How to interpret the SSIM

[pelle412]

I'm an x264 enthusiast and I'm wondering about the utility of the SSIM metric. I understand that some options such as psy-rd doesn't help SSIM but makes the picture look better (for certain material). I don't have particularly good eyes and the only way I compare encodes is by watching them at full frame rate on my 19" PC monitor. One of my blurays is Batman Begins. A straight crf 21 tune film encode of a 1280x528 version yielded ~1400 kbit/s with a SSIM of 0.9839. To me it looks like the source, so I should be happy right? I also suspect if I do crf 22 it may end up with a SSIM still > 0.98.

Since I don't have a very large TV to test my encodes on, I'm concerned that I may accept an encode as "good" and later having to redo it because I got myself a TV that shows what it really looks like. Based on your experience, is there a SSIM value that regardless of resulting bitrate one can consider the encode as "good enough"? The viewing medium for me will likely be a 55-65" LCD TV sometime in the future. I know that SSIM 0.98 is roughly 50% better than 0.97, mathematically speaking anyway.

Any insights from you experienced encoders out there with big-a** TVs?

[Dark Shikari]

SSIM is not that useful, but as a threshold it's even less useful.  I have sources that look nearly perfect at 0.90 SSIM and I have sources that look like crap at 0.99 SSIM.

Among film content, it probably depends heavily on the properties of the grain.

[Esurnir]

White or whole wheat? What kind of properties if I may ask?

[chengbin]

For film >0.98 is excellent.

When DS is referring to sources that look crap on 0.99, he meant anime. Anime require something like at least 0.996 to look good.

SSIM isn't a very good as a threshold. Always use your eyes to judge.

[Dark Shikari]

For film >0.98 is excellent.

When DS is referring to sources that look crap on 0.99, he meant anime. Anime require something like at least 0.996 to look good.

Not true at all.  I was referring to cases where the primary artifacts consisted of blocking in flat areas, something that SSIM completely does not capture.

[Dstln]

If you're not sure if you can tell a difference on your smaller monitor, put your face right up there and check lol.

Being right up close to a 19" monitor would show more to someone with nearsightedness than being across the room from a 60" >_>

And yeah basically, SSIM means SOMETHING and would generally go up and down with bitrate but going for any certain number is counterproductive.