Abstract: To investigate the suppression of the speckle noise in laser active imaging, a denoising method based on Time-Domain Constrained (TDC) in signal subspace is proposed and a laser active imaging system based on range-gating ICCD is constructed for experiment. First, homomorphic transformation is performed to convert the multiplicative noise to additive noise. Second, wavelet transformation is performed to estimate the covariance of speckle noise. Third, the noise image is decomposed into signal subspace and noisy subspace, and singular value decomposing is used to estimate the dimension of the signal subspace. The covariance of clean image is decomposed using eigenvalue decomposing, and denoising estimating matrix is computed. Fourth, the denoising estimating matrix is convolved with noisy image. Finally, the inverse homomorphic transform is carried out to get the denoised image. Experiment results indicate that, compared with classical Lee, Frost and Kuan filtering, the proposed method has advanced denoising performance and consts less computation time.

Key words: information processing, laser active imaging, signal subspace, speckle noise, TDC, homomorphic transformation