Wednesday, June 08, 2005

HBO-HD's Mystic River: Missing "OAR"

I recently "taped" (actually, recorded to my cable DVR) HBO HD's cablecast of director Clint Eastwood's 2003 noir thriller Mystic River and then watched it yesterday. I just so happened to have the DVD of the same movie on hand from Netflix for comparison purposes. The thing that leapt out at me is that the transfer HBO used is "zoomed in" to fill the entire height of a 16:9 (or 1.78:1) screen. The original aspect ratio of this Panavision film was 2:35:1, which the DVD honors with an anamorphic transfer that puts black bars at the top and bottom of the screen.

I toggled back and forth and was surprised to find that the full-screen zoom on HBO made for (in my humble opinion) a noticeably ugly composition, compared to the anamorphic letterbox on the DVD. To put the same sentiment in reverse, the actual original-aspect-ratio composition of the film's shots on DVD was as aesthetically pleasing as the HBO 16:9 crop was not.

I say I was surprised, because I don't usuaally consider myself a purist about such things.

When you think about it, the 2:35-to-1.78 crop gives you fully 75% of the scene, with the remaining 25% shaved off at an average of just 12.5% per side ... though I'm sure the film transfer can be panned slightly within those confines to take a little more off one side than the other, when need be. How important can twice 12.5% be?

As it turns out, quite important.

It's not that anything crucial to seeing what's going on is lost. Rather, it's that the framing of a film shot "says" something crucial — something ephemeral, something subliminal — that gets trampled on by the crop.

That's why home theater aficionados are always nattering on and on about preserving OAR: the original aspect ratio. My side-by-side test with Mystic River, the HD cable version vs. the DVD, says they're absolutely right. Even though the DVD looks noticeably softer because it's not hi-def, it still provides the more pleasing viewing experience.

So why is HBO using a zoomed-in 16:9 transfer? The most likely reason is that there are so many customers who resent the letterbox bars. "I spent a kazillion dollars on this big-screen plasma TV," many probably say, "and I want every pixel lit."

That, and black bars can cause screen burn-in, an uneven dimming of the pixels that do get lit vs. the ones that stay dark and never age. Supposedly the bane of plasma sets, it's less problematic for other TV types.

My attitude is, the TV itself should offer a Zoom function or mode that will optionally remove excise the black bars, so the program source doesn't have to. Unfortunately, all too many TV sets' Zoom modes inexplicbly disappear when 720p/1080i HD is input. That's true of both my Samsung DLP rear projector and my Hitachi wall-mounted plasma flat panel.

So we urgently need HDTVs and monitors that don't disable hi-def Zoom. It can be done. I'm presently ogling a Sony KD-34XBR960 Direct View CRT for my bedroom that enables all aspect modes for all inputs.

HBO and cable companies, as well as consumers in general, might also note that more and more of us are watching DVDs, anamorphic or otherwise, via hi-def digital connections to our HDTVs. A number of high-end DVD players can upconvert any DVD's content to 720p or 1080i at their digital DVI or HDMI output.

This doesn't improve picture detail, but it still gives a better picture because the video stays in the digital domain all the way from disc to TV. No digital-to-analog conversions degrade the picture. But when the typical HDTV monitor receives the digital video input, it lacks the ability to Zoom away whatever black bars there are. And plasma HDTV owners and others are putting up with that.

Black bars are not the end of the world, even for plasma owners. The cable industry ought to consider leaving all movies in their original aspect ratio, black bars or no.

For one thing, the black bars make the video easier to compress. MPEG compression takes advantage of redundancy in the picture — such as in unrelieved black bars on the screen — permitting itself a lower output bitrate from the compressor. The same picture quality can be acheived at a lower number of megabits per second.

Lower bitrates in turn mean a channel, hi-def or not, takes up a smaller slice of a digital slot in the cable bandwidth spectrum. (See HDTV and Cable Systems for more on how cable slots are allocated.) The arithmetic here is simple. Each digital slot in the cable system's bandwidth "shelf space" can hold 10-12 SD channels or 2-3 HD channels. It's more likely to be able to use the higher number, with no picture degradation, if each channel's actual bitrate is lower than its maximum theoretical bitrate — which is exactly what happens when the MPEG encoder can take advantage of lots of black-bar redundancy.

This is not a matter on which everyone will agree, unfortunately. It's the longstanding letterbox-vs.-pan & scan dispute brought up to date.

Before the home video era began back in the 1970s, there was no such thing as letterboxing. Purists began to howl about the cropping of movies on cable and VHS, and when the now-defunct laserdisc was introduced, widescreen movies were presented in a letterbox transfer for the first time. Unsurprisingly, the same "correct" film-to-video transfers began to invade premium cable and VHS ... and run-of-the-mill non-purists began to fume.

After all, TV screens were small and squarish back then, with marginal vertical resolution. Letterboxing made the picture yet smaller and sacrficed much of what little vertical resolution there was.

Digital TV's designers had that complaint in mind when they agreed on a 16:9 screen aspect ratio: not quite wide enough for most movies, but the lingering presence of (thinner) letterboxing bars was ostensibly to be made up for by larger, wider screens with greater vertical resolution.

Still, there remains a psychological aversion to letterboxing among many TV consumers. A lot of folks feel they're getting cheated if every pixel isn't lit.

Perhaps the answer is multiple transfers, one for the every-pixel-lit crowd and one for the OAR crowd. HBO could alternate between the two, since they show each movie umpty-ump times a week anyway. People could pick the version they prefer, record it to their HD DVRs, and watch it whenever.

Or am I being too pie-in-the-sky here?

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