A method of joint denoising and demosaicing using a neural network to generate an output image and to a computing device for implementing the method is provided. The method includes obtaining image data collected by a color filter array (CFA), and jointly performing denoising and demosaicing on the CFA image data using a trained neural network to generate an output image, wherein the neural network has a lightweight U-Net architecture and is trained on a plurality of pairs of training images. One image in each pair of training images is obtained with a lower ISO value than another image in the pair of training images, and is processed by a processing algorithm (image signal processor (ISP)), and the other image in each pair of training images is in a format of CFA image data.