A fast hadamard transform for demultiplexed illumination in the 3D capture system

The variable illumination 3D capture system uses kinds of cameras and lighting equipment to acquire the object information in different angles, which greatly enhances the reality of the 3D model under the arbitrary illumination conditions. In practice, the images captured are underexposed and have a low signal-to-noise ratio if the traditional way of the variable illumination is adopted in a large-scale capture system. A new multiplexed illumination method based on the Hadamard matrix is presented in this paper. It greatly increases the light sources and the brightness at each capture moment, which makes an adequate exposure and clear images. A fast Hadamard transform is applied to the demultiplexed illumination to reduce the huge computational cost bought by the hundreds and thousands of light sources and cameras. Experiment results have been shown that the qualities of the images are enhanced by the new multiplexed illumination method. The signal-to-noise ratio is improved from 1.826 to 2.325. The demultiplexed illumination based on the fast Hadamard transform reduces the complexity of the algorithm from N2 to Nlog2N and greatly makes the speed about 26 times faster than the original one with the comparative image quality.