Thought it might be interesting to see how the AVISynth SSIM filter compares also. This plugin has a rather nebulous history going back to the original implementation by LeFungus in 2003:
https://forum.doom9.org/showthread.php?t=61128
His last update was version 0.24, although the results log still reports it as 0.23.
It appears the plugin then received further fixes and modifications made by others, but in the absence of associated documentation, it is not clear exactly what changes were made.
This thread attempted to make sense of it:
https://forum.doom9.org/showthread.p...03#post1089303
I decided to test both the original (as assumed) 'LeFungus' 0.24 version and the 0.25.1 version posted by Mitsubishi in that thread. They produced identical results:
Wow, very different from the other SSIM implementations, with the CRF=30 x264 encode scoring way down at 33 (0.33).
Yet, according to LeFungus, it was developed from the original code.
I suspect this stems from the 'luma masking' parameter that was given as an option (Default: True) in the original (LeFungus) 0.24 plugin. In 0.25.1 that option is not accessible, as such (returns an error), but since 0.25.1 produced identical results, it's reasonable to assume that 'Luma Masking' was being applied.
Possibly it equates with the luminance normalization filtering that is applied in the original SSIM algorithm ? In the AVISynth plugin it is applied as a weighting:
Quote:
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This filter is designed to compute an SSIM value by two methods, the original one, and a "enhanced" one that weight these results by lumimasking........In the csv file, when lumimasking is activated, both SSIM values and its weight is written.
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https://avisynth.org.ru/docs/english...lters/ssim.htm
Unfortunately, I only recorded the final aggregate SSIM score reported in the log file and didn't generate the csv file that lists the individual frame scores and weightings. I'll maybe re-run some tests to see what difference the weightings made. But really, these results and the vagaries surrounding this plugin, don't exactly instill confidence in it's use.