Cascaded and Recursive ConvNets (CRCNN): An effective and flexible approach for image denoising.

Recently, discriminative learning methods have gained substantial interest in solving inverse imaging problems due to their decent performance and fast inferencing capability. Those methods need separate models for specific noise levels, which in turn require multiple models to be trained to denoise an image. However, images exhibit spatial variant noise which limits the applicability of such methods. In addition, the discriminative learning methods introduce artifacts such as blurring, deblocking, and so forth while denoising an image. To address these issues, we propose a cascaded and recursive convolutional neural network (CRCNN) framework which can cope with spatial variant noise and blur artifacts in a single denoising framework. The CRCNN takes into account down-sampled sub-images for fast inferencing along with the noise level map. We adopt the hybrid orthogonal projection and estimation method on the convolutional layers to improve the generalization capability of the network in terms of non-uniform and spatial variant noise levels. In contrast to the existing methods, the CRCNN framework allows both denoising and deblurring of images using a single framework which preserves the fine details in a denoised image. Extensive experiments have been conducted to validate the effectiveness and flexibility of the CRCNN framework on real as well as synthetic noisy images in comparison to the state-of-the-art denoising methods. The results show that the CRCNN performs effectively on both synthetic as well as spatial variant noise-induced images, thus, proving the practicability of the framework. • The proposed CRCNN framework deals with various noise levels and spatially variant noises. • A total noise loss function is proposed to generalize the denoising task and preserve fine details in restored images. • The noise level mismatch is effectively handled using the Hybrid Orthogonal Projection and Estimation (HOPE) framework. • We prove that the recursive denoising can leverage a deblurring process in order to improve the image quality. • The CRCNN achieves better results on both synthetic and real-world noisy images compared to the state-of-the-art methods. [ABSTRACT FROM AUTHOR]