Originally Posted by elario
Using photoshop difference filter is of no practical value in a video quality comparison.
It tells us that there is a difference but that's it. It doesnt tell us anything about that difference - if it is due to scaling artifacts, misalignment, compression artifacts in either image, higher level of detail etc. It doesnt tell us anything particularly relevant to the human visual system.
And that is another issue with some of your comparisons - boosting the contrast to make compression issues more readily apparent. Lossy video compression deliberately makes use of limations in the human visual system so if dark-area artifacts are not visible on a calibrated display, that is all that matters
. Altering contrast/ or brightness to make these issues visible serves no useful purpose.
On the subject of scaling we don't even know the scaling algorithms you used or the native resolution of the source. I believe the iTunes 1080p video is not exactly 1920 px wide - can you confirm this?
Any way you slice it iTunes 1080p is beating 720p when it comes to detail rendition in Life of Pi. As for the artifacts in the shadows, plenty of people see them, they are a real issue. A good TV won't leave anywhere for the artifacts to hide, you'll see them in the shadows. That's the whole impetus behind these comparisons, what got me started is how very much improved the shadow regions look these days. When it comes to video quality comparisons, we're not talking about raw footage for editing, we're talking about already mastered and compressed video being delivered through a known platform at a known resolution. Comparing the final, rendered frames is the proper approach.
In the examples that look deep into the shadows I don't boost the contrast, I only shift the gamma. Thank you for your input, I am always open to suggestions and constructive criticism. In this instance, I don't see your point. Collectively the observations all lead to the same conclusion - specifically for Life of Pi, iTunes 720p looks blurry compared to Blu-ray, Vudu HDX and iTunes 1080p. That's a fact and I'm not going to waste more time debating a fact.