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Multiscale structural similarity (MS-SSIM) index for image quality

calculates the multi-scale structural similarity (MS-SSIM) index,
`score`

= multissim(`I`

,`Iref`

)`score`

, for image `I`

, using
`Iref`

as the reference image.

MS-SSIM is only defined for grayscale images. For inputs with more than two dimensions,
`multissim`

treats each element of higher dimensions as a separate 2-D
grayscale image.

`[`

also returns the local MS-SSIM index value for each pixel in each scaled version of
`score`

,`qualityMaps`

] = multissim(`I`

,`Iref`

)`I`

. The `qualitymap`

output is a cell array
containing maps for each of the scaled versions of `I`

. Each quality map
is the same size as the corresponding scaled version of `I`

.

`[___] = multissim(`

controls aspects of the computation using one or more name-value arguments. For example,
specify the number of scales using the `I`

,`Iref`

,`Name,Value`

)`'NumScales'`

argument.

The structural similarity (SSIM) index measures perceived quality by quantifying the SSIM
between an image and a reference image (see `ssim`

). The `multissim`

function calculates the MS-SSIM index
by combining the SSIM index of several versions of the image at various scales. The MS-SSIM
index can be more robust when compared to the SSIM index with regard to variations in viewing
conditions.

The `multissim`

function uses double-precision arithmetic for input
images of class `double`

. All other types of input images use
single-precision arithmetic.

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