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Discussion Starter · #1 ·
Well, thanks to the help of all you fellow forum members, and to my HT Consultant extraordinare - Lee Wallace (big time forum-lurker-never-posted - hi, Lee!), I've now got an awesome (D-ILA based) system, something I didn't even know existed 6 months ago. To use a software development analogy, it's still in prototype mode, but will be going beta tonight, when we view our first entire film. I'm going to post pictures, etc, but I'll be waiting until at least release 1.


I hope that someday (soon!), I'll be able to just enjoy a movie, without thinking about the technology, but presently I'm still obsessed with making it run to its full capabilities. Right now, I've got two projector issues I'm concerned with.


I've got a G20, projected onto a 7 foot wide 16x9 Greyhawk, driven by an (AVS) Geforce HTPC. I'm running at 1360x768 on SXGA3, until I get my Pannie, and am using the Video settings from the 1360x768 settings in Powerstrip. The projector was calibrated by JVC Digital, and I've also set the tracking to -24 and the phase to 4, using Dilard. I also dropped the brightness down a bit, to get rid of the halo.


Here are the issues:


1) The image is tinted green on the left (the projector is inverted, so that's the projector's right), moving to red on the right. Do other people have this? I've only seen mention of this in this thread, but I am unsure how common this is, if JVC Digital should have fixed this in their calibration, and if I can fix it with Dilard. Anyone?


2) I'm also seeing what I can only describe as "video noise". It looks similar to the noise you see on VHS tapes, and is also similar to what you see when the phase isn't adjusted on the projector. It's kind of squiggly interference visible in areas of one color, like sky. I only seem to see it when watching movies (WinDVD), not on the desktop display from the HTPC. It also remains when you pause the movie. I've mostly been using Fifth Element, which is a good transfer, so I don't think it's the DVD. I'm going to try connecting the projector to a standalone DVD player, both with and without my current cables, to try to eliminate the PC and the cables as a cause. But, in the meantime, I'd like to ask if other people have seen this - if it's normal, and if there's anything to do about it.


Again, overall, I'm thrilled with what I've got now. But, since I haven't seen much mention of these problems, I'm wondering if they can be fixed.


Thanks!


- Dave


[This message has been edited by Dave T (edited 05-25-2001).]
 

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Dave,


There is an adjustment screw on the bottom of the projector that realigns the condenser lens for inverted operation. It sounds as if you have not adjusted this for inverted operation. Procedure is covered in the owner's manual.


The noise you describe sounds like a problem with tracking and phase but you should have gotten that right using DILARD. What vertical refresh rate are you using?


Regards,


------------------

Tom Stites

Director, Business Development

Digital Systems Division

JVC Professional Products

"My opinions do not necessarily reflect..."
 

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Discussion Starter · #3 ·
Tom:


A reply from Mr. JVC! Thanks!


You know, I was wondering about that exact thing this morning! (the screw.) When the projector was calibrated, I had told them that I would be mounting it inverted, and figured that between them and my installer, that it would have been set that way. But, I bet you're right - I'll make sure the screw is set.


Regarding the refresh rate - I'm running at the rate the D-ILA settings give you in Powerstrip, I'm not at the projector, but I think it's 71.997 Hz.


- Dave
 

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Dave,


I did notice the green and red fog from the corners, as noted in the original post you refer to. I found that after the first 50 hours of use, the intensity of the fog fell to where it wasn't nearly as bothersome. Then, after the latest Dilard versions I have been able to adjust black level to where the fog isn't noticable (almost at all).


As far as the noise goes that you mention, I do notice that type of noise when the phase is incorrect. Just moving the phase one way or the other with desktop text displayed from Windows Explorer allows me to nail it. However, the noise that you are referring to, IMO seems to be related to the gamma curve being out of what and allowing for posterization to show from the MPEG-2 source. The reason why I say this is because when my D-ILA was bone stock, I didn't have much of an issue with posterization or noise in video from DVD, though I fought the black level issues. Then as Dilard progressed I fixed the black level and 8bar and started noticing posterization. To me, it seems related to gamma adjustments and I won't know for sure until I am able to fully calibrate my D-ILA's gamma profile. Hopefully, the last phase in the puzzle, gamma, will really dial in the D-ILA projectors out there.


I have also noticed that without being able to adjust gamma along the way, my whites from 80%-100% are getting crushed, and the blacks from 0-15% are also getting crushed (or incorrect because of adjusted black level, combined with less than perfect gamma out-of-box ...IMO.)


I'm anxious to test out gamma adjustments - it sounds to me as though you are as well.


Brian



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Our Home Theater - http://www.fatbulldog.com - Last updated 5/17/01
 

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Discussion Starter · #6 ·
Jaime:


That's news to me about the 75.1 Hz. I'm using the stock D-ILA settings from Powerstrip. I thought those were determined to be best. Is 75.1 Hz now the consensus as the best rate? What about the other Powerstrip setttings (front porch, back steps, bay window, etc, etc). Do those matter?


Brian:


That's good to hear about the "fog" going away over time! So, I should just wait a while? Regarding the rest of your comments - I'm wondering if my gamma is right. I do think I have some posterization. As I said, I had the JVC Calibration done, so it should be right on, but who knows? I wouldn't expect to have to tweak it more, but I'll probably give it a shot, since I can back up my settings.


However, I don't think that gamma could explain the noise - that wouldn't explain why it's still there even when I pause DVD playback, would it? Even when paused, I'm still seeing "noisy" motion. It's similar to what happens when phase is off, but I already adjusted phase, using Dilard, and found it to look best at 4 or 5.


Lee is going to double check that the "inverted screw" is set right, but he said that he thought he had already set it.


- Dave
 

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Mark,


I can't believe that I missed your post on gamma the other day. I have been interested in this for a long time and have been looking for information on it.


I wish that William would give us some useful information regarding the posterization issue, especially if he knows the cause for the D-ILA projectors or the cause in general. I am very interested in this, and I too drew the same conclusion as you regarding the steepness/flatness of the curve to reduce banding. I do understand he reluctance if it relates to his difficult to develop procedure, I'm just personally interested in this topic and the effects of changing the gamma curve...


I hope to read more information on this. I will be putting up a link in a few minutes to my gamma curve with an explanation.


Brian



------------------

Our Home Theater - http://www.fatbulldog.com

Last updated 5/17/01
 

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Below is a link to my gamma profile. The curve is from my G11 which has black level adjustment done, as well as 8 bar (though minimal changes).

brian_vh G11 gamma profile


Brian


Our Home Theater - http://www.fatbulldog.com

Last updated 5/25/01




[This message has been edited by brian_vh (edited 05-25-2001).]
 

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Discussion Starter · #9 ·
Well, I just checked the "noise" thing I was talking about again, and I'm not seeing any more what I was claiming I saw. I don't see any "noise" when DVD's are paused, after all. I could swear I was seeing this before, but (perhaps due to something I changed), I'm not seeing it now. But, I do see the "noise" big time, while movies are playing. We now think that what we're seeing is posterization. Apparently, when there is slight shading changes from frame to frame in an area where adjacent pixels have subtle color differences, you get sudden jumps from one color to the next, in adjacent pixels. This appears as random noise.


So, I'd like to upload my gamma profile for analysis/critique. Can anyone suggest a free site that hosts files?


- Dave
 

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Posterization is caused by spikes taking place in between calibration points in the gamma look-up table.


The calibration which William and I both perform uses a 2.2 gamma value. As William stated in a previous post each curve that you see drawn in DILARD software is not a graph of the gamma correction. What you are looking at is the amount of correction required for the particular projector to achieve the proper color temperature/Gray Scale that is desired with a particular gamma setting. Each projector will respond differently to the same gamma correction of 2.2 .


If a projector displays multiple shading errors on the screen (Red on one side/ Green on the opposite side) the error can only be minimized as reducing a large error in Red will cause the opposite side of the screen to go Blue. Shading requires compromises to come up with the best solution for each display. Some displays will definitely perform better than others.


By adjusting your Black level on a calibrated projector you will upset the entire gamma reprofiling which was performed by JVC on your display. By changing the 0 ire point of the calibration all points in between 0-100 ire will be altered with a good chance of posterization being introduced as a result of this. You will also have upset the contrast and brightness setting which is instrumental in achieving a proper calibration.

 

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Discussion Starter · #11 ·
Cliff:


Thanks for that explanation.


If I implied I was planning on changing my black level, that was a misunderstanding - I wasn't planning on touching anything. All I'm trying to do is figure out if posterization is causing what I'm describing as noise, if it can be fixed, and if it was caused by JVC's changes to my gamma. If you have any opinions on this, or on how I might go about figuring out the answers to these questions, I'm all ears!


Thanks again.


- Dave
 

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Quote:
each curve that you see drawn in DILARD software is not a graph of the gamma correction....[it] is the...correction...to achieve...a gamma setting
Pretty fine symantics, there, Cliff. I understand what you are trying to say, so will let it ride. It is called the "Gamma Correction Wizard" because "Correction To Achieve a Particular Gamma Setting Wizard" is a bit too verbose.


So, Cliff, would you agree that the posterization is most likely coming from the gamma settings?
 

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Hi Dave,


The gamma correction is in effect even when the DVD is paused. It is active (if turned on in the projector) with any input at any time.


If you have noise that looks like "posterization", it may be due to a gamma curve that is too steep as shown in this thread .


Mr. Phelps has hinted that there is something else that he does to address posterization, but did not share what that could be. A steep gamma (like the one that JVC digital uses) could cause (or at least exacerbate) posterization.


The Dilard Gamma Correction Wizard is coming...but I would recommend getting your full value for your calibration first.


The interesting thing about the Dilard Gamma Wizard is that you can "dial-in" your gamma correction. You can use the standard 2.2 gamma (similar or identical to the JVC Digital and Richard Martin gamma factors) or use a lower value as William Phelps/Cliff appears to do. That is really the only decision to make in the Wizard, as the rest is automatic.


Dave, if you have a moment, post the .JPG picture of your Gamma Curve that the Back Up Wizard creates (it will be in the same folder as the back up file). We can see how steep the curve is, and see if that has anything to do with it.


Mark
 

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Discussion Starter · #14 ·
Ok. Thanks, Mark.


I didn't know that the gamma curve was visible from the backup wizard. I'll post that over the weekend.


In the meantime, I'm confused about something. I realize the gamma curve is in effect even when you're paused, but how could the gamma curve cause "noise" in a paused DVD? I thought that just affected the intensity of colors. Remember, I'm talking about moving noise - little lines shooting around, dancing pixels, whatever you want to call it. When paused, even if there is posterization, the image should be still, shouldn't it? Or, am I missing something?


- Dave
 

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FWIW, the red/green corners issue was described in a review of the G15 (or G20) in The Perfect Vision (I believe Greg Cushman wrote the review). If anyone is interested, I'm sure I could find a URL...


- m
 

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Sorry, Dave. You are right. Moving noise is not from the gamma.


Is it very minute like phase misadjustment (i.e. - are you an extremem videophile http://www.avsforum.com/ubb/biggrin.gif ) or is it much larger? Have you tried any other source material? There is a "Pulse Adjustment" setting in the Image Geometry Wizard (Advanced section) that clears up all sort of strange little things with just a minor tweak.


However, that setting is source specific. If you have this "noise" with only DVD playback, you can give that a shot. However, if you have it on all sources, than it is something else.
 

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Discussion Starter · #17 ·
Mark:


No, it's not all that subtle. I don't think a "normal" person would comment on it, but if you look for it, even from a distance, it's pretty noticeable. Up close, it's very noticeable. The thing that confused me was that it's there even when the image is paused. Since it's a digital projector, I would have thought that the image would be fixed once each pixel was told what color to show. This is an analog noise similar to what you see on televisions. So, my first suspect would be the graphics card or the cables.


In any case, I don't want to take too much of people's time on this one yet - I can pretty easily get much more useful data than I've given now, such as how much better/worse it is when the image is paused, whether it remains when using a standalone DVD player, and whether the cable length affects it.


I'll also try the 75.1 Hz refresh rate. Does anyone know what the rest of the Powerstrip settings are that I should use with this rate? Should I just change refresh and leave the rest alone?


- Dave


[This message has been edited by Dave T (edited 05-25-2001).]
 

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Dave, I don't use powerstrip as I'm using The Rock. The 75.1 refresh was a topic that was covered in the TAW forum. TAW did some tweaking of a Dila and found out to work best at 75Hz. Some weeks later JVC used The Rock as *the* processor at some show and apparently were very impressed. During this time it was learned that infact the optimum refresh for Dila is 75.1Hz, which is very close to the initial 75Hz used. The Rock will soon, if not already, have incremental increase and derease of refresh-so will be able to dial in exactly 75.1.


Jaime
 
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