Method for filtering laser range data

A system for filtering a range image reflected from a target being tracked by a laser detection and ranging system comprising:

• receiving means for receiving an array of range pixels representing said range image of said target;
• said receiving means receiving an array of intensity pixels representing an intensity image of said target;
• means for calculating a mean value and a standard deviation for said array of intensity pixels of said target in accordance with the equations:
• ##EQU4## where X.sub.i represents an intensity value for each of the intensity pixels X.sub.1, X.sub.2, X.sub.3. . . X.sub.n in the array of intensity pixels of said target and n is the number of intensity pixels in the array of intensity pixels of said target;
• means for initially setting an intensity threshold at a predetermined intensity level and then adjusting said intensity threshold to the greater value of said predetermined intensity level and a calculated intensity threshold determined in accordance with the following equation:
• Calibrated Threshold=mean-3.multidot.sigma where mean is the mean intensity value for said array of intensity pixels and sigma is the standard deviation for said array of intensity pixels;
• moving window means for simultaneously scanning a sub-image of said array of range pixels of said target and a corresponding sub-image of said array of intensity pixels of said target;
• and
• filtering means for replacing the range value of a center pixel within the sub-image of said array of range pixels being scanned by said moving window means with a median value of the remaining range pixels in the sub-image of said array of range pixels being scanned by said moving window means whenever a corresponding center pixel of the corresponding sub-image of said array of intensity pixels is below said intensity threshold;
• said sub-image of said array of range pixels being scanned by said moving window means and said corresponding sub-image of said array of intensity pixels being scanned by said moving window means each comprising an array having an array size of at least five pixels per row by five pixels per column.

A method for filtering a range image reflected from a target being tracked by a laser detection and ranging system comprising the steps of:

• (a) receiving an array of range pixels representing said range image of said target;
• (b) receiving an array of intensity pixels representing an intensity image of said target;
• (c) calculating a mean value and a standard deviation for said array of intensity pixels of said target in accordance with the equations:
• ##EQU6## where X.sub.i represents an intensity value for each of the intensity pixels X.sub.1, X.sub.2, X.sub.3. . . X.sub.n in the array of intensity pixels of said target and n is the number of intensity pixels in the array of intensity pixels of said target;
• (e) setting an intensity threshold at a predetermined intensity level;
• (f) adjusting said intensity threshold to the greater value of said predetermined intensity level and a calculated intensity threshold determined in accordance with the following equation:
• Calibrated Threshold=mean-3.multidot.sigma
• where mean is the mean intensity value for said array of intensity pixels and sigma is the standard deviation for said array of intensity pixels;
• (g) scanning simultaneously sub-images of said array of range pixels of said target and corresponding sub-images of said array of intensity pixels of said target;
• and
• (h) replacing the range value of a center pixel within the sub-image of said array of range pixels currently being scanned with a median value of the remaining range pixels in the sub-image currently being scanned whenever a corresponding center pixel of the corresponding sub-image of said array of intensity pixels is below said intensity threshold.