Determining star-image location: A new sub-pixel interpolation technique to process image centroids

We develop a theoretical methodology to estimate the location of star centroids in images recorded by CCD and active pixel sensors. The approach may be generalized to other applications were point-sources must be located with high accuracy. In contrast with other approaches, our technique is suitable for use with non-100% fill ratio sensors. The approach is applied experimentally to two camera systems employing sensors with fill-ratios of approximately 50%. We describe experimental approaches to implement the new paradigm and characterize centroid performance using laboratory targets and against real night-sky images. Applied to a conventional CCD camera, a centroid performance of 11.6 times the raw pixel resolution is achieved. Applied to a camera employing an active-pixel sensor a performance of 12.8 is demonstrated. The approach enables the rapid development of autonomous star-camera systems without the extensive characterizations required to derive polynomic fitting coefficients employed by traditional centroid algorithms.