This paper describes background removal, point source detection, and position and irradiance extraction data processing algorithms that have been developed for the Spatial Infrared Imaging Telescope (SPIRIT) III design. The SPIRIT III sensor is the primary instrument on the Midcourse Space Experiment (MSX) satellite and is scheduled for launch in early 1996. The sensor consists of an off-axis reimaging telescope, and, among other instruments, a six-band scanning radiometer that covers the spectrum from midwave infrared to longwave infrared. The radiometer has five arsenic-doped silicon (Si:As) focal plane detector arrays with 8 X 192 pixels. The angular separation between adjacent pixels is 90 (mu) rad. A single axis scan mirror can operate at a constant 0.46 deg/sec scan rate to give programmable fields of regard of 1 X 0.75, 1 X 1.5, and 1 X 3 degrees or can remain fixed. Scanned images are non-uniformly sampled because of non-linear scan mirror motion, array misalignment, optical distortion, detector readout ordering, and satellite rotation. In addition, three of the five arrays contain multiple cross-scan aligned columns of pixels that five scanned images that have spatially overlapping in- scan data. Algorithms for processing data sampled on a uniform grid, such as data obtained from a CCD array, are enhanced and applied to the SPIRIT III radiometer where scanned images are non-uniformly sampled and have spatially overlapping data. The performance of these algorithms are evaluated with point source data acquired during ground measurements.