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rainbows

Discussion in 'Projectors, Screens & Video Processors' started by doubledrat, Jan 30, 2004.

  1. doubledrat

    doubledrat
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    I have just had a demo of both the screenplay 5700 and the sim2 Domino 20

    unfortunately I could see rainbows with both of them

    For those of you have been around a while I have a question - how long do you think it will be before three chip DLP projectors are being sold at around 3000 pound mark?

    only I don't think I can put up with seeing rainbows all over the picture :(
     
  2. Gary Lightfoot

    Gary Lightfoot
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    I think that's a little while off yet.

    The new Sim2 500 is reputed to be around £20,000, so it'll be around 3 years at a rough guess before these will be affordable on the second hand market.

    How bad did you see rainbows? Sometimes people have become used to them after a while, and no longer see them, but I think they have to be minimal (ish) to start with.

    The newer LCD models may have to suffice in the mean time, unless you have the room for CRT.

    Gary.
     
  3. doubledrat

    doubledrat
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    Interestingly, the rainbow effect was much worse with the region one discs than with the region 2's. I don't know if anyone else has noticed this?

    The domino seemed to be affected less, but at £3,500, I am afraid I am not prepared to put up with any!

    I don't have room for a CRT projector, and the extra noise of the L C D puts me off that option. I also have the gut feeling that the dlp option is a superior one to the lcd option, my experience of lcds makes me feel that they are unsuitable for for moving images (with ghosting etc). Perhaps someone with direct experience can put me straight?
     
  4. Gary Lightfoot

    Gary Lightfoot
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    I don't see rainbows at all, so I can't comment directly, but I think that the colour wheel rotates faster for PAL, which is why you see less rainbows.

    Gary.
     
  5. gandley

    gandley
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    similar to gary, 3 chippers for the masses is way off.
    but new colour wheels are supposed to reduce the rainbow effect in later PJs. for 1 chip DLP it could be a matter of patience.
    Maybe....


    I wouldnt say lcd is noiser than DLP.(thats if u mean Db)

    But sounds like you need plasma
     
  6. explicitlyrics

    explicitlyrics
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    ive had a few of each at the house for a night or so just borrowed off people and I wouldnt say that dlp is inherantly better than lcd, nor quieter. If you are willing to pay that amount, in my opinion id say you can get a very nice lcd projector that could match the performance fine at the moment.
     
  7. RTFM

    RTFM
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    Gary,

    The colour wheel is slower with PAL @50Hz than NTSC @ 60Hz

    Explicitlyrics,

    DLPs have a rotating colour wheel in addition to cooling fan(s) so can potentially be noisier than LCD units. Although the latest DLPs have become much quieter, one of the reasons is the use of smaller colour wheels.
    Besides the colour separation issues with DLP (very minimal with 6 segment 5 speed wheels ), they tend to produce a more life-like image with less picture structure, higher contrast and blacker blacks.
     
  8. Gary Lightfoot

    Gary Lightfoot
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    Hi Jeff,

    I thought I'd read something about the colour wheel being able to rotate at 250hz for PAL (5x CW at 50hz) and 240hz for NTSC (4x CW at 60hz) in the new NEC HT1100, but this might be just an NEC thing.

    Gary.
     
  9. JohnWH

    JohnWH
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    Hmm, its an interresting question, which (if not all) sequential DLP PJ's drop there colour refresh rate to cope with higher V rates...

    They don't bother me, and they're not very visible on 5x PJ's anyway, but I was thinking about taking progressive out and doubling the vertical rate (100Hz for PAL and 120Hz for NTSC, although think my pj maxes out at 100Hz) in an attempt to further reduce rainbows (this would mean 500/600Hz colour).

    Was just going to try this using my PC, but the annoying DVI plug and play minitor detection has decided that the PJ is some cheapo LCD flat panel thats limited to 60Hz....

    Edit: anyone know what the update limits are on the various DLP chips? Would be interresting to know if the colour ref rate is limited by the processing/drive logic or the DLP chip itself. If its the former its quite possible that rate will ramp up quite quickly, wonder what the threshold is where three chip solutions become unnecessary...

    John.
     
  10. Gary Lightfoot

    Gary Lightfoot
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    On my old Davis DLS8, the colour wheel would match the input frequency from the htpc, so running PAL at 75hz and NTSC at 72hz produced smooth pans. You could hear the colour wheel speed up and slow down with the different refresh rates (I tried 60 for NTSC and that obviously ran at a different speed because it was audibly fifferent to the other two).

    I think that with the newer colour wheels, the pj itself decides the speed for the colour wheel, and limits the c/w frequencies to 50 or 60 so that the cw rotates at the correct speed for the format (ntsc/pal).

    Gary.
     
  11. They

    They
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    It is the data processing and addressing rates that are the limiting factors, more so the SRAM data speeds. The actual physical and optical switching speeds of the mirrors are not an issue.

    It's difficult to describe the Pulse Width Modulation (PWM), artifact and data rate reduction schemes used to make DLP work, particularly 1-chip systems, it's a very complex subject. However, temporal dithering (and sometimes spatial dithering) is used to reduce the data burden for high frame rate and high speed colour wheel systems. (This includes 50Hz & 60Hz)

    Each time a primary colour segment of the wheel passes between lamp and DMD, only part of the sub-field package is displayed. So there is a carefully assessed and balanced compromise all the time between total data rate capability, bit depth, dithering, sequential colour rate, contrast, colour gamut and artifact reduction. It's a tricky business!

    Current colour wheels are specified to 6x speed at 60Hz (10800rmp) and will increase a little further soon. The SRAM data rates will improve significantly as have the DSP capabilities in recent months. New processes such as SmoothPicture and DynamicBlack should add worthwhile picture improvments for lower cost consumer HDTV 1-chip systems.

    But although 3-chip systems are complex and expensive, they will tumble in price faster than you might think. There are a lot more companies working on the vaious aspects of the optical systems now (not just for DLP but other microdisplays as well) and economies of scale, particularly in TI's DMD manufacture will bring benefits sooner rather than later.
     

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