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Author Topic: The latest "what is AMC doing wrong" query: high black levels Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 08-20-2014 03:16 AM                     quote: Monte L Fullmer Course, you can easily blame the washout due to the decaying LCoS chipset that Sony uses, where light passes through the chip and not reflected like the DLP setup. LCoS or Sony's implementation called SXRD uses reflective technology, just like DLP. The difference is that DLP is a matrix of tiny switchable mirrors and LCoS is essentially a mirror with a thin LCD layer on top of it. So, the light would only pass trough this very thin layer of LCD. Maybe this LCD layer wears out over time, due to the excessive heat it has to endure, but I doubt that it would result in a problem as being described here. This problem feels more like a calibration problem or maybe there was another light source illuminating the screen? I've had a curious case where someone left on a projector used for some kind of business presentation, projecting some kind of blackish image and washing out the 35mm picture... Actually, you could suspect that the "blackness" of DLP also washes out a bit over time. Modern DLP chips have their "backside" coated in some kind of black/light absorbing substrate, but if you have ever witnessed what the excessive heat does to the heatsinks in your DLP light engine over time, you could argue that this substrate will also evaporate/burn away over time, causing more light to leak trough. In general, you would expect the DLP technology to have a better contrast ratio, because it actually diverts the light into heatsinks using those switchable mirrors. Still, even with all the mirrors in the "off" position, there is a considerable amount of light leaking trough. Curiously, the best "true black" representation using a checkerboard pattern I've seen, without the use of auto-iris or other tricks came from a JVC projector using their version of LCoS called D-ILA. Unfortunately, nobody is currently planning building DCI equipment based on that technology.  |  IP: Logged Jarod Reddig Jedi Master Film Handler Posts: 513 From: Hays, Ks Registered: Jun 2011 posted 08-21-2014 04:27 AM                     The D-ILA JVC's are the best I've seen in that performance area as well.  |  IP: Logged William Kucharski Expert Film Handler Posts: 244 From: Louisville, Colorado, United States of America Registered: Oct 2012 posted 08-21-2014 07:34 PM                     To bring this all back full-circle, what's the easiest way their black levels could have gotten off given they likely don't recalibrate frequently? My guess was that they did an autoconfiguration of brightness levels with an old bulb and relamped, but there has to be some answer as in general theatres in the same area tend to be calibrated by the same people and other AMCs here don't have this issue with their theatres and this one didn't have this issue in the past. BTW, I am very, very impressed with the JVCs.  |  IP: Logged Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 08-22-2014 04:17 AM                     It's really hard to guess, because there are so many things that might have caused this. How did it look in between trailers? There probably was a format change, since The Giver is in scope, how did it look before/after/during format change? Does the theater have movable masking? If it didn't, how did the edges look? Was there a distinct runoff in brightness? Did you check if there was another ambient light source in the theater? Someone leaving the lights on in the booth? (Although that would probably not result in a uniformly brightened screen, but a few irritating bright spots.)  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 08-22-2014 05:36 PM                     Again, there is no calibration for black on a D-Cinema projector. There may be an option to tweak the brightness on the Server input - can't remember on top of my head - but it should not be used and it is not meant to calibrate anything. Lamp alignment does not change black level either (well, if you raise the brightness, the black level will increase but that's not the point).  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 08-24-2014 03:41 PM                     D-ILA are truly great at blacks but ANSI - on consumer machines - is poor. It would be interesting to see a D-ILA with a pro light engine and lens. You can measure 30000:1 with no iris or tricks. But then ANSI goes down to 100:1 - which is still very decent, don't get me wrong! (my apologies for the double post, I found this on my laptop, I was writing it when the battery died. And I posted it without checking first the status of the thread)  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 08-24-2014 05:05 PM                     It's not that bad, Marco, e.g. recent JVC D-ILAs show ANSI contrast into the 1:300 to 350 range. Even in optimized screening rooms, the visible difference to 1:500 to 1:700 of single-chip DLPs is barely there, so they offer both a very good in-picture contrast as a very high on/off contrast. But these machines are optimized for black level/contrast, they have a comparably low light efficiency. - Carsten  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 08-27-2014 10:17 AM                     Carsten, ANSI contrast is never measured unfortunately, can I ask you where did you find those values? Not that I don't believe you, just want to confirm the source. I personally measured 1:126 on one, but that was years ago. Back IT: Yes, the 320 have a "limited/full" RGB level option on the Server input - not sure for what reason - but the server works on "full", so the wrong one will provide crushed blacks, but not washed out images. However, the same input has also the option to tweak brightness and contrast. The default levels are not "zero" and if you raise the brightness you raise the black level indeed. I don't really know what those controls are doing in a D-Cinema projector, but as far as I know they shouldn't be touched. If someone did it, I would blame the installer and not the projector.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 09-08-2014 06:17 PM                     Here is a thread summarizing measurements on some prominent and well performing home video projectors. As you can see, these numbers reflect my statement from above, that DLPs shine in the ANSI contrast field, while LCoS/SXRD and optimized LCD achieve higher on/off contrast. The test patterns used are also shown. When you understand the effect of stray light and the difference between ANSI and on/off, it can easily be understand that the EBU test pattern gives results somewhere between ANSI and on/off or 1% white. Most values have been measured without dynamic iris or light modulation techniques used in many projectors to improve on/off contrast or black level. http://www.hifi-forum.de/index.php?action=browseT&back=1&sort=lpost&forum_id=94&thread=13598 - Carsten  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 09-09-2014 01:21 PM                     My German language skills are not great (I don't speak a word) but that seems very interesting. I know that old DILA were not going any further than 150/200:1, it's great that recent ones have improved. I believe I measured 500:1 on a series 1 DLP. I'll ask Google to help me on that thread! Thanks Marco  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 09-09-2014 02:09 PM                     Yes, recent LCoS/SXRD have improved a lot in ANSI contrast, some come close to DLPs. - Carsten  |  IP: Logged Mark Strube Master Film Handler Posts: 322 From: Milwaukee, WI, United States Registered: Feb 2007 posted 09-10-2014 07:56 PM                        Could be as simple as port glass that hasn't been cleaned in a very long time... dust and dirt buildup will give a very glowy look that will cause black areas of the picture to appear lighter when it's not a 100% black image.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 09-11-2014 03:25 PM                     in a very long time = since installation time. It's the norm. Many are simply not accessible on the outside and not removable on the inside -> they never get cleaned.  |  IP: Logged William Kucharski Expert Film Handler Posts: 244 From: Louisville, Colorado, United States of America Registered: Oct 2012 posted 10-02-2014 03:58 AM                     Just as an update - I spoke to the GM of the theater rather than the night manager, and a week later, whatever was wrong was fixed.  |  IP: Logged

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