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Author Topic: Why was DCI designed as neither common width or common height Lyle Romer Phenomenal Film Handler Posts: 1400 From: Davie, FL, USA Registered: May 2002 posted 06-12-2008 06:57 AM                     In the DCI spec, the 2k image dimenstions are (4k is just double each): Flat 1998x1080 Scope 2048x858 While the imager size is 2048x1080. Why would it have been defined this way instead of using either common height or common width. Doesn't this method guarantee that the lens must zoom somewhat even on a common height screen? To make flat 2048 wide the imager chips only needed 27 more rows to make it 1107 (or I guess they would have made it 1108 to keep it even). I am glad that they didn't just use an HDTV ratio chip and crop both. 2k scope at 2048x848 is 1.747 Megapixels compared to scope cropped on hdtv at 1920x803 giving 1.594 Megapixels. So at least for scope, 2k Digital Cinema has almost 10% more resolution. Of course, scope digital cinema still has less pixels than 1080p hdtv.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 06-12-2008 08:34 AM                        As stated in other posts, the chip "we" use is also used in office & auditorium projectors. It is NOT made just for us, hence, we had no say. Louis  |  IP: Logged David Zylstra Master Film Handler Posts: 432 From: Novi, MI, USA Registered: Mar 2007 posted 06-12-2008 11:46 AM                     It seems that DCI fit the spec into an existing chip and by default it favors fixed side masking for those exhibitors trying to save $$ on new construction - i.e. with DC and a fixed width screen you only need one lens and the resulting scope picture is cropped only 25 pixels on each side, not to mention there is no change to lamp power needed to light each format - if you have 14FL in flat at 95% power you have 14FL in scope at 95% power. With a fixed height screen the scope image that uses 20% less chip area (and therefore less light) is projected onto 30% more screen area - in this case the math says scope needs almost 60% more lumens than flat. I definitely prefer fixed height and deal with the resulting hassle of ensuring proper light levels.  |  IP: Logged Lyle Romer Phenomenal Film Handler Posts: 1400 From: Davie, FL, USA Registered: May 2002 posted 06-12-2008 12:10 PM                     Are the lenses set to zoom in for flat or do they set up the auditoriums to cut off the sides of scope (since scope is 50 pixels wider than flat)  |  IP: Logged David Zylstra Master Film Handler Posts: 432 From: Novi, MI, USA Registered: Mar 2007 posted 06-12-2008 12:49 PM                     AFAIK the practice is to simply crop scope by 50 pixels on the width - the lenses are not true zoom lenses so the picture has to be refocused when you resize. Don't forget that with 35mm today there are many screens that end up cropping flat height and/or scope width in order to line up both formats on the same screen so cropping 50 pixels is not too bad in comparison. And if I was ever stuck with fixed width screens I would prefer to have no one touching the lenses - too much margin of error for a bad presentation due to someone forgetting to resize the picture.  |  IP: Logged Mike Renlund Film Handler Posts: 71 From: San Francisco Registered: Feb 2008 posted 06-13-2008 06:56 PM                     In digital cinema, the best movable masking is vertical. In flat, you use the whole vertical range of the DLP chip (Zooming out a bit to gain the 50 or so pixels in the horizontal aspect). Then for scope, you are using only 858 pixels in the vertical, so you just have the masking close up to that point. No, or nearly no lens adjustment needed. No changes in light level either. If you have horizontal moving masking, you are making some lens zooming changes. The TI system makes things quite easy to set things up, so with either style of masking, you can usually make it work.  |  IP: Logged Galen Murphy-Fahlgren Master Film Handler Posts: 405 From: Canton, MI, USA Registered: Oct 2007 posted 06-18-2008 09:51 PM                     David, this somewhat relates to a question that occurred to me when touring your booth, which is, why do they not use an actual anamorphic to create a real scope image? I have my suspicions, but I don't know enough about how an anamorphic image is translated onto grain structure and then translated again into projected light. I'm assuming that since the chip has to have a grid pattern of essentially square elements, that the distortion of the projected image would distort the square/circle element into a sort of squoval, which would look ugly. Maybe you could explain this phenomenon. Regardless, I was disappointed to discover that scope has become the inferior format, because I have a nerdy passion for anamorphic optics.  |  IP: Logged David Zylstra Master Film Handler Posts: 432 From: Novi, MI, USA Registered: Mar 2007 posted 06-19-2008 03:00 PM                     The reason pertains to DCI - "...All spatial conversions are required to be done at an exact ratio of 2:1 in each axis..." the required 1.25X vertical scaling violates this 2:1 requirement. The upside of an anamorphic is light efficiency but the downside is non square pixels - my assumption is that the studios did not want to record an already anamorphicly squeezed image due to the resulting pixel shape. DCI is open to interpretation because the above mentioned statement could be argued that it pertains to the scaling of 2K content to be shown on a 4K projector and not lens configuration (but good luck arguing with the studios). My fear is that we will see more fixed width screens since that becomes the cheaper format to equip (i.e. no extra lenses or motorized mounts). The NATO document addresses this somewhat in saying that lens configuration should be in the hands of the exhibitor and how the image is presented should be up to us - only question is how strongly the studios feel about lens configurations (anamorphics, magnifier or single lens) and they could possibly deny delivery of movies to a projector that does not fit their interpretation of DCI. I've tested anamorphics on our larger screens and they give a good picture; I could not see any issues with the resulting picture, but then again I don't know exactly what to look for.  |  IP: Logged Galen Murphy-Fahlgren Master Film Handler Posts: 405 From: Canton, MI, USA Registered: Oct 2007 posted 06-19-2008 04:26 PM                     So, in your opinion, non-square pixels are a non-issue, and anamorphics are in fact a viable way of presenting scope movies? I just have always been delighted by anamorphics, and feel a sentimental attachment towards scope, I guess.  |  IP: Logged David Zylstra Master Film Handler Posts: 432 From: Novi, MI, USA Registered: Mar 2007 posted 06-19-2008 05:16 PM                     In my opinion the anamorphic gives a picture such that if there are issues with the pixel shape or scaling the general public will not be able to tell (and I don't see any glaring issues). I was told by someone who did some early TDC installs that they were installing anamorphics but I have not confirmed that by anyone running a TDC installed package (anyone here?) I would definitely defer to Mark or Steve's (or other's) opinion on the resulting picture when using an anamorphic and if there are easily detectable issues with the non-square pixels or the vertical scaling.  |  IP: Logged Alan Gouger Jedi Master Film Handler Posts: 501 From: Bradenton, FL, USA Registered: Jul 2000 posted 06-19-2008 06:45 PM                        Once we get 4k displays, scope movies without an anamorphic will not be an issue but throwing away 1/3rd the vertical fill factor on a 2k panel on such a large screen then using the zoom method for a constant height system must result results in screen door effect. Vertical scaling is simple math. With good processing I would not expect any vissible artifacting.  |  IP: Logged Brian Guckian Jedi Master Film Handler Posts: 594 From: Dublin, Ireland Registered: Apr 2003 posted 09-06-2008 04:51 PM                     Out of interest, what do people reckon is the most common way (in 2008) that 2K digital video is being presented on common height screens in the field (remembering that 'Scope is always supposed to be wider than 1.85)? Is the change of ratio predominantly done (a) as Alan says, by zooming the image, or is it accomplished (b) by fixing the image at 2048 x 858 for 'Scope, then simply sitting the 1.85 image within that area to yield just 1587 x 858 for 1.85? I have in fact seen the latter practice being carried out on rather too many occasions on this side of the Atlantic - I was wondering what the "standard" practice was (if one could say there is one). (Am also assuming the use of anamorphics is very limited across the current total of installed digital screens).  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 09-06-2008 08:44 PM                     It kinda depends on the manufacturer of the equipment as to how it is done. Christie swings in a 1.26X magnifier lens for scope and BARCO has zooms(some motorized) with overlapping ranges... I have one BARCO using an ISCO anamorphic... the anamorphic eats up the most light by far... about 8 fl to be exact... and looks a tad bit soft. You also end up with rectangular pixels which is a DCI no-no. The Christie Magnifiers are of extremely high quality and not all that expsneive but do eat up some light. Mark  |  IP: Logged David Zylstra Master Film Handler Posts: 432 From: Novi, MI, USA Registered: Mar 2007 posted 09-06-2008 11:55 PM                     quote: Mark Gulbrandsen the anamorphic eats up the most light by far... about 8 fl to be exact My testing with anamorphics did not show any loss - the straight math showed me that the lumens required to give me 14FL for flat would give me 11.3FL for scope, real world measurements showed 11 FL for scope (my tests were with the Christie and Isco anamorphic). quote: Brian Guckian I was wondering what the "standard" practice was Many fixed height screens were set up with a single lens solution, currently all these installs are being converted to display each format with full pixel count; but I think in 2008 there are a significant number still scaling flat down to fit the scope height. The "standard" practice in the States is going to be that each format is shown un-scaled, the method is up to the exhibitor/integrator (i.e. magnifier lens, motorized zoom, etc). quote: Mark Gulbrandsen not all that expsneive Unless there was a price drop recently the cost of the WCL lens plus motorized mount adds almost 50% to the lens cost.  |  IP: Logged Brian Guckian Jedi Master Film Handler Posts: 594 From: Dublin, Ireland Registered: Apr 2003 posted 09-07-2008 01:50 PM                     Thanks - useful to know how this is panning out. One also longs to see the end of the verboten common width screen configuration in cinemas...even if it "suits" current digital display technologies!  |  IP: Logged

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