----- HDTV Magazine Tips List -----
Tom,
A digital TV should not show flicker at 1/60 speed when displaying progressive full frames, or at
1/30 speed when showing frames as interlaced fields with half the lines, each of those displayed at
1/60.
Regardless if showing 480i or 1080i, the eye should not see flicker at 1/30. It is based on how
fast frames are shown not how resolved each frame is in pixels (SD or HD).
If your CRT TV is digital you would probably be watching 480p or 1080i, 480p is displayed at 1/60
per full frame, 1080i is displayed at 1/30 and the eye should not see flicker at that speed because
the frames are displayed as fields of half the lines (540) at 1/60, our brain puts them together so
we see them as entire frames at 1/30 but the interlaced presentation would not show flicker.
The interlace concept was a creative method invented over 50 years ago to save in the transmission
bandwidth allotted for each analog channel, and still show an image that does not flick to the eye,
but also was counting with the fact that the TV screens where small enough not to see the interlaced
lines.
The world of analog TV changed to larger and larger sets, and that pushed the viewing position
farther and farther back, and the angle of vision that one thought would be increased to provide a
cinematic experience (with the larger screen) was actually maintained when the viewer had to sit
further back to avoid seeing resolution lines.
If your CRT TV is analog you are watching NTSC at 480i as two fields of 240 lines each displayed at
1/60 each, totaling the complete frame of 480i in 1/30.
The speed to digitally show a full frame in a progressive format is doubled because the set needs to
sync to show all the 480 lines in one pass, rather than just 240 of interlaced, at 1/60.
That applies to 1080i and p as well, so a new set showing specs for 1080p has been designed to work
at double the speed of a 1080i set, to show full 1080 line frames in 1/60, rather than just one
field of 540.
540 would have given the set more time to get to the bottom 540 line of the field. In other words,
to double the lines to show in 1/60, double the speed to handle all those lines and still get to the
bottom at the same instant.
In typical CRT terms:
To display 480i (actually handling a total of 525 lines, 45 are not viewable) as 262.5 (half) on
each pass, the set has to be able to sync to 15.75 KHz (262.5x60).
To display 480p (actually handling a total of 525 lines,45 are not viewable) as 525 on each pass,
the set has to be able to sync to double that speed (31.5 KHz).
To display 720p (actually 750) as 750 on each pass, the set has to be able to sync to 45 KHz.
To display 1080i (actually 1125) as 562.5 on each pass, the set has to be able to sync to 33.75 KHz
(one reason it is said that a 720p costs more to build, if the 1080i set is done correctly).
To display 1080p (actually 1125) as 1080 on each pass, the set has to be able to sync to 67.5 KHz,
regardless if the input signal is just 1080i, remember the other email of calculated/interpolated
lines/pixels.
On a FPTV CRT projector that claims to handle 1080p add another 3db to the spec of 67.5, which puts
the minimum spec as 100 KHz to been able to handle that signal/speed.
Best Regards,
Rodolfo La Maestra
-----Original Message-----
From: HDTV Magazine On Behalf Of
Tom Vrolyk
Sent: Sunday, July 03, 2005 1:56 PM
To: HDTV Magazine
Subject: Re: Another of Tom's questions> LCD pixel refresh time
----- HDTV Magazine Tips List -----
Thx for all the info, it is interesting to say the
least.
After I emailed I realized that with my dir view CRT I
am seeing 60 "pictures"/sec however even 1/60th of a
sec is 16.6ms so isn't "in theory" any TV has a
"response time" of 16ms.. why do we not see flicker?
The link in Brents email helped a lot, the LCD
response time is only a black/white kinda deal and not
at all "real world", here is the link to just the
"latency response" page for those interested.
http://graphics.tomshardware.com/displa ... ic-05.html
thx Rodolfo for another great email and link to the
pull down issues
--- Rodolfo La Maestra <
[email protected]>
wrote:
> ----- HDTV Magazine Tips List -----
>
> Tom,
>
> At 1/30 of second to show progressive frames would
> not be sufficient speed, only interlaced images
> would not show flicker a 1/30 (by showing half of
> the lines at every 1/60). In progressive the full
> frames have to be shown faster, at 1/60 of a second.
>
> It seems by your comment that you were able to
> experience by yourself motion trails at even 8ms.
> It
> is interesting you mention that because I have
> noticed on the new Aquos prototypes shown at CES in
> January, at 8ms, pixel activity that was not
> responsive enough, the panels were great but not
> fast
> enough for some fast scenes.
>
> Unfortunately once your eyes get accustomed to pay
> attention to those imperfections it becomes a
> distraction factor that, at least on my case,
> diminishes the pleasure of watching otherwise good
> images, not to mention distracting one out of the
> actual content.
>
> That is why I commented at CES that we should wait
> to experience what 4ms would do and start from
> there, rather than spending a lot of money on large
> panels with slower pixel speeds, if one can
> wait.
>
> 4ms is coming, as the link below shows, this is one
> of the specs that LCD manufacturers are showing
> off in their competence and technical statements.
> Similar to the show off of the 1080p spec for
> RPTVs no matter the chip.
>
> Regarding the question of Erik about showing film
> sourced video of 24 fps at multiples (up to 72),
> he is correct:
>
> If the display is able to handle the speed it would
> be much better, rather than going to field
> processing with 3:2 pulldown, bring that up to 30
> for video, and then double up to 60 for the
> flicker.
>
> In fact Pioneer Elite plasmas are doing 3:3 pulldown
> to avoid exactly that processing on 24fps
> video, the following is a good graphic
> representation of what we are discussing:
>
>
http://www.pioneerpurevision.com/demo.html (click on
> advanced purecinema for the demo)
>
> A good CRT projector would have to have an
> horizontal scan rate spec of 67.5 KHz for 60 fps
> 1080p,
> faster for tripling 24 to 72, the old and great Sony
> G70 with 8" CRTs can handle 110.
>
> Best Regards,
>
> Rodolfo La Maestra
>
>
>
> -----Original Message-----
> From: HDTV Magazine
> On Behalf Of
> Brent Yates
> Sent: Saturday, July 02, 2005 8:17 PM
> To: HDTV Magazine
> Subject: Re: Another of Tom's questions> LCD pixel
> refresh time
>
>
> ----- HDTV Magazine Tips List -----
>
> TomV,
> Here is a review of the ViewSonic VX924 which goes
> into great detail
> about the latency issues (general and specific to
> the VX924). It seems that
> (surprise!) the manufacturers play games with the
> definition of terms and
> with their measurements. LCD's are getting better
> though.
>
>
http://graphics.tomshardware.com/displa ... index.html
>
> Brent Yates
>
>
> -----Original Message-----
> From: HDTV Magazine
> On Behalf
> Of
> Tom Vrolyk
> Sent: Saturday, July 02, 2005 6:35 PM
> To: HDTV Magazine
> Subject: Another of Tom's questions> LCD pixel
> refresh time
>
> ----- HDTV Magazine Tips List -----
>
> These questions can be tough to describe, well here
> goes
>
> Can you explain why you had mentioned that the
> newest
> LCD sets have pixel? response time of say 16ms or
> now
> down to 8ms.
>
> If 1/30th of a sec is 33ms and we can not see the
> flicker of each frame then why would we see color
> motion trails on a LCD with a response time of 16ms
> never mind the 8ms of the latest and greatest?
>
> Is it that maybe the pixels cannot turn "Off" fast
> enough?
> I do not understand this or maybe my math is wrong.
> Thanks in advance, I cc Rodolfo on this email.
> TomV
>
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