Adaptive guided image filter for improved in-loop filtering in video coding

This paper proposes a new adaptive sharpening filter based on guided image filter and improves HEVC's in-loop filter architecture by embedding sharpening filter between deblocking filter and SAO. The proposed algorithm classifies pixels of a frame into several groups according to uniform quantization of each pixel's Sum-Modified-Laplacian value and assigns identical optimal filtering parameters to the pixels belonging to the same group based on rate-distortion optimization. Simulation results show that our proposed algorithm achieves 0.7% on average and up to 8% BD-rate reduction with respect to the original HEVC in-loop filtering method. Encoding time increases slightly by about 15% and decoding time increases by 70% on average without special optimization of C++ program integrated in HM-16.5.