[apple]

It seem odd that the 1080i dynamic resolution is greater than the static resolution. Is the 1780 number correct?

 

[John Mason]

It's correct if you use their published numbers, but it may be a test anomaly--the reason I flagged it. Guess it'll take someone from the test committee, or approximately duplicate results, to pin it down. -- John

 

[Michael St. Clair]

Is it still as surprising that much HD material looks the same when downsampled (to 540p, 480p, 800x600, etc)?


How much of the difference that we see between upsampled DVD and HDTV is due to bitrate and not native resolution?

 

[PVR]

I hope manufacturers DON'T see this as an excuse to avoid producing true 1920x1080 displays.


If they use the numbers then they should at least target the 1600x800 value since some programs do contain black and white stills. (KQED Sin/Fire/Gold for example had lots of old black and white photographs of early San Francisco mixed in with live footage of modern day SFO).




[This message has been edited by PVR (edited 08-21-2001).]

 

[John Mason]

Michael St. Clair,

Here' a quote from the committee's resolution introduction hyperlinked above: "In the case of an interlaced scanning system, for vertical resolution under motion, the picture will take on the characteristics of a progressively scanned system with half the number of scanning lines (i.e., vertical resolution of 1080I becomes 540P under motion)."


Getting into upsampled (or plain) DVDs vs. HDTV is often discussed here. IMO, the key factor is the original method of capturing images. A 1080X1920 camera or telecine scanner can record those resolutions, and later filtering/viewing them may produce the results shown above. An NTSC DVD may be prefiltered to something less than 720X480 and see similar reductions, percent-wise, when displayed.


PVR,

My suspicion is that you have to start out with displays capable of nearly the full 1080i ATSC spec in order to achieve what the FCC's committee saw. Seems to me that if you 'dumb down' set resolution capabilities to match what's displayed in the results above, images would really suffer. That is, to obtain the 800 and 400 (static, dynamic) vertical resolution the committee measured for 1080i, you have to start out with displays approximating 1080 scan lines or the equivalent. Remember, sets filter image signals before displaying them. And vertical resolution is what can be resolved by displaying image signals on these scan lines, not the scan lines themselves. And of course many sets lack the bandwidth or basic display technology to handle the higher horizontal resolutions measured by the committee.


There's a new Samsung 16:9 LCD computer monitor now available that matches the 1080i ATSC spec perfectly. Signals can be piped into it via DVI, which bypasses any analog conversions. So, assuming you could track down a full 1080i or 1080p source, what happens to a presumably unfiltered HDTV image on the Samsung screen? -- John






[This message has been edited by John Mason (edited 08-21-2001).]

 

[John Mason]

This 1000th post summarizes part of a committee of expert's report to the FCC. As I sometimes cite their numbers, thought I'd simplify their test data here. It's unclear what mid-1990s display equipment was used, but suspect most of us still couldn't afford it. Reviewing the numbers reminds me that 1080iX1920 or 720pX1280 isn't really what I'm watching daily. Broadcasts of stationary and moving (dynamic) test patterns by stations would help viewers evaluate their equipment. Moving HDTV video, of course, is the supreme test. Corrections or suggested modifications are welcome.

*******************

Code:

[B]Measured resolutions of the ATSC 1080iX1920 HDTV system[/B]
           
Scan format         
1080 vertical lines
1920 horizontal pixels

                                     Vertical       Horizontal        
Measured B&W Static Resolution       800            1638
Measured B&W Dynamic Resolution      400            1780^
Measured Color Static Resolution     280            890
Measured Color Dynamic Resolution    200            481


[B]Measured resolutions of the ATSC 720pX1280 HDTV system[/B]
           
Scan format         
720 vertical lines
1280 horizontal pixels
                                     Vertical       Horizontal         
Measured B&W Static Resolution       550            1139
Measured B&W Dynamic Resolution      420            1068
Measured Color Static Resolution     360            641
Measured Color Dynamic Resolution    320            605

Data is from the 1995 FCC Advisory Committee on Advanced Television Service http://www.psps.com/pages_frames/tech_talk/atsc_report.htm ] "Final Technical Report" [/url]. This committee approved the U.S. Grand Alliance ATSC DTV system. Measurements are converted from cycles per picture height to alternating lines/pixels (16:9 screen width/height, for static/dynamic resolution). The committee assumed a 20% reduction of horizontal resolution due to filtering. The 1780 value (^) for dynamic 1080i horizontal resolution exceeds this 20% reduction assumption. Color resolution was assumed to be half the B&W resolution, both vertically and horizontally (table 2.3 target specifications). See notes in the technical report for other details. -- John