Wednesday, January 07, 2004

Home theatre versus cinema

James Russell has some comments on the cinema versus home theatre experience, making the point that picture quality is much better in the cinema, and however convenient it is and how big your screen is, the home cinema experience does not match it. He gets a couple of things slightly wrong though, so I will elaborate a little here. (You may want to go and read James' post first).

Analogue PAL television is normally described as having 625 lines. However it takes time for the electron gun in a conventional television to move from the bottom of the screen to the top, so those lines which are being transmitted while the gun moves from the bottom to the top are not seen. The number of lines actually seen varies slightly depending on the TV, but as James says it is about 580. (The BBC invented a neat hack to transmit information in this hidden lines, which is how we got teletext). Digital television only transmits 576 lines, as this is enough to fill the screen, and with digital technology it is okay to not transmit quite in real time. (In fact it is required). High definition television uses either 720 or 1080 lines. (1150 was used for a couple of semi-experimental analogue HDTV formats, but is no more. The full resolutions for the two current formats are 1920x1080 and 1280x720). The digital movie cameras used for the best digital movies are produced by Sony, and use 1080 lines shot at 24 frames per second. (The 720 line HDTV mode also has 50fps and 60fps modes, and some people claim that these look better than 1080 lines at 24fps. However as film projectors normally use 24fps, this won't help if you are transferring to film and projecting in a cinema).

However, there have been a number of films that have been shot on digital equipment and blown up to film and then projected in cinemas that have used varients of the DV semi-professional format. (For instance "The Anniversary Party"). These have usually been shot in 576 lines and then blown up to film, and they look pretty muddy when projected. Films such as Russian Ark, which have actually been shot in 1080 line HD, look much better, although in my mind still not as good as film.

One final proviso is that one reason you have all that resolution for films is that you want it to look good from anywhere in the cinema, including right up the front. Most of these formats are fine down the back, but up front you can see the lines. In your living room, you are close to the screen, but the screen is much smaller and the lines are much thinner, so in terms of the arc width of each pixel, the situation is akin to sitting in the middle or back of a cinema. What that means is that although there are fewer lines on the screen, in practice a 1080 line plasma screen showing HDTV is in most instances going to look as good or nearly as good as watching a film in a cinema. (However, HDTV shown in a cinema is not going to look nearly as good as film in a cinema). In short, I disagree that cinema is always going to win out, but I agree that it wins out for now although in the best possible case only by a little.

The trouble is that at the moment we have few opportunities to actually watch movies in that best possible case at home. Plasma screens with 1080 (actually more commonly 1024) lines do exist, and formats for storing high definition movies on optical discs do exist, but not as consumer products yet. It is not generally possible to buy recorded movies in HDTV format (although there are one or two high definition movie channels on American satellite television). For now, even if we have high definition screens we are normally restricted to watching DVD format movies, and these have resolutions of either 720x576 (The PAL/SECAM world) or 720x480 (The NTSC/PAL-M world). So for now, home viewing is not as good as cinema viewing. But home viewing that is as good as cinema viewing is not far off.

And it is worth considering just how far things have improved. A decade ago we were watching pan and scanned VHS video tapes on 20 inch televisions and listening to mono sound on one tinny speaker on the front of the television. In my opinion, the distance to genuine cinema quality from where we are now is rather less than the journey since those days.

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