Using 4K Projectors with ‘Scope’ Screens
A few months ago Art received a message from a visitor of the Projector Reviews web site that discussed the implications of using one of the Sony 4K projectors for displaying wide aspect ratio ‘scope’ movies with a constant image height (CIH) setup. This blog includes the contents of the message we received as well as some background and discussion on the subject of using a ‘Scope’ screen, with an aspect ratio of 2.35:1 or 2.40:1, instead of the traditional HDTV aspect ratio of 1.78:1 (i.e., 16 x 9).
Over the more than a century of commercial cinema productions, the movie studios have used dozens of different film formats, with differing aspect ratios (Wiki is HERE). Over the past few decades the presentation formats (i.e., what is seen in the movie theater) used in North America seems to have settled down to just two presentation formats, with some small variations, being used for the vast majority of commercial movie productions. The vast major of Hollywood productions are now presented in either 1.85:1 aspect ratio, known as the Cinema Standard format, or in a widescreen (‘scope’) format with an aspect ratio of at of near 2.39:1. As indicated above, these are the presentation formats and not the formats captured on film by the movie camera. The transition from film to digital, for both commercial cinema cameras and projectors, has placed additional practical constraints on the aspect ratios being used for commercial movies.
The consumer standard for HDTV uses a aspect ratio of 1.78:1 (i.e., 16 x 9) which is close to the cinema standard 1.85:1 format. Such movies provided on Blu-ray Disc, for example, may be slightly cropped by removing approx. 2% of the image from each the right and left edges of the 1.85:1 frame to produce the HDTV 1.78:1 format. The alternative would be to add thin black bars to the top and bottom of the 1.78:1 HDTV image to create a 1.85:1 image format (generally called letterbox). The bottom line is consumer HDTVs and projectors with a 1.78:1 apect ratio work well for displaying commercial movies using the cinema standard format.
The real issue comes once we go from the cinema standard format up to the ‘scope’ widescreen format. Several companies have offered competing cameras and projection system to the cinema industry that have used aspect ratios in the range of 2.3:1 to 2.4:1. The early CinemaScope(TM) and Panavision(TM) systems used an aspect ratio of 2.35:1. However, the modern version of both of these popular widescreen systems have evolved to a 2.39:1 aspect ratio.
Up until very recently all commercial theaters used film projectors and widescreen ‘scope’ movies (e.g., using CinemaScope or Panavision) captured the image on a standard film frame but with the image compressed in the horizontal direction in order to fit it onto the film’s more squarish frame. The theater would, when projecting such ‘scope’ movies, the place an anamorphic lens in the projector’s light path to stretch the image horizontal to restore the image to the correct widescreen proportions.
Home theater owners now have three basic options for how to best display HDTV programming (including movies in cinema standard format) as well as widescreen ‘scope’ movies. Today’s highest quality, and widely available, source for movies in HD resolution is Blu-ray Discs. When widescreen movies are recorded on Blu-ray Discs the video content is presented in a letterbox format with black bars across the top and bottom of the image. If you take a look at the fine print on the rear cover of your Blu-ray Disc collection you will find some widescreen movie titles (e.g, Night at the Museum, Enemy of the State, etc.) are provided in 2.35:1 format while other widescreen movie titles (e.g., Harry Potter and the Chamber of Secrets, Cowboy and Aliens, etc.) are provided in 2.40:1 format. The currently Blu-ray Disc standard does not support using an anamorphic compressed format as the means of distributing widescreen ‘scope’ movies and it is currently unknown what will be supported, in this regard, by the upcoming Blu-ray 4K/UHD standard.
Basically there are the following three ways in which consumers using a HD or 4K/UHD video projector, with a 1.78:1 aspect ratio, in their home theater (HT) can accommodate both the standard HDTV format as well as the widescreen ‘scope’ format.
- Use a HDTV standard 1.78:1 (16 x 9) screen where the full screen width and height is used to display HDTV and cinema standard format movies and widescreen scope movies are displayed letterboxed, with black bars across the top and bottom of the screen. Some HT owner go one additional step and use a 16 x 9 screen with horizontal masking panels that can be moved (either motorized on manual) into place to form a widescreen ‘scope’ format opening across the central area of the screen. Thus with this setup a widescreen image (e.g., with 2.4:1 aspect ratio) will be projected using the same image width as used for the 1.78:1 HDTV images. This is a constant image width (CIW) setup, since the image width does not change when going between normal HD and ‘scope’ image formats.
- Use a ‘scope’ format projection screen with an aspect ratio between 2.35:1 and 2.40:1, then when projecting standard HDTV format (i.e., 1.78:1) programming the full height of the screen will be used but only the central ~75% of the screen width will be needed. Some HT owners add a masking system using vertical panels to cover the right and left sides of the screen to create a 1.78:1 central opening for displaying HDTV broadcasts and movies in (close to) cinema standard format. When displaying a widescreen ‘scope’ movie the projector’s zoom lens is used to enlarge the image size so that the image fills the full width and full height of the ‘scope’ format screen. In this case no masking is needed since the screen closely matches the 2.35:1 or 2.40:1 aspect ratio of the widescreen movie. This scheme for using a ‘scope’ format projection screen is referred to as a constant image height (CIH) approach. This is the “Zoom” approach for CIH and has been popular in recent years as a few projector manufacturers (started by Panasonic) have added a lens memory feature to certain of their projectors. With lens memory the settings for Zoom, Focus, and in some cases Lens Shift, can be stored and easily recalled to automate switching the projector to display multiple aspect ratios. Panasonic has now been jointed by Sony, JVC and Sharp offering lens memory on some of their popular projector models. Even without a lens memory feature, the “Zoom” approach for CIH is practical, if a little inconvenient, for use with projectors have power zoom, focus and ideally also power lens shift.
- Use a ‘scope’ format projection screen with an aspect ratio between 2.35:1 and 2.40:1, then when projecting standard HDTV format (i.e., 1.78:1) programming the full height of the screen will be used, but only the central ~75% of the screen width will be needed. Some HT owners add a masking system using vertical panels to cover the right and left sides of the screen to create a 1.78:1 central opening for displaying HDTV broadcasts and movies in close to a cinema standard format. When displaying a widescreen ‘scope’ movie either the projector must have internal processing or an external video processor must be used to stretch the widescreen image to use the full height (or nearly so) of the projector’s display chip and then an external anamorphic lens is slid into place just in front of the projector’s lens to horizontally stretch the image to restore the correct proportions to the image. For example, if the projector is using display chip(s) with a HDTV standard 1.78:1 aspect ratio and the widescreen image has a 2.35:1 aspect ratio then video processing would be used to digitally apply to the image a vertical stretch of (2.35/1.78 = 1.32) 32% in order for the image to use the full vertical resolution of the display chip. The external anamorphic lens would need to horizontally expand/stretch the image by the same 32% percent to restore the original image geometry. As a practical matter most anamorphic lens being offered to consumers provide about a 33% horizontal stretch which works well for movies recorded using using either 2.35:1 or 2.40:1 formats.
The advantage of using a anamorphic lens over the first two methods described above is the projected image will be brighter and with increased pixel density in the vertical direction (since all of the pixels of the projector’s display chip(s) are being used.
However, there are also disadvantages associated with using the anamorphic lens approach. First: this is the most expensive approach for a consumer to support use of a ‘scope’ format projection screen as the cost of a quality anamorphic lens, plus the mechanical slide assembly, runs into thousands of dollars. Also if the projector does not include the necessary digital video processing to vertically stretch the image, then a stand-alone video processor will been to be purchased. Second: the video processing to vertically stretch the image can introduce digital scaling artifacts, but this is becoming less of an issue as manufacturers have generally improved digital scaling performance in recent years. Third: the anamorphic lens can optically degrade the image by introducing color fringing (chromatic aberration), introduce non-uniform focus across the image, and/or create geometric distortions. The more expensive anamorphic lenses tend to be better quality and cause less of these optical issues. There are also constraints when using an external anamorphic lens that required the projector’s own lens to be set for a long throw so as to minimize the size of the light cone coming from the projector the projector’s lens configuration must be suitable for use with an external lens.
Displaying ‘Scope’ Movies with 4K/UHD Projectors
After my above long-winded background, I’ll now get to the subject of the message that Projector Reviews received from Cameron Thorne. Cameron’s input was related to using one of the Sony 4K/UHD projectors (such as the VPL-VW1000Es or the newer or VPL-VW600ES) for displaying a video material with a range of different aspect ratios. These Sony 4K projectors are unique in the consumer market in that they are using display chips with a native resolution of 4096 x 2160 which produces an aspect ratio of approx. 1.9:1. This is the same resolution and aspect ratio that Sony uses for their 4K projectors found in commercial movie theaters around the world, but is greater then the consumer Ultra-HD standard of 3840 x 2160 resolution (with 1.78:1 aspect ratio, the same as for HDTV). In normal operation these Sony projectors will display normal HD or UHD video, with its 1.78:1 format, by using only 3820 of the available horizontal 4096 pixels. These projectors also have lens memory and the zoom method would be the normal means for displaying widescreen ‘scope’ movies when a 2.35:1 or 2.40:1 projection screen is being used. However, some HT owners, lucky enough to own one of the superb 4K/UHD projectors, are also proponents of using an anamorphic lens, They generally are promoting the anamorphic lens alternative primarily as a means of achieving the maximum possible image brightness when the projector is used with a larger (i..e, wider) ‘scope’ screen.
Below is what Cameron Thorne had to say on this subject in the message received by Projector Reviews:
I have been doing some math, and I think the Sony engineers have hit on something just about magical for constant-image-height users, and I haven’t really seen it reported on. I wonder – if I am not way wrong about how it works – if you might be able to mention it in your upcoming reviews or blog posts.
The “magic” I referred to comes in the aspect ratio of the 4K panel combined with their more power hungry eco mode than most, which solves a really neat problem. Commercial 4K is 4096×2160, which is about 1.9:1. Basically zero content is going to use the entire panel at once, but this is a GOOD THING. They have struck an engineering balance here that basically makes these the perfect projectors for >2.35:1 screens using lens memory without an external anamorphic lens.
Let me explain my thinking…
The big problem with using super-wide screens with lens memory is the light output drops considerably. A 1920×1080 panel on a 2.4:1 blu-ray is using something like 1920×800 – 74% of the panel. Lets assume in a zoom lens setup you put the 2.4 setting at the widest angle for no additional light loss from the zoom lens. Now your constant-image-height setup is using 35% more surface area at 2.4:1 than it does at 16:9. 74% of the light across 135% of the area = 55% of the luminance on screen than when watching full-panel 16:9 material in constant-image-height setup. In reality it is not quite that bad, because the 16:9 material suffers from zoom lens loss, but still it’s a big drop.
Anamorphic lenses on sleds mitigate the panel utilization problem by using the full panel all the time, but they still suffer from the problem of having the surface area change. There are other solutions, like constant area, but all of that requires special calibration too.
On this 1.9:1 4K panel, ALL aspect ratios are somewhat diminished from full light output because of lack of full panel usage ever, but watch what happens when we combine zoom lens loss (I am guessing at these based somewhat on your reviews).
2.39:1 4096×1707 = 79% panel utilization …1.35X screen area 0% lens loss 59% of max luminance
2.35:1. . 4096×1743 = 81% panel utilization ..1.32X screen area .. ~0% lens loss . 61% of max luminance
1.85:1 .. 3996×2160 = 98% panel utilization ..1.04X screen area .. 8% lens loss .. 87% of max luminance
*16:9 … 3840×2160 = 94% panel utilization ..1.00X screen area .. 9% lens loss .. 85% of max luminance
4:3 …….2880×2160 = 70% panel utilization .. 0.75X screen area . 9% lens loss ….85% of max luminance
(*made-up reference aspect ratio point for luminance percentages to base upon)
Now look what happens when we turn eco mode on for “flat” aspect ratios and leave it off to run full power for “scope” aspect ratios. (assuming 30% light loss in eco mode on the 1100ES – the 600ES probably follows the 40% rule like the others that use a similar light source):
2.39:1 .. 4096×1707 = 79% panel utilization …1.35X screen area … 0% lens loss .. 100% bulb power 59% of max luminance
2.35:1 .. 4096×1743 = 81% panel utilization ..1.32X screen area .. ~0% lens loss . 100% bulb power 61% of max luminance
1.85:1 .. 3996×2160 = 98% panel utilization …1.04X screen area … 8% lens loss … 70% bulb power 61% of max luminance
*16:9 …. 3840×2160 = 94% panel utilization …1.00X screen area … 9% lens loss …70% bulb power 60% of max luminance
4:3 ………2880×2160 = 70% panel utilization ..0.75X screen area … 9% lens loss ….70% bulb power ..59% of max luminance
(*made-up reference aspect ratio point for luminance percentages to base upon)
That’s a MAXIMUM luminance deviation of 3% across all aspect ratios in a constant-image-height setup, using creative control of lens memory, eco mode, and making use of the unique panel shape. That is something even the A-Lens crowd cannot claim without getting into manual iris settings. I am not sure if iris can be programmed into memory, but they have other effects such as contrast. The math on this seems too good not to be coincidence. It seems engineered to be beautiful. The Panamorph guys can’t be too happy about this.
Basically, on the VW1000ES/1100ES you get the same foot-lamberts on screen all the time in every aspect ratio using only internal features on the projector, and still letting dynamic iris be used. I am not aware of any other projector that can make that claim. Of course there is a downside to 4K panels, and that is you can kiss your perfect pixel mapping goodbye on the vast amount of 1080p content that you have today. 4K source materials solves that, but most people will want to continue enjoying their blu-rays, and that means video scaling for EVERY aspect ratio. I hope the scaler is good. Do the Sony projectors have a non-scaled mode that just quadruples all the source pixels to 3840×2160? It would be no worse than a 1080p projector on the same size screen in that mode, for those who find the scaling bothersome.
Anyway…I thought it was interesting. My numbers are based on various published reports and assumptions, not on actual measurements, so my figures may be wrong. But I thought you guys would find this interesting. Of course some people may want the 16:9 Super Bowl brighter than their movies, and for that they have just to turn eco mode back to full power and they get the brightness back.
(April 9, 2014 – additional material added below)
Below is my own independent attempt to calculate what the different in brightness would be using the zoom method vs. an anamorphic lens with a Sony 4K projector (or any other future 4K projector offering a 4096 x 2160 resolution mode).
If you use a conventional ~1.32X anamorphic lens, such as a Panamorph UH480, that provides a 32% horizontal stretch, is it really worthwhile with the Sony 4K projectors?.
If you use this with a VW500/VW600/VW1000/VW1100 and want to maintain the correct image geometry then you would need to be operating the projector in 1.78:1 mode instead of the projector’s native (almost) 1.9:1 mode. In this case you are still only using 93.75% of the projector’s available pixels. While using the zoom method and when projecting a ~2.35:1 image you could set the projector to electronically zoom the image so as to use the projector’s full 4096 horizontal pixels width but only 1742 vertical pixels or 80.7% of the projector’s available vertical pixels, which means 80.7% of the projector’s total pixels.
So under the above conditions, using a perfect, no loss 1.32 X anamorphic lens would result in a 93.75/80.7 = 1.16 or the image would be 16% brighter when using an anamorphic lens as compared to the optical zoom method. With a more realistic 3% to 5% light loss thru the anamorphic lens then the real world brightness gain might be more like 11% to 13%.
The bottom line for me would be is it really worthwhile to consider using a ~1.32X anamorphic on the Sony 4K projectors or perhaps only consider one that is (2.35/1.9 =) ~ 1.25X where all of the projector’s pixels could be used, which would get you 100/80.7 = 1.24 or a 24% brighter image as compared to the zoom method if an ideal, zero loss, anamorphic lens is assumed or perhaps around a 20% gain in brightness in the real-world, as compared to the zoom method.
If found Cameron’s input interesting and for me the most significant single point of Cameron’s argument is if you are using a Sony 4K projector and IF you can get enough image brightness in Eco mode (low lamp mode) for displaying normal 16 x 9 video then by going to normal lamp mode for displaying widescreen scope movies, the overall image brightness is nearly the same.
Since the Sony 4K projectors, having a native ~1.9:1 (1.896:1) aspect ratio, the gain in image brightness through the use of an anamorphic lens (either 1.32X or even a 1.25X) will be less than with conventional HD projectors, with a native 1.78:1 aspect ratio. Given that a high quality anamorphic lens with a mechanical slide assembly can cost upwards of $5,000, I do question the cost vs. benefits for such an investment.
I feel the only positive point for using the anamorphic lens approach with a Sony 4K projector, or any other 4K projector with a native 4096 x 2160 resolution, is you can get the maximum image brightness possible for the widescreen scope format. Whether you really need that increase in brightness really depends on the screen size and gain, but I would suggest that the zoom method will generally produce an widescreen ‘scope’ image with a quality equal or better than possible with the anamorphic lens method. However, the zoom method will generally provide a little dimmer image. With a 4K projector, with its already very high pixel density, the modest increase in vertical pixel density possible with the anamorphic lens method is no longer a factor with any realistic screen size that would be used with a consumer 4K projectors. The bottom line is I generally agree with Cameron that the zoom method when using a Sony 4K projector in conjunction with a scope screen is a good way to go, at least in the vast majority of cases.
I would note that Sony’s use of a 1.9:1 aspect ratio in their 4K projectors opens the potential for some other interesting alternatives. For example, using a screen with an aspect ratio somewhere between 1.78:1 and 2.40:1 along with a good motorized masking system (one with both vertical and horizontal masking would be ideal) for handling video with different aspect ratios. Such a screen setup could be expensive, but perhaps no more so than the cost of an good anamorphic lens. One benefit this type of screen setup would offer is that it would generally support the largest image size (or close to it) for displaying both 1.78:1 and 2:35 (or 2.40:1) formats that your home theater room can accommodate.