Analysis of in-loop denoising in lossy transform coding

When compressing noisy image sequences, the compression efficiency is limited by the noise amount within these image sequences as the noise part cannot be predicted. In this paper, we investigate the influence of noise within the reference frame on lossy video coding of noisy image sequences. We estimate how much noise is left within a lossy coded reference frame. Therefore we analyze the transform and quantization step inside a hybrid video coder, specifically H.264/AVC. The noise power after transform, quantization, and inverse transform is calculated analytically. We use knowledge of the noise power within the reference frame in order to improve the inter frame prediction. For noise filtering of the reference frame, we implemented a simple denoising algorithm inside the H.264/AVC reference software JM15.1. We show that the bitrate can be decreased by up to 8.1% compared to the H.264/AVC standard for high resolution noisy image sequences.