DVDFILE - Analysis shows Blu-ray better

[Go Blu]

Written by Dan Ramer
Friday, 19 October 2007
A small analysis of high definition video quality on disc

When I was particularly impressed with 20th Century Fox’s return to Blu-ray Disc, I noted that the video CODEC for each is AVC. I then vaguely recalled that many of the discs that impressed me were also compressed using the AVC CODEC. So I thought it might be interesting to correlate CODEC type against video quality rating for those discs that I’ve reviewed to see if there was anything to be learned. Since I began reviewing HD on disc in the spring of 2006, I believe I’ve accumulated a sufficiently large enough sample to identify valid trends (assuming they exist).

From this little analysis, I might learn a few other things. I was curious to discover whether or not my ratings were consistent and reliable. Since I routinely watched (and continue to watch) broadcast HDTV, I had a baseline of experience, but HD discs are so impressive compared to DVD that I might have given HD discs in early reviews a higher rating than they deserved simply because I was so initially impressed. If that had happened, after I became accustomed to the look of HD discs, my ratings would have dropped off.

I was also interested to see if, as the production houses became more accustomed to the compression tools, and as advanced CODEC tools came on line, if there had been an improvement in the quality of the transfers.

But perhaps the most contentious question is whether there is any statistically noticeable numerical difference in the video ratings between HD DVD and Blu-ray Disc. As you can imagine, I’ve received quite a few emails from readers who disagree with my expressed preference for Blu-ray Disc, which I find offers a more film-like presentation. I’ve written that the best of BD looks better than the best of HD DVD and I’ve suggested that the differences in bit rate and storage capacity are the technical reasons why. As a result, I’ve been accused of blatant prejudice.

So I gathered the video ratings and CODECs from all my reviews, dumped the data into an Excel spreadsheet, and began to analyze. And the results are . . . interesting.

A plot of the raw data is difficult to read because of the variability, so I calculated a moving average with a sample size of three, but although the curves became a lot easier to read, the plotted values are distorted. I also ran a linear regression of the data for each format. To put technobabble aside, a linear regression is simply a way of fitting the numerical data to a straight line approximation. The slope or tilt of that line represents a trend.

The resulting graph reveals several interesting things. First, for the most part, BD seems to have scored higher than HD DVD in video quality. Second, the trend analysis seems to indicate that BD is improving (the trend line indicates that during the review period its score improved by 0.76 video points), while HD DVD had a slightly negative quality trend (losing 0.12 video points on its trend line). But Blu-ray Disc’s quality trend may not be an indicator of a dramatic improvement in the skills of compression houses; it’s more likely a consequence of the early use of MPEG-2 and single layer discs. Once Blu-ray Disc’s capacity doubled and advanced CODECs dominated, such a dramatic improvement should be inevitable. It’s nice to see that the analysis demonstrates an expected result.



Now, one could argue that I gave HD DVD lower ratings from bias, but I can assure you that’s not the case. I simply report what I see. One could also argue that my HD DVD scores dropped slightly as I experienced the video quality of Blu-ray Disc. That is possible. Regardless, the differences in my perceptions of the two formats remain valid. So even if HD DVD had improved over time, Blu-ray Disc must have improved more.

MPEG-2 was used for early BD releases and was used for a small handful of HD DVDs, but the real CODEC workhorses for HD on disc are VC-1 and AVC.

Several findings are of particular interest. First, regardless of the format, the AVC CODEC seems to produce a more pleasing presentation than the VC-1 CODEC. Second, regardless of CODEC, Blu-ray Disc seems to offer a more pleasing presentation than HD DVD. Third, the differences between the appearance of transfers compressed with the two CODECs are more noticeable on Blu-ray Disc than on HD DVD, suggesting once again that BD is more revealing. Admittedly, the original data points are based on purely subjective assessments, but I’m confident that the data are representative of accurate observations rather than bias.

When DVD was young and some studios were issuing discs in non-anamorphic video, there were respected reviewers who took the position that since most people did not have displays capable of the anamorphic squeeze that non-anamorphic discs should be the norm. Those writers objected to anamorphic DVDs because they were reviewing discs on non-anamorphic displays; for a 4:3 display, DVD players throw away every third scan line of an anamorphic transfer to restore proper proportions, which reduces video resolution. What they saw was real, but theirs was an incredibly short-sighted position. When those same reviewers purchased displays capable of the anamorphic squeeze, they suddenly flipped their positions. They became anamorphic video advocates and complained whenever a studio resurrected a non-anamorphic laserdisc master for a DVD release. What, you may ask, does this have to do with the subject matter at hand?

My point is this. I recommend that consumers support the highest possible quality HD disc format to ensure that when they eventually purchase a sufficiently revealing display, the quality of the discs will maximize the enjoyment factor. Consumer electronics (and PCs) have a wonderful tendency to offer more for less over time. Average HD-ready display prices are dropping. Average HD-ready display performance is improving. Within five years, most of you will purchase displays that will reveal the subtle differences between Blu-ray Disc and HD DVD. I humbly suggest that your dollars should be invested in the format that is more able to deliver a viewing experience that comes closest to the motion picture theater experience.

And I would be remiss if I didn’t suggest to the studios that if the AVC video CODEC produces better results, perhaps that would be the better choice for future releases.

Some HD DVD proponents will interpret this article as prejudiced support for Blu-ray Disc. In response, I can only write that I report simply what I observe, and I have no vested interest in either format other than a desire to maximize my and your enjoyment of home theater. Let the flames begin.


you can find the article HERE