A DVD or Blu-ray disc is a pretty neat and compact way of storing a film. From an aesthetic standpoint I have two quibbles: 1) the information is lossily compressed (albeit imperceptibly); 2) playing the disc requires a computer to decode the stored data and send data to the display. Film projectors
do not suffer from either of these quibbles, but are extremely bulky.
So my question is: "could a movie be stored uncompressed and playable merely by projecting light through it, but in a media as portable as a DVD?". Of course, given how cheap DVD players are, this makes for an over-engineered/unnecessary yet elegant invention.
First consider frames of a movie stored as tiny microfiche sized images. A DVD sized disc has a surface area of approximately 110cm². If the images were standard microfiche size (1cm²), that would fit about about 4 seconds of movie. If the images were instead 1mm², that would fit about 6 minutes of movie. I don't think it's practical to get images much smaller than 1mm² while retaining full-HD resolution (approx 1000x2000 pixels), especially since 1/1000th of a mm is close to the wavelength of light.
So instead of images, how about diffraction patterns that form images at a particular distance when illuminated by a laser? If we just use single layer diffraction patterns, we run into the same limits as the 1mm² microfiche images. But if we use a 1mm³ stack of diffraction gratings (i.e. a hologram) instead, we can easily fit in 60 minutes or more of movie.
I hear you say, "You prolix bastard, this is just a boring old holographic storage disc then, here's a wikipedia link for ya!". Yes, this is a holographic disc but works in a slightly different way to typical holographic discs.
As I understand it, a typical holographic disc requires the reading laser beam to change angles to squeeze out all the juicy data stored in the hologram. This is a great way of storing terabytes of data, but not suitable for the purposes I had in mind: i.e. a simple set-up of three stationary lasers (red, green, blue) firing at a rotating disc.
What I have in mind is all the holograms that encode the various frames/images are 'overlapping'. So for each frame of the movie, the three lasers are aimed toward a unique point (e.g. of size 10µm²) on the surface of the disc. The light is diffracted and diverges through the various layers of the holographic disc to come out through the other side of the disc through a square of 1mm². Now each of these 1mm² squares must overlap the neighboring squares to fit in the several hundred thousand squares necessary to fit a movie.
I'll try a cross-section illustration with ascii art:
.__\ /__\ /
In this illustration the two carrots (^) represent two adjacent points where the laser light enters the holographic disc, the slashes (\) represent the diverging path of light, and the line (___) at the top represents two overlapping diffraction pattern squares.
The light would continue to diverge from the disc until it hits a screen where it forms the image that can be viewed.
I have no idea how difficult it would be (if indeed possible) to pack in the overlapping holographic information to make the images. I think the amount of information present in the images of the movie would be a few hundred gigabytes, whereas the amount of information packed into the holograms would need to be much larger e.g. several terabytes.
So, in effect, the laser light interacting with all the extra bits of information in the hologram make a 'passive' decoding device.
to summarize the idea:
-use a holographic disc to store normal (flat) images of a movie.
-beam three stationary lasers (red, green, blue) at a point on a rotating disc (like a typical DVD player)
-the laser light diverges through the holographic disc and forms an image on a screen distant from and parallel to the disc.
OK, this may be completely impractical (insane?) but it may be, at the very least, a fun little gizmo in a sci-fi movie. And if we're using it for a sci-fi movie, it could be a sphere rather than a disc.-- xaviergisz,
Sep 28 2009
Here's a monchrome version [xaviergisz, May 02 2016]
Diffractive Optical Element
https://www.materia...ive-optical-elementYou can buy one here for 12 (currently out of stock) [xaviergisz, May 02 2016]
You prolix bastard, get out of my head!-- phoenix,
Sep 28 2009
The limiting factor is probably going to be the energy density at the point of focus of the lasers.
To get a bright, sharp image, the lasers will be piling a lot of power into a very small area of the disc.
Film projectors get round heating effects by moving on one frame many times a second; so each cell only gets a momentary exposure to the full energy of the light source. And even so, a strip of film is noticeably warm when it winds onto the takeup reel.
Video projectors filter out as much of the IR as possible, and have elaborate cooling strategies for the LCD shutters.
This idea, while interesting, probably isn't scalable. At the beam energies required for effectiveness, the disc may not actually melt, but it will probably degrade quite fast.
[+] for some thoughtful design, though.-- 8th of 7,
Sep 28 2009
good points 8th.
I had envisaged that the projected image would be only a few centimeters wide. As a portable media player the projected image could be viewed directly on the screen. For larger applications the image would project onto a CCD which would then transmit the image to a screen. Alternatively a very faint image is projected onto a large screen made of a, yet to be invented, photomultiplier material which increases the image brightness.
Since this is in the realm of sci-fi, the disc could be made of diamond and the diffraction pattern of a high melting point material (e.g. iridium). Diamond being very scratch resistant and an excellent thermal conductor.-- xaviergisz,
Sep 28 2009
For this to make sense, the recording platform would have to store the picture directly onto the disc, or onto some analogue precursor. Otherwise you would be storing digital data in an analogue fashion, which is a lossy procedure all by itself.
On the other hand, i noticed a tendency towards weirdly degraded pictures in depictions of future playback technology, so maybe your idea feeds a trend.-- loonquawl,
Sep 29 2009
I suppose you could say the image data is stored in a quasi-analogue fashion. I think if the hologram is of sufficiently high quality, the resulting image will be displayed to the same level of reproduction a TV screen can produce. What fundamental limitations of a hologram make this impossible?-- xaviergisz,
Sep 29 2009
//A DVD or Blu-ray disc is a pretty neat and compact way of storing a film. From an aesthetic standpoint I have two quibbles: 1) the information is lossily compressed (albeit imperceptibly); 2) playing the disc requires a computer to decode the stored data and send data to the display. Film projectors do not suffer from either of these quibbles, but are extremely bulky.//
Laserdisc also does not suffer from either of these quibbles. In a sense, your idea does for film what laserdisc did for video.-- spidermother,
Jan 20 2012