indicates that the reconstruction is of higher quality, in some cases it may not. One has to be extremely careful with the range of validity of this metric; it is only conclusively valid when it is used to compare results from the same codec (or codec type) and same content. Generally, PSNR has been shown to perform poorly compared to other quality metrics when it comes to estimating the quality of images and particularly videos as perceived by humans. Variants PSNR-HVS is an extension of PSNR that incorporates properties of the human visual system such as contrast perception. PSNR-HVS-M improves on PSNR-HVS by additionally taking into account visual masking. In a 2007 study, it delivered better approximations of human visual quality judgements than PSNR and SSIM by large margin. It was also shown to have a distinct advantage over DCTune and PSNR-HVS. See also Data compression ratio Perceptual Evaluation of Video Quality (PEVQ) Structural similarity (SSIM) index Subjective video quality Video Multimethod Assessment Fusion Video quality References Image compression Noise (graphics) Film and video technology Digital television Engineering ratios vi:PSNR