Deep Learning

One Size Fits All: Can We Train One Denoiser for All Noise Levels?

International Conference on Machine Learning (ICML), 2020. (Acceptance rate = 21%)
Manuscript: https://arxiv.org/abs/2005.09627
Abhiram Gnansambandam and Stanley H. Chan

When training an estimator such as a neural network for tasks like image denoising, it is generally preferred to train emph{one} estimator and apply it to emph{all} noise levels. The de facto training protocol to achieve this goal is to train the estimator with noisy samples whose noise levels are uniformly distributed across the range of interest. However, why should we allocate the samples uniformly? Can we have more training samples that are less noisy, and fewer samples that are more noisy? What is the optimal distribution? How do we obtain such a distribution? The goal of this paper is to address this training sample distribution problem from a minimax risk optimization perspective. We derive a dual ascent algorithm to determine the optimal sampling distribution of which the convergence is guaranteed as long as the set of admissible estimators is closed and convex. For estimators with non-convex admissible sets such as deep neural networks, our dual formulation converges to a solution of the convex relaxation. We discuss how the algorithm can be implemented in practice. We evaluate the algorithm on linear estimators and deep networks.

ConsensusNet: Optimal Combination of Image Denoisers

CsNet.png 

Given a set of image denoisers, each having a different denoising capability, is there a provably optimal way of combining these denoisers to produce an overall better result? An answer to this question is fundamental to designing ensembles of weak estimators for complex scenes. In this paper, we present an optimal procedure leveraging deep neural networks and convex optimization. The proposed framework, called the Consensus Neural Network (CsNet), introduces three new concepts in image denoising: (1) A deep neural network to estimate the mean squared error (MSE) of denoised images without needing the ground truths; (2) A provably optimal procedure to combine the denoised outputs via convex optimization; (3) An image boosting procedure using a deep neural network to improve contrast and to recover lost details of the combined images. Experimental results show that CsNet can consistently improve denoising performance for both deterministic and neural network denoisers.

Publication:

  1. Joon Hee Choi, Omar A. Elgendy and Stanley H. Chan, ‘‘Optimal Combination of Image Denoisers’’, IEEE Trans. Image Process., vol. 28, no. 8, pp. 4016-4031, Aug. 2019.
    (Supplementary Material)

Deep Learning for QIS Image Reconstruction

QISNet 

Quanta Image Sensor (QIS) is a single-photon image sensor that oversamples the light field to generate binary measurements. Its single-photon sensitivity makes it an ideal candidate for the next generation image sensor after CMOS. However, image reconstruction of the sensor remains a challenging issue. Existing image reconstruction algorithms are largely based on optimization. In this paper, we present the first deep neural network approach for QIS image reconstruction. Our deep neural network takes the binary bit stream of QIS as input, learns the nonlinear transformation and denoising simultaneously. Experimental results show that the proposed network produces significantly better reconstruction results compared to existing methods.

Publication:

  1. Joon Hee Choi, Omar A. Elgendy and Stanley H. Chan, ‘‘Image reconstruction for Quanta Image Sensors using deep neural networks’’, IEEE ICASSP, pp. 6543–6547, Calgary, Canada, Apr. 2018.