210 research outputs found
Progressive Joint Low-light Enhancement and Noise Removal for Raw Images
Low-light imaging on mobile devices is typically challenging due to
insufficient incident light coming through the relatively small aperture,
resulting in a low signal-to-noise ratio. Most of the previous works on
low-light image processing focus either only on a single task such as
illumination adjustment, color enhancement, or noise removal; or on a joint
illumination adjustment and denoising task that heavily relies on short-long
exposure image pairs collected from specific camera models, and thus these
approaches are less practical and generalizable in real-world settings where
camera-specific joint enhancement and restoration is required. To tackle this
problem, in this paper, we propose a low-light image processing framework that
performs joint illumination adjustment, color enhancement, and denoising.
Considering the difficulty in model-specific data collection and the ultra-high
definition of the captured images, we design two branches: a coefficient
estimation branch as well as a joint enhancement and denoising branch. The
coefficient estimation branch works in a low-resolution space and predicts the
coefficients for enhancement via bilateral learning, whereas the joint
enhancement and denoising branch works in a full-resolution space and
progressively performs joint enhancement and denoising. In contrast to existing
methods, our framework does not need to recollect massive data when being
adapted to another camera model, which significantly reduces the efforts
required to fine-tune our approach for practical usage. Through extensive
experiments, we demonstrate its great potential in real-world low-light imaging
applications when compared with current state-of-the-art methods
Retinex-based Image Denoising / Contrast Enhancement using Gradient Graph Laplacian Regularizer
Images captured in poorly lit conditions are often corrupted by acquisition
noise. Leveraging recent advances in graph-based regularization, we propose a
fast Retinex-based restoration scheme that denoises and contrast-enhances an
image. Specifically, by Retinex theory we first assume that each image pixel is
a multiplication of its reflectance and illumination components. We next assume
that the reflectance and illumination components are piecewise constant (PWC)
and continuous piecewise planar (PWP) signals, which can be recovered via graph
Laplacian regularizer (GLR) and gradient graph Laplacian regularizer (GGLR)
respectively. We formulate quadratic objectives regularized by GLR and GGLR,
which are minimized alternately until convergence by solving linear systems --
with improved condition numbers via proposed preconditioners -- via conjugate
gradient (CG) efficiently. Experimental results show that our algorithm
achieves competitive visual image quality while reducing computation complexity
noticeably
Self-Reference Deep Adaptive Curve Estimation for Low-Light Image Enhancement
In this paper, we propose a 2-stage low-light image enhancement method called
Self-Reference Deep Adaptive Curve Estimation (Self-DACE). In the first stage,
we present an intuitive, lightweight, fast, and unsupervised luminance
enhancement algorithm. The algorithm is based on a novel low-light enhancement
curve that can be used to locally boost image brightness. We also propose a new
loss function with a simplified physical model designed to preserve natural
images' color, structure, and fidelity. We use a vanilla CNN to map each pixel
through deep Adaptive Adjustment Curves (AAC) while preserving the local image
structure. Secondly, we introduce the corresponding denoising scheme to remove
the latent noise in the darkness. We approximately model the noise in the dark
and deploy a Denoising-Net to estimate and remove the noise after the first
stage. Exhaustive qualitative and quantitative analysis shows that our method
outperforms existing state-of-the-art algorithms on multiple real-world
datasets
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