Implement Structural Similarity Index Measure (SSIM) for spectral images

[EBRogers]

SSIM is useful for quantifying the structural difference between two images. Most implementations in R are tailored to geospatial applications; most do not allow irregularly shaped images. Could SSIM be implemented in matter - say to compute across two features/mz values? This may be better suited to Cardinal.

Citation for the original SSIM paper: Zhou Wang, A. C. Bovik, H. R. Sheikh and E. P. Simoncelli, "Image quality assessment: from error visibility to structural similarity," in IEEE Transactions on Image Processing, vol. 13, no. 4, pp. 600-612, April 2004, doi: 10.1109/TIP.2003.819861.