Blu-ray discs of varying quality are starting to appear on the market, challenging the video processor capability of Blu-ray players.

It should have been simple. There should have been two sorts of Blu-ray disc: the type that brought cinema-style film into the home, and a much smaller collection of material shot with high-definition video cameras.

That’s what Blu-ray players were designed to handle and they do an excellent job with both types.

However, new discs are starting to appear on the market. They comply with Blu-ray specifications but, judging by the way Blu-ray players handle them, electronics manufacturers never expected these discs to materialise.

Ordinary movie Blu-ray discs are by far the most prevalent and carry the video at 24 frames per second. That’s the same as a movie shown at the cinema.

Playing them on a current-day Blu-ray player is easy (although some early models didn’t support this mode). The encoded video stream is read from the disc, a frame is decoded and it is sent to the HDMI video output.

For component video it is not so easy. Getting to the single frame is easy enough, but then things get difficult.

That frame has to be split in half, creating two fields. One field consists of each odd-numbered row of pixels, and the other consists of each even-numbered row.

Those digital pixels then have to be converted to analogue video signals. Remember, all current Blu-ray players are limited to 1080i (‘i’ for interlaced) output over component video, and this is not likely to change.

So HDMI is clearly the way to go, and 1080p24 (‘p’ for progressive, ‘24’ for 24 frames per second) is the best way to handle movies.

When it comes to music concerts and some high-definition TV shows, the video is already interlaced (although not normally dramas, which tend to be shot on film or film-like media).

Instead of 24 full frames per second, they capture either 50 or 60 half-frames per second. Their video is therefore 1080i50 or 1080i60.

I’ll talk mostly about 1080i60 because most interlaced material on Blu-ray was produced this way by US companies.

With this format, the video camera captures half a frame 60 times per second. Each half is the same type of ‘every second row of pixels’ field mentioned above.

With a static scene it would be easy enough to ‘weave’ two fields together to create one fully detailed frame. These frames would be delivered 30 times per second, so 1080i60 could be converted to 1080p30.

In the real world, things have usually changed in the 60th of a second that has elapsed between the two halves of the frame being captured. If the Blu-ray player is set to 1080p60 output, it has to de-interlace the 1080i60 to 1080p60.

The most basic technique for doing this is called ‘bobbing’, in which each half is simply scaled from its 540 lines to 1080, and they are then shown in sequence.

Modern de-interlacers are cleverer than that – they examine the two fields. For those parts of the frame in which there has been no apparent movement between the two fields, they ‘weave’ the frames together. For the moving parts they ‘bob’ it.

In my reviews of various Blu-ray players, it has become obvious that all of them do a competent job with both of these techniques, although there can be subtle differences.

1080i60 and 1080i50 for film

The high quality in Blu-ray disc production is starting to dissipate. We are beginning to see some unusual formats, two of which have popped up in the past couple of months.

The first is the Australian release of John Carpenter’s 1978 hit film Halloween. This was shot on film, of course, and so should be in 1080p24. Indeed, the US version released by Starz Home Entertainment is presented in this way.

But the Australian distributors, Beyond Home Entertainment, tell me they were limited to a 1080i60 source for their version, so that is what they encoded to Blu-ray.

Here we are presented an oddity. The source is inherently progressive because it comes from film. But it is presented in a video format best suited to interlaced formats, such as those produced by high-definition studio video cameras. What is a Blu-ray player to do with it?

What most do is treat the video the same way as they do other 1080i60 material: they assume that it is video sourced and apply motion adaptive de-interlacing.

That produces excellent – potentially perfect – results on those parts of the image that aren’t moving. But it does harm the moving parts of the picture, sometimes very badly.

The chrome strip on the car is moving within the frame, therefore bob de-interlacing is applied. The video should be woven together just as a high-quality progressive scan DVD player does with PAL DVDs.

In Halloween, just after the start of chapter four, the camera pans left and brings into view a car parked in a driveway. This car, which is brown, has a chrome strip down its side.

With most Blu-ray players this strip is shown as jagged and broken. The chrome strip is moving within the frame, therefore ‘bob’ de-interlacing is applied.

In fact, the video should be ‘woven’ together just as a high-quality progressive scan DVD player does with PAL DVDs.

So far I have found two exceptions to this behaviour.

First, Sony’s premium ($2,000+) BDP-S5000ES Blu-ray player detects the film source and does a good job of avoiding jaggies. Second, Pioneer’s premium BDP-LX71A ($1,000+) Blu-ray player allows the user to turn on ‘pure cinema’, which tells the unit to weave the video.

One complaint about PAL DVDs from movie aficionados is that the process of turning the 24 frames per second of film into 50 fields per second speeds up the movie by about 4% and raises the pitch of the sound accordingly.

Blu-ray solve that problem, except for at least two discs from Icon Film Distribution that have appeared in Australia recently: Miss Potter and In Bruges. Both are primarily UK productions featuring big stars and appeared in cinemas – but both come to Blu-ray as 1080i50.

Presenting these in 1080i50 format stresses out Blu-ray players. It seems the designers of these players never envisaged that they would have to cope with a film-sourced 1080i50 signal.

Consequently, all of them (including the expensive Sony player) make a mess of the de-interlacing. You can see this at the start of chapter 10 in Miss Potter.

The camera pans down over a pastoral scene to reveal Miss Potter’s cottage. As the camera pan slows, the windows visibly break up on all Blu-ray players – or at least those using automatic de-interlacing.

Again, the Pioneer can employ film-mode de-iinterlacing for 1080i50 as well. And the Sony PS3 just won’t de-interlace 1080i50 at all, outputting in its native format and leaving it up to the TV to handle all that.

As time passes we will probably see more peculiar Blu-ray formats on the market and they will present new challenges to the video processing circuitry of Blu-ray players.

In the meantime, players offering more control over their performance – such as those from Pioneer and probably the current model from Panasonic – will let customers experience the best performance from all their disc media.