1080p24: true home cinema

One of the most interesting new features that Blu-ray and HD DVD bring us is the ability, at last, to watch movies at 24 frames per second, without having to convert the frame rate because of atavistic technological constraints that limited us to 50 and 60 Hz. 1080p24 should become the holy grail for all home cinema fans. A real luxury, at last within our reach, although not always.

The arrival of the Blu-ray and HD DVD formats, together with the proliferation of Full HD televisions (that is, those with a native horizontal resolution of 1,080 pixels), has brought the concept of 24p into the home audiovisual scene, the frame rate closest (identical, in fact) to the traditional film standard. Is it really that important? Yes, it is.

For a long half-century, the convergence between cinema and television has been compromised precisely by frame rate (the relationship between frames and time). Cinema uses a rate of 24 images per second. As you know, thanks to the sluggishness of our eye, with just 24 still images projected per second our brain interprets them as moving images. That is the magic of cinema. A magic that soon reached the world of television, which is why telecine transfers are carried out, a process by which each and every frame of a movie is converted into video images. But there is a problem. The two current broadcasting standards, PAL and NTSC, use other (and different) refresh rates, both incompatible with the 24 fps (frames per second) of cinema.

One of the main differences between NTSC and PAL is that the former runs at 60 Hz (or 60 frames per second), whereas PAL runs at 50 Hz. This is because the frequency of the alternating current that reaches every home is used as the clock: in the United States, alternating current runs at 60 Hz, while in most European countries (among others) it runs at 50 Hz.

Video cameras (analog and digital) record images at precisely 50 or 60 Hz (depending on the chosen broadcasting standard), so there are no problems in this respect. But film, as we have seen, is only available at 24 fps. When film is transferred to video, something has to happen to make this change possible.

In the case of NTSC, a 3:2 conversion is carried out. The first frame of any movie becomes part of the first 3 frames of the video signal, the second film frame becomes part of the next two, the third again takes the next 3, while the fourth takes only 2 (3, 2, 3, 2...). In this way, 24 fps can be converted into the 60 fps of the video signal. What is the problem, then? Broadly speaking, in any movie transferred with 3:2 pulldown, motion is never fluid, and it will also be perceived as "jerky and juddering".

Conversion to PAL is much easier: every film frame "occupies" its corresponding video frame, but instead of being shown at 24 images per second, it is shown at 25. This is 4% faster. Obviously, this method produces no motion judder, but it does produce another noticeable defect: a change in audio pitch and faster movements. Anyone who feels like it can test the differences involved in playing audio 4% faster: bass is lost and the pitch is higher.



THE SOLUTION



Changing the refresh rate of PAL or NTSC was impossible; a new standard had to be introduced. And this has now become possible, with the need for a video format that would increase the resolution of signals. In fact, two have arrived, Blu-ray and HD DVD, and both have taken this issue fully into account. A warm welcome to 1080p24. What does 1080p24 mean? Many will know. The first number defines the resolution, currently the highest in the home domain. The p confirms progressive scanning, while the 24 defines the exact rate of 24 images per second.

The professional industry adopted 24p long ago, aware that sooner or later there would be a home video format that accepted that frame rate, as has turned out to be the case. There is a great deal of material (both feature films and documentaries) stored in 24p, which is making native re-releases at 1,080p24 possible.

Blu-ray and HD DVD can record (store) video signals at 24p. In fact, the vast majority of movies currently available in stores that state they are in 1080p are also 24p.

With this solution, all the problems related to NTSC and PAL and the corresponding telecine transfer disappear, since there is no change of speed whatsoever and fluid motion is guaranteed.

But to enjoy these advantages, all the display equipment we are using must be compatible with it, which means both the source and the display.

As of today, not all HD DVD and Blu-ray players are 1080p24 compatible. For example, in this very issue we test the Toshiba HD-XE1, the only Toshiba model that meets our requirements. The PlayStation 3, Sony's forthcoming player and Pioneer's current one are compatible; Samsung's and Panasonic's Blu-ray players, on the other hand, are not. The same goes for displays. They must not only accept the 1080p24 video format, but also display it correctly. This is one of the requirements that will give users the most headaches.

It is also true that it is still early days to judge any device for its lack of 1080p24 compatibility. Non-compatible high-definition sources are, in fact, cheaper than compatible ones. The televisions that handle 24p well are high-end models. The same goes for projectors.

Until this becomes the norm, it is well worth at least knowing that this possibility exists and that, at last, the video industry respects the film industry, something we greatly appreciate.

1080p24 ON DISPLAYS

There are Full HD televisions that, in order to gain a market advantage, claim to accept 1,080p24 signals. That may be true, but do they really display them? Being compatible with these signals is not the same as reproducing them perfectly. Very few do the latter.

Some, such as Pioneer's recent new G8 generation of panels, do accept and display these signals perfectly, although in reality they are not 24 still images per second. In Pioneer's case, for example, they are 72 images per second (3 x 24). The same technique used in conventional cinemas to avoid flicker on large screens. Few cinemas actually display 24 images per second, since they repeat the same frame two or even three times.

There are some recent televisions which, with the stated aim of avoiding flicker and although they accept these 1080p24 signals, use a 100 Hz refresh rate. Although this is close to 24 x 4 (96 fps), there is still a problem with speed and/or judder.