboring pixel as current pixel; the spot contour tracing further comprising the steps of - repeating the tracing step until the current pixel is again equal to the last scanned pixel, - determining the spot as the set of pixels comprising the logged contour pixels and the pixels surrounded by the logged contour pixels. <EOS>