TheaterBlog - The Screen Part I: Choosing an Aspect Ratio
by Anand Lal Shimpi on February 6, 2008 12:00 AM EST- Posted in
- Anand
When I started planning the theater what I didn't want to have was a room with a big TV in it; I could have that anywhere, but for this room I wanted the theater experience. A big part of that meant a large screen, but size was only part of the equation: aspect ratio mattered.
Movies are filmed in a variety of aspect ratios, while current HDTV resolutions measure 16:9 (1.78:1), the same can't be said about movies seen in the theater. Let's have a look at some recent releases and their corresponding aspect ratios:
Rambo - 2.35:1
27 Dresses - 2.35:1
Cloverfield - 1.85:1
Untraceable - 2.35:1
Bucket List - 1.85:1
Juno - 1.85:1
National Treasure: Book of Secrets - 2.35:1
There Will Be Blood - 2.35:1
Mad Money - 2.35:1
That's right, even though we just spent the past several years making the move from 4:3 displays to 16:9/16:10 displays, there's content available in an even wider aspect ratio: 2.35:1.
I don't expect to see widespread movement towards 2.35:1 displays anytime soon since only a subset of movies are filmed in this wide, also referred to as Cinemascope, aspect ratio. That's why, even on a 16:9 display, you get black bars at the top and bottom; you're watching content that's filmed in an even wider aspect ratio.
Keep an eye on the screen the next time you're at the movies; chances are the previews are in a different aspect ratio than the feature. Movie theaters handle various aspect ratios by opening/closing curtains to mask the black bars. There's nothing wrong with the black bars themselves, but projecting black is tough to do. If you move a light absorbing black curtain in the way, you get much better perceived contrast ratio since a black mask is always darker than any black a projector could produce.
As soon as I heard that it was possible to build a home theater with a 2.35:1 screen, I knew it was what I wanted. All logic went out the window and emotion took over: I wanted a superwide screen.
There are a couple of problems you run into with a 2.35:1 screen, the first being that there are no consumer projectors available that will project a 2.35:1 image. The name of the game is 1080p and that's 1920 x 1080, a 16:9 ratio. So how do you get a 2.35:1 image from a 16:9 projector? There are a few ways:
Manually Zoom the 2.35:1 image so it vertically takes up the entire screen. You maintain 1:1 pixel mapping with this method, but you aren't using the full resolution of the projector to display the screen. The projector is still projecting the black bars at the top and bottom of the screen, they are just zoomed off the screen so you can't see them.
Use a video processor to scale the 16:9 image vertically, then use a horizontal expansion lens in front of the projector to stretch the scaled image horizontally. This is referred to as a Constant Image Height (CIH) setup, since both 16:9 and 2.35:1 content are viewed at the same height. Only the width changes and masking systems are sometimes used (like in theaters) to improve the experience.
Alternatively you can use a vertical compression lens which works similarly to #2, except instead of stretching the image horizontally you compress the image vertically. This is known as a Constant Image Width (CIW) setup as 16:9 and 2.35:1 content will be the same width, but the screen height will vary.
The zoom method seemed a bit cumbersome to me, so I started looking at anamorphic lens systems. The CIH/CIW methods made the most sense to me as you are using the full resolution of your projector on visible content, not for projecting black bars. Many 1080p projectors are now coming with built in vertical scalers for CIH setups, not to mention that a HTPC could do the same task without a problem.
I liked the idea of having a fixed height screen with variable width, I figured I'd include a masking system to complete the effect. While 2.35:1 content would take up the full 11 feet of screen, 16:9 content would only be about 100" wide. I'd need automated masks on the sides of the screen to mask off the black bars when viewing 16:9 content, but how hard could that be?
It turns out that 2.35:1 screens with automated masking systems are very expensive. To make matters worse, I wanted to complete the cinematic experience with a slightly curved screen. At the end of the day I was looking at $10K - $20K just for the screen and masking system if I wanted to buy one ready made. I wasn't about to spend that sort of money on something with no modern day electronics in it, so DIY it is.
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Deusfaux - Monday, February 11, 2008 - link
He better be going with a fixed height screen setup.Really, its the best way to go.
BugSmashR - Wednesday, February 6, 2008 - link
Quote:"There are a couple of problems you run into with a 2.35:1 screen, the first being that there are no consumer projectors available that will project a 2.35:1 image. The name of the game is 1080p and that's 1920 x 1080, a 16:9 ratio. So how do you get a 2.35:1 image from a 16:9 projector?"Answer:
Use more than one projector. In fact, a cluster of inexpensive projectors. (raid+projectors?)
I don't know if you've heard of this but HP has a project called Pluribus in the works. Here's a link.
http://www.hpl.hp.com/news/2007/apr-jun/pluribus.h...">http://www.hpl.hp.com/news/2007/apr-jun/pluribus.h...
http://www.hpl.hp.com/research/pluribus/">http://www.hpl.hp.com/research/pluribus/
I am interested if this might be the way to go to get super-wide, super-high resolution projection.
I recently bought an Optoma 1690 DLP projector (1280x768) for $380 and if I can pick a few more I thought I might give Pluribus a try.
yonzie - Saturday, March 8, 2008 - link
That is, in theoru, a really great idea.The problem is that in order to get an uniform picture, you need to calibrate the projectors to give an identical picture. This may be a problem, especially if they are not the same age/brand/model. LCD panels age and the bulbs age fast.
customcoms - Thursday, February 7, 2008 - link
That is an excellent idea, however the software may be a limiting factor (and trust me, you do not want to be writing software to make a projector work).Two summers ago, I had the opportunity to visit NASA Ames, out in Moffett California. They showed us the most impressive visual demonstration I have seen, better than IMAX. Three "high definition projectors, projected on a 25 foot wide by 7 feet tall (aprox. from what I remember), all connected to the third fastest super computer in Silicon Valley. They ran google earth for us, and they could zoom in and out sooo fast it felt like you were bungee jumping over LA. Then they did a flyby of the moon, and finally, the most spectacular thing, a fly by of the Martian surface filmed in high definition. By high definition, I mean 3x 1080p type stuff. STUNNING.
So yes, theoretically, this is a somewhat possible solution, but I am not sure if the software/computing power is available.
MGSsancho - Friday, February 8, 2008 - link
you bring up a good point. But I assume Anand will send HP an email for request for more information and what not. Since Anand will have a rack of equipment, a rack mount server doing these task isn't really out of the question. but you never know till you try. I hope it works. this would be a godsend not just to Anand but all of us. DIY home theater.crimson117 - Wednesday, February 6, 2008 - link
I hate watching content that's stretched in some way.I had some sony dvd player that seemed to stretch everything taller, and for the life of me I couldn't get it to stop doing that.
Personally I'd prefer to see a smaller image rather than stretch it to fit a screen.
Anand Lal Shimpi - Wednesday, February 6, 2008 - link
Ah but that's the point of the horizontal expansion lens: it corrects the distortion caused by the vertical stretch. The end result is a screen that is a full 2.35:1 ratio, just like the source content, without any distortion or black bars :)Houdani - Wednesday, February 6, 2008 - link
So if I understand correctly, you're leaning towards scaling vertically and using a CIH lens to tweak the width of the pixels. Onto a curved screen. DIY style.Yeah, I'm pretty sure I'd get an ulcer trying to make everything just right. Mostly because my pocket book would tell me that I only get one shot. (Yeah, OK. I probably would have run out of money somewhere around buying the lumber for the walls.)
puffpio - Wednesday, February 6, 2008 - link
It doesn't seem THAT hardmedia player classic handles a ton of aspect ratio/scaling things on it's own right now automagically.
I could have a 640x480 (4:3) source video playing in a 1280x600 (2.13:1) desktop resolution on a 16:10 widescreen LCD and it will scale everything just dandy and put the right amount of black bars up when I full screen the video (i have to tell it to correct the monitor/desktop aspect ratio difference)
Starglider - Wednesday, February 6, 2008 - link
I don't understand how scaling then stretching a letterboxed widescreen image can possibly look better. A '1:1 pixel mapping' is already 'using the full resolution of your projector'. There's simply no more image data to display. Stretching the image area out over the otherwise unused pixels is just going to cause blurring as the image is interpolated. It may be an invisibly small amount of blurring with a good scaler, but it certainly can't /improve/ the image quality and might significantly decrease it.