Obviously, in today’s world, we’re no longer in a single-standard environment.High definition (HD) choices add a level of complexity for the producer who is trying to make the right decision among various kinds of high definition formats. What are they? And what differences will they make to your final production?

Of course, the first consideration in HD is image quality. The entire reason for converting to high definition is that it has much higher “spatial resolution” than standard definition television. An image composed of 1920 by 1080 pixels has quite a bit more spatial resolution than your standard 720 by 480 format. The motion content of the video is referred to as its “temporal resolution.” This is affected by frame rates and how the individual fields are interlaced. The choice of 1080i (interlaced) versus 1080p (progressive) has production consequences. The method of delivery is an important issue. The signal is going to be compressed in some way – whether it’s delivered through a free-to-air broadcast or via a disk format such as HD-DVD or Blu-Ray – it will be compressed and probably many times. So we have to consider the delivery vehicle when looking at which format works best. Finally, you have to consider the destination of your program. Is your production designed to be seen on a large-format, high definition plasma screen in a consumer’s home? Or is it destined to be played on a huge theater display in front of a massive concert audience? The final destination is really one of the strong determining factors in the choice of high-definition formats.

SPATIAL RESOLUTION: SITTING IN THE SHADE

More pixels equal more details, but can they be seen? That’s going to depend entirely
on the television screen size and the customer’s viewing distance. The average viewing
distance in a typical home is between 6 to 12 feet.

SPATIAL RESOLUTION AT COMFORTABLE VIEWING DISTANCES

High definition (HD) pictures are expanded to a wider rectangle that looks more like a movie theater screen. In HD’s 16:9 aspect ratio, the 1080 display is actually 1920 pixels wide by 1080 pixels high. This calculates out to just over two megapixels. Compared to the 720 display (1280 by 720), the 1080 image contains 125% more pixels. It has more than twice the spatial resolution of the 720 format. So there’s quite a difference in spatial resolution among the three TV formats. On the chart, the average viewing distance is indicated by the shaded areas. At a comfortable 12-foot viewing distance, a standard-def screen would measure approximately 37 inches diagonally (2½ feet wide by about 2 feet tall). At the same comfortable 12-foot viewing distance, the 720 high-def screen would be a big 57 inches diagonally (4 feet wide by 2⅓ feet tall), and a 1080 screen would top out at about 85 inches (6 feet wide by 3½ feet tall). The intriguing part of this is in the sections where the shaded areas overlap. At the average viewing distance of 12 feet, the typical home viewer will not be able to see a marked difference between a standard definition screen measuring 32 to 35 inches and the same size high definition 720-pixel screen. Similarly, 720 and 1080 displays look much the same within screen sizes of 45 to 57 inches. [Consumer electronics sales personnel take note – Editor].

As we all transition to high definition television, we must know our market. As professional communicators, we need to know our audience – and how they are viewing our product. During this transition period, standard definition will tend to look worse and worse, as images destined for 4:3 screens are received and reinterpreted for 16:9. You then suffer from the fact that pixels are no longer square. They’ve now rectangular, since you’re actually stretching the information, making the picture worse. Remember: this is the average viewer we’re talking about, and not a trained video professional. Obviously, this chart is drawn up from data based on the normal resolution of the eye, versus the screen’s resolution, and taking into account typical viewing distances in the home environment. An educated viewer is honestly going to see the difference at the same viewing distance on a 37-inch screen between a standard definition image and a high definition image, but it won’t be remarkable. Not significant enough to make him remark, ‘Well this picture is so much better!” This means that, on the production side of things, you really need to consider the fact that consumers are now living in a changing world and they can make lots of different choices. All of these variables can have an impact on your cost of production. [For example, a decade ago, we didn’t have to dedicate production resources to ensuring great sound quality, because home video speakers were small and insignificant. This is no longer the case – Editor]. At the end of the day, producers have to decide who’s going to be watching their programs and how they’re going to be watching them. It’s a very difficult decision.

MOTION ERROR WHEN DE-INTERLACED

If we were to look at that in an interlaced system, whether standard definition or high definition, the motion component is actually half resolution because there are fields of data. Motion error can be introduced when the video is de-interlaced. As noted earlier, our video signals are destined to be compressed in some way – whether it’s during broadcast or when recorded to a disk format – it will be compressed and probably many times. In order to make compression work properly, the original video needs to be de-interlaced. Those fields of data are transformed into single frames – and that’s where some blurry (half-resolution) images and jumpy (badly flowing) motion errors can be introduced. [A live broadcast received by a TV antenna should provide a better signal than satellite delivery or recording of any kind – Editor].

TEMPORAL RESOLUTION IN PROGRESSIVE SYSTEMS

In an effort to solve these problems, progressive systems were invented. In progressive video, each frame is complete, so there’s no interlace involved. In a 1080p progressive system, where the production frame rate is the same as the display frame rate, we have the best temporal resolution for images that are in motion and the best spatial resolution, too. So, what’s the problem? Look again at that frame rate on the progressive graph. Neither PAL nor NTSC cameras record at 60 frames per second. If the interlaced field rate and the progressive frame rate were the same, then their temporal resolution would be the same. In other words, the actual quality of motion, the perception of smooth motion, would be the same, even though one is interlaced and one is progressive.

WHEN CAPTURE AND DISPLAY RATES ARE UNEQUAL

Unfortunately, if you’re using a progressive camera shooting at a 30 frame rate and being shown on a display at a 60 frame rate, your temporal resolution will be unequal. It now contains a “step” function since you’ll have to repeat a frame twice before it can move on to the next one. This is because there are only half as many frames in the original capture as there are in the display. In progressive systems, the display’s spatial resolution is still equal to the original shooting resolution, but the smoothness of the temporal resolution is cut in half. Spatial resolution is still great, but if you shoot at 30 and display at 60, the temporal resolution is halved. [This challenge is the same for PAL systems, even though the frame rates are different than NTSC systems – Editor].