I received an email today, originating from Panasonic, in which polite issue was taken with a statement I had made in a review I had written of the Panasonic DMP-BD100 Blu-ray player. The statement was: ‘there is five times as much detail in a Blu-ray movie than there is in its DVD equivalent.’
Panasonic noted that ‘Technically speaking, “a Blu-ray disk can have up to 10x the resolution of a conventional DVD”.’ Naturally, I disagree. What follows is based largely on my response.
This is correct — potentially, and in a limited range of circumstances.
If the original source was captured using a 1080p50 camera, then there would indeed be 10 times the amount of data compared to a 576i50 camera (pps= pixels per second):
576i50 capture: 720 pixels x 288 pixels x 50 hertz = 10,368,000pps
1080p50 capture: 1,920 x 1,080 x 50 = 103,680,000pps
Ratio is 10:1
It is actually even higher in the US where 60 hertz systems are used:
480i/60: 720 x 240 x 60 = 10,368,000pps
1080p60: 1,920 x 1,080 x 60 = 124,416,000pps
Ratio is 12:1
So, to be completely accurate, one should say that Blu-ray/HD DVD can deliver up to 12 times the number of pixels.
So that’s the potentiality, and all it awaits is the extensive use of 1080p50 or 60 video cameras.
But back to the present. The great majority of DVD and Blu-ray/HD DVD content is derived from either film, or film-like video camera (eg, Episodes 1-3 of Star Wars). These run at 24 frames per second.
Let us consider one film frame. With, say, 576i50 telecining, this is indeed captured in each cycle at a resolution of only 720 by 288 pixels, to constitute the first field. But there are two fields. The following cycle also captures only 720 by 288 pixels, but these are actually different pixels to those captured in the first cycle. The first cycle captures one set of 288 horizontal lines, reaching from the top to the bottom of the screen, while the second cycle captures the in-between set of lines. So the total amount of information captured for that frame is 720 by 576, which is 414,720 pixels.
With 1080p telecining, you would be mad to capture the exact same film frame twice. All that does is double the amount of data to store. So each film frame is captured once, at full HD resolution of 1,920 by 1,080, which is 2,073,600 pixels. All film-sourced content on Blu-ray discs, which I have confirmed with Twentieth Century Fox, Warner Bros and Sony Pictures Entertainment, will be presented on Blu-ray in the 1080p24 format.
So, right now, with virtually all currently available content, and for the great majority of content into the forseeable future, the number of pixels per frame for most Australian DVDs and Australian BDs are:
DVD: 720 x 288 x 50 = 10,368,000pps
BD: 1,920 x 1,080 x 24 = 49,766,400pps
Ratio is 4.8:1
This is being unfair to BD because the DVD is running the movie around 4% fast (actually, 4.1666 repeated). So in terms of actual total data presented per film frame we have:
DVD: 720 x 576 = 414,720 pixels
BD: 1,920 by 1,080 = 2,073,600 pixels
Ratio is exactly 5:1
I think that justifies my claim (note, I specifically said ‘Blu-ray movie’). The important point to remember is that everything is limited by its source. A 1080p projector can’t really lift a 576i DVD out of its humble origins, and a 1080p60 BD can’t generate more data out of a 24 frame per second movie than was originally contained in the frame.
But that does bring me to one point which: the output of the current Blu-ray players is 1080p60 or 1080i60. In either case, this damages the 1080p24 source.
The reason is that the 24 film frames in each second must be translated into 60 BD frames per second. How to do this? Consider four sequential film frames, which I’ll call A, B, C and D. When shown in a cinema, a technique of double shuttering is used to eliminate flicker. This is straightforward: each film frame is exposed twice, thus: A A B B C C D D. So in modern terms, you might say that the output of a cinema film projector is 48p.
But with the DMP-BD60’s output at, say, 1080p60, extra frames are required (24 is not a factor of 60). So the film frames are shown as so:
A A A B B C C C D D
As you can see, every second film frame is displayed for 50% longer than the intermediate ones. This is painfully obvious when watching Blu-ray discs. Camera pans become jerky, and so does other movement which should be smoothly moving. Watch the credits roll up on the end of a DVD movie, then watch them on a BD and the difference will be obvious.
The obvious solution is to produce a Blu-ray disc player capable of outputting 1080p24 (or 1080p48, but that’s unnecessary). I note that most modern 1080p display devices are capable of accepting 1080p24 input. So why won’t current Blu-ray players deliver it?