Extend the package with newer variants of MS-SSIM

[danieltudosiu]

What are your thoughts about extending the library to include the following metrics:

• 3-SSIM
• 3-MS-SSIM
• G-SSIM
• G-MS-SSIM
• 3-G-SSIM
• 3-G-MS-SSIM
• 4-SSIM
• 4-MS-SSIM
• 4-G-SSIM
• 4-G-MS-SSIM

From a quick look, the required changes are:

• Decoupling the scalar SSIM calculation from the calculation of the SSIM map (here).
• Allowing for padding during the SSIM map calculation (here).

An implementation choice that I did not understand is why do you apply multiple 1D gaussian smoothings (here) instead of a 2D or 3D one. Could you please explain it?

What would you think about a collaboration to extend the codebase and improve it?

[danieltudosiu]

@VainF I have based my implementation of the metrics I outlined in the original post on your library.

I am to submit a push request to MONAI after I benchmark it against another open-source implementation in JAVA.

How would you like to be acknowledged in the code?