No, it was not the same film, but the 1080p on iTunes was clearly not what it would be if it were Blu-Ray. I could tell.. the picture just wasn't as crystal as the disc I got.
You can say that to yourself, and even believe it, but it's not true. You're mixing up two very different things. Bluray is a format, it's not a transfer. Just because a film comes out on bluray does not mean its going to be "crystal clear". That lies in the hands of the people in charge of the film transfer process.
If you take a modern movie with special effects, etc like let's, say Iron Man, it's going to look "crystal clear" even in an 1080p iTunes rental because the originals and transfer itself are so pristine.
If you take an older movie like, let's say, Back to the Future, and watch that on bluray, it's not going to be "crystal clear" at all because the film transfer and restoration of the original film elements isn't crystal clear from the start. It may never look "crystal clear" because the original elements are poor compared to modern films, etc.
So again, a film put on bluray doesn't mean it's automatically crystal clear.
However, I will do a side by side comparison at some point just to verify. I watched The Duchess on Blu-Ray, and I've also watched parts of The Shawshank Redemption and Babel to test out the system... there's just no way that iTunes could look like this with these films.. I have no doubt that if I got the 1080p version of any of these films from iTunes, the difference would be stark. It just can't be done in 4GB.
edit: In fact, I'll rent the 1080p Shawshank from iTunes right now. I'm curious. I actually watched the HD Shawshank on my 23" screen not too long ago.. and I don't remember being particularly blown away by the picture quality. When I pulled up the Blu-Ray on the 30" screen, that was mind blowing. But anyways.. I've got the 1080p iTunes version downloading again, we'll see.....
If you have only a 23" display, then you need to be sitting like 18" or closer to even see the benefits of 1080p vs. 1080i in the first place. On a 30" display? You have to sit within 5 feet of the display. This applies, blu ray or not. The human eye can't even see the difference.
Again, using a reference film like the transfer for Shawshank Redemption on a 23" or 30" display is in no way reference material by any means. I'm happy that you enjoy the picture quality of bluray. It's nice. But Shawshank on BD mind blowing? Ok. Its pretty clear that you've sold yourself on the idea that a bluray file with a much larger file size must automatically blow away an iTunes rental no matter what since it's a much bigger file size. But at some point you hit diminishing returns, and the sheer file size itself isn't a reason that it's clearer any more so than a film being released on bluray doesn't automatically make it look amazing.
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So there is a difference, but going back to what I was talking about earlier in this thread, there are simply not enough people out there anymore that care enough. To most consumers, HD is HD, and their understanding of video quality doesn't go very far past screen resolution. So to most people, 1080 iTunes video is "good enough" and they can stream it to their Apple TV and other iOS devices (yay, convenience!).
I agree, and I am one of those people who care. But when I read people talking about how amazing bluray looks over a 1080p rental, and then they're viewing the Shawshank Redemption on a 23" display, it just seems kind of silly and part of the other side of the spectrum. Just like you said, I agree there are people that see heavily compressed HD on cable TV and don't care because it's HD. (Yay, HD!)
But then on the other side of the spectrum you have people that ignore the film transfer process, the original source material itself, even intentional film grain, but then say, wow cool, this bluray is 40GB (Yay! big file must mean its amazing quality!)