Film-Tech Cinema Systems
Film-Tech Forum ARCHIVE


  
my profile | my password | search | faq & rules | forum home
  next oldest topic   next newest topic
» Film-Tech Forum ARCHIVE   » Operations   » Digital Cinema Forum   » A few questions about aspect ratio and 2K vs 4K (Page 1)

 
This topic comprises 2 pages: 1  2 
 
Author Topic: A few questions about aspect ratio and 2K vs 4K
Nastia Motovilova
Film Handler

Posts: 30
From: Nicosia, Nicosia, Cyprus
Registered: Sep 2012


 - posted 01-18-2013 04:11 AM      Profile for Nastia Motovilova     Send New Private Message       Edit/Delete Post 
Hi to everyone,

I am trying to clear my head around the flat vs scope format and screen size. Regarding the DCI spec for the 2K aspect ratio, if the ratio for Flat is 1998X1080 and for Scope the ratio is 2048X858,

what are the options that one has to accomodate both the 2K flat & scope formats?

For example, the picture of a flat film would exactly fit in a screen size of 18.5ft X 10ft. A picture of a scope film would fit in a screen size of 23.9 ft X10 ft.

If a 23.9X10ft screen is installed and in this screen we'll watch a flat film, then we'll get the letterbox effect.

If we do the opposite and install a 28.5ft screen and we watch a scope film, we get the pillar box effect.

Is my above understanding correct?

And is this completely unavoidable? If yes, why can't a zoom lens used so that we can get the full screen effect in both flat and scope format irregarding of screen size?

Thanks!

 |  IP: Logged

Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999


 - posted 01-18-2013 04:21 AM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
Zoom lenses are how the industry deals with it. A serious flaw in the zoom lens concept is the light demands are dramatically different between Flat and Scope on adjustable side masking screens (the 10 x 23.9 screen in your example). A better way that has been shunned due to cost is an anamorphic lens for scope (kinda like that previous format...film) as it would negate the need for the zoom (improves format change reliability over time) and would keep the light requirements closer (narrows the difference by half).

 |  IP: Logged

Antti Nayha
Master Film Handler

Posts: 268
From: Helsinki, Finland
Registered: Oct 2008


 - posted 01-18-2013 04:33 AM      Profile for Antti Nayha   Email Antti Nayha   Send New Private Message       Edit/Delete Post 
This is why should install a zoom lens and adjustable masking. The latter is actually a DCI requirement, although sadly it’s becoming more and more popular to ignore it. [Frown]

Traditionally a common image height setup is preferred – that means your screen size is eg. 23.9 x 10 feet to accommodate the widest aspect ratio. Then when you’re projecting 1.85:1 content, you use adjustable side masking to reduce the visible screen area to 18.5 x 10 feet.

Ideally your masking should go as narrow as 1.33:1, or even 1.2:1 to accommodate Movietone silent films. (In the digital world, these are simply pillarboxed 1.85:1 DCP’s.)

Some theatres opt for a common image width solution, where only the top and bottom masking are movable. This might fit some narrow rooms better. However, it’s shunned by traditionalists who tend to feel strongly that Scope image should be larger than Flat, instead of being just shorter.

And some theatres even install four-way adjustable masking, where each of the four sides can be adjusted independently. This can be useful for a specialty venue where a lot of weird old formats are projected.

Edit: Steve beat me to it, and also included some wise words about the anamorphic option.

 |  IP: Logged

Nastia Motovilova
Film Handler

Posts: 30
From: Nicosia, Nicosia, Cyprus
Registered: Sep 2012


 - posted 01-18-2013 04:49 AM      Profile for Nastia Motovilova     Send New Private Message       Edit/Delete Post 
Hi Steve & Antti,

So if I understand correct there are two options available:

to either use an anamorphic lens so when projecting on a screen 23.9 ft X10 ft, we can fit a flat film without getting the letterbox effect? Or is this not the case?

or

use a scope screen i.e. 23.9X10ft and when showing a 1.85 film, it's necessary to use adjustable side masking.

Thanks for your replies!

 |  IP: Logged

Marco Giustini
Film God

Posts: 2713
From: Reading, UK
Registered: Nov 2007


 - posted 01-18-2013 05:11 AM      Profile for Marco Giustini   Email Marco Giustini   Send New Private Message       Edit/Delete Post 
quote: Nastia Motovilova
And is this completely unavoidable? If yes, why can't a zoom lens used so that we can get the full screen effect in both flat and scope format irregarding of screen size?
Because Flat e Scope were designed to be different - particularly Scope was designed to be 'bigger'. If Flat and Scope were the same area on the screen, well, there wouldn't be any purpose for them anymore.

To avoid black bars, you just install a masking.

 |  IP: Logged

Marcel Birgelen
Film God

Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012


 - posted 01-18-2013 06:47 AM      Profile for Marcel Birgelen   Email Marcel Birgelen   Send New Private Message       Edit/Delete Post 
If you go anamorphic in a digital setup for scope, you need to stretch the image vertically.

That will give you more light, since you now use the whole DMD, but it also deteriorates the image quality. With a low quality scaler, you can even end up with ugly scaling artifacts.

 |  IP: Logged

Marco Giustini
Film God

Posts: 2713
From: Reading, UK
Registered: Nov 2007


 - posted 01-18-2013 07:29 AM      Profile for Marco Giustini   Email Marco Giustini   Send New Private Message       Edit/Delete Post 
If you go for anamorphic, the scaling will be done by the TI electronics inside the projector.

 |  IP: Logged

Bajsic Bojan
Expert Film Handler

Posts: 190
From: Ljubljana, Si, Eu
Registered: Aug 2008


 - posted 01-18-2013 12:35 PM      Profile for Bajsic Bojan   Email Bajsic Bojan   Send New Private Message       Edit/Delete Post 
@Nastia

You first need to understand the very basics.

FLAT film and SCOPE film in digital both use square pixels. The one or the other is not 'stretched' or 'squashed'.

In DCI there are two standardized formats:
1.85 (referred to as Flat sometimes) and 2.39 (referred to as Scope)

The numbers represent aspect ratio, correlation between width and height of a projected image. In 1.85, while the image height is 1 unit, the height of the picture SHOULD BE 1.85 units.

Conversely on a 2.39 picture, while the image height is 1 unit, the width of the projected image should be 2.39 units.

Therefore, it is pretty much clear, that a picture that is projected in "scope" IS WIDER than the picture projected in "flat". Not necessarily physically, just imagine drawing equally high giant SQUARES, where you would get ie 4 side by side in 1.85, you would be getting more than 5 equally high squares side by side in 2.39.

If you project all pictures in the same aspect ratio, you will destroy the desired effect of the film maker(s).

In simpler terms: yes, you CAN project all films at 1.85:1, 2.39:1 or even 1.0:1 if that is what you wish. The problem is, this is completely WRONG.
Projecting a 1.85 film filling a 2.39 screen, you are cropping (as in, deleting, loosing, not showing) 20,6% of the image height. Projecting a 2.39 film filling a 1.85 screen, you are cropping 22,8% of the image width.

Your (everybody's) only options are using a masking system if you don't want to show the unused parts of the screen.

 |  IP: Logged

Nastia Motovilova
Film Handler

Posts: 30
From: Nicosia, Nicosia, Cyprus
Registered: Sep 2012


 - posted 01-21-2013 04:15 PM      Profile for Nastia Motovilova     Send New Private Message       Edit/Delete Post 
Hi guys,

Sorry for replying late, I was away for the weekend.

The above clears a lot of confusion. So using adjustable side masking would be the most "right" way of projecting the images as they were intended to be previewed.

quote: Bajsic Bojan
Projecting a 1.85 film filling a 2.39 screen, you are cropping (as in, deleting, loosing, not showing) 20,6% of the image height. Projecting a 2.39 film filling a 1.85 screen, you are cropping 22,8% of the image width.
- How are the above figures derived?

- I also imagined that i.e. projecting projecting a flat film on a scope screen using an anamorphic lens, no picture is cropped - as this would be one of the reasons of using the anamorphic in the first place. For example,

http://www.schneideroptics.com/pdfs/projection/home%20theater%20brochure.pdf

using an anamorphic lens I imagined that the effect would be similar as in p3.

Thanks for all the replies.

 |  IP: Logged

Chris Slycord
Film God

Posts: 2986
From: 퍼항시, 경상푹도, South Korea
Registered: Mar 2007


 - posted 01-22-2013 03:00 AM      Profile for Chris Slycord   Email Chris Slycord   Send New Private Message       Edit/Delete Post 
quote: Nastia Motovilova
How are the above figures derived?
I get similar numbers to his by simply looking at a percentage-difference formula.

The percentage change from an original value of x to a new value of y would be:
100 * [abs(y-x)/x]

So if you have a 2.39x1 image that is cropped to 1.85, the change in the ratio of the areas is 100 * [abs(1.85-2.39)/2.39] = 100* [0.540/2.39] = 22.6%

And if you crop a 1.85 image to a 2.39 screen, the change is 100*[0.540/1.85] = 29.2%

Now perhaps my numbers differ from his since I'm using the change in ratio instead of the area contained itself, although I think these would change at the same ratio I gave.

 |  IP: Logged

Nastia Motovilova
Film Handler

Posts: 30
From: Nicosia, Nicosia, Cyprus
Registered: Sep 2012


 - posted 01-22-2013 05:04 AM      Profile for Nastia Motovilova     Send New Private Message       Edit/Delete Post 
Excellent, thank you for the figures and the clarification. I've been learning a lot here on this great forum. [Smile]

I accept that a 1.85 or 2.39 films are to be previewed as they were intended, however what confuses me a little is that when reading up different articles, some claim that an anamorphic lens should be used (or should be used when possible), for example in the pdf "Optimizing Lens Choices for Digital Cinema" by Schneider.
Do you know why this may be the case?

Also, what would be the options for incorporating masking, are there
many ways of doing this? I've visited a cinema where curtains were used. Is curtains the only way to go?

Thanks for all the replies.

 |  IP: Logged

Antti Nayha
Master Film Handler

Posts: 268
From: Helsinki, Finland
Registered: Oct 2008


 - posted 01-22-2013 05:20 AM      Profile for Antti Nayha   Email Antti Nayha   Send New Private Message       Edit/Delete Post 
The anamorphic lens is really just an alternative to a motorized zoom lens. It’s a popular choice for high-end home theatre enthusiasts who want a common-height image screen just like the best cinemas out there. In such a case, the native screen shape is 2.39:1 – but they will still need adjustable side masking, otherwise they will get black bars on the sides when running content in a narrower ratio.

Masking and curtains are two different things (although there are solutions that combine them into one). The classically preferred setup has black adjustable masking to deal with the various aspect ratios, and a beautiful curtain on top of that mainly for aesthetic/showmanship reasons. Sadly, curtains are getting very rare, and there are more and more screens without any masking at all (even though masking is required by the DCI as I mentioned).

 |  IP: Logged

Bajsic Bojan
Expert Film Handler

Posts: 190
From: Ljubljana, Si, Eu
Registered: Aug 2008


 - posted 01-22-2013 08:15 AM      Profile for Bajsic Bojan   Email Bajsic Bojan   Send New Private Message       Edit/Delete Post 
I thought about my previous calculation as it just didnt seem right so i redid them and the answer is that when playing 1.85 content filling a 2.39 screen completely (without pillarboxing), you are cutting 22.5% of image height.

When playing back 2.39 content filling a 1.85 screen completely (without letterboxing), you are cutting 22.5% of image width.

 |  IP: Logged

Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999


 - posted 01-22-2013 09:35 AM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
To clarify the statement:
quote: Antti Nayha
The anamorphic lens is really just an alternative to a motorized zoom lens.
While it is an alternative, they are NOT equivalent. The anamorphic lens also recovers approximately 23% of the light that would be lost by showing blank pixels on the ceiling/floor and puts that light back on the screen. They only make sense for constant height screens. They make progressively more sense, financially, as one moves towards higher wattage lamps such as 4.5-7KW since they can often reduce the lamp demand for Scope and move one to a smaller wattage but with proper light.

 |  IP: Logged

Nastia Motovilova
Film Handler

Posts: 30
From: Nicosia, Nicosia, Cyprus
Registered: Sep 2012


 - posted 01-23-2013 09:15 AM      Profile for Nastia Motovilova     Send New Private Message       Edit/Delete Post 
quote: Bajsic Bojan
Projecting a 1.85 film filling a 2.39 screen, you are cropping (as in, deleting, loosing, not showing) 20,6% of the image height. Projecting a 2.39 film filling a 1.85 screen, you are cropping 22,8% of the image width.
Just to clear this in my head, this is when using an anamorphic lens,correct?

Also, as I understand, showing a scope film in a flat screen, are we essentially forced to crop the sides of the scope to fit the width of the flat screen? Using my example above, playing a scope film on a 18.5X10 ft screen, we would lose 2.7ft on each side of the screen - where otherwise the picture would have extended?

 |  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.