JVC Professional APRIL 2007 NAB-2007 The ProHD Report
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The Reality of 6x the Image Resolution The SD digital video frame of 720x480 equals about 340,000 pixels, while the HD
frame of 1920x1080 equals about 2,074,000 pixels, a multiple of about 6. We can
introduce the old Kell factor for viewing of interlaced TV signals, where,
depending on program material (fast or slow motion, much or little detail, bright or
dim scenes), Kell says that maximum perceived viewer resolution is only 50% to
70% of interlaced program/display resolution. Kell is applicable to both SD and HD
interlaced video. 1280x720 is the progressive ATSC format with an HD frame of
about 921,600 pixels, but occurring 60 times a second, and substantially unaffected
by the Kell factor because it is progressive. The 1920x1080 raster happens only 30
times a second, really as 60 fields per second each field being 1920x540. Also,
remember that all HD encoding intended for “last mile” consumer distribution (like
ATSC OTA and cable QAM) is at 4:2:0 sampling or total effective delivered “live”
pixels to the HDTV display is 1.5 times luminance pixels. Now, look at total number
of effective/perceived maximum pixels per second being presented to the home
viewer, based on the Kell/Interlaced factor of 70%:
1280x720p60 x 1.5 = 83 million “effective maximum presented” pixels/sec
(no Kell reduction because progressive)
1920x1080i60 x 1.5 (x70%) = 65 million “effective maximum presented”
pixels/sec (after Kell/Interlaced factor: 70% of 93 million)
720x480i60 x 1.5 (x70%) = 11 million “effective maximum presented” pixels/sec
(after Kell/Interlaced factor: 70% of 16 million)
The above figures imply that the 1280x720p60 images appear to be 7.5 times the
perceived temporal resolution of interlaced SD, while the 1920x1080i60 images are,
as we stated above, 6 times the temporal resolution of interlaced SD.
We note that the ProHD native acquisition format is full bandwidth 1280x720 at
60 frames progressive in the GY-HD250U model.
Through the years, a number of surveys have concluded that the average TV viewing
distance in the typical North American home is 9 feet. Assuming that the home
viewer is experiencing optimum SD image quality and resolution (but not seeing
lines or pixels) on his current SD TV set, the home viewer, when the SD set is
replaced with a HDTV with 3x the viewing area placed in the same location, can
potentially “experience only” twice the SD area resolution per measure of viewing
angle with 1920x1080 interlaced (6 divided by 3 = 2) while 2.5 times with 1280x720
progressive (7.5 divided by 3 = 2.5). In other words, the viewer may then move
closer to the HD set (reducing the viewing distance) to a distance just before lines or
pixels are visible.