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Discussion Starter · #1 ·
I was watching "The fifth element" for the umpteenth time...first time with an LT150. The picture is AWESOME so to speak..

I noticed something similar to a "swarm of mosquitoes" on a few of the sky scenes..(the first scene in egypt). I have all the recommended tweaks for LT150( white segment off etc).

I am just curious what might be the cause for it..the source DVD?? my dvd player (prog scan)..or the LT150.
 

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It could also be the dreaded DLP dithering...


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/frode
 

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I have this to some extent on my D-ILA (G20), too. I call it "video noise". I still haven't found out what causes it. I suspect my video card (ASUS Geforce II), but I could be wrong. One day I'll try another video card to see if it helps. So, your mosquitoes may not be color-wheel related at all. Or, you may be seeing something different from me.


- Dave
 

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For the Geforce 2 it could be related to the DAC ^_^. Radeon is better in this respect.


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/frode
 

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I have always heard that this can be caused by compression, and that care must be taken on certain scenes to avoid this.


The problem is that a surface, such as the sky, will have small and subtle gradations of color and luminance. Compression algorithms can push this to an all-or-nothing situation.


I often notice this effect on CRT monitors as well as digital projectors. My guess is that digital projectors, especially with dithering of colors and white-segment issues, accentuate the appearance of this on the screen.


Try taking a look at the source on a very good CRT monitor, and see if you don't notice some amount of this effect.


If someone knows more about this, I would appreciate being enlightened.

 

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Yes, actually - it could be the source, too. Another thing to check for is to compare similar scenes in a DVD and in a hi-def movie, if you have access to hi-def. That's something I should check as well.
 

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Discussion Starter · #7 ·
I want to see if the source is a probem...Can anyone with a fith element DVD confirm if they see "mosquitoes" (crawlies) in the very first sky scene (the one in egypt)
 

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i have seen this on my dlp with hdtv and dvd. it happens on bright parts of the screen. i reduced it by lowering white level. i thought it was white oversaturation.


greg


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Compaq MP2800 DLP, 1Ghz htpc w radeon aiw, 45 x 80" diy accoustically transparent screen, lexicon dc-1. ipaq touchscreen for control
 

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There is a very easy way to determine if its the projector or the source - pause the DVD. If the mosquitos stop, its compression artifacts. If they continue, its temporal dithering done by the projector.


I suspect its the former. Digital projectors (particularly ones that werent designed with video in mind) have a different gamma response than a CRT does. DVD compression artifacts are well hidden by (and designed for) the gamma curve of a CRT display, but they tend to be revealed by these digital projectors.


If (or when) some kind of Gamma table calibration becomes available for the LT150, I suspect you will be able to minimize or eliminate it.


Andy K.



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"L T One-Fifty

Did your light guide the wisemen,

to baby Jesus?"
 

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I would think what you are seeing are the "dreaded crawlies". Usually turning the "white segment" off will ameliorate this and in some cases eradicate it completely. There has been a great deal of discussion of this artifact on this forum in the past. Do a search and you will find several heated discussions, however, I think the best one was inadvertently "lost".


What you will notice is that some DVDs with similar sky scenes (white segment on or off) will not display this while others will. If you really want to see crawlies in all their glory try the opening scene of City of Industry or the driving over the bridge or sitting by the bay scenes in City of Angels!


Cheers,


Grant
 

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Quote:
Originally posted by kromkamp:
There is a very easy way to determine if its the projector or the source - pause the DVD. If the mosquitos stop, its compression artifacts. If they continue, its temporal dithering done by the projector.
Sorry, I don't get it. Are you talking the dithering motion artiface I talked about in my LT150 review? If so I MUST SAY IT AGAIN AND AGAIN, there is NO dithering effect in static image (pause the DVD). The dithering effect ONLY appears in motion scene.


regards,


Li On
 

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As grant mentioned what has been labeled "The Mosquito Effect" by some industry technicians is synonymous with what we have all come to know here as "crawlies". The only thing crawlies share with your dithering, Li On, is that both are seen during movement and not when a scene is paused. What Schintam is describing in his initial post, however, surely sounds like crawlies to me.

It's been debated extensively on the forum whether crawlies is a source related phenomenon or instead is related to certain types of displays.

My feeling is that it's due to both. It originates with the source but can be exacerbated with some displays. I've noticed with some source material that it's visible to some degree with any display I'm using. It's also true that when it is present it will be visibly more pronounced on some displays, particulary many XGA DLP's. But since some CRT FPTV's possess "mosquito filters" I don't think the problem is unique to DLP.

So far I haven't found it to be much of a problem with my LT150. It's certainly not visible to the degree it was with my LT100.


Bob
 

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Hi Bob,


Yes, I know the "The Mosquito Effect", "crawlies" and all sort of these ugly things. Before I turned off the White Section, I saw TONS of these. With White Section off, it gone. Maybe there was still some "crawlies" in a few scenes but it never bother me. As you said, the remaining "crawlies" maybe just in the source.


Then Andy mentioned "dithering" so I said my finding.


regards,


Li On
 

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Quote:
"mosquitoes" can show up in, for example, a static sky scene where nothing is really moving on the screen, even when the scene isn't paused.
Absolutely true, Herb.


Bob


[This message has been edited by RobertWood (edited 09-24-2001).]
 

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Bob:


Do you see this phenomenon on your (now calibrated) D-ILA? I do on mine (also calibrated). I'd be interested to know if you see it, and what video card and software DVD player you use. I'm using WinDVD, with an ASUS GeForce II.
 

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Hi Dave,


Up to this point all I've watched is HDTV.

Haven't seen DVD on it yet. My HTPC is giving me fits again.

It's been down since I got the D-ILA back. I think I've isolated the problem and hope to find time to get it going again before the week is out. It's Radeon with both the ATI player and WinDVD in it. I'll look for crawlies with both when I get it back up again.


I did notice some crawlie in the sky on one of the 1080i movies. But it was minimal.


Bob


[This message has been edited by RobertWood (edited 09-24-2001).]
 

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Li On,


I've never seen an LT150, and you're right it probably isnt dithering (which is what I've said). In fact, I'm not sure if this artifact has *ever* been a dithering issue. But if it were, pausing the image would reveal that to be the case.


Andy K.



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Did your light guide the wisemen,

to baby Jesus?"
 

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Quote:
Originally posted by RobertWood:

The only thing crawlies share with your dithering, Li On, is that both are seen during movement and not when a scene is paused.
I agree that these crawlies are different from dithering.

It's true that neither is seen when a scene is paused. But "mosquitoes" can show up in, for example, a static sky scene where nothing is really moving on the screen, even when the scene isn't paused. Although nothing's really moving, the compression can nonetheless have fluctuations in color and brightness levels of different pixels over time, thus creating "mosquitoes". Dithering occurs only when there's some object in the image that is changing position.

Quote:
It's been debated extensively on the forum whether crawlies is a source related phenomenon or instead is related to certain types of displays.

My feeling is that it's due to both. It originates with the source but can be exacerbated with some displays.


-Bob
I think you're dead right, here, Bob. The debate originally started because of assertions that SVGA DLP projectors didn't show crawlies and XGA DLP's did. Some XGA DLP people responded by saying, "The crawlies are in the source!", implying that their projectors were simply more accurate at showing everything in the source than SVGA projectors were. My feeling is that this is simply not true; crawlies are in the source, but some projectors do exacerbate them, and I think it's probably true that XGA DLP's were generally worse than SVGA DLP's. Don't know whether that's still the case.


-- Herb
 
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