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1.Introduction of HDTV
“The world is moving towards High Definition Television [HDTV]” “Don’t buy a regular TV now, they are going to be better in every way when HDTV comes into market”. Some phrases dropped by people who are loosely following the HDTV effort. When asked, “How do you know?”, these people confidently responded with, “Because technology is just going to get better and better.”
1.1What is HDTV?
Today’s HDTV systems stem from research directed by Dr. Fujio at NHK (NipponHoso Kyokai, the Japan Broadcasting Corporation).There are three major mature standards in the world, that is
a. ATSC standard from America (8 VSB single carrier modulation method)
b. DVB-T standard from Europe. (COFDM multilevel carriers modulation method)
c. ISDB-T standard from Japan (COFDM multilevel carriers modulation method)
HDTV was conceived to have twice the vertical and twice the horizontal resolution of conventional television, a picture aspect ratio of 5:3 (later altered to 16:9), and at least two channels of CD-quality audio. Today we can augment this by specifying a frame rate of 23.976 Hz or higher. NHK conceived HDTV to have interlaced scanning; however, progressive HDTV systems have emerged. Developmental HDTV systems had 1125/60.00/2:1 scanning, an aspect ratio of 5:3, and 1035 active lines. The alternate 59.94 Hz field rate was added later. Aspect ratio was changed to 16:9 to achieve international agreement upon standards. Active line count of 1080 was eventually agreed upon to provide square sampling. Studio HDTV has a sampling rate of 74.25 MHz, 5.5 times that of the Rec. 601 standard for SDTV. HDTV has a pixel rate of about 60 mega pixels per second. Other parameters are similar or identical to SDTV standards.
1.2 HDTV Aspect Ratio
Figure 1.1 below, based upon the difference in aspect ratio between 4:3 and 16:9. Comparisons were made on the basis of equal height, equal width, equal diagonal, and equal area.
Figure 1.1 Comparison of aspect ratios betweenconventional television and HDTV wasattemptedusing various measures:equal height,equal width,equal diagonal, and equalarea. Allof these comparisonsoverlooked thefundamentalimprovementof HDTV: its increasedpixel count. The correctcomparison is based uponequal picturedetail.
All of those measures overlooked the fundamental improvement of HDTV: Its “high definition” – that is, its resolution – does not squeeze six times the number of pixels into the same visual angle! Instead, the angular subtense of a single pixel should be maintained, and the entire image may now occupy a much larger area of the viewer’s visual field. HDTV allows a greatly increased picture angle. The correct comparison between conventional television and HDTV is not based upon aspect ratio; it is based upon picture detail.
1.3HDTV Scanning
A great debate took place in the 1980s and 1990s concerning whether HDTV should have interlaced or progressive scanning. At given flicker and data rates, interlace offers some increase in static spatial resolution, as suggested by Figure1.1.
Figure 1.2 Progressive and interlaced scanning are compared. The top left sketch depicts an image of 4×3 pixels transmitted during an interval of 1⁄60 s. The top center sketch shows image data from the same 12 locations transmitted in the following 1⁄60 s interval. The top right sketch shows the spatial arrangement of the 4×3 image, totalling 12 pixels; the data rate is 12 pixels per 1⁄60 s. At the bottom left, 12 pixels comprising image rows 0 and 2 of a 6×4 image array are transmitted in 1⁄60 s. At the bottom center, the 12 pixels of image rows 1 and 3 are transmitted in the following 1⁄60 s interval. At the bottom right, the spatial arrangement of the 6×4 image is shown: The 24 pixel image is transmitted in 1⁄30 s. Interlaced scanning has the same data rate as progressive, but at first glance has twice the number of pixels, and potentially twice the resolution.
Broadcasters have historically accepted the motion artifacts and spatial aliasing that accompany interlace, in order to gain some static spatial resolution. In the HDTV debate, the computer industry and the creative film community were set against interlace. Eventually, both interlaced and progressive scanning was standardized; to be commercially viable, a receiver must decode both formats.
 
Figure 1.3 HDTV rasters at 30 and 60 frames per second are standardized in two formats, 1280×720 (1 Mpx, always progressive), and 1920×1080 (2 Mpx, interlaced or progressive). The latter is often denoted 1080i, but the standards accommodate progressive scan.
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