Photon-sensitive mapping lidar systems are able to image at greater collection area rates and ranges than linear-mode systems. However, these systems also experience greater noise levels due to shot noise, image blur, and dark current, which must be filtered out before the imagery can be exploited. Described in this report is a synthetic test data set of imagery from a notional airborne Geiger-mode lidar. Also described is the Bridge Sign algorithm, which uses a least-squares technique for noise filtering. The algorithm's performance was validated using synthetic test imagery of both a toy scene and of a realistic scene, which were generated using the parameters of a notional airborne Geiger-mode system. Analysis of the results shows the technique effectively removes noise and preserves fine details with good fidelity. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.