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Why 1080p is (not always) better than 720p

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Anyone thinks that definition = resolution. This is not (always) true!

To me, definition is the maximum resolution (in pixel) a given display, or source, could show; so, an high definition image (1080i/p) is made by 1920 (sometimes 1440) x 1080 pixels. Does it mean I have always a 1920x1080 resolution? Think about it... if you take an high resolution source - like a BD made using a 4K master - and compare it with an upscaled DVD, will they look like the same? Obviously not!

So, resolution is not (always) the same as definition... back to the example, if we downscale the 1920x1080 BD image, mastered from a 4K source (hence more than 2x the BD definition) to DVD definition, it should be better than previous DVD of the same movie, but made with a 2K master...

At the end, the resolution of the master used for the source is the most important thing, but not the only factor in the resolution "affaire"... for example, if we have two different HDTV broadcast recordings, one 1080i, and the other 720p, sometimes we discover that the 720p seems better, even if we know that they use the same master (same colors, same cut, same dirt spots placed in the same places etc.); with the hypotesis of a low resolution master (again, resolution <> definition), there could be some reasons for that...
  • bitrate: a 1080 FHD video has an image size of 1920x1080 = 2073600 pixels, while a 720 HD video has 1280x720 = 921600, so a FHD video file size is 2,25x the HD video (given the same codec is used); if the size difference (minus audio/subs tracks) is much different, and the ratio is lower, than the 720 video has obviously an higher bitrate; there are times where the 720 video has almost the same size of the 1080 one!
  • codec: previous comparison has taken in account two videos with different sizes but the same codec; what if one uses a codec and the other another? You should calculate also this factor; roughly, AVC encoded video has the same perceived quality when compressed at half bitrate of an MPEG-2 video: so, if you have an MPEG-2 1080 video, it should be around 4.5x the size of an AVC 720 video to have the same quality
  • encoder: different encoders give different results, depending not only on the settings used, but also on the encoder inherent quality; did you know that the best MPEG-2 hardware encoders (the ones used by the professionals) are about 20-25% more efficient than the software ones?
At the end, you should take the previous factors in account to know if an inferior definition video could be somehow better than a superior definition one.

For examples, there are some makers that uses 1080p BD as source for their projects, but release only a 720p AVCHD, saying that the BD resolution is, more or less, equal to a 720p. Again, the resolution is only a factor, and not always the most important... has those AVC 1280x720 10mps video the same quality of an AVC 1920x1080 22.5mbps?

Apparently yes, but there are quality loss in the scaling (unless you watch them in a 1280x720 display), and the eventual grain present will be 2.25x bigger when upscaled, giving the impression of a coarser grain. Even 480/576 video, upscaled properly to 1080, with a grain plate added, encoded at 2.25x bitrate, usually looks better than the 720 version when watched in a 1920x1080 display (projector); will be this difference evident for anybody?

Real answer: it depends... on the display, on the viewer's eyesight, on codec settings... to me, if space is not a concern, I use always the source definition - because, even if apparent resolution seems lower, it could happen that in particular scenes/shots, it stays higher; more, the grain plate applied will have the effective size...

Opinions, personal experiences, interesting articles about all of this?
Sadly my projects are lost due to an HDD crash... Sad
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