MPEG-2 Transcoding Method for Reducing Re-quantization Noise Based on a Two-tiered Quantizer Matrix

We developed an MPEG-2 transcoding method on the basis of a two-tiered quantizer matrix that reduces re-quantization noise. The proposed method changes the quantization matrix to decrease the re-quantization noise, instead of changing the value of the quantization parameters as conventional methods do. Using this two-tiered matrix makes it possible to reduce re-quantization noise in the high-frequency domain. The main feature of the proposed method is that it does not cause any differences in image quality between adjacent macroblocks, which the conventional method does. Experimental results show that our proposed method produces transcoding scores of structural similarity (SSIM) and video quality model (VQM) that are 0.044 and 0.0938, respectively, better than those of the best conventional method. The proposed method always produced superior SSIM and VQM scores when the bit reduction ratio was smaller than 0.1015 for all the tested sequences.