[HN Gopher] Microscopes can see video on a laserdisc
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Microscopes can see video on a laserdisc
Author : zdw
Score : 602 points
Date : 2026-03-07 22:03 UTC (2 days ago)
(HTM) web link (www.youtube.com)
(TXT) w3m dump (www.youtube.com)
| BobMcBob wrote:
| Tech Tangents is one of the best retro channels on youtube but by
| retro I dont mean glorified nostalgia either. Shelby puts a lot
| of work into his videos and likes to showcase what awesome
| engineering went into some of the early tech that was practically
| magic. Love the channel and glad to see it on HN.
| lysace wrote:
| The real fun is on his Twitch channel.
| https://www.twitch.tv/techtangents
| smusamashah wrote:
| So CAV (constant angular velocity) is an encoding format for
| laser disks. When something is written with CAV, it is basically
| analogue data and therefore repeating patterns can be recognized
| on the disk.
| jmkd wrote:
| Not simply repeating patterns, readable text from the credits
| as shown in the video.
| accrual wrote:
| Here's where the text comes into focus, pretty cool:
|
| https://youtu.be/qZuR-772cks?t=1540
| wtallis wrote:
| No, CAV has nothing to do with encoding, and both analog and
| digital formats have used both CAV and CLV and hybrids of the
| two.
|
| The legible text seen in the microscope images happens because
| of the _combination_ of LaserDisc recording a raw and
| uncompressed encoding of the analog video signal, the way that
| LaserDisc used CAV to store an integer number of frames per
| track so that the image data for corresponding on-screen
| locations of subsequent frames would be aligned at the same
| radial position on the disc, and the credits scrolling
| vertically at constant speed.
|
| If LaserDisc had used a digital encoding (especially a
| compressed encoding), the data on disc may still have had
| discernible patterns but the text would not necessarily have
| been legible. If it had used CAV but not stored a whole number
| of frames per track, then temporal and spatial locality on
| screen would not have corresponded so well to spatial locality
| on disc. And the vertically-scrolling credits are pretty much
| the only kind of content that can produce the recognizable and
| legible images on the disc surface.
|
| I _think_ the fact that the aspect ratio of the text came out
| approximately right probably is a consequence of the scrolling
| speed of the credits being chosen to suit the vertical
| resolution of the video. If the text had appeared squished in
| the microscope, it would probably have been moving too fast on
| screen to be clearly legible.
| xattt wrote:
| Is the image seen via microscope basically a readout of the
| image on a spectroscope?
|
| Those can have near-legible images, but most of the time they
| are not.
| wtallis wrote:
| For the images seen through the microscope, the horizontal
| axis is the same as the horizontal axis of the video. The
| vertical axis of what the microscope sees is the _time_
| axis of the video: it 's essentially a slit camera view of
| a particular individual scan line position within the
| frame.
| Zafira wrote:
| Sorta?
|
| The data being written to the disk is the same in CAV or CLV
| disks, but the player just needs to know how to spin the disk
| at the right speed so that the laser can read the pits/lands
| correctly. It is purely a detail about the speed that the disk
| is spun at so they can cram more data on it with CLV disks.
|
| What CAV LaserDiscs allow for, though, is to make it extremely
| obvious where scanlines and blanking intervals are in the video
| signal.
| VerifiedReports wrote:
| No; it's strictly a reference to constant RPM or variable RPM.
|
| CAV discs contained one frame per rotation. While this meant
| you could only fit half an hour on one side of a disc, it did
| give you perfect slow-motion and freeze-frames.
|
| I worked in a video store and loved LaserDiscs. The Duran Duran
| video album was CAV, and the Pioneer LD-700 had such a fast
| transport mechanism and remote control that I could to DJ-style
| "scratching" with it.
| VorpalWay wrote:
| The live stream of this had more interesting things as well, such
| as looking at the ink on mimeographs compared to inkjet printing.
| Long and rambly as live streams tend to be, but it is there if
| anyone cares.
|
| https://m.youtube.com/watch?v=zIsCswtkozI (mimeograph around
| 3:36:00 mark)
| amelius wrote:
| But the opto mechanical parts of a laserdisc reader are way more
| interesting than a microscope.
| rustyhancock wrote:
| Here's a screen capture of the end credits visible on the disc
| the videos worth it but I do think sometimes you need to start
| with the money shot https://ibb.co/v4KK88fF
| crazydoggers wrote:
| This is from a CED not a laserdisc.
| iamtedd wrote:
| If you watch the video, he looked at both.
| crazydoggers wrote:
| Yes, but the end credits mentioned by the parent and the
| link to the image is the CED. That and the title of this
| post make it seem like this level of image clarity is from
| a LaserDisc which its not. I think it's worth being clear.
| jmkd wrote:
| Watch the video if you believe it's worth being clear.
| The credits are perfectly visible on both the LaserDisc
| AND the CED. Approx 22:00-24:00 is the laser disc and
| 25:00 onwards is the CED. Enjoy.
| jmkd wrote:
| Wow. Downvoted for factual clarification and helpful
| citation. No idea what drives such people, but must
| logically assume deception and obfuscation.
| irl_zebra wrote:
| Ugh, I'm pretty sure it's Big CED deceptively here to
| muddy the waters and obfuscate superior LaserDisc
| Technology. Perhaps flag the post so the moderators can
| see it and make sure we root Big CED out of these forums
| and out of our lives for good.
| jmkd wrote:
| I'm making placards now. Meet you on the corner of
| Pioneer and 78th st.
| K0balt wrote:
| I'm in.
| sixothree wrote:
| And to support your point even further, in the video he
| captures the credits off a disc with constant angular
| velocity, but he _also_ completely lucks out and captures
| an image from a disc with constant linear velocity.
|
| I'm so sick of this negative attitude. I get it when it
| comes to politics or more complex systems or conceptual
| ideas. But holy hell, we're talking about a "money shot"
| to get people interested in the subject.
| ralferoo wrote:
| Actually amazing being able to read the text like that, and on
| two different types of discs. Great video, was much better than I
| was expecting it to be from the title!
| csours wrote:
| Not nearly as cool, but I was able to show a colleague the
| letters in a raster image section of a pdf using xxd by varying
| the output width
| EvanAnderson wrote:
| I wrote a simple tool, when I was a kid, that dumped binaries
| into VGA mode 0x13 and allowed me to vary the width. Mode 0x13
| is one byte per pixel so it was just a simple REP MOVSB to put
| data into the buffer (no worrying about bitplanes). It was so
| useful in reverse engineering software. Besides raster data,
| regular data structures often jump out.
| Retr0id wrote:
| Fun fact, if you load a file with extension ".data" into GIMP
| there's a UI where you can set the pixel format and adjust
| the width/height with sliders
| userbinator wrote:
| Photoshop does the same with the .raw extension.
| CamelCaseCondo wrote:
| I did the same thing to evaluate random number generators by
| drawing pixels with the count value. You see a pattern, line
| or clusters? Bad generator.
| sixothree wrote:
| I feel like everyone needs a peek inside a file in this manner
| at least once in their life. I just like to show people various
| file headers.
|
| Without you showing them, they might never see this kind of
| stuff.
| oofbey wrote:
| Fun fact about laser discs. They are analogue not digital. CD's
| store digital information with the presence or absence of pits.
| Fairly ancient but still fundamentally feels like a very old
| version of a thumb drive.
|
| Laser discs are not digital. They encode the analogue video
| signal's value as the length of the pit. It is digitized in the
| time domain - sampled at some frequency, but the "vertical"
| signal value is stored entirely analogue. In terms of encoding
| it's more similar to a VHS tape than a CD. Kinda crazy.
| a-dub wrote:
| yeah i remember learning this as a kid and being surprised. i
| originally thought laserdiscs were modern high tech, but then
| they turned out to actually be from the late 70s/early 80s with
| the primitive analog video encoding where red book audio cds of
| the mid to late 80s were actually digital.
| mh- wrote:
| I just learned this in my 40s and am surprised. Very cool.
| VerifiedReports wrote:
| BUT... Pioneer put AC-3 (Dolby Digital) surround on
| LaserDiscs before DVDs came out. So LaserDiscs were the first
| video medium to offer digital sound at home.
|
| And at that point, most players sold were combo players that
| could also play CDs.
|
| And there was one more disc format: CD Video. It was a CD-
| sized digital single that also had a LaserDisc section for
| the (analog) music video. I have a couple; one is Bon Jovi.
| throwaway85825 wrote:
| Was CD video compressed? I thought it existed at the same
| time as DVD but cheaper.
| yourusername wrote:
| That's Video CD. It existed before DVD but survived
| alongside it (mainly in Asia) as a cheaper alternative.
| a-dub wrote:
| no, apparently there was both. i was familiar with video
| cd which was mpeg-1 on a cd-rom (with some weird
| partitioning scheme). cd video is apparently a very
| obscure hybrid format with an analog video section and a
| digital audio section.
| https://en.wikipedia.org/wiki/CD_Video
| qsera wrote:
| So how does writes work? Does an analog signal translate into
| pit-lengths with absolute precision?
| throwaway290 wrote:
| Everything is analog when it gets to real world
| bregma wrote:
| > Laser discs are not digital... It is digitized in the time
| domain
|
| Laser disks are 100% digital (as you said, they store digits in
| the time domain).
|
| They don't encode their data using binary like a CD does.
|
| "Binary" and "digital" are two separate and unrelated concepts.
| actionfromafar wrote:
| Um... I think they store "PCM encoded-ish" but the length of
| the pits are not discrete on / off like on a CD but various
| arbitrary lengths, so _analog_.
|
| The sound was also analog to begin with, then the same
| encoding as CDs, then after that AC-3 and DTS.
| SV_BubbleTime wrote:
| Very cool but, I was hoping he was going to spin it and align
| with the camera's refresh rate.
| system2 wrote:
| That would be cool with a variable motor and a 3d printed mount
| maybe.
| onnimonni wrote:
| I'm not that familiar with CED but the fact that we can see the
| images with microscopes is because these are analog discs? And
| that was because computing power back then was non-existent so
| they didn't use any kind of compression?
| throwaway27448 wrote:
| This is a distinction without meaning: all digital anything is
| analogue if you look closely enough
|
| > And that was because computing power back then was non-
| existent so they didn't use any kind of compression?
|
| Compression is not a medium-level detail. You can easily store
| compressed data on a laserdisc.
| system2 wrote:
| No, with digital, you need encoding. How can you even compare
| binary with embedded images.
| throwaway27448 wrote:
| > How can you even compare binary with embedded images.
|
| How are the images encoded?
| brazzy wrote:
| In ways that ensure that they are not visually
| recognizable on the physical medium afterwards, because
| the visual layout represents a whole lot of redundancy,
| and the job of compression is to remove redundancy. If
| the end result has _any_ recognizable patterns, the
| compression is not doing its job well.
| system2 wrote:
| If you watch the video, you can see that the images are
| burnt to the medium and can be seen optically. With 1 and
| 0, you cannot do this. All you'd see would be random dots
| everywhere.
| roywiggins wrote:
| Your CED or laserdisc player needs to be smart enough to be
| able to decode whatever you put on it, which- in the era that
| they were relevant- pretty severely limited what you could
| do.
| brazzy wrote:
| Uncompressed digital encoding might still result in
| recognizable structures, but probably not as nicely as here.
| throwaway85825 wrote:
| Only the CD had uncompressed data.
| brazzy wrote:
| CED, not CD. And LDs most definitely also have uncompressed
| data, resulting in visible text at 22:30 in the video.
| actionfromafar wrote:
| This is where we get into semantics, but it sort of has
| compressed color data, in the analog domain. :)
| happycube wrote:
| CD's have repatterened uncompressed data using scrambling
| codes to keep the waveform stable (i.e. ~50% on/off)
|
| And a Laserdisc with digital sound literally has that CD
| audio EFM waveform in the lower frequencies.
| gf000 wrote:
| The key point is that there has to be a slow vertical panning
| happening as actual content. If that happens, then the on-disk
| representation of a color channel can end up physically
| below/above what happens before/after in the movie, drawing out
| the "actual content". This is why end credits were the most
| likely visible artifacts.
|
| One other important aspect is that by changing the angle of
| lighting, he could basically filter out data at a relevant
| wavelength.
|
| --
|
| At least that's what I got from the video.
| ErroneousBosh wrote:
| There wasn't any computing involved. The video was recorded as
| a sampled analogue signal, with pits of varying length setting
| the "output voltage".
|
| If you look at a Constant Angular Velocity disc you can
| actually see "spokes" radiating out from the centre, with two
| broad ones 180deg apart. The narrow spokes are the horizontal
| sync pulses occuring every 0.576deg - the disc rotates at 25
| revs per second and each concentric track is one complete
| frame. The broader spokes are of course the vertical sync
| pulses and colour burst occurring every 1/50th of a second.
|
| If you're in the US or Japan, these numbers are 30 revs per
| second, 0.686deg and 1/60th of a second, because of the lower
| resolution video standard, but it doesn't look like Laserdisc
| was much of a "thing" in those countries.
|
| Here in the UK, in the 1980s all the schools took part in a
| thing called "The Domesday Project" [1] - the name is a
| reference to The Domesday Book, a survey of England and Wales
| carried out in the 11th century by William the Conqueror.
|
| The Domesday Discs were CAV Laserdiscs that were played in a
| special player with a SCSI interface, attached to a BBC Micro
| computer. Because each concentric track was a complete frame it
| was possible to get perfect still frame video by just keeping
| the head still, so you could look at photos of places all
| around the UK and read a bit of information about them
| genlocked over the top.
|
| [1] https://en.wikipedia.org/wiki/BBC_Domesday_Project
| grishka wrote:
| This is 1970s tech, so of course there was no compression. It's
| basically a composite video signal etched into the medium.
| Every revolution of the disc is one full frame (or two fields).
| So when you look at it, the adjacent grooves represent the same
| lines of video in different frames.
|
| Now imagine if you picked a Y coordinate and extracted the
| corresponding row of pixels from every frame of a video file,
| and stacked them vertically. If there was scrolling text, or if
| the camera moved vertically, you would see a meaningful image,
| the same way a scanner obtains a complete image by moving a
| single-row sensor across whatever you're scanning. This is the
| same effect, just arising from the way the video signal is laid
| out on the disc.
| throwaway27448 wrote:
| Is there a version that doesn't require watching a video please?
| This would be 10x faster and easier as a text blob
| nilslice wrote:
| yes, you must save it to a laserdisc, and then observe it
| though a highly magnified digital microscope looking for a
| specific frame.
| imtringued wrote:
| You can ask your human to watch the video and write the text
| blob for you.
| comboy wrote:
| Just post it to social media to generate the text description
| for free (multiple humans in parallel work better)
| ptman wrote:
| use gemini and ask it to summarize a youtube link
| queeerkopf wrote:
| https://wiki.techtangents.net/wiki/Seeing_Media
|
| writeup from the author linked in the video description
| apples_oranges wrote:
| this should be the main link
| brettermeier wrote:
| No!
| randunel wrote:
| Most people would get a "Making sure you're not a bot"
| anime girl with that link.
| sixothree wrote:
| It flashed too briefly for me to understand what I was
| seeing.
| crazygringo wrote:
| Thank you! So much more helpful.
| eurekin wrote:
| It took me like 2 minutes to find the relevant part:
|
| https://youtu.be/qZuR-772cks?si=rYM4EjvV7VeTEzx8&t=1570
| gwbas1c wrote:
| Short answer: Skip to 22:45
|
| Long answer: Just jump around. Once you get to the last 1/3rd
| of the video, there's a lot of close ups of the part of the
| laserdisc that recorded the credit sequence. The on-screen
| (laserdisc) text is clearly visible.
|
| The author moves a flashlight around to show how the angle is
| important; something that won't come across as well in a blog
| entry.
| luzionlighting wrote:
| Interesting to see how optical technology has evolved. In
| lighting design we also deal a lot with how light interacts with
| surfaces, lenses and reflectors.
|
| Even small changes in optics can drastically change how light
| spreads or how uniform illumination appears in a space.
| Aardwolf wrote:
| Now I wonder if something similar is possible with the magnetic
| fields on VHS tape
| valleyer wrote:
| Thoughts on that: (1) you'd need a way to visualize the
| magnetic fields, (2) the data is frequency modulated, (3) due
| to helical scan, the video field lines do not line up evenly
| one over the next as they did so nicely in the Laserdisc / CED
| (there'd be a skew).
|
| So I don't want to say it's impossible, but I think it would
| require a lot more creativity.
| grishka wrote:
| I thought about that recently while researching how VCRs work
| before attempting to fix one. I didn't even think about seeing
| the actual video signal, I was just curious what the diagonal
| lines and control pulses on the tape look like. There are many
| other things as well that would be interesting to look at (all
| kinds of tapes, all kinds of floppies, hard drive platters,
| magstripe cards), but unfortunately I don't think there exists
| a technology capable of visualizing magnetic fields with enough
| precision.
| geon wrote:
| As I understand it, this only works with still images that scroll
| vertically.
|
| Each revolution is one frame, so if you compare the data paths
| next to each other, they don't make up an image but the same
| single line of several consecutive frames.
|
| Scrolling a still image makes the same line on the screen cover a
| different part of the image each frame, so you can sort of make
| out what the original image looked like.
|
| The end credits should show up as a single tall image, since the
| only limit to the height is the radius of the disc.
| sixothree wrote:
| Great points.
|
| And it just so happens in this video that the scrolling was at
| a speed where everything was preserved and also not stretched.
| Too slow and it would be elongated vertically on the disc and
| too fast and it would be compressed and you'd miss information.
| harrall wrote:
| If I'm not mistaken, it also doesn't work with LaserDiscs... it
| works only with CEDs.
|
| The title is a bit misleading. LaserDiscs are digital but CEDs
| are analog.
|
| Very different technologies.
| NoMoreNicksLeft wrote:
| I was under the impression that laserdisc encoded the video
| signal in analog. Some (all?) audio tracks were digital/pcm,
| however.
| itisit wrote:
| LaserDiscs are not quite a digital medium. The video is an FM
| analog signal (composite). Digital PCM audio was introduced
| about half a decade into the format's life.
| IAmGraydon wrote:
| Just an aside - I love that he's using The Mind's Eye
| (https://www.imdb.com/title/tt0167285/), which is a video that
| really captured my imagination when I was young (along with
| Beyond the Mind's Eye) and changed the course of my life as it
| got me into 3D animation at a young age.
| withinboredom wrote:
| 1000 years from now, someone will discover these discs and wonder
| why we wrote text so small and so many times across the disk.
| They'll say the rainbow is for artistic effect and the repetition
| for religious reasons.
|
| Some people will argue that it is for primitive digital
| technology and be called crazy people. Nobody will be allowed to
| study it except for those who go to the right schools or have the
| right connections.
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