Gradient Guided Image Deblocking Using Convolutional Neural Networks

Block-based transform coding in its nature causes blocking artifacts, which severely degrades picture quality especially in a high compression rate. Although convolutional neural networks (CNNs) achieve good performance in image restoration tasks, existing methods mainly focus on deep or efficient network architecture. The gradient of compressed images has different characteristics from the original gradient that has dramatic changes in pixel values along block boundaries. Motivated by them, we propose gradient guided image deblocking based on CNNs in this paper. Guided by the gradient information of the input blocky image, the proposed network successfully preserves textural edges while reducing blocky edges, and thus restores the original clean image from compression degradation. Experimental results demonstrate that the gradient information in the input compressed image contributes to blocking artifact reduction as well as the proposed method achieves a significant performance improvement in terms of visual quality and objective measurements.