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Discussion Starter · #1 ·
Would there be a major loss, if using Dilard, a G11 was set to have an active area of 1280x1024?

If this was then connected to a FE CS-1 with sxga output, a frame rate of 72Hz can then be used.

Would there be any pluses/minuses to this situation?

Would it be better to use sxga3 and a 60hz refresh?

Appreciate any insight on this.

Thanks,

Sanjiv
 

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sprakash,


I believe the G11 will convert the 72Hz refresh rate into 60 Hz internally.


Just as the G11 converts whatever resolution you send it to its own native 1365x1024 native resolution - it does the

same with timings. The "native refresh rate" of the G11 is 60 Hz.


Dr. Gregory Greenman

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Sanjiv,


If you use a 1280x1024 resolution with perfect pixel mapping (Resize Off) then the image will be slightly smaller than 1360x1024 (by 40 pixels a side). This is the only real disadvantage.


You can turn Resize on and have 1280x1024 fill the panel, but then you will be introducing scaling artifacts. On video it probably won't be noticable but computer text will look blocky.


A 72Hz (actually 71.928Hz) refresh rate is better than 60Hz since it is a perfect multiple of film's 24fps so will give you liquid-smooth motion and pans. Unlike some DLP projectors, D-ILA's do not convert the refresh rate to 60Hz so don't introduce temporal artifacts (3/2 judder).


If you want to use the AutoSync feature then you'll need to use a 75Hz rate to have the projector automatically switch to SXGA3 when this rate is detected, but if you're always using the same resolution then it's not an issue.


Cheers,

Dave.
 

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Just to add that I do this currently (send SXGA, resize off). You lose a tiny bit of screen area but I its really not noticable in terms of added resolution or brightness IMO. Other than that its completely transparent.


Andy K.
 

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Quote:
Originally posted by David Panko


A 72Hz (actually 71.928Hz) refresh rate is better than 60Hz since it is a perfect multiple of film's 24fps so will give you liquid-smooth motion and pans. Unlike some DLP projectors, D-ILA's do not convert the refresh rate to 60Hz so don't introduce temporal artifacts (3/2 judder).
David,


The 72Hz refresh rate is actually lost on the D-ILA.


If you go to:

http://www.jvcdig.com/technology.htm#whitepapers


and get the white paper "DILA Technology..." by Dr. W. P. Bleha, the paper gives a response time for the D-ILA chip

of about 16 ms:


"The D-ILA device has a true video-rate response time (the rise time plus fall time equals less than 16 milliseconds).

The temporal response curve is shown in Figure 6." [Pg 5.]


The 16 ms response time corresponds to a refresh rate of 60 Hz.


Later, Dr. Bleha addresses the vertical scan frequency:


"Vertical scan frequencies of 50 to 78 Hz are accommodated. The D-ILA is addressed at double the vertical frequency of

the input signal. However the liquid crystal responds at the rate shown in Figure 6." [Pg 7.]


Although you can certainly input a 72 Hz signal to the D-ILA since 72 Hz is in the range of 50 to 78 Hz specified above -

the D-ILA chip can only respond at 60 Hz.


The D-ILA device has its own "native temporal resolution" and one does not gain an advantage by driving the chip at

a rate higher than the limiting response rate.


Dr. Gregory Greenman

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Hi Morbius,


Based on my tests with the projector I'm 99.99% sure that I'm correct on this point. Feel free to shoot holes in my arguments. :)


I agree that the response time of the panel is 16 ms, but this doesn't necessarily mean that the panel is being driven at 60Hz. According to the white paper the panel is driven at twice the input refresh rate (so with a 72Hz signal the panel is driven at 144Hz).


A 16ms response time limits the projector to a 60fps framerate, not a 60Hz refresh rate.


Let's see if I can explain..


Film has a framerate of 24fps, which I think we agree is well within the response time of the panels.


With a 72Hz refresh rate, the same frames are sent to the projector three times, and the panel is driven six times with the same data (twice the input rate). The panels have no problem keeping up since the image is only changing at 24fps.


If your claim were true and the projector was converting 72Hz to 60Hz then it would need to drop every sixth repeated frame which would result in 3/2 judder (similar to viewing film-based material on NTSC). I observe no such judder on the D-ILA, so my conclusion is that it's not internally converting to 60Hz.


In fact, when I run my CRT monitor and D-ILA side by side I see exactly the same temporal artifacts on both. If I set the refresh rate to 60Hz I see 3/2 judder on both. With a refresh rate near a multiple of 24 I see "beating" on both. And with a perfect multiple of 24 I see smooth motion on both. This tells me that both the CRT and D-ILA are able to sync to multiple refresh rates and the D-ILA isn't adding any temporal artifacts of its own by internally converting to 60Hz.


The 16ms response time means the D-ILA is limited to 60fps and I agree that any framerate faster than 60fps will be lost on a D-ILA. But this is very different than refreshing a 24fps source at 72Hz, and in this case there is an advantage to using a higher rate (ie. smoother motion).


Cheers,

Dave.
 

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Discussion Starter · #7 ·
Thanks a lot guys. I am understanding a little better now.

So the negative of using sxga is the 80 lost pixels, but if I input from a scaler at 72hz refresh rate, for film-based material, the 3:2 pulldown(@60hz) is now actually a 3:3 pulldown and that would remove any judder.

Would I be correct in assuming that this would be carried out in the scaler while de-interlacing and the G11 would just lock on to the input?

I have a Quadscan pro right now and I'm trying to see what the advantage would be to upgrade to the new CS-1.

Thanks again,

Sanjiv
 

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Dave,

You obviously have this stuff down. Thanks. Is it true then that the 75.1 refresh rate that I have read about as ideal is only right for the autosensing feature? Art
 

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Hi Sanjiv,

Quote:
Would I be correct in assuming that this would be carried out in the scaler while de-interlacing and the G11 would just lock on to the input?
You've got it! If you feed a progressive scan signal to the computer input and turn Resize off then the projector is simply locking onto and displaying the image without scaling or deinterlacing it.


I'm not familiar with the CS-1, so sorry I can't help there.


Art, you are correct, 75Hz is the rate that the D-ILA uses to detect and automatically switch to SXGA3 mode. The "ideal" rates for judder free playback are 47.952Hz (or 71.928Hz) for film and 59.94Hz for video.


Cheers,

Dave.
 

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Although the JVC D-ILA can sync to a faster rate - in fact, any rate within the range of 58 Hz to 78 Hz; the claim that

the faster rate will give you increased picture quality is false.


As explained in the JVC whitepaper by Dr. Bleha - the D-ILA chip has a limiting response time of 16ms. or 60 Hz.


Feeding the D-ILA a faster refresh rate doesn't buy you anything.


This was made clear by the AVS Forum's resident expert on the JVC D-ILA; Tom Stites of JVC in this post:

http://www.avsforum.com/avs-vb/showt...hlight=refresh


where Tom states:


"For HT applications, you would not want to run your input source any higher than 1365x1024 at 60hz, assuming you were

using a HTPC or external scaler.


Running higher refresh rates gains you nothing with a D-ILA based projector...and in fact by running higher refresh

rates, you are trying to force a higher bandwith signal through all your electronics with no increase in actual

display resolution. The D-ILA will not flicker as would a

CRT based monitor or projector when run at lower refresh rates."


I think JVC's Tom Stites sums up the solution to this question quite succinctly.


Dr. Gregory Greenman

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Hi Morbius,


Ahh.. I think we're arguing different points here. I agree completely that you won't improve picture quality by going to a higher bandwidth, in fact the lower the better so as not to stress the electronics as Tom points out.


What is gained by going to 72Hz is the elimination of temporal artifacts, not improved picture quality. For the best possible picture quality a low bandwith rate like 48Hz should be used, or ideally a DVI connection at 24fps.


I think you're still missing my point that 60Hz introduces 3/2 judder and should be avoided with film-based DVDs. Film is shot at 24 frames per second, and since 60 is not an even multiple of 24 the frames are repeated an uneven number of time which results in robotic looking motion and pans.


At 60Hz, the frames are sent to the projector in a repeating 3/2 sequence:


Frame 1

Frame 1

Frame 2

Frame 2

Frame 2

Frame 3

Frame 3

etc..


At 72Hz each frame is repeated exactly three times, so pans don't "skip along" like they do at 60Hz.


Notice also that the panels are often being refreshed with the same information, so the 16ms response time is not exceeded. The panels only have to respond to a change in the frame, which happens at 24fps or every 41ms.


If the D-ILA used 60Hz to drive the panels it would introduce 3/2, which it doesn't. The advantage of using 72Hz is to eliminate 3/2 judder.


Cheers,

Dave.
 

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"Is it true then that the 75.1 refresh rate that I have read about as ideal is only right for the autosensing feature?"


"Art, you are correct, 75Hz is the rate that the D-ILA uses to detect and automatically switch to SXGA3 mode."


David, how is your system configured? On my G11/Radeon/Powerstrip setup I see a change in SXGAs at mid 71s to 72s and mid 63s. SXGA1 will be below 63Hz and SXGA3 will be above 72Hz. SXGA2 will be in between. This has been very consistent through my various video cards as well.


Yes, you can force any sync to any Hz combination as long as you adjust the image accordingly, but I've found it most accommodating to always leave the G11 in 'Auto' so that no matter what device I switch to, the 'source' always follows. This is most convenient in a system to which you might have many variables. HDTV receiver, standard Windows 800 x 600 desktop, 1360 x 1024 or 1360 x 768 desktop for DVD player, etc.


If you force to a specific sync, you must manually change every time you switch sources, correct?


Before I bought a Panamorph, I used to have three seperate SXGAs for three aspect ratios. It worked quite well.


Greg, I have to agree with David, 72Hz is not converted to 60Hz on the DILA.


White paper, Tom Stites or otherwise, 60Hz does indeed introduce more 'judder' than with the example of 72Hz. I've done this comparison many, many times in the 900 hours of my G11, and I just did it again, just for the sake of this discussion. Many have done the Hertz test on the various DILAs over the past few years. I've seen folks swear that 48Hz is the refresh rate to use, others 75Hz. Go figure. :)


The one thing I do believe though is......not all DILAs are created equal. Strange, but true. My G11 compared to fellow forum member Hugo's G11 resulted in drastic differences when raising or lowering refresh rates through Powerstrip. Mine would show an obvious difference in focus as I ran up or down through the Hz range whereas his showed little to no change. Motion artifacts were also different between our projectors and we use basically the same HTPC setups.


It's nice to see some DILA discussion here again. I thought we were a lost breed. :D


Chris
 

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Hi Chris,


Agreed, nice to see another good D-ILA thread again!


Originally I ran my system at 75Hz and with Auto On to automatically switch resolutions for DVD's, games and the boot screen.


Since then I've noticed that 48Hz gives me much better picture quality and smoother motion for DVD's so I've disabled the Auto switching and just leave it on SXGA3 (Dilard modified to top-aligned 1360x768).


I found that having Auto Off isn't much of an inconvenience since I rarely play games on the D-ILA now and I have a secondary monitor if I need to see the boot screen. Other sources like HDTV and video don't need their resolutions switched so Auto has no effect on them.


I'm not surprised that a range of rates close to 75Hz works to auto-switch to SXGA3. I think I had trouble getting it to switch at 72Hz, but as you said every D-ILA is different.


I've found that the refresh rate also has a big effect on the pixel tracking, with lower rates making it much easier to dial in perfect tracking. A one pixel checkerboard pattern is a good test of this. At 48Hz I can get a rock solid checkerboard, but at higher rates I see a lot of noise in the checkerboard (flickering horizontal lines) even though I still have 1:1 mapping.


The DVI connection on the 150CL is a great feature since it will solve the problem of poor pixel clock tracking (including phase drift during warmup). Also the elimination of the extra D/A, A/D conversions should significantly improve colour gradients, removing a layer of analog "grunge" from the picture. Inital reports on this forum have been very positive, but I'd still like to see confirmation from someone that 1365x1024 works over DVI with perfect mapping on the 150CL.


Going back to the panel response time, I think I can make the explanation clearer with a timeline.


From the whitepaper, the 16ms response time is a round-trip response from off to on and back to off again. So the time it takes to flip states from off to on is only 8ms. An HTPC playing a DVD with 72Hz refresh rate would look like this:


0ms: Frame 1 sent. Panel starts responding to Frame 1.

8ms: Panel finishes responding to Frame 1.

14ms: Frame 1 re-sent. Panel holds its state.

28ms: Frame 1 re-sent. Panel holds its state.

42ms: Frame 2 sent. Panel starts responding to Frame 2.

50ms: Panel finishes reponding to Frame 2.

56ms: Frame 2 re-sent. Panel holds its state.

70ms: Frame 2 re-sent. Panel holds its state.

etc..


The panel response time is irrelevant to the refresh rate. Only the frame rate matters, and this is always 24fps with a film-based DVD regardless of the refresh rate. The D-ILA does not drop frames if the refresh rate is higher than 60Hz.


Hope this helps clear things up!


Cheers,

Dave.
 

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I agree with David about using 72 hz refresh to eliminate the 3:2 pulldown artifacts. The panel may be refreshing at 60hz, I'll have to get out my com voltage tools and measure that.


If you want to use 48 hz or 60 hz and still have auto switching, this is possible to do. I've been modifying the SXGA1 area data to accomodate Faroudja NRS scalers for some time now, it works great. Just copy the SXGA3 data to SXGA1. Not sure if you can do this with Dilard or not but I have a simple utility program that does it.


William
 

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Other sources like HDTV and video don't need their resolutions switched so Auto has no effect on them."


Hi David. Are you saying that you also keep the DILA in SXGA3 for HDTV? Hmmm, I've never tried that.


Boy, I'll have to go back and try the 48Hz refresh again. I run the TT player with a 71.899 r/r, and although I love the player and it's ease of use, my biggest complaint is the stuttering on ocassional pans. I'd love to find a cure.


William, yes, the Image Geometry Wizard in Dilard will modify any source to the Nth degree. It's actually quite fun to see just how far you can push the image around the screen. :D


The software comes in quite handy.


Chris
 

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Quote:
Hi David. Are you saying that you also keep the DILA in SXGA3 for HDTV?
Hi Chris. I'm using COMPUTER1 for the HTPC and COMPUTER2 for HDTV. I leave COMPUTER1 on SXGA3 and COMPUTER2 on 1080i. All the source switching is done through the computer/video buttons on the remote. The only time I need to switch modes is if I change the resolution on my HTPC (for games, etc).


There is still some stuttering at 47.952Hz but I only notice it once or twice a movie. Stuttering is an intrinsic problem of HTPCs since the video and audio clocks aren't locked together. The best solution is a DVD player with scaler (ideally with an all digital signal path).


Cheers,

Dave.
 

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"I'm using COMPUTER1 for the HTPC and COMPUTER2 for HDTV."


Doh!!


Of course you are. So am I. :eek:


It's been so long since I've had to think about any of this. :D


Chris
 

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Just for my own clarification, the reason you want to force it to SXGA3 is because SXGA3 allows 1365x1024, while SXGA1&2 only allow 1280x1024, correct?


In my own case, I like having the AUTO feature on because I use different resolutions for different things (WinAmp visualizations, Games, etc), but I also dont use 1365x1024 (I'm OK with losing the few extra pixels). So I should have no problems?


Andy K.
 

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Quote:
Originally posted by kromkamp
Just for my own clarification, the reason you want to force it to SXGA3 is because SXGA3 allows 1365x1024, while SXGA1&2 only allow 1280x1024, correct?
Correct, unless they've been modified by Dilard in which case anything is possible. I'm actually using a custom top-aligned 1368x768 mode so that Windows "plays nice" with my 16:9 screen and I don't need to mess around with YxY.


Switching modes for Geiss and games is a bit of a pain though.


Cheers,

Dave.
 
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