The Structural SIMilarity (SSIM) index is a method for measuring the similarity between two images. The SSIM index is a full reference metric, in other words, the measuring of image quality based on an initial uncompressed or distortion-free image as reference. SSIM is designed to improve on traditional methods like PSNR and MSE, which have proved to be inconsistent with human eye perception. SSIM is also commonly used as a method of testing the quality of various lossyvideo compression methods. For example, the popular open source H.264 encoder x264 is set by default to display an SSIM value at the end of an encoding operation. The phrase peak signal-to-noise ratio, often abbreviated PSNR, is an engineering term for the ratio between the maximum value of a signal and the magnitude of background noise. ... In statistics the mean squared error of an estimator T of an unobservable parameter θ is i. ... A lossy data compression method is one where compressing a file and then decompressing it retrieves a file that may well be different to the original, but is close enough to be useful in some way. ... Video compression refers to making a digital video signal use less data, without noticeably reducing the quality of the picture. ... H.264 is a high compression digital video codec standard written by the ITU-T Video Coding Experts Group (VCEG) together with the ISO/IEC Moving Picture Experts Group (MPEG) as the product of a collective partnership effort known as the Joint Video Team (JVT). ... x264 is a free software library for encoding H.264/MPEG-4 AVC video streams. ...
The SSIM index is a decimal value between 0 and 1. 0 would mean zero correlation with the original image, and 1 means the exact same image. 0.95 SSIM, for example, would imply half as much variation from the original image as 0.90 SSIM. Through this index, image and video compression methods can be effectively compared.
References
Z. Wang, A. C. Bovik, H. R. Sheikh and E. P. Simoncelli, "Image quality assessment: From error visibility to structural similarity," IEEE Transactions on Image Processing, vol. 13, no. 4, pp. 600-612, Apr. 2004.
The phrase peak signal-to-noise ratio, often abbreviated PSNR, is an engineering term for the ratio between the maximum value of a signal and the magnitude of background noise. ... Video quality is a characteristic of video passed through a video processing system. ...
The Structural SIMilarity (SSIM) index is a novel method for measuring the similarity between two images.
The SSIM index can be viewed as a quality measure of one of the images being compared, provided the other image is regarded as of perfect quality.
Close piece-by-piece comparison of the SSIM index and the absolute error maps, we observe that the SSIM index is more consistent with perceived quality measurement.
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