Contrast enhancement for the infrared vein image of leg based on the optical angular spectrum theory.

The near-infrared (NIR) imaging method was required for the diagnosis of varicose veins, which mean that the veins have become enlarged and twisted on leg. In some cases, the hair on leg could be dense and formed a noise during the NIR vein images. Here, a preliminary treatment to filter out the effect of hair on the NIR image was carried out. The filter design was based on the optical angular spectrum theory to select a threshold spatial frequency in order to separate a specific vein infrared image of leg from that of the hair. An experimental setup combined a NIR light, a charge coupled device camera with the filtering algorithms which were implemented to prove the effectiveness on the hair noise removal. The results demonstrated that an annulus Butterworth filter was more effective to reduce the hair noise and simultaneously enhance the contrast of the venous images on leg than the others. This design processed a NIR image in terms of an optical angular spectrum theory, thereby an all-optical treatment for the contrast enhancement of a veins image being possible in the future. [ABSTRACT FROM AUTHOR]