Thread: Test pattern?
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Old 12-29-2011, 08:32 PM
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Quote:
Originally Posted by jr_tech View Post
Interesting info! Thanks!
Does this Kell/NTSC facto apply in about the same way to DTV or must another factor be used? Perhaps a different factor for 1080i than 720p?

jr
HDTV makes a little difference, in that the line structure is smaller/finer compared to the overall picture size. Some of the effects of interlace can be reduced with progressive display, as on a plasma or LCD TV, but the conversion to progressive is never perfect. Thus, 1920x1080 interlace generally has noticeably better resolution on static scenes, but 1280x720 progressive generally looks better on sports.

The best for resolution and motion at the same time would be 1920x1080P at 60 frames per second, but there are no sources at that rate. Blu-Ray discs carry 1920x1080P movies at 24 frames per second, which is converted to 60 frames for display - this is close to the ultimate depending on how well the conversion is done.

By the way, digital images have the same sort of factor in the horizontal direction because they are made of discrete pixels in both directions.
Without interlace, the factor is perhaps 0.9 instead of 0.7. The SMPTE standard for digitizing NTSC or PAL component video has filters that start to roll off (70% response) at a factor of 0.85. I estimate that for a test pattern you can still see the resolution in the wedges when the amplitude is down to 10%, which is probably around a factor of 0.9. So, a system with 640x480 pixels scanned progressively and displayed progressively would have a useful resolution of about 430 TV lines per picture height (lph) both vertically and horizontally. The 1280x720 progressive standard gives about 648 lph both vertical and horizontal, and the 1920x1080 interlaced system gives about 972 lph horizontal resolution, and a variable amount of vertical depending on camera settings and motion, nominally 756 lph.
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