Results are significantly different compared to ffmpeg implementation of SSIM and PSNR

[ichlubna]

I've noticed that the SSIM and PSNR values are much higher when using your tool than when trying ffmpeg method such as:
ffmpeg -i first.png -i second.png -lavfi ssim -f null -
Why is that?
Thanks for the tool anyway ^_^.

[sfalkena]

Hi, I noticed this at first as well. It most certainly has to do with the data range that is being used in calculating the values. As a standard in this tool the value is set to 12 bits (4095) (check implementation here. I am not sure what ffmpeg uses, but I suspect it finds it from the datatype of the images. Hope this helps!

[ichlubna]

the value is set to 12 bits (4095)

Hmm would be nice to be able to change it as an argument or to have an automatic detection then. Otherwise the tool can't be really used when comparing for example compression methods etc. with already published results. Thanks for the answer anyway!

[nekhtiari]

@sfalkena thanks for the explanation. that is the reason for your inconsistent result @ichlubna. Fair point and nice suggestion, I will make a PR to make this a flexible argument.

[nekhtiari]

Sorry for taking this so long. Unfortunately, I am a bit busy at the moment with other projects. So it might take some time I can get back to this. In the meantime feel free to contribute or make PR if you feel like it. I would be more than happy :)

[lumiaxth]

Hi, can I ask that ffmpeg's results are reliable? Thx for your attention!

[ichlubna]

Hi, can I ask that ffmpeg's results are reliable? Thx for your attention!

I took ffmpeg as a generally accepted and widely used tool even among scientific community. Do you think the results are not correct? They were usually according to my expectations when I used it.

[lumiaxth]

Hi, can I ask that ffmpeg's results are reliable? Thx for your attention!

I took ffmpeg as a generally accepted and widely used tool even among scientific community. Do you think the results are not correct? They were usually according to my expectations when I used it.

Ok, got it. I'm new here, so I feel confused about two different data. Thanks for your kind reply!

[grapemaidaa]

What's "the value is set to 12 bits (4095)" mean?
And where should I set it in this code?