NEC LT150: DLP rainbows

Discussion in 'Archived Threads 2001-2004' started by Matt Stryker, Jan 5, 2002.

  1. Matt Stryker

    Matt Stryker Screenwriter

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    (First to post! Sweet!)

    I just wanted to thank the owners for setting this little area up; great.

    And I also wanted to add that if anyone in the Atlanta area is debating purchasing a DLP projector and wants to make sure they don't suffer from the "rainbow" problem, I would be happy to have them over to check out my LT150.

    It seems that many consider this a deal killing factor for DLP purchase, and its diffcult to find dealers who have a DLP set up. Shoot me an email.
     
  2. Jon_B

    Jon_B Screenwriter

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    Sure wish I lived in Atlanta. [​IMG] I'd come check it out.
    Good to see the new specialized area. [​IMG]
    Jon
     
  3. AaronP

    AaronP Stunt Coordinator

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    I haven't seen the LT150, but I've seen the Yamaha DXP1 which has the same DMD chip and color wheel, and I found the rainbows to be annoying, and so bad that I wouldn't buy a projector with that problem. But, honestly they weren't as bad as many people say. I bet most people wouldn't even notice tthe rainbows unless they were told what to look for.

    I think in about a year, there won't be any DLP's out that have the rainbow problem, they already have new color wheels in a few of em (Sharp 9000) that have corrected the problem by increasing the number of segments on the color wheel and speeding up the RPM.
     
  4. Jason Harbaugh

    Jason Harbaugh Cinematographer

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    I bought the LT150 sight unseen and was worried that I would be one to see rainbows but after 250 hours of viewing I have yet to see one. I've even tried hard to find one by using the opening credits to X-men which is supposed to be the motherload of rainbows. High contrast moving light.

    I have heard of people still being able to see rainbows on the Sharp 9000.
     
  5. Matt Stryker

    Matt Stryker Screenwriter

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    I just think its important for each person to see for themself, as many people overblow the rainbow effect and it scares people away from otherwise excellent projectors. That's why I'm offering; I really think that if you don't see the rainbows, there is no reason not to consider a DLP projector instead of a RPTV or and LCD/CRT PJ.

    I can see them if I move my head quickly while watching, but last night during Red Planet, I didn't see a single one.
     
  6. Dave Poehlman

    Dave Poehlman Producer

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    This is a bit of a newbie FPTV question, but what exactly is a "rainbow" and what causes them? (Or, is it better that I don't know in hopes I will never look for them.)

    I was actually looking at the LT150 for my future HT. The screen shots posted from other users look tremendous.
     
  7. Guy Kuo

    Guy Kuo Supporting Actor

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    Rainbows are an artifact of the single chip/color wheel projection process. The DLP chip is used to project one color at a time as the color wheel spins each primary color filter into position. On other types of displays, all three color images are present on screen at the same time. With a single chip DLP, they aren't. As a result some people, see the three different color images separate when the image moves relative to the eye. This happens during pans, motion, and even rapid eye movement from one part of the screen to another. The separate primary colors are easiest to spot if a hard contrast edge is present on screen. For instance a white spot against a dark backbround can split into a red, green, and blue spot if you move your eye. For some people, this is very noticeable, but your vision does get used to seeing and ignoring the effect over time. It never goes away completely and people vary in their senstivity to seeing the artifact.

    If the artifact is seen along a bright edge of a large object, it shows up as a red, green, and blue outlining as motion or eye movement occurs. Even a blink can make it appear. It would be advisable to watch a DLP for an hour or so to see if the rainbows are a problem for you. Learn to see rainbows by looking at the projector and quickly moving your eyes. That separation into red, green, and blue of the projection lens is the "rainbowing."

    Some projectors are going to faster changing of the color filters by higher RPM or more color segments, etc. This reduces the temporal separation of the color images and makes the rainbow finer and less noticable.
     
  8. AaronP

    AaronP Stunt Coordinator

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    I was gonna answer, but Guy answered first, and he's the master so there's nothing I could add. [​IMG] [​IMG] [​IMG]
     
  9. Jerry Klawiter

    Jerry Klawiter Screenwriter

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    Rainbow effect is blown way out of proportion, and when it comes to choosing the right dlp projector, this is truly a personal decision.
    What's best for one, is not always for all.
    So take your time and bring a few home to audition.
    Have all your family members veiw it,
    Make a DIY screen for under $15.
    Here
    And let your own eyes decide.
    There are many dlp's to pick from in a wide price range.
     
  10. Dave Poehlman

    Dave Poehlman Producer

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    Thanks for the info guys. And thanks Jerry for the great info on the DIY screen!
     
  11. brian a

    brian a Second Unit

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    I've been reading a lot about the rainbow on these boxes and want to check it out for myself. Other than the above mentioned X-men opening credits, what other sources are known to be a good test if you are sensative to this effect?

    brianca.
     
  12. Matt Stryker

    Matt Stryker Screenwriter

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    The opening battle scene in Gladiator is where I see them the most; I haven't tried XMen. I can barely notice them now, but I can see them if I try.
     
  13. Scott Dautel

    Scott Dautel Second Unit

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    Matt ... I've had questions about the LT150 for months ... wish I had a unpcoming trip to Atlanta planned to have a look.
    I have a Proxima DX3 and a InFocus LP350 at work, which I occasionally take on the road with me for business. Both of these are XGA (1024x768) resolution and cost approx $4000. I believe your unit is SVGA (800x600), right?
    Now, my XGA units look great with DVD via s-video (from Pioneer PDV-LC10), but I'm wondering if the SVGA version looks just as good? Logic tells me that DVD's have 500 horizintal lines, so it shouldn't matter if the projector has 600 vertical pixels or 768, as long as that number is > 500 (actually 480 viewable) right?
    Question 2 - are you using a DVD player with component out, or HTPC? If standalone, does your player do 3:2 pulldown and does it improve picture quality.
    With my players ... I can see the rainbow effect if I move my head rapidly while watching a bright scene ... but this is not something I would do while movie watching ... unless I'm trying to get water out of my ears or something [​IMG]
    Anyway ... one of these days, Ill get to see an LT150, till then I'll just be jealous of those of you that have such a nice setup.
    Scott
     
  14. PhilS

    PhilS Stunt Coordinator

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    "Rainbow effect is blown way out of proportion . . . ."

    True, unless you spend thousands of dollars on a projector, and then after you watch it four of five hours over a few days, you notice rainbows all over the place, and you see them whether you move your head or not, and the projector becomes virtually unwatchable. On other hand, if you don't see them, then they are overblown to you.

    In other words, the effect is not blown out of proportion, nor it is underestimated; it is just that people who can't stand it complain vehemently, and those who can't see it wonder what the fuss is about.

    My advice (and it's free): If you're going to buy a DLP, make darn sure that you don't see them or they won't bother you before you buy (and at a minimum that your family or those who are going to enjoy your projector with you on a regular basis don't see them). And don't rely on seeing a DLP for 15 minutes. I am very senstive to them, but didn't notice them at all until after about 4 to 5 hours, which caused me to have to return a $10,000 DLP before I went looney.
     
  15. Matt Stryker

    Matt Stryker Screenwriter

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    Scott- I still owe you for the free case to my LC10, so anytime you're in Atlanta, send me an email.
    The LT150 is native XGA (1024x768) and I drive it with a HTPC; I haven't seen one with a progressive scan player so I don't know how well that would look. The HTPC image looks incredible, and the software player I use performs 3:2 pulldown and outputs the image progressively.
    The thing to consider with SVGA is 16:9 mode. When projecting a 16:9 image, I have 575 lines to use, so all 480 can be displayed on the screen. With an SVGA projector, you only have 440 lines available with 16:9 image.
    The LT150 is a little cheaper than your two projectors, I paid $2400 delivered for mine about a month ago. The bulbs run about $300, and they last 1000 hours.
    PhilS- I totally agree. It is very important for people to realize that these projectors represent a MAJOR investment and that they should treat them just like they would a car purchase. Read, ask, compare, demo, and then buy. Thats why I wanted to offer my setup as a demo, because I didn't have that luxury when I bought my LT150.
     
  16. Guy Kuo

    Guy Kuo Supporting Actor

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    You definitely want to use a HTPC or external scaler set to 1024 x 768. The internal scaler on the LT150Z decimates a great deal of image detail when fed a 480P image. It easily does 30% better when fed a pre-scaled image rather than letting it do the work itself.

    While you are at it, also pick up a photographic fluorescent to daylight color correction filter to correct the projector's greenish-blue light output. Makes absolute black level darker and allows you to get closer to correct white balance without running out of adjustment range.
     
  17. Matt Stryker

    Matt Stryker Screenwriter

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    Guy-

    Do you have a size of filter that I should use? Brand name, rating, or model number?

    I'd been wondering about this, I haven't noticed the bluish tint yet, but my screen isn't here yet.
     
  18. Guy Kuo

    Guy Kuo Supporting Actor

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    I'm using a Cokin P046, but it is a plastic filter. Works quite well when positioned about three inches in front of the projector and angled slightly to keep the waste light off the projector. A glass filter would have even better clarity and would be preferable for more permanent usage. You'll need something 25 mm minimum in size. Larger is much easier to position and cover the entire exiting light spray. The Cokin is large, about three inches square.

    Once you put the filter in front of the machine, go into color balance and set gamma to natural 1. White balance on mine is set to.

    Brightness Red - center

    Brightness Green - down 7 clicks

    Brightness Blue - down 2 clicks

    Contrast Red - center

    Contrast Green - up 7 clicks

    Contrast Blue - up 21 clicks

    The resultant grayscale on a neutral white screen is a bit bluer than D65, but aiming for true D65 on this machine ends up with some brightness and grayscale tracking problems. Your optimal settings will probably vary from mine. Note that this will drop overall light output, but I find the image much more natural looking. It may be to much of a light drop if you don't have a real screen yet.

    Update -----

    After another round of work, I think I'm going to revamp my recommendation for doing things. Instead of attempting any color correction with white balance, use the white balance controls to force each primary color to maximal output level. You can do that by displaying and AVIA pattern which has the moving white bars. View only one primary color at a time and adjust for maximal output of that color with the white balance controls. You can hit maximal level before clipping by intentionally going too high on the contrast for a color unit the lighter moving white bar just disappears into white. Then back down until the bar comes back into view at about 1/3 to 1/2 the darkness of the darker white bar. That puts the light output for that color to maximum possible without clipping. You'll need to touch up brightness for each color and repeat contrast as the controls interact. Repeat for each primary color. Once done for all three colors the machine will be set for maximal light output and contrast range.

    You'll notice that the grayscale will be totally whacked, but now put the color correction filter in front of the machine. I'm noticing, more light ouput, greater detail in all APL ranges, and the color correction filter brings color balance into viewable range while also taking absolute black down. It's enough that I'm going to have to zoom the picture further out to stop huring my eyes with the extra light and this is in economode. With the Cokin filter, the white balance is still a bit too blue green, but it is close enough that in the absence of a white reference, you eyes will accept "white" on the projector as white. A different filter could be used to fully correct to D65 while still allowing the digital range to run full out.

    After all is said and done, ANSI contrast ratio measures 380:1, on/off contrast is 690:1, full off black is 0.02 at left edge of screen and 0.03 center, 0.02 right edge. The lower left corner has a black level of 0.04. That is WITH the color correction filter in front of the machine. It looks a ton bettter than out of the box and I think would give entry level CRT's a good run for the money for the majority of scenes. Even dark scenes in Legend of the Fall look good. I can scarcely believe what this little thing is capable of doing after being modified
     
  19. Glenn

    Glenn Stunt Coordinator

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    Hi Matt,
    >>I also wanted to add that if anyone in the Atlanta area is debating purchasing a DLP projector and wants to make sure they don't suffer from the "rainbow" problem, I would be happy to have them over to check out my LT150.
    I would LOVE to see your LT150 sometime because I am considering buying it or it's replacement this year.
    Please send me an e-mail and maybe we can work out a date sometime in the future?
    Thanks,
    Glenn
    [email protected]
     
  20. Matt Stryker

    Matt Stryker Screenwriter

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    Glenn, YGM
     

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