Multispectral Fusion of RGB and NIR Images Using Weighted Least Squares and Convolution Neural Networks

In low light condition, color (RGB) images captured by visible sensors suffer from severe noise causing loss of colors and textures. However, near infrared (NIR) images captured by NIR sensors are robust to noise even in low light condition without color. Since RGB and NIR images are complementary in low light condition, the multispectral fusion of RGB and NIR images provides a viable solution to low light imaging. In this paper, we propose multispectral fusion of RGB and NIR images using weighted least squares (WLS) and convolution neural networks (CNNs). We combine traditional WLS filtering for layer decomposition and denoising with latest deep learning for image enhancement and texture transfer into the multispectral fusion to take both advantages. We build two networks based on CNN: image enhancement network (IEN) for image enhancement and texture transfer network (TTN) for NIR texture transfer. First, we perform RGB image denoising based on WLS filtering and generate the base layer. We use both RGB and NIR images for WLS filtering as weights to filter out noise in low light RGB images. Second, we conduct IEN to enhance contrast of the base layer. Third, we perform TTN to deliver NIR details completely and naturally to the fusion result. The combination of WLS, TTN and IEN leads to noise reduction, contrast enhancement, and detail preservation in fusion. Experimental results show that the proposed method achieves good performance in both noise reduction and detail transfer as well as outperforms state-of-the-art methods in terms of visual quality and quantitative measurements.