Film-Tech Cinema Systems
Film-Tech Forum


  
my profile | my password | search | faq & rules | forum home
  next oldest topic   next newest topic
» Film-Tech Forum   » Operations   » Digital Cinema Forum   » Why was DCI designed as neither common width or common height (Page 1)

 
This topic comprises 2 pages: 1  2 
 
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      Profile for Lyle Romer   Email Lyle Romer   Send New Private Message       Edit/Delete Post 
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      Profile for Louis Bornwasser   Author's Homepage   Email Louis Bornwasser   Send New Private Message       Edit/Delete Post 
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      Profile for David Zylstra   Email David Zylstra   Send New Private Message       Edit/Delete Post 
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      Profile for Lyle Romer   Email Lyle Romer   Send New Private Message       Edit/Delete Post 
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      Profile for David Zylstra   Email David Zylstra   Send New Private Message       Edit/Delete Post 
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      Profile for Mike Renlund   Email Mike Renlund   Send New Private Message       Edit/Delete Post 
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      Profile for Galen Murphy-Fahlgren   Email Galen Murphy-Fahlgren   Send New Private Message       Edit/Delete Post 
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      Profile for David Zylstra   Email David Zylstra   Send New Private Message       Edit/Delete Post 
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      Profile for Galen Murphy-Fahlgren   Email Galen Murphy-Fahlgren   Send New Private Message       Edit/Delete Post 
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      Profile for David Zylstra   Email David Zylstra   Send New Private Message       Edit/Delete Post 
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      Profile for Alan Gouger   Author's Homepage   Email Alan Gouger   Send New Private Message       Edit/Delete Post 
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      Profile for Brian Guckian   Email Brian Guckian   Send New Private Message       Edit/Delete Post 
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      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
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      Profile for David Zylstra   Email David Zylstra   Send New Private Message       Edit/Delete Post 
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      Profile for Brian Guckian   Email Brian Guckian   Send New Private Message       Edit/Delete Post 
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! [Mad]

 |  IP: Logged



All times are Central (GMT -6:00)
This topic comprises 2 pages: 1  2 
 
   Close Topic    Move Topic    Delete Topic    next oldest topic   next newest topic
 - Printer-friendly view of this topic
Hop To:



Powered by Infopop Corporation
UBB.classicTM 6.3.1.2

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.

© 1999-2020 Film-Tech Cinema Systems, LLC. All rights reserved.