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Discussion Starter · #1 ·
I just received my LT 150 today to replace an Electrohome 4101 CRT behemoth. I am very please with the sharpness and black level!


One question though... Do all DLP's have a problem with quick motion noise? I am noticing a big jump in noise that looks similar to dithering during fast motion scenes. Any fixes? The unit seems to be fine otherwise. I have noticed this with a friend's Viewsonic DLP projector, but the effect is not as pronounced.


One interesting note.. The noise, when it occurs, happens across the entire image, even if I am watching a letterboxed film...?!? http://www.avsforum.com/ubb/rolleyes.gif


I have searched for motion and noise in this forum without any luck. Hmmm.


Thanks in advance.
 

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The only problem I am seeing is what is called the "Matrix" effect or blurring around motion - most noticeable when the central figure moves and then stops! Some DVDs are worse than others and I don't notice it on sat. T.V. except in some movies, but not Television shows. I now see this effect on my RPTV too!


I am awaiting Frode's review of the LT150 - that should be interesting.


Please define "dithering".


Cheers,


Grant
 

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Discussion Starter · #4 ·
Grant and Pham,


Thanks for responding. From your description, it sounds like I am seeing the "Matrix" effect.


Here's an example of dithering. Notice the dots?

http://www.avsforum.com/ubb/image_uploads/DSCN3254.gif


Dithering is often used on computer images to reduce the needed colors and subsequentially reduce the file size of the image. When I see the motion artifact it resembles this effect, but mainly in dark portions of the image.


BTW, my video sources are an iScan pro @ 640x480P component and an HTPC @ the projector's native 1024x768 60Hz.
 

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This artifact has been discussed several times before, though it may be so long ago that they aren't in the archives any longer. All single-chip DLP show this artifact. Larry Davis and others have termed it (I believe) a "feathering" and you might try searching in archives for that word. I can't notice it when I'm at any reasonable viewing distance (say distance equal to width of the screen) though if you get up close to the screen it's very obvious. It's sort of a dithering or cross-hatching pattern on portions of the image that are in movement.


If I recall, a TI white paper on single chip DLP discusses this phenomenon explicitly. Don't remember which paper or what they called it. -- Herb



[This message has been edited by hsitz (edited 07-21-2001).]
 

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Take a look at the girl's neck - I see this in very dark scenes with my HTPC (Radeon Video card). I don't notice it with the proscan DVD player, but I'll check again.


The "Matrix" effect is more like you're seeng one frame after another and everything catches up when the object stops - looks like Alan and David when the image slides across the screen (jerky) at the intro to this forum, but not that exeraggerated. I don't see this on video based material only film and I see it on my RPTV and at the theatre so it may be inherent to film. I guess I've only recently become sensitive to it.


This feathering or "dither like" problem, I think, may be linked to too much contrast. Try increasing contrast or decreasing contrast in those scenes where it is apparent and see what happens. Might be an oversaturation thing. This is a blotchy like look.


Cheers,


Grant
 

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Discussion Starter · #7 ·
I have been able to subdue the feathering a tad by dropping the brightness. On my CRT, the only way to get good shadow detail was to hike up the brightness, and my first instinct was to do the same with the DLP.


It seems that the LT 150 handles lower brightness and pulling back on the contrast better than just simply turning the brightness up.


I'll eventually find the magic calibration! http://www.avsforum.com/ubb/biggrin.gif


Thanks for your help. I plan to check out "feathering" to find out more about this anomaly.
 

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KilgoreT,


Not to change the topic (and I hope you can correct your problem). But since you're going from a CRT fp to the LT150 I'm very anxious to get your thoughts on how you like the LT150's black level. In fact I would be interested in anyone's opinion who is making the same transition.


Bob Wood


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~ The Sultan of Cheap ~


[This message has been edited by RobertWood (edited 07-21-2001).]
 

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Grant,


I can't find any mention of video filter on page E-39. On E-38 however there is mention of a noise reduction filter. IMO this should be set to OFF for high quality sources such as DVD. Any other setting will lead to the dithering effect mentioned.


I'll post more detailed thoughts on the LT150 once I have some more time to do some real testing.


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/frode


[This message has been edited by Frode (edited 07-21-2001).]
 

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Bob,


I use a Barco BG808s in my HT, but I ordered the LT150 from Dell just for "research." If it ever gets here I'll probably just end up using it at work for presentations, but I do plan to compare it to my CRT projector on my Stewart Studiotek 130 screen.


In addition to comparing black levels, I'm curious to know how much of the rainbow effect I'm susceptible to.
 

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Hopefully, Jim, you will be one of us who do not see the rainbow effect as readily as others. Of the four 1-chip DLP's I've had now I saw it with only one (Infocus LP340).


Bob


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~ The Sultan of Cheap ~
 

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Frode,


We must have different manuals! I double checked mine and on page E-39 (I am looking at it right now) there is mention of a video filter (low pass filter), however, it is not applicable for an RGB connection and when auto adjust is on - probably not aplicable with respect to this problem. I am certainly in agreement that the other filters should be left off, unless the DVD is so grainy it is unwatchable without some help!


I am not seeing any "dithering", banding, tearing etc. in my setup. The blurring, I think, is a source problem since I notice it on T.V., at the theatre etc. Probably has something to do with film and focusing - not noticing it on video material though!


KilgoreT - The video noise here - "happens across the entire video image" - I haven't seen anything like that. What movie were you watching (Chapter etc.) and I'll have a look.


Awaiting your comments, Frode!


Cheers,


Grant
 

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Thanks for that KT. I like long responses.

I'm sure it was a pleasant experience to replace that big monster with one of these cute little buggers. It's hard for me to take in the size and weight of these things.

BTW, how is it on fan noise?


Bob


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I finally have the answer to this one. It _is_ a source issue. The problem is that MPEG2 cannot properly handle panning. Horizontal pans results in blurring and dithering, while vertical pans can result in scanlines, blurring and dithering. It's further accentuated by the following factors:


- progressive

- scaling

- screen size

- viewing distance


I could barely see the dithering artifacts on a 32" interlaced widescreen set, but only because I knew exactly what I was looking for. When I used the frame step functionality it was also very apparent. Incidentally the difference in going from FPTV back to interlaced 32" was horrible - I now hate scanlines with a passion. Sometimes I wish I could hit the entire MPEG group with a clue-by-four for creating an algorithm that cannot handle curves, edges, gradients and panning properly - not to mention blacks etc.


There is a solution to the whole dithering problem - sit further back from the screen! Either that or use a smaller screen. I learned a lot today just fiddling around with my setup, and most importantly I think many here are using screens that are too large compared to the resolution of the projector and their viewing distance. I noticed that by moving back less than a meter from my normal viewing distance most of the artifacts I saw were reduced from annoying to merely negligable. The 2:1 rule for distance:width is actually a bit too close. I'd say 2.2-2.3:1 is my recommendation as the closest distance for the LT150 and DVD at least. Further back is recommended, but then you don't necessarily get the same effect of the picture filling most of your view. If you do reduce the screen size that has the added benefit of increasing light output - though with only 800 ANSI almost any ambient light will kill the picture anyway.


Incidentally - I just love my new box http://www.avsforum.com/ubb/smile.gif . Thanks for doing a lot of the groundwork in figuring out the best options Grant. Expect a full review from me sometime this coming week.


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/frode
 

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Discussion Starter · #16 ·
The fan noise is OK. It's about the same as my CRT, but a bit higher pitched. I watch my movies loud! Though, I may build a hush box. Does anyone know a safe design?


Frode, I'm not sure that the dither problem is caused by MPEG2 artifacts. I don't see the problem on a good CRT monitor and I have seen it on computer based graphics like flash movies.
 

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KilgoreT, I've seen that effect too mostly in the black areas, my solution was to use 72Hz refresh and the blacks now are really film like.

Note: I'm don't have the lt150 but the LT100

BTW I would like to use the Geforce video card but I cannot get rid of that stuttering, so I'm using Mpact2 less sharpness but not stuttering. What about the Radeon LE, not stuttering? I know that even the Faroudja 5000 has microstuttering but not that big jump of the image.

Federico
 

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Federico,


If you see it in the blacks, then it's an MPEG2 artifact. Pumping up the contrast will make it easier to notice too.


As for 72Hz - that's unfortunately impossible on the LT150. The picture looks absolutely horrible in 72Hz and it cannot be used at all IMO. I've tried autosynching and manually synching it, but it still looks bad. I switched over to 59.94Hz personally and that works great.


Kilgore,


I can see the dithering on my 21" Sony G-500 monitor. It is however more difficult to see due to screen size. I have not seen any dithering on flash related material or anything similar. Have you checked if phase and clock is set correctly? Open up an explorer window so it fills the screen. Press the shutdown button in windows - but don't shutdown. You should now have a nice crosshatch pattern. If you have noise and shimmering then phase and clock is not set correctly. Use the auto-adjust button on your remote until it looks good. If you can't get that to synch.. try manually adjusting phase and clock.


Incidentally this kind of dithering is very apparent on my dtv setup. They use way too low bitrate and so every channel except the movie channels look bad. Worst part is they're shutting down the analog equivalents and increasing the monthly fees. If that isn't corporate greed then I don't know what is. But I digress..back to the LT150 discussion.


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/frode
 

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Frode,


I agree with you - increase contrast and it gets worse. I am gong to try the night beach scene from Castaway with my DVD player and see if it makes a difference.


The 72hz refresh works great on my LT150 - video material shakes and shimmers, but when the film starts it looks good! The original LT150 I demoed wouldn't sync properly to 72Hz so I thought none of the LT150s would - got a big surprise when the one I bought did! In fact, Randy emailed about trying different refresh rates, so I immediately tried all kinds up to 90Hz - everything worked!


Cheers,


Grant

 
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