基于结构和纹理感知的井下低光照自监督图像增强方法

Underground low-light self-supervised image enhancement method based on structure and texture perception

  • 摘要: 受井下复杂空间环境和不均匀人造光源影响,井下视觉设备采集的图像易呈现整体或部分区域光线不足、图像内容可见度差的问题。对于井下低光照图像的增强,现有图像增强方法的结果易出现对比度差以及部分区域过曝和欠曝的问题。基于此,提出一种基于结构和纹理感知的井下低光照自监督图像增强方法,以摆脱训练时对配对的井下低光照/正常光照图像的依赖。首先,为产生分段平滑的光照图,设计了一种自监督结构和纹理感知的光照估计网络,根据自监督训练损失保留场景的边缘结构并平滑纹理细节。为了深入挖掘低光照图像中的局部纹理特征和全局结构特征来提高光照估计网络的性能,在光照估计网络中引入了局部−全局感知模块。该模块利用卷积操作中较小感受也能够捕获局部特征的能力以及视觉Transformer的自注意力机制能够实现全局信息交互的特性来实现低光照图像中局部和全局特征的提取。其次,为了实现自监督学习的训练方式,针对光照图分段平滑的特性,采用了一种结构感知的平滑损失。为了进一步细化光照估计网络产生的光照图,使其具有合理的亮度和对比度,引入了伪标签图像生成器来合成具有良好对比度和亮度的伪标签图像。通过重建损失约束,增强图像与伪标签图像之间亮度和对比度之间的一致性,从而间接约束光照图。在多个公开的基准数据集和井下真实场景的低光照图像数据集上进行主观和客观评价的试验结果表明:该方法具有较好的低光照图像增强效果,在面对井下场景的低光照图像时,该方法也具有良好的泛化性能。

     

    Abstract: Due to the complex spatial environment and uneven artificial lighting underground, images captured by underground visual equipment often suffer from insufficient overall or partial lighting and poor visibility of image content. Existing image enhancement methods for low-light underground images often result in poor contrast and issues with overexposure and underexposure in certain areas. Within this article, we propose a self-supervised image enhancement method for low-light underground conditions based on structural and texture perception, aiming to alleviate the dependence on paired low-light/normal-light images during training. Firstly, to generate smoothly segmented illumination maps, we design a self-supervised structural and texture-aware illumination estimation network, which preserves scene edge structures and smooths texture details based on self-supervised training losses. To further exploit local texture features and global structural features in low-light images to improve the performance of the illumination estimation network, we introduce a local-global perception module into the illumination estimation network. This module leverages the ability of convolutional operations with small receptive fields to capture local features and the self-attention mechanism of visual transformers to facilitate global information interaction, thus extracting local and global features from low-light images. Secondly, to facilitate self-supervised learning, we adopt a structure-aware smoothness loss considering the segmented smoothness property of illumination maps. Finally, to refine the illumination maps generated by the illumination estimation network for reasonable brightness and contrast, we introduce a pseudo-label image generator to synthesize pseudo-label images with good contrast and brightness. By constraining the consistency between brightness and contrast of the enhanced images and pseudo-label images through reconstruction loss, we indirectly constrain the illumination maps. Experimental results on multiple public benchmark datasets and a dataset of low-light images in real underground scenes demonstrate the effectiveness of our method in enhancing low-light images, as well as its good generalization performance when faced with low-light images in underground scenarios.

     

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