I was curious about how these projectors are able to project images up to these huge displays with such a crisp and high-quality definition. What resolutions are these films being filmed / played at? These are the questions I have lol
Thanks!
In: Technology
Old-school film projectors could display at the distance/size because they used extremely bright xenon-filled bulbs inside the projector housing. All complexities aside, film was run in front of these extremely bright lights at 24 frames per second (for standard, 35mm theatrical film). Couple that with having expertly calibrated lenses, and there you go – a damn good picture on a screen.
Think of it like a shadow puppet. The better and brighter the light you shine on your hand, the “crisper” and darker the puppet image will be on a wall. Obviously this doesn’t take into account color grades and the like, but for ELI5, the answer is “the lights are bright as hell.”
Source: Old school film projectionist for many years.
The crispness of the picture is actually very similar to what you might have at home. A cinema projector has a light blub inside that helps shine the movie onto the big screen. Your projector at home also has a light bulb but it’s just not as strong as the light inside the cinema projector.
The stronger the light bulb the bigger the movie can be. But the crispness is actually very similar to what you see at home. The light bulb inside the cinema projector is so strong that it needs to be cooled down or it could create a fire. So upstairs in the projection room, the cinema will have special tubes that suck the hot air out of the projector and keep it cool. This is why you can’t have a cinema projector at home.
They also cost more than mummy and daddy can afford.
I work (currently furloughed) at a movie theater as the regional tech. Biggest difference between theater image and home image is bit depth and compression of the file. Most DCP’s (movies) for 2k film are 120gigs.
Also, each projector is color calibrated often so color reproduction should be spot on.
Of course the projectors are bigger, make more noise, require lots of cooling. Oh, the sound in the theater is calibrated often as well, at least at my theaters.
Standard digital movie projectors are 2k which is a little more than 1080p. The picture looks so good because the projector is colour calibrated for accuracy to a standard and the theater is blacked out to maintain contrast ratio.
The digital film is encoded in dci-p3 colour which is a bigger range of colours than TV broadcast standard of rec 709. Also the digital movies in theatres are totally uncompressed.
Basically digital theatres meet every technical standard to high degree without cutting any corners.
Home projectors and TVs cut a bunch of corners like using 6 bit decoding chips and heavily compressed video streams that destroy detail. Overall resolution isn’t as important as the other factors because there are limits to keeping video sharp anyway such as lens resolution and motion blur.
4K is just a marketing term that attracts people because bigger numbers make sense to people. Content providers could provide a bigger quality bump by providing higher bitrate streams.
“They” say the equivalent resolution of 35mm film is something like 5,600 × 3,620 pixels.
Most digital projection theaters are 4k, is 4096×2160. So film still has it beat out.
If you are wondering how the cinema projectors differ form the ones we use at home, this is how it differ.
The cinema projectors are much more brighter because they a have to project on a larger screen . They have better optics (lenses) . The resolution is mostly comparable, older one 2k -DCI and the newer ones 4k-DCI. A lot of home projectors are UHD which is very close to 4K DCI.
The most important difference is its ability to show vastly more colors and subtitle differences in tones than what a regular home projector is able to do. Also the source material is of much better quality.
Non ELI5 explanation :
Movie Theater films are mastered at 4k DCI resolution in a DCP-3 color space with very little compression. The projectors are designed to project this Image very faithfully.
Media for home are regularly created at UHD in rec 709 and is highly compressed. This is vastly inferior to the theater master. Unfortunately most of the sub $2000 k home projectors don’t even project this with the full color gamut. A few Epson 3 LCD 1080 projectors are an exception.
I’m not a projectionist but I’ve spoken with some people who work with these projectors, and while I don’t fully understand much of it I can give you a rough idea of how projectors work in modern cinemas.
Most cinemas have transitioned to digital projectors many years ago (with the exception of true IMAX and other special film formats). They’re huge, extremely expensive projectors with water cooling and a server that goes with it. The server contains the DCP which is a huge and complex file structure that contains the image and sound data. The projectors usually have a 1998 x 1080 resolution (called “2K” with a 1:1.85 ratio) and a bit depth of 10, though some bigger cinemas are starting to buy 4K projectors, and I imagine that soon it will become the norm. But transitioning to 4K isn’t cheap so smaller cinemas are holding onto their 2K systems. Especially with smaller screens in smaller rooms, 2K works fine and the benefit of 4K won’t be very obvious unless you’re in the very front rows (which sucks anyway).
The most obvious difference between cinema projectors and what you’d get for your home is the light output. The further away the screen is, the bigger the image can get, but the more light you will need. This however produces a LOT of heat and needs a lot of cooling. The bulbs are incredibly expensive and have a limited life span, so smaller cinemas usually dial down the bulb brightness to save some costs and extend the life of the bulb. But this of course results in a duller image. I guess there are regulations in place to prevent cinemas from doing this as distributers want to have control over the experience, but I’ve heard it’s common practice to dim the bulb.
So all in all, the resolution of these projectors is nothing fancy, but of course they have better optics and the projection screen itself is much more reflective (it has little shiny specs inside that help it reflect more light towards the audience but not towards the side). This allows the room to be darker while the screen is brighter. Combine this with high bit-depth images with no visible compression, good quality color reproduction, a ton of light, and you get a very clean looking image.
Film doesn’t have a pixel resolution as such. The size of the silver grains determines the quality of the image and that depends on film type and development. At highest quality you could get something around 200 lines per millimetre. A line in that context is a transition from black to white so that would need two digital pixels. Nevettheless, on the largest cinema film, 70mm, thats around 14000 lines across the frame but that would not necessarily be reasonable because other factors come into play. On top of that, the images are formed differently with overlapping dye layers rather than separate RGB sensors in an array so comparisons are not directly transferable.
It seems that you got your explanation. If you have any more questions I invite you to post on r/cinemaengineering 🙂
Not an EL5 comment:
Cinema projectors are absolutely brilliant pieces of engineering. In a 4k DLP projector, there are more than 24.9 millions tiny mirrors that reflect the RGB light towards the lens. Each of them is controlled separately at minimum 60/120 times a second. The bulb in them can be even higher than 7kw working from thousands of volts AC (to start the electrical arc) and then goes down to around 20v DC (to keep the arc).
Anyway, I’m quite bad at explaining this as I’m absolutely amazed by the engineering behind the cinema.
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