Essay on the Hdtv

HDTV Television - An Introduction

Two lectures of material

I. The movement toward HDTV

The original impetus for HDTV came from wide-screen movies. Soon after wide-screen was introduced, movie producers discovered that individuals seated in the first few rows enjoyed a level of participation in the action not possible with conventional movies. Evidently, having the screen occupy a great field of view (especially peripherally) significantly increases the sense of "being there".

Early in the 1980s, movie producers were offered a high-definition television system developed by Sony and NHK in the late 70s. This system (called NHK Hi-vision) and its variants are capable of producing images having essentially the same detail as 35 mm film[1]. With these systems, a scene could be recorded, played and edited immediately, and then transferred to film. As a consequence, many of the intermediate delays in conventional film production were eliminated. The new medium also offered a number of possibilities for special effects not possible in conventional film production.

Following the introduction of HDTV to the film industry, interest began to build in developing an HDTV system for commercial broadcasting. Such a system would have roughly double the number of vertical lines and horizontal lines when compared to conventional systems.

Now, the most significant problem faced with HDTV is exactly the same problem faced with color TV in 1954. There are approximately 600 million television sets in the world and approximately 70% of them are color TVs. An important and critical consideration is whether the new HDTV standard should be compatible with the existing color TV standards, supplant the existing standards, or be simultaneously broadcast with the existing standards (with the understanding that the existing standards would be faded out over time).

There is precedence for both compatibility and simultaneous broadcast. In 1957, the US chose compatibility when developing the color TV standard. Although there were some minor carrier interference problems due to the additional chrominance signal -- to a large extent, both monochrome and color TVs could read the same signal.

As a example of simultaneous broadcast, consider Britain. Monochrome broadcast began in Britain in 1936 with a 405 line standard. In 1967, the 625 line PAL color standard was introduced. The color and monochrome standards then operated in parallel for fifty years. In 1986, when the 405 line service was terminated, so few 405 line monochrome monitors remained that it was seriously considered that Parliament simply purchase 625 line monitors for the remaining 405 line users, as that was considerably cheaper than maintaining the 405 line service. (This amusing idea did not happen however, due to possible political repercussions!)

II. Basic ideas for HDTV

The basic concept behind high-definition television is actually not to increase the definition per unit area ... but rather to increase the percentage of the visual field contained by the image.

The majority of proposed analog and digital HDTV systems are working toward approximately a 100% increase in the number of horizontal and vertical pixels. (Proposals are roughly 1 MB per frame with roughly 1000 lines by 1000 horizontal points). This typically results in a factor of 2-3 improvement in the angle of the vertical and horizontal fields. The majority of HDTV proposals also change the aspect ratio to 16/9 from 4/3 -- making the image more "movie-like".

The following table summarizes a few of the more conventional analog HDTV proposals in comparison with existing TV systems[2]. (Note Grand Alliance and other fully digital proposals are not included in this table.)

Name Prog. Total Active Vert. Horz. Opt. Asp. Vert. Horz. freq.

or lines lines res. res. view ratio field field MHz

inter. dist.

HDTV p 1050 960 675 600 2.5H 16/9 23 deg 41 deg 8

USA,

analog

HDTV p 1250 1000 700 700 2.4 16/9 23 deg 41 deg 9

Europe,

analog

HDTV NHK i 1125 1080 540 600 3.3 16/9 17 deg 30 deg 20

NTSC i 525 484 242 330 7 4/3 8 deg 11 deg 4.2

conv.

NTSC p 525 484 340 330 5 4/3 12 deg 16 deg 4.2

prog.

PAL i 625 575 290 425 6 4/3 10 deg 13 deg 5.5

conv.

PAL prog p 625 575 400 425 4.3 4/3 13 deg 18 deg 5.5

SECAM i 625 575 290 465 6 4/3 10 deg 13 deg 6

conv.

SECAM p 625 575 400 465 4.3 4/3 13 deg 18 deg 6

prog

NOTE: The aspect ratio of the picture is defined to be the ratio of the picture width W to its height H. The optimal viewing distance

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