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Discussion Starter · #1 ·
Do you other LT240/LT260/HT1000 users see that R/B/G noise that occurs where the image should be black? I think it may be because the algorithms in the pj are flawed.


Clue: You cannot match the pj's preset Color Temp 6500 with ANY amount of fiddling (at least using RGB1 input). The pj is using some magic hidden saturation adjustment.


So here are my theoretical gripes:


1) Black Detail Gamma causes color banding in the image. This may just be the brakes as the pj gets a post-scaled 8-bit-per-color image, whereas the Radeon works with 10 bit YUV prescaled I think.


2) Color Temp 6500 enables bad saturation algorithm. I think this is the main culprit.


My solution is to cut as much projector processing out of the loop as possible.


1) Choose sRBG template (has Natural Gamma).

2) Disable Color Temp. This removes some saturation.

3) Lower contrasts: R a little, B/G quite a bit more (to counter step 2's loss of 6500) All must be lowered, else saturation in step 5 will bloom.

4) HTPC Radeon: choose 1.45 Gamma (to counter step 1)

5) HTPC Radeon: choose >100% saturation. (to counter step 2's loss of saturation)


This eliminatates that funky R/G/B noise in the dark areas.


(Too bad Windows driver doesn't expose individual R/G/B adjustments for the overlay like I can access in Linux! Then I could cut out step 3 on the pj, and move that to the Radeon also.)


So can anyone duplicate this on their HTPC/LT240?


/xorbe
 

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What do you mean by RGB noise? DLP dithering? I don't notice any dithering noise at all on a completely black background, using my HTPC with a Geforce 4 Ti 4400 and Theatertek.


I do notice that, in Film/Movie mode with the preset color temp of 7800 and natural or dynamic gamma, I get a reddish tint on 10 IRE and 20 IRE.


I haven't used Black Detail Gamma much, as I think it "washes out" the picture a bit. I didn't check for banding in that mode though.


I need to upgrade my colorimeter first before I can properly calibrate my LT240 though...just gotta cough up the $$$ first. :)
 

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Discussion Starter · #3 ·
(I tried using a GeForce 4 Ti 4200, and could never get pleasing results! Then my buddy told me to use a Radeon... much better. GF4 doesn't have overlay gamma either.)


The noise is from "black" pixels that aren't [0,0,0] that get color boosted far too much, like [1,1,2] goes to [1,1,20] on the screen. [1,1,2] is black, but [1,1,20] shows up as dark blue. Now mix some true black pixels in there, and that's what I see, black+dark blue (or red or green) noise.
 

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Ah. Sounds like a general color correction issue to me, and not a flaw in the algorithms. Too bad NEC didn't calibrate the grayscale properly like they did with the HT1000, which was nearly perfect out of the box (when compared to my grayscale calibrated RPTV).


The LT240's color tracking is not that great out of the box. I found setting the color temp to 6500K resulted in a terrible picture. Using the preset 7800K was much better for color accuracy (at least people don't look green!). The low IRE end of the grayscale still looks bad though...reddish on my projector.


Of course, correcting grayscale still may not help with [1,1,20] looking too blue, but a colorimeter can help you determine how far off it is.


I wish someone figured out how to access the service menu of the LT240...that would be very helpful in tweaking the RGB gammas, if such a feature exists...
 

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Discussion Starter · #5 ·
Quote:
Originally posted by maxleung
I wish someone figured out how to access the service menu of the LT240...that would be very helpful in tweaking the RGB gammas, if such a feature exists...
help help help enter menu

down up right up enter

menu


There's not many interesting things to do. I believe the tables are accessed with software (that I don't have).


Here's another problem with the pj's 6500: it lowers the contrast a bundle, in order to pump up saturation. When I simulate this from the Radeon, it is clear to me that the LT240 does not have enough contrast to pull this trick off. (Or at least my unit.) The unit cannot pleasingly achieve the saturation levels that it is attempting.


I've made changes to my settings:

1) pj: sRGB, disable color temp, lower (128->96?) B and G in white balance menu (leave R alone).

2) pj: sRGB color correction is 4/3/-3/10/-11/-4. I meet this halfway at 2/1/-1/5/-5/-2.

3) htpc: boost saturation 5%, gamma 1.2


The LT240's "6500" drops the contrast like 25% and boosts the saturation 40% or something insane. I'm sorry, but I'll take the contrast over the high saturation levels.


(Why isn't saturation implemented as a gamma curve instead of a linear adjustment!!)


/xorbe
 

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Thanks xorbe! Maybe when I have time I'll try exploring the service menus.


As for losing contrast at D6500, that's to be expected with all projectors with specs rated only at the highest temperature setting with full white peak on, especially projectors with a white segment. Yep, it sucks. The only way around it is to not buy these "business" projectors, and go with the more expensive "HT-level" projectors with RGBRGB wheels. Even then, the contrast is lower when you calibrate to D6500.


Of course, you could try painting the white segment of the wheel black...but that is a very bad idea if the LT240 uses the white segment to sync the wheel like the Infocus X1! You may want to read some of the LT150 mod posts (particularly by KBK) for some ideas you can try.


You get the same effect with CRTs...you lose contrast when you calibrate to the lower color temperature.


I measured 800:1 contrast ratio on the HT1000, for example. The only way to improve it would be to paint the walls black, and do a colorimetric calibration (to hopefully improve the gamma of the HT1000). It was at least as good as my calibrated RPTV. The NEC LT240 isn't as good in terms of shadow detail, for sure.


I'm not exactly sure what you mean by saturation...do you mean pure RGB primary colors?


Anyways, you really do need a colorimeter or something like Colorfacts to be absolutely sure. Do you have an ISF'd CRT kicking around that you can compare to? Comparing to CRT computer monitors isn't always the best, as there is usually no way to adjust RGB cuts and drives...


Have you considered trying a Hoya FL-D filter?
 

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BTW, I wouldn't be to concerned about the contrast ratio at this point. It is pretty good. Your issue is more concerned with gamma, and that's tricky with digital projectors. People confuse gamma with contrast all the time, which isn't a big deal if you're talking about direct-view or rear-projector CRTs.


Gamma is a huge issue with digital projectors.
 

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Discussion Starter · #8 ·
As for losing contrast at D6500, that's to be expected with all projectors with specs rated only at the highest temperature setting with full white peak on, especially projectors with a white segment. Yep, it sucks.


Step 1) Projector adjusts R/G/B peaks to 6500. Contrast lost. Ok this step is fine and required.

Step 2) It tries really hard to boost the saturation. It cannot boost saturation without lowering contrast even further (else the saturation will bloom). This is a BAD idea because now the luminosity of colors exceeds that of grayscales!! (Linear saturation algorithm)


ie, selecting D6500 does more than just tuning to 6500, making it useless to me.

Of course, you could try painting the white segment of the wheel black...


I plan on trying this one day...

I'm not exactly sure what you mean by saturation...do you mean pure RGB primary colors?


Saturation = 1.0 - (3 / [R+G+B]) * min(R,G,B); where R,G,B are 0.0-1.0 -- ie, "color" is saturated, and black/gray/white is unsaturated. Any color that has R/G/B as 0 has max saturation of 1.0

Have you considered trying a Hoya FL-D filter?


Does that cut green and blue?


/xorbe
 

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Yes, the FL-D filter does cut green and blue. When you look at the filter, it will look reddish. An FL-D filter is popular with the LCD projectors, because they tend to have "neon" greens. The reason why you want to cut green and blue is because, traditionally, digital projectors (especially the older DLP ones) had trouble with red, so you would use the FL-D filter so that you can raise the G and B cuts and drives (contrast and brightness) without having to reduce the red, because the red is already at maximum, and is generally a weak point of the projector.


An FL-D filter may not be necessary for the LT240...it may have an excellent red filter and a bulb that is not weak in the reds.


My dealer hasn't responded to my questions on when he can give me a refund on the HT1000 I returned, and when I can get the Sanyo PLV-Z1 replacement, so my cash is in limbo...can't try all those things yet. Grrr. :(


As for saturation, I assume you already tried the RGBCMYK controls? I still haven't mastered them myself yet.
 

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Discussion Starter · #10 ·
Quote:
Originally posted by maxleung
As for saturation, I assume you already tried the RGBCMYK controls? I still haven't mastered them myself yet.
For the RGBCMY controls, I played with them tonight. sRGB is good, except I like to bring Yellow back towards zero by 2 or 3 notches -- sRGB makes it too orangish for my taste.

/xorbe
 

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Yeah I thought yellow was on the orangey side myself (in film mode at least). For laughs a few weeks ago, I used my CA-1 colorimeter to adjust the CMYK controls, and it actually helped! Of course, the colors were all way off, since no LT240 calibration file is available for the CA-1, but it was an interesting excercise to say the least. :)


But, my dealer came through and said my refund will be coming soon, so I'll be able to upgrade to a better colorimeter that can handle digital projectors without the need for a calibration file. :D


Do you find sRGB to be better than movie mode? Do you lose color temperature settings in that mode? I really should set up my LT240 again, and see if the gamma is better in sRGB compared to the other modes.
 
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