Low complexity sub-block perceptual distortion assessment for mode decision and rate-control

Video is being used in a variety of portable and low powered devices, via online/on-demand services, for personal communications or over heterogeneous/wireless sensor networks. Likewise, perceptual evaluation is being sought, to ensure video sequences maintain perceptual integrity. This raises a challenge, to bring high complexity perceptual algorithms into a low complexity environment. Existing perceptual solutions minimise the overall complexity by making the Lagrange multiplier (λ), the quantisation stage perceptually aware. These solutions are restricted to the block level using the original pixels, a model or previous encoded block, thus avoiding assessing individual subblock candidates. Current perceptual algorithms like structured similarity (SSIM) uses statistical based calculations, and in order to be compatible with existing scores a further high complexity function is required for scaling. This paper presents a perceptual distortion and activity assessment that can operate at the subblock for each candidate during the later stages of encoding, in mode-decision and in rate-control, without the need for statistical calculations nor the high complexity associated with scaling a perceptual algorithm. The paper will show how several perceptual techniques of SSIM luma function, just noticeable detection (JND) and a new proposed edge detection can be used to form a low complexity solution. Consequently, the proposed low perceptual assessment has additional timing increase of <; +4 % for medium and low activity video sequences.