Demosaicing of CFA 3.0 with Applications to Low Lighting Images

Abstract

Low lighting images usually contain Poisson noise, which is pixel amplitude-dependent. More panchromatic or white pixels in a color filter array (CFA) are believed to help the demosaicing performance in dark environments. In this paper, we first introduce a CFA pattern known as CFA 3.0 that has 75% white pixels, 12.5% green pixels, and 6.25% of red and blue pixels. We then present algorithms to demosaic this CFA, and demonstrate its performance for normal and low lighting images. In addition, a comparative study was performed to evaluate the demosaicing performance of three CFAs, namely the Bayer pattern (CFA 1.0), the Kodak CFA 2.0, and the proposed CFA 3.0. Using a clean Kodak dataset with 12 images, we emulated low lighting conditions by introducing Poisson noise into the clean images. In our experiments, normal and low lighting images were used. For the low lighting conditions, images with signal-to-noise (SNR) of 10 dBs and 20 dBs were studied. We observed that the demosaicing performance in low lighting conditions was improved when there are more white pixels. Moreover, denoising can further enhance the demosaicing performance for all CFAs. The most important finding is that CFA 3.0 performs better than CFA 1.0, but is slightly inferior to CFA 2.0, in low lighting images.

Untitled

“…Details of the demosaicing algorithms for CFA 3.0 can be found in a companion paper [19]. We skip the details here.…”

“…The Baseline method refers to the demosaicing of the low resolution color Bayer pattern in Figure 3 (c). The Standard method is the method shown in Figure 2 of [19]. The other methods involve the use of pansharpening methods, including Principal Component Analysis (PCA) [29], Smoothing Filter-based Intensity Modulation (SFIM) [30], Modulation Transfer Function Generalized Laplacian Pyramid (MTF-GLP) [31], MTF-GLP with High Pass Modulation (MTF-GLP-HPM) [32], Gram Schmidt (GS) [33], GS Adaptive (GSA) [34], Guided Filter PCA (GFPCA) [35], PRACS [36] and hybrid color mapping (HCM) [37]- [40].…”

“…Numerous other CFA patterns have been invented in the past few decades [16]- [18]. Recently, we proposed a simple CFA pattern [19] in which the RGB pixels are evenly distributed. In particular, as shown in Figure 3 (c), each 4x4 block has 75% or 12 white pixels, 12.5% or two green pixels, 6.25% or one red and blue pixels.…”

The Geometry of Noise in Color and Spectral Image Sensors

“…So from a spectral point of view, the W channel does not have benefit. However, we did not perform pansharpening [6] in this study, so the interest of W channel is not highlighted here.…”

“…In the literature, one common problem is to find the best hardware/software configuration to minimize the amount of noise of the output image [6]. The question of sensor optimization is very complex, because it is a spatio-spectral inverse problem [7].…”