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DLP, black level, and those pesky mirrors..

Discussion in 'Projectors, Screens & Video Processors' started by Gary Lightfoot, Dec 4, 2003.

  1. Gary Lightfoot

    Gary Lightfoot
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    After getting the Smart calibration tool to play around with, I thought I'd do some quick contrast readings. While I was up close to the screen taking a reading for 'black' (using the black 0ire field from Avia), I noticed a lot of DMD mirror activity. They were all flicking grey, so I figured it wasn't one particular colour responsible. I was getting a reading of 0.08 lux which seemed pretty low, but thought that any light coming from the mirrors would be affecting the black level.

    I'd already used Avias needle pulse tests to check white and black levels, and they were pretty much correct as far as I could see - I'd only increased contrast 2 dits on the PowerDVD video adjustment, as reducing brightness had no effect (I'd done this when I installed it). I wasn't able to do this in the pj so that's why I went to PDVD. Idealy with HTPC and a Radeon, you have to leave everything at 0 and adjust at the pj (IIRC).

    I was using DVI, so contrast and brightness are greyed out on the HT1000. The only way to adjust these was to untick the colour temp box in the NECs menu, then adjust the RGB brightness settings.

    To stop mirror activity I found that Blue's brightness needed dropping down to -6. Green and Red stopped mirror activity earlier, but in order to try and keep colours the same without making the image more green or red, I dropped them all down to -6.

    I checked the black bars in Avia, and found they were still set correctly, with the second black bar just visible. I now needed to check and adjust the white bars. This resulted in me increasing each colours contrast up to around 140 (can't remember the exact number but will have a look if anyone is interested). Again, I did them all the same so that there wouldn't be any obvious colour push.

    I remeasured the white level and the lux reading was the same as I'd measured prior to any adjustment - 93. Not a hugely bright image, but I'm running in eco with the iris closed.

    Contrast has obviously improved, but I needed to make sure I hadn't adversly affected the colour temps so I put up the Avia grey scale which shows all ire fields from 0 to 100 in steps of 10. All were visible, so no crushing was occuring at either end, and all still looked grey. I then brought up each ire field full screen, and they all still looked grey to my eye. One or two may have had a slight blue push, but I couldn't be sure. Idealy a colour temp meter (like the one Jeff Paynter of projectorsareus uses) would have helped here.

    I played a few scenes from DVDs, and I felt that there was now more depth to the images in darker scenes, and no obvious colour changes. I have an untrained eye, but the images now looked better to me, so I was quite pleased with the results.

    I need to do a similar thing with all the other inputs now, but this should be easier, as they allow the brightness and contrast to be available in the normal menu.

    Next is to try colour calibration (when I have the time) and see if there are any further improvements to be had.

    So, for those of you with DLPs, if you want to improve your black level, try to make sure there is no mirror activity when you're 'projecting black'. It can make a lot of difference. :)

    Gary.
     
  2. Kramer

    Kramer
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    I'd wager you were seeing slight mirror activity as a result of the DVI connection you're using.

    IRE 0 through component should be better.

    Still, looks like you've improved things which is what we're all after :smashin:
     
  3. Gary Lightfoot

    Gary Lightfoot
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    Hi Kramer,

    I think I see what you mean, but I don't beliieve that's the case here.

    After reducing the brightness down, I no longer see any mirror activity when projecting black, and I think it was because of the settings in the HT1000, not cable length or interference etc.

    When playing the black bars in Avia, I can see the mirrors working in the bars, but not in the black area behind them, so I'm getting the darkest black the pj can produce without adding a filter.

    I saw them via component out from my Skyworth too, and managed to stop that by just reducing brightness a tad. I double checked the Avia black bars to ensure I wasn't crushing black level, and it seems fine. I'm getting a lower lux reading for 100ire, but I haven't had a chance to fully tweak the Skyworth yet. Hopefully I should be able to get similar results there too. :)

    Gary.
     
  4. Gary Lightfoot

    Gary Lightfoot
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    I'm going to recheck the contrast ratio again by taking readings a little closer to the projector. With the lightmeter being further away and at the lower limit of it's sensitivity, there may be a bit of error creaping in. Taking readings at the screen is fine for 100ire but probably not for the other readings as it turns out.

    Gary.
     

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