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基于双树复小波变换的低光图像可读性增强方法
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更新于2024-08-28
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本文主要探讨了"基于双树复波let变换的低光图像可读性增强方法"。作者Tingting Sun 和 Cheolkon Jung 来自西安电子科技大学电子工程学院,针对低光照条件下的图像处理问题提出了创新性的解决方案。由于这类图像通常动态范围有限且噪声严重,提高对比度和降低噪声是一个具有挑战性的任务。 该研究的核心思想是利用双树复杂波let变换(DTCWT)进行处理。首先,通过照明补偿技术,确保图像能够保留细微细节并充分利用动态范围,这对于提升图像质量至关重要。然后,将图像分解为高频和低频两个子带,分别采取不同的策略进行处理。在低频子带,作者采用对比度受限自适应直方图均衡化(CLAHE)来增强对比度,同时减少图像噪声。而在高频子带,采用了一种非线性变换,旨在进一步提升细节的清晰度,同时抑制可能存在的高频噪声。 值得注意的是,作者并没有忽视色彩表现的问题,他们认识到颜色失真可能会影响图像的可读性。因此,在整个流程的最后,进行色彩校正,以纠正由于亮度调整导致的颜色失真,从而确保最终图像既能具有良好的对比度,又能保持自然的色彩平衡。 这篇研究论文提供了一种有效的方法,通过结合双树复杂波let变换的特性与适当的图像处理技术,实现了在低光照条件下既增强图像对比度又抑制噪声,同时保持色彩真实性的目标。这种方法对于提高夜间或弱光环境下的图像质量具有实际应用价值,对于计算机视觉、安防监控以及摄影等领域具有重要意义。
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READABILITY ENHANCEMENT OF LOW LIGHT IMAGES BASED ON DUAL-TREE
COMPLEX WAVELET TRANSFORM
Tingting Sun and Cheolkon Jung
School of Electronic Engineering, Xidian University, Xi’an 710071, China
zhengzk@xidian.edu.cn
ABSTRACT
Since images captured under low light conditions have low
dynamic range and are seriously degraded by noise, it is a
challengeable task to achieve both contrast enhancement
and noise reduction from low light images. In this paper, we
propose a readability enhancement method of low light
images based on dual-tree complex wavelet transform
(DTCWT). We perform contrast enhancement and noise
reduction for low light images based on wavelet coefficients.
First, we conduct illumination compensation to contain fine
details and fully utilize dynamic range. Then, we decompose
the image into high-pass and low-pass sub-bands by
DTCWT, and perform contrast limited adaptive histogram
equalization (CLAHE) and a nonlinear transform in low-
pass and high-pass sub-bands, respectively, to achieve both
contrast enhancement and noise reduction. Finally, we
perform color correction to deal with the color distortion
problem caused by contrast enhancement. Experimental
results demonstrate that the proposed method outperforms
state-of-the-art ones in contrast enhancement, noise
reduction, and color reproduction in terms of both subjective
and objective evaluations.
1
Index Terms—Contrast enhancement, color correction,
dual-tree complex wavelet transform, noise reduction,
wavelet coefficient.
1. INTRODUCTION
Ambient light is an indispensable factor for the quality of
images captured by imaging devices. In general, images
captured in the dark condition have a narrow dynamic range
and low contrast [1]. It is required to improve contrast of
images captured under low light condition to make the
image have a perceptually more pleasing or visually more
informative vision effect [2]. Up to now, researchers have
proposed a lot of contrast enhancement methods to improve
the contrast of the images [3][4]. However, they didn’t
consider the characteristics of low-light images with low
signal-to-noise ratio (SNR) and noise, which are different
1
This work was supported by the National Natural Science Foundation of
China (No. 61271298) and the International S&T Cooperation Program of
China (No. 2014DFG12780).
from natural scenes captured under ordinary conditions [5].
Thus, traditional contrast enhancement methods had a limit
in achieving noise reduction and color reproduction while
enhancing contrast. For this reason, some enhancement and
de-noising methods have been proposed in recent years. Yin
et al. presented a novel framework for low light image
enhancement and noise reduction by performing
brightness/contrast stretching and noise reduction in the HSI
and YCbCr color spaces [6]. Huang et al. provided a
automatic transformation technique to improve the
brightness of dimmed images using gamma correction and
probability distribution of luminance pixels [7]. Artur et al.
proposed an automatic contrast enhancement method for
low-light images based on local statistics of wavelet
coefficients. They used a nonlinear enhancement function
based on the local distribution of the wavelet coefficients
modeled as a Cauchy distribution to stretch brightness/
contrast and utilized a shrinkage function to prevent noise
amplification [8]. Although they have improved visual
quality of low-light images to some extent, it is hard to
achieve both noise reduction and color reproduction from
low light images.
In this paper, we propose readability enhancement of low
light images to achieve both noise reduction and color
reproduction while enhancing contrast based on dual-tree
complex wavelet transform (DT-CWT). We first convert the
original RGB image into the YUV color space. Then, we
perform illumination compensation on the Y-component to
make the output contain more details and fully utilize the
dynamic range. After DT-CWT, we perform contrast
enhancement and noise reduction to improve the readability
of images captured under low-light conditions based on the
characteristics of wavelet coefficients in the wavelet domain,
and then conduct the inverse DT-CWT to change the image
to the spatial domain. Finally, we perform color correction
to overcome the color distortions caused by the contrast
enhancement process. The flow chart of the proposed
method is illustrated in Fig. 1. Compared with existing
methods, our main contributions are as follows:
1) We achieve both contrast enhancement and noise
reduction using DTCWT. Since noise mainly appears in
high-pass sub-bands, we perform noise reduction in high-
pass sub-bands after DTCWT.
1741978-1-4799-9988-0/16/$31.00 ©2016 IEEE ICASSP 2016
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