Denoising Algorithm for CFA Image Sensors Considering Inter-Channel Correlation

Min Lee, Sang Park, Moon Kang
2017 Sensors  
In this paper, a spatio-spectral-temporal filter considering an inter-channel correlation is proposed for the denoising of a color filter array (CFA) sequence acquired by CCD/CMOS image sensors. Owing to the alternating under-sampled grid of the CFA pattern, the inter-channel correlation must be considered in the direct denoising process. The proposed filter is applied in the spatial, spectral, and temporal domain, considering the spatio-tempo-spectral correlation. First, nonlocal means (NLM)
more » ... atial filtering with patch-based difference (PBD) refinement is performed by considering both the intra-channel correlation and inter-channel correlation to overcome the spatial resolution degradation occurring with the alternating under-sampled pattern. Second, a motion-compensated temporal filter that employs inter-channel correlated motion estimation and compensation is proposed to remove the noise in the temporal domain. Then, a motion adaptive detection value controls the ratio of the spatial filter and the temporal filter. The denoised CFA sequence can thus be obtained without motion artifacts. Experimental results for both simulated and real CFA sequences are presented with visual and numerical comparisons to several state-of-the-art denoising methods combined with a demosaicing method. Experimental results confirmed that the proposed frameworks outperformed the other techniques in terms of the objective criteria and subjective visual perception in CFA sequences. 3 of 22 correlation must be analyzed to detect the edges and details in the under-sampled pattern. Owing to the alternating under-sampling of the CFA pattern, the inter-channel correlation is difficult to consider in the direct denoising process. Hence, when conventional methods are used for the CFA pattern, spatial resolution degradation occurs. Conventional methods, which involve direct removal of noise from CFA, do not take into account the inter-channel correlation. To overcome the spatial resolution degradation while removing noise, both inter-channel and intra-channel correlations are used in the direct denoising process. In the proposed spatial filter, the patch is computed from the pixel values of all the color channels, such as a monochromatic NLM filter. The PBD values of the pixel locations are obtained from the intra-channels. Then, PBD refinement is conducted by considering both the intra-channel and inter-channel correlations in the CFA pattern. Sensors 2017, 17, 1236 3 of 22 spatial domain. However, edge estimation on an alternating under-sampled grid can be very difficult. Hence, the spatio-spectral correlation must be considered in the spatial filter, and the inter-channel correlation must be analyzed to detect the edges and details in the under-sampled pattern. Owing to the alternating under-sampling of the CFA pattern, the inter-channel correlation is difficult to consider in the direct denoising process. Hence, when conventional methods are used for the CFA pattern, spatial resolution degradation occurs. Conventional methods, which involve direct removal of noise from CFA, do not take into account the inter-channel correlation. To overcome the spatial resolution degradation while removing noise, both inter-channel and intra-channel correlations are used in the direct denoising process. In the proposed spatial filter, the patch is computed from the pixel values of all the color channels, such as a monochromatic NLM filter. The PBD values of the pixel locations are obtained from the intra-channels. Then, PBD refinement is conducted by considering both the intra-channel and inter-channel correlations in the CFA pattern.
doi:10.3390/s17061236 pmid:28555044 pmcid:PMC5492375 fatcat:evgzvzbu2zdwzlcwl6gi3d7ava