7 ms·

CRTs are still slightly magical to me. The image doesn't really exist. It's an illusion. If your eyes operated at electronic speeds, you would see a single i

by retrac 1y ago

CRTs are still slightly magical to me. The image doesn't really exist. It's an illusion. If your eyes operated at electronic speeds, you would see a single incredibly bright dot-point drawing the raster pattern over and over. This YouTube video by "The Slow Mo Guys" shows this in action: https://youtu.be/3BJU2drrtCM?t=190 https://youtu.be/3BJU2drrtCM?t=190

snovymgodym 1y ago
> It's an illusion. In a sense, all vision is.
- grishka 1y ago
  All our senses are.
  - flysand7 1y ago
    Except the pain of hitting your pinky on a corner. That one's very real
YZF 1y ago
There is some persistence in the pixels/phosphor though so it's not a complete illusion. But yes, your eyes are integrating over the frame. There is also interlacing... I read something interesting recent but I'm not sure if it's true or not. That as you age your integration frame rate decreases.
jagged-chisel 1y ago
When I learned how TV worked at the beginning of television history, I found it super cool that the camera and all the TVs across the country had their scanning beams synchronized. That camera was driving your TV, almost literally.
- eastbound 1y ago
  I only recently found out that the tech to save images wasn’t invented, so they couldn’t display a revolving logo between shows. So… so the BBC had a permanent real-life logo with a permanent camera in front of it. So yes, any image was extremely ephemeral at the time. PS: Apparently it’s called a Noddy, it’s a video camera controlled by a servomotor to pan and tilt (or 'nod', hence the name Noddy): https://en.wikipedia.org/wiki/Noddy_(camera) https://en.wikipedia.org/wiki/Noddy_(camera)
  - kuhsaft 1y ago
    I don’t think that was why the Noddy was used. At the time film and projection were available. They could have recorded film and projected onto a sensor for re-broadcast. The Noddy was used since it was a live broadcast and “allowed the idents to be of no fixed length as the clock symbols could continue for many minutes at a time”. So, it’s not really because they couldn’t store video. It’s because they needed an indefinite amount of video for the clock idents and couldn’t generate them digitally.
    - jameshart 1y ago
      Film wears out through repeated use. While a loop of film would have been theoretically possible, the tech to transmit it would have required just as much TV camera electronic equipment, plus a complex film projection device; the film would have gradually gotten scratched and picked up dust and worn out, and it would have had a great many failure modes. In contrast, pointing a TV camera at a spinning globe was much easier. And for showing the time, pointing at a physical clock was much easier than, what, having twelve hours of film footage available and having to synch the right frame? I think what’s maybe more surprising for people than that moving station idents were typically in camera props, is that broadcasting even a static image pre-digital was also much more easily accomplished by just pointing a camera at a piece of card - even repeating a single frame over and over again was not something that could be easily reproduced some other way; having a camera continually capture and immediately broadcast the frame was just much easier. Video tape, once it came in, allowed freeze frames but continually reading from the same spot on a tape caused wear so you couldn’t rely on being able to show a single frame from tape indefinitely. Digital freeze frame machines that could capture a frame of video and repeatedly play it back from a memory buffer only started showing up in the 1980s.
hinterlands 1y ago
That slo-mo video is somewhat misleading, though. The phosphor glows for a good while, so there is a reasonable chunk of the image that's visible at any given time. The problem in that video is that the exact location the beam is hitting is momentarily very bright, so they calibrated the exposure to that and everything else looks really dark.
- f1shy 1y ago
  And still it was possible as a side attack, with just looking at the reflected brightness of a screen, to get a perfect image back.
- layer8 1y ago
  The phosphor still drops off very quickly [0][1][2], roughly within a millisecond. That’s why you would need a 1000 Hz LCD/OLED screen with really high brightness (and strobing logic) to approximate CRT motion clarity. On a traditional NTSC/PAL CRT, 1 ms is just under 16 lines, but the latest line is already much brighter than the rest. The slow-motion recording showing roughly one line at a time therefore seems accurate. [0] https://blurbusters.com/wp-content/uploads/2018/01/crt-phosphor-versus-strobe-backlights.png https://blurbusters.com/wp-content/uploads/2018/01/crt-phosp... [1] https://www.researchgate.net/figure/Phosphor-persistence-of-CRT-monitor-Phosphor-persistence-lasts-approximately-64-ms_fig16_5550239 https://www.researchgate.net/figure/Phosphor-persistence-of-... [2] https://www.researchgate.net/figure/Stimulus-succession-on-CRT-vs-LCD-monitors-Schematic-of-the-luminance-course-of-a-disk_fig4_47358140 https://www.researchgate.net/figure/Stimulus-succession-on-C...
  - wincy 1y ago
    I definitely like my new 240hz 4k oled HDR monitor, though. They're getting there! The data rate it's pushing through the displayport cable for uncompressed 4k HDR is something 80gb/s though. Absolutely mind boggling. Huge upgrade from my 1440p 165hz IPS monitor that had huge amounts of smearing when playing games.
    - BenjiWiebe 1y ago
grishka 1y ago
To me the magical part about CRTs is color. I don't quite understand how the shadow mask works. Like, yeah, there are three guns, one for each color channel, and the openings in the mask match their layout, and somehow the beam coming out of each gun can only ever hit its corresponding phosphor dots. Even after being deflected. But... how? Also, wouldn't the deflection coils affect each of the three beams slightly differently?
- pulvinar 1y ago
  Each hole in the shadow mask acts as a pinhole camera, giving an inverted image (in electrons) of the three guns. All three beams get bent nearly the same amount, but yes there is some distortion which is traditionally corrected for by a set of convergence coils and corresponding circuit with knobs for static and dynamic convergence [0]. A pain to adjust, BTW. [0] https://antiqueradio.org/art/RCACTC-11ConvergBoardNewRC.jpg https://antiqueradio.org/art/RCACTC-11ConvergBoardNewRC.jpg
- Sharlin 1y ago
  It's parallax, basically. The pigment dots and mask holes are positioned such that when you look from the perspective of the "red" electron gun (*), you only see red pigment dots. Move a couple cm to the "blue" gun and the parallax shift now makes you to see only blue pigment dots instead. Or from the other direction, no matter which "red" dot you stand at, you only see the "red" gun through "your" hole. The exact sizes, shapes, and positions of the pigment dot triples (and/or the mask holes) are presumably chosen so that this holds even away from the main axis. Also, the shape of the deflecting field is probably tuned to keep the rays as well-focused as possible. Similarly to how photographic lenses are carefully designed to minimize aberrations and softness even far from the optical axis. (*) Simplifying a bit by assuming that the beam gets deflected immediately as it leaves the gun, which is of course inaccurate.
- somat 1y ago
  For me it was the opposite. Learning how a monochrome CRT requires no mask sort of destroyed my world view of what a display had to have. pixels(even the quasi pixels as found in a color CRT mask) were not actually required or present. As a result monochrome terminal text has this surprising sharpness to it.(surprising if you are used to color displays). But the real visual treat are the long persistence phosphor radar scopes.

by retrac 1y ago

snovymgodym 1y ago

> It's an illusion. In a sense, all vision is.

grishka 1y ago
All our senses are.
- flysand7 1y ago
  Except the pain of hitting your pinky on a corner. That one's very real

YZF 1y ago

There is some persistence in the pixels/phosphor though so it's not a complete illusion. But yes, your eyes are integrating over the frame. There is also interlacing... I read something interesting recent but I'm not sure if it's true or not. That as you age your integration frame rate decreases.

jagged-chisel 1y ago

When I learned how TV worked at the beginning of television history, I found it super cool that the camera and all the TVs across the country had their scanning beams synchronized. That camera was driving your TV, almost literally.

eastbound 1y ago
I only recently found out that the tech to save images wasn’t invented, so they couldn’t display a revolving logo between shows. So… so the BBC had a permanent real-life logo with a permanent camera in front of it. So yes, any image was extremely ephemeral at the time. PS: Apparently it’s called a Noddy, it’s a video camera controlled by a servomotor to pan and tilt (or 'nod', hence the name Noddy): https://en.wikipedia.org/wiki/Noddy_(camera) https://en.wikipedia.org/wiki/Noddy_(camera)
- kuhsaft 1y ago
  I don’t think that was why the Noddy was used. At the time film and projection were available. They could have recorded film and projected onto a sensor for re-broadcast. The Noddy was used since it was a live broadcast and “allowed the idents to be of no fixed length as the clock symbols could continue for many minutes at a time”. So, it’s not really because they couldn’t store video. It’s because they needed an indefinite amount of video for the clock idents and couldn’t generate them digitally.
  - jameshart 1y ago
    Film wears out through repeated use. While a loop of film would have been theoretically possible, the tech to transmit it would have required just as much TV camera electronic equipment, plus a complex film projection device; the film would have gradually gotten scratched and picked up dust and worn out, and it would have had a great many failure modes. In contrast, pointing a TV camera at a spinning globe was much easier. And for showing the time, pointing at a physical clock was much easier than, what, having twelve hours of film footage available and having to synch the right frame? I think what’s maybe more surprising for people than that moving station idents were typically in camera props, is that broadcasting even a static image pre-digital was also much more easily accomplished by just pointing a camera at a piece of card - even repeating a single frame over and over again was not something that could be easily reproduced some other way; having a camera continually capture and immediately broadcast the frame was just much easier. Video tape, once it came in, allowed freeze frames but continually reading from the same spot on a tape caused wear so you couldn’t rely on being able to show a single frame from tape indefinitely. Digital freeze frame machines that could capture a frame of video and repeatedly play it back from a memory buffer only started showing up in the 1980s.

hinterlands 1y ago

That slo-mo video is somewhat misleading, though. The phosphor glows for a good while, so there is a reasonable chunk of the image that's visible at any given time. The problem in that video is that the exact location the beam is hitting is momentarily very bright, so they calibrated the exposure to that and everything else looks really dark.

f1shy 1y ago
And still it was possible as a side attack, with just looking at the reflected brightness of a screen, to get a perfect image back.
layer8 1y ago
The phosphor still drops off very quickly [0][1][2], roughly within a millisecond. That’s why you would need a 1000 Hz LCD/OLED screen with really high brightness (and strobing logic) to approximate CRT motion clarity. On a traditional NTSC/PAL CRT, 1 ms is just under 16 lines, but the latest line is already much brighter than the rest. The slow-motion recording showing roughly one line at a time therefore seems accurate. [0] https://blurbusters.com/wp-content/uploads/2018/01/crt-phosphor-versus-strobe-backlights.png https://blurbusters.com/wp-content/uploads/2018/01/crt-phosp... [1] https://www.researchgate.net/figure/Phosphor-persistence-of-CRT-monitor-Phosphor-persistence-lasts-approximately-64-ms_fig16_5550239 https://www.researchgate.net/figure/Phosphor-persistence-of-... [2] https://www.researchgate.net/figure/Stimulus-succession-on-CRT-vs-LCD-monitors-Schematic-of-the-luminance-course-of-a-disk_fig4_47358140 https://www.researchgate.net/figure/Stimulus-succession-on-C...
- wincy 1y ago
  I definitely like my new 240hz 4k oled HDR monitor, though. They're getting there! The data rate it's pushing through the displayport cable for uncompressed 4k HDR is something 80gb/s though. Absolutely mind boggling. Huge upgrade from my 1440p 165hz IPS monitor that had huge amounts of smearing when playing games.
  - BenjiWiebe 1y ago

grishka 1y ago

To me the magical part about CRTs is color. I don't quite understand how the shadow mask works. Like, yeah, there are three guns, one for each color channel, and the openings in the mask match their layout, and somehow the beam coming out of each gun can only ever hit its corresponding phosphor dots. Even after being deflected. But... how? Also, wouldn't the deflection coils affect each of the three beams slightly differently?

pulvinar 1y ago
Each hole in the shadow mask acts as a pinhole camera, giving an inverted image (in electrons) of the three guns. All three beams get bent nearly the same amount, but yes there is some distortion which is traditionally corrected for by a set of convergence coils and corresponding circuit with knobs for static and dynamic convergence [0]. A pain to adjust, BTW. [0] https://antiqueradio.org/art/RCACTC-11ConvergBoardNewRC.jpg https://antiqueradio.org/art/RCACTC-11ConvergBoardNewRC.jpg
Sharlin 1y ago
It's parallax, basically. The pigment dots and mask holes are positioned such that when you look from the perspective of the "red" electron gun (*), you only see red pigment dots. Move a couple cm to the "blue" gun and the parallax shift now makes you to see only blue pigment dots instead. Or from the other direction, no matter which "red" dot you stand at, you only see the "red" gun through "your" hole. The exact sizes, shapes, and positions of the pigment dot triples (and/or the mask holes) are presumably chosen so that this holds even away from the main axis. Also, the shape of the deflecting field is probably tuned to keep the rays as well-focused as possible. Similarly to how photographic lenses are carefully designed to minimize aberrations and softness even far from the optical axis. (*) Simplifying a bit by assuming that the beam gets deflected immediately as it leaves the gun, which is of course inaccurate.
somat 1y ago
For me it was the opposite. Learning how a monochrome CRT requires no mask sort of destroyed my world view of what a display had to have. pixels(even the quasi pixels as found in a color CRT mask) were not actually required or present. As a result monochrome terminal text has this surprising sharpness to it.(surprising if you are used to color displays). But the real visual treat are the long persistence phosphor radar scopes.