Abstract: Surface defects in a reflection scan of a print made with visible light are corrected by using a scan of the print made with infrared light. This correction of surface defects is performed by controlling the intensity of defect detail in the infrared record by multiplying that defect detail by a gain. The gain varies for each region of the image as a function of the brightness of the image in that region. The gain approaches unity for white areas of the image, drops toward zero for darker areas, and approaches a small negative number for black areas of the image. The gain-multiplied defect detail is then subtracted from the visible image to create the corrected image free of the surface defects.

Abstract: A multi-level correlation technique and apparatus for detecting symbol and data frame synchronization in high noise and multi-path environments, wherein received signals are correlated with known pseudorandom noise (PN) or other known codes at the base level and the base level correlation results are in turn correlated with PN or other known codes at the next higher level, such that the top level of correlation includes all lower levels of encoding in the complete synchronization pattern. In a two level implementation, the base level codes define symbols while the top level code defines the synchronization pattern in terms of the base level symbols. Correlation hardware is minimized while processing gain is maximized for enhancing low signal to noise levels over a long synchronization pattern. Additionally, precise ranging is facilitated because the top level correlation result covers the entire synchronization pattern.