Iterative Joint Image Demosaicking and Denoising using a Residual Denoising Network (1807.06403v3)

Abstract: Modern digital cameras rely on the sequential execution of separate image processing steps to produce realistic images. The first two steps are usually related to denoising and demosaicking where the former aims to reduce noise from the sensor and the latter converts a series of light intensity readings to color images. Modern approaches try to jointly solve these problems, i.e. joint denoising-demosaicking which is an inherently ill-posed problem given that two-thirds of the intensity information is missing and the rest are perturbed by noise. While there are several machine learning systems that have been recently introduced to solve this problem, the majority of them relies on generic network architectures which do not explicitly take into account the physical image model. In this work we propose a novel algorithm which is inspired by powerful classical image regularization methods, large-scale optimization, and deep learning techniques. Consequently, our derived iterative optimization algorithm, which involves a trainable denoising network, has a transparent and clear interpretation compared to other black-box data driven approaches. Our extensive experimentation line demonstrates that our proposed method outperforms any previous approaches for both noisy and noise-free data across many different datasets. This improvement in reconstruction quality is attributed to the rigorous derivation of an iterative solution and the principled way we design our denoising network architecture, which as a result requires fewer trainable parameters than the current state-of-the-art solution and furthermore can be efficiently trained by using a significantly smaller number of training data than existing deep demosaicking networks. Code and results can be found at https://github.com/cig-skoltech/deep_demosaick

Iterative Joint Image Demosaicking and Denoising Using a Residual Denoising Network

The paper authored by Filippos Kokkinos and Stamatios Lefkimmiatis proposes an advanced method for jointly addressing the problems of image demosaicking and denoising, which are fundamental steps in digital image processing pipelines. This method is particularly notable for integrating principles from classical image regularization, large-scale optimization, and deep learning.

Overview

Demosaicking and denoising typically occur sequentially in traditional digital camera pipelines, with demosaicking converting sensor data into color images and denoising removing sensor noise. However, treating these processes sequentially can degrade image quality due to cumulative errors. The paper highlights the challenge and ill-posed nature of jointly solving these tasks due to incomplete and noisy data. This research introduces an iterative optimization algorithm that employs a trainable denoising network and offers a transparent interpretation compared to other black-box machine learning solutions.

Methodology

The proposed method is an implementation of a Majorization-Minimization (MM) strategy within an iterative framework, paired with a Residual Denoising Network (ResDNet). The main idea is to leverage the MM method to transform the demosaicking-denoising problem into a series of simpler denoising problems. The ResDNet itself is inspired by the DnCNN architecture and adapts noise variance during the denoising phase to improve accuracy. One significant advancement in the paper is the reduction of parameters through network sharing across iterations, allowing for efficient training on smaller datasets.

Key Results

The paper's experimental results demonstrate that their proposed method significantly outperforms existing state-of-the-art systems in terms of PSNR and other image quality metrics across various datasets, including both synthetic and real, raw images. Notably, their algorithm produces superior outputs while using fewer training parameters and data. The adaptability to different Color Filter Array (CFA) patterns and noise levels further illustrates the robustness of the method. Additionally, the algorithm's iterative nature allows for nuanced control over image refinement processes.

Implications

Practically, this research can influence the design of more efficient and versatile image processing pipelines in consumer electronics, offering improvements in scenarios involving complex noise patterns and non-standard CFA configurations. Theoretically, it suggests that blending deep learning with classic optimization methods can yield interpretable and highly effective solutions to complex computer vision problems.

Future Directions

The potential for further developments is significant. One area is exploring improved efficiencies in handling different noise characteristics and the development of deeper adaptive networks with even fewer parameters. Another avenue is expanding the joint processing capability to include more complex image processing tasks beyond denoising and demosaicking, possibly integrating more elements of the classical image processing pipeline into a unified deep learning framework.

In conclusion, the paper effectively lays the groundwork for more advanced and efficient joint demosaicking-denoising systems, potentially leading to better image quality in digital imaging technologies. It opens doors to future research into extending these methodologies to other areas within image restoration and beyond, reinforcing the viable intersection of optimization strategies and deep learning architectures in computer vision tasks.