There are some sentences in this that are technically vague enough to pass, but I don't think are strictly speaking correct, and I believe will likely lead to a mistaken understanding:
> modern displays don't paint the image line-by-line (...) They light up each pixel simultaneously, refreshing the entire display at once.
The entire screen area is lit all the time now, yes, but refresh still typically happens line by line, top to bottom [0], left to right [0], for both LCDs and OLEDs. It's a scanning refresh, not a global refresh (sadly).
You can experimentally confirm this using a typical smartphone. Assuming a 60 Hz screen refresh, recording in slow motion will give you enough extra frames that the smartphone camera also likely operating in a scanning fashion (rolling shutter) won't impact the experiment. On the recording, you should see your screen refreshing in the aforementioned fashion.
[0] actual refresh direction depends on the display, this is for a typical desktop monitor
I was glad they at least mentioned how IPS (PLS) and VA differ from older TN.
But you're right both LCD and OLED refresh a stored voltage on the cell (or caps) on a roughly line by line (OLED can easily be 5 clocks on the GIP to cancel internal transistor offset voltages).
I was mostly annoyed that they didn't mention the circular polarizer on OLEDs. Although there is discussion of going to color filters with Quantum Dot OLED, the circular polarizer is what makes the blacks so black on mobile OLED devices.
Also, didn't really mention pentile RGGB sub-pixel pattern which is dominant in mobile OLED (which is more than 50% of devices). Now they're moving to "tandem" stacked OLED for higher brightness and lower current density, but no latteral sub-pixel pattern.
Maybe slightly off topic but I was surprised to discover that my glasses with photoreactive lenses (SpecSavers ‘Reactions’) are actually circularly polarised but only when they go dark. I originally thought they didn’t work because they didn’t interact with another pair of polarised sunglasses (no changing brightness as I rotated one lens in front of the other) but later noticed that my phone screen with its circularly polarised IPS screen was almost black in bright sunlight… until I took my glasses off.
There were a few things I personally found lacking as well, albeit they're fairly minor.
Regarding CRTs, at the vector CRTs section, they mention "they were mostly monochrome and so the phosphor dots could be tightly packed" - this is not true either I believe, monochrome CRTs had a uniform phosphor coat on the inside, no subpixel patches. I'd have also liked if they delved a bit into the decay times of the various phosphor chemistries used for color CRTs, and how they compare to LCDs and OLEDs. It's an entertaining comparison, grounds motion performance related discussions really well.
Regarding LCDs, I missed the mention of multi-layer LCDs, especially since they bring up tandem OLEDs.
Regarding OLEDs, now that you mention, the subpixel layouts were left unaddressed.
Regarding quantum dots, I missed both the mention of QDEL as a somewhat promising future contender, and the mentioning of the drawback of their typical implementation. External light also provides them with energy to activate, which I believe is at least partially the cause behind the relatively poor black levels of QD-OLEDs in environments with significant ambient light (+ something about it not being possible to put a polarizer in front of them?)
I was also generally expecting a more in-depth look by the title, would have loved to learn about the driving electronics, maybe learn about why OLEDs aren't ran anywhere near as fast as their full potential (I'd assume throughput limitations), etc. Overall, it basically only covers as much as my own enthusiast but not in-the-area self gathered over the years too.
> Regarding CRTs, at the vector CRTs section, they mention "they were mostly monochrome and so the phosphor dots could be tightly packed" - this is not true either I believe, monochrome CRTs had a uniform phosphor coat on the inside, no pixel patches.
This is one of the reasons why emulated versions of Asteroids (arcade game) can never match the real thing: the razor-sharp, perfectly straight lines with zero aliasing used to paint the display. The computer also has fine-grained control of how bright to make the electron beam that raster displays typically don't allow (this is perhaps as simple as holding the beam in place, or drawing back and forth over the same line segment), meaning that your ship's projectiles and enemy shots appear as super-bright points with a phosphor bloom around them, glittering in the dark. Most emulators simply draw them as nondescript pixels. I suppose with some effort a CRT simulator can be hooked up to the emulator... but it still wouldn't be the same.
I'm glad I got to play an authentic Asteroids before I died. Working machines are getting rarer. Some of those who come after me may not get that chance.
My first and only time playing Asteroids in its original vector CRT glory was a bit shocking to me. I remember the evolution of CRTs in the 80s and 90s. My family had a small B&W CRT that fascinated me with its image quality, in that it always reminded me more of a b&w photo than color CRTs reminded me of color photos.
Still, that vector CRT that I saw perhaps a dozen years ago was quite a surprise. Lack of rastering and the utterly insane brightness sent me down a rabbit hole. I ultimately concluded I'm not ever likely to own a basement Asteroids cabinet.
I had similar reactions, only it all happened while I was in grade school!
Oh yes! The bright projectiles really add to the game impact. And on some cabinets, the lines were not perfectly straight. It looked for all the world like the phosphor coating had a bit of texture to it. Now being older, I realize an effect like that could just be a marginal DAC too.
IMHO the best vector experiences, in order are:
STAR WARS
This is a color vector display cranked up to the nines! The processor handling the vector drawing is fast! Tons of vectors are possible with only subtle impact on display refresh speed and overall quality. There is some global image size artifacts that happen when some of the brightest objects occupy a significant percentage of the display.
And that is a feature! Love it. Get into a sit down cabinet if you ever get the chance.
TEMPEST
This game is not for everyone. Most of these drive people to their limits, but TEMPEST ramps up and beyond normal human limits! Not everyone can play this game at its peak. Same can be said of nearly everything on this list, but without that aggressive ramp up.
ASTEROIDS
I prefer the original cabinet with the somewhat slower object motion. That one is a bit easier to play. Depending on the operator and how hard they drive the CRT, image brightness ranges from a bit old, washed out and tired looking to WOW! How do those tiny projectiles not just carve a line right into the phosphors.
Cinematronics games: TAIL GUNNER, STAR CASTLE, RIP OFF.
These use overlays for a bit of color. Oh, I forgot ARMOR ATTACK, which uses large ones like STAR CASTLE.
The quality of the vectors is not quite as good as the ATARI displays and this too is a feature. That gives Cinematronics a bit of charm I find quite enjoyable
And sound! Hoo boy! STAR CASTLE has great, loud --> I mean loud sounds with full bass notes able to rumble you and the cabinet!
OTHER COLOR VECTOR GAMES
I like playing all of these, but they simply were not peak experiences. Still damn good, if you ask me:
MAJOR HAVOC, GRAVITAR, A Two Player tandem Asteroids game I cannot recall. Fun though!
And last place: QUANTUM played with the Trackball. You circle atoms over and over. This game looks cool and is hard.
GRAVITAR uses the Asteroids movement dynamics to great effect! A fun thing in this game is massive changes in scale happen often. Rare to see.
Vector gaming delivered many of my very highly cherished arcade gaming experiences for sure.
ATARI and Tektronix deserve special mention in this context:
Atari made color vector games work! Did anyone else? Those look amazing! And hold up today in my view.
Tektronix invented both a pure storage tube CRT. Their graphics terminals often doubled as Minicomputers programmable in Tek Basic. The large ones offered a 4K vector space! Crazy good detail for the 70's. And one in good condition, operating in a reduced light room is beautiful to use.
My first manufacturing CAM software experience was on one of these. Used a fixed record length cassette so that many "files" could be accessed almost like a floppy disk drive. User data went right to the paper tape puncher / reader. 1200 baud punch, reads could be faster, up to 9600, if one had a good reader unit.
One ran applications from that cassette and stored and used user data from the paper tape.
But I digress!
Right near the end, Tek managed to get both storage graphics and dynamic refresh capable graphics, both in a different color. I only got to use one of those one time. I loved it because many different work flows were possible.
Man, for the chance to code a UI on one today!
One last thought: in my view vector displays are best on a CRT, mostly because of the image contrast and speed possible, but great vector experiences can also be had on a wall, or perhaps a screen with some coating to bring out the best possible.
We may yet see vectors appear from time to time in these and other ways simply because of how great they are. Hope so, and building a small, color capable one using a low power laser and screen with coatings sure to deliver motion trails is on ky bucket list.
Assuming a 60Hz refresh rate, does it take ~16ms (± the vblank inteval) for a complete cycle from top-left to bottom-right? Or does the scan happen faster than that (with something else being the limiting factor on overall refresh rate)?
Yes, the refresh cycle takes ~16.6 ms. There's another "point" chasing behind the refresh "point", that will be where the panel's response time has finished catching up with the refresh. In between these points, the pixels are slowly morphing from one color to the next. On LCDs, the area between these two points is quite sizeable, definitely more than a few lines, sometimes even hundreds of lines. On a 1080p 60 Hz display, just 1 ms of response time corresponds to 64.8 lines (6% of the screen) being constantly in flux, for example.
The difference between LCDs and CRTs in this regard then, is that on a CRT you only ever got light during that chase section. The initial state is full darkness, and the final state is full darkness too. It's a pulse.
I don't know how common it is now, but a lot of high-resolution LCDs with dual LVDS interfaces were essentially two separate panels, with one lane feeding the top half and the other the bottom half.
Indeed, one feature of active-matrix (and even passive-matrix) displays is that it needs only m + n signal lines to address a pixel in an m + n display. To change the color of a pixel, a signal goes out over the lines corresponding to the row and column of the addressed pixel, selecting it; and then another signal is transmitted over another line to actually change the value of that pixel. In this scheme, it would be impossible to address all pixels simultaneously. Nor would you actually want to, as this would require millions of control lines to drive the display!
Not only was the initial diagram all/explaining, but the "pop"-"pip" on zoom-unzoom of the image was just as nice as playing with a sheet of bubble wrap.
Wow, and that ruler on the right side, even with the sound.
So crisply done. I wish if Dan writes textbooks for all science & math books for High School students. World would be a better place for those who struggle to understand academics.
Adding my congrats as well. The combination of well-written explanations for the semi-technical layperson combined with clear, intuitive graphics is a powerful instruction platform.
This appears to be a lovely project. I wish the author all possible luck and success. I haven't joined a mailing list in a very long time, but I sure did in this case.
CRT displays are one of those analog technologies that are arguably much cooler than their digital successors. Think – a literan raygun, a particle accelerator, inside your monitor, creating the image you're looking at.
True – but on the other hand, it was "only" a few million elements, and very large ones, compared to, say, the DRAM chips of the time. Monitors certainly make the engineering feat more tangible, though!
It’s certainly one the bits of tech that would be an insane pitch if invented today: “Yes, please stick your face in front of this particle accelerator. I assure you, it’s completely safe. You may experience some visual side effects but that’s completely intended.”
It's much cooler if you haven't used it. That mass of a 19in was crazy. Then you had all of those that had the high pitched noise. And if you were unlucky you had to degauss them. Cool concept, but in practice the digital successors are better.
"I was there" too and somehow this is not my reaction at all.
Everyone knows the obvious reasons we don't use crts any more.
It's true but it's a most uninteresting observation that only cares about practical aspects. Practical aspects matter, none of my own desks has a crt, but they do not define life itself.
Those facts do not at all invalidate the point about the desirable aspects which have been lost, or the fact that the merely interesting and remarkable aspects are interesting and remarkable.
The desirable and/or interesting and remarkable features of a crt are still cool, impressive, fun, desirable, even though we all voluntarily choose to use something else basically everywhere we want a screen because of the practical reasons that just happen to overwhelm.
Trust me, I remember. Cool does not equal convenient. Once a friend and I dragged three extra CRTs to a demo party just so we could put them side by side and write a program that displayed random scrolling messages. Controllable via an IRC bot, even! Today you could do that with a single ultrawide…
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
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.
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.
> The phosphor still drops off very quickly [0][1][2], roughly within a millisecond.
It's phosphor chemistry dependent. Different color patches on the same glass would decay at different rates even. But yeah, 1 ms is a good lower bound, although when I last researched this, it was definitely the best case scenario for CRTs. I'm fairly sure the ~500 Hz OLEDs that are already floating around are beating the more typical CRTs of old already.
> That’s why you would need a 1000 Hz LCD/OLED screen with really high brightness (and strobing logic) to approximate CRT motion clarity.
At 1000 Hz you wouldn't need the strobing anymore (I believe?), that's the whole point of going that fast. We're kinda getting there btw! Hopefully with HDMI 2.2 out, we'll see something cool.
> On a traditional NTSC/PAL CRT, 1 ms is just under 16 lines, but the latest line is already much brighter than the rest.
That doesn't really math for me. NTSC would be 480 visible lines at 60 Hz, and so 480 lines / ~16.6 ms = 28.8 lines/ms (6% of the screen). Note that of course PAL works out to the same number: 576 lines / 20 ms = 28.8 lines/ms (just 5% of the screen here though!).
I'm not quite sure what you're saying here. My assertion is that a visible image persists on the screen longer than it appears in the slo-mo clip. You can just point a camera with an adjustable shutter speed at a CRT and see it for yourself. Here's an example (might need to copy the URL and open in a new tab, they don't like hotlinking):
The brightly-lit band is the part of the frame scanned by the beam while the shutter was open. The part above is the afterimage, which, while not as bright, is definitely there.
That link shows an error with Access Denied to me. I didn’t deny that an afterimage is there. I meant to point out that the brightest part by far, which what is most prominently perceived by the eye, isn’t much more than one scanline, in SD.
> The part above is the afterimage, which, while not as bright, is definitely there.
Yes it's there, but it's much less bright than the the scanned area, so it will be hardly perceptible relative to the bright part. The receptors in the eye will hardly respond to it after being excited so strongly by the bright part.
I'm not sure about this calculation though. Phosphor decays exponentially with a time constant of roughly 5ms (according to HP [1]). This means when a new frame comes at 60Hz refresh rate there is still 10-15% of the previous frame related excitation is present. This means there is considerable amount of nonlinearity, hence the performance is even worse than 10ms LCD/OLED displays.
Genuine question: why do you think CRTs are better?
That HP reference is from 1970; CRTs did improve over time. The references I gave show that the intensity drops to below 10-15% within about a millisecond. The difference with LCD/OLED displays is that the latter are sample-and-hold, meaning that they show the image at full brightness for the duration of the whole frame. Their pixel response time may be faster than CRT phosphor persistence, but that is less relevant. The problem with LCD/OLED is that they hold the picture for the duration of the frame, which means that a depicted moving object that is supposed to move smoothly during the duration of a frame, is shown as not moving for that duration, which the eye perceives as motion blur. That motion blur is significantly reduced on CRTs, because they show the object only for a fraction of the frame duration at high brightness, as if under a stroboscope, which makes it easier for the eye (or brain) to interpolate the intervening positions of the object.
> Genuine question: why do you think CRTs are better?
CRTs are worse in most aspects than modern displays, but they are better in motion clarity. As to why I think that: I used both in parallel for many years. The experience for moving objects is very different. It is a well-known drawback of sample-and-hold display technologies. And it is supported by the more systematic analyses done by the likes of Blur Busters.
Yeah, they do backlight strobing (LCD) or black frame insertion (OLED), to reduce blurring during smooth eye movements, at the cost of overall screen brightness. I actually think small CRTs would be perfect for VR headsets in this regard, as they are naturally have very short frame persistence.
One likely problem for battery powered headsets is the (I believe) relatively high CRT power draw. Another is probably the fact that they aren't used for anything else anymore, meaning CRT development has stopped a long time ago. There were quite small CRTs in the past for special applications, but probably not as small as is optimal for modern VR headsets. Both for optics and weight and space reasons.
> Genuine question: why do you think CRTs are better?
They have many disadvantages, but an advantage is that CRTs mostly remove the "persistence blur" induced by smooth pursuit eye movements on sample-and-hold displays like LCD and OLED. Here is an explanation:
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.
The ASUS PG27UCDM 26.5" 4K UHD (3840 x 2160) 240Hz Gaming Monitor [0] paired with an RTX 5090 for my home desktop, but I got a USB switcher (for peripherals), and keep it on my standing desk that I plug in my work laptop too with a USB-C to DisplayPort cable. Only 60hz on the work laptop but I really like having a quad monitor setup in a T shape (3 27” monitors and the laptop plugged in with screen open below the central monitor, which is the OLED). It’s great for both productivity and for gaming. I turned off HDR for work, though.
The only annoying thing is every couple hours it asks me to run a 7 minute pixel refresh cycle to avoid burn in, but according to the dashboard I run it every 2.5 hours or so when I go on breaks, so I think I’m good.
Overall the monitor is just fantastic, my LAN party buddies and I dreamed about OLEDs like this back in 2003 and kept saying it was “just around the corner”. The biggest thing is in dark scenes in games there’s absolutely zero noticeable smearing.
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.
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)
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.
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.
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.
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?
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.
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.
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.
That's the cool thing about analog video, it doesn't really have the concept of horizontal resolution. Especially when it's monochrome. It's made up of lines that continuously change brightness as they're drawn.
Color composite video, as far as I understand, does have a limit to the horizontal resolution because in all three standards the color information is encoded as a high-frequency signal added to the main (luminance) one, so that frequency is your upper limit on how quickly the luminance can change.
S-video, VGA, and component should, in theory, allow infinite horizontal resolution and color.
I'm much more interested in the hardware driver. This thing gets digital encoded input, has to decode it, and then multiplex it to 8 million pixels. 60 times a second. Being able to hit at least 4 million different levels (talking about 4K 60fps 12 bit color).
The input is roughly serial, so it takes a massive serial to parallel conversion.
But the output of the scaler chip is still serial, just now it's guaranteed to have the same dimensions as the panel itself, and includes whatever OSD overlay might be active, and any gamma/contrast/whatever adjustments. I believe in some cases, this is also where dithering takes place, to take a 6-bit panel and try to give it 7-bit (or, yikes, 8-bit) color depth by PWMing pixels that have intermediate values.
Look at the connector pinout of the panel itself. There's only 50 pins or so, and a lot of them are grounds. Whether the scaler-to-panel format is eDP, or LVDS (FPD-Link), or V-by-One, it's all still differential serial lanes at that point.
Around the perimeter of the panel, then, are the actual TCON and row/column driver chips, bonded right to the ITO traces on the glass, flip-chip-on-glass style. These have an outrageous number of pins, and directly connect to the gate (row) and source (column) traces. It's here that the serial becomes parallel, and the next stop is the transistors themselves (hence the MOSFET signal terminology of gate and source) in the individual pixels.
Older displays would have basically a bunch of serial-to-parallel register chips with each one's SO connected to the next one's SI. I ran across a fasincating video of replacing a bad chip in such a display, which happens to be gas plasma so the voltages involved are also pretty high too:
Yeah, with an electron beam it's clear that it's a continuous signal and a single beam is being controlled, but how do you drive millions of individual digital pixels all at once, how does the signal get routed correctly to each one if them?
I have to take issue with the usage of the terms "pixel" and "subpixel" with regards to CRT. CRTs do not display discrete pixels. They display discrete scanlines, each one made up of a smoothly varying voltage across the line (and thus resolution is a function of both the DAC in the display device in the case of systems that generate a digital signal and then convert it to analog for display, and the hardware inside the CRT monitor). Also, there is no mapping between any "pixels" represented within that varying voltage and the separate color phosphor dots.
Even "digital RGB" isn't digital in terms of the CRT. It's only "digital" because each color channel has a nominal on and off voltage, with no in-between (outside of the separate intensity pin). However, the electron gun still has a rise and fall time that is not instant.
Displays didn't truly become digital for the masses until the LCD era, with DVI and HDMI signals. Even analog HD CRTs could accept these digital signals and display them.
I don't think this is an entirely fair characterization either. Note that everything I lay out here is just based on accumulated information gathered over the years due to vague interest, I haven't worked on or with CRTs (did use them though).
Monochromatic CRTs were well and truly resolution agnostic, there were legitimately no pixels or subpixels or anything similar to speak of. That said, the driving signal still had to be modulated to produce an image, and so it's not magic either. You can conceivably represent [0] all the available information in them using just 720 samples per line, which is exactly why DVDs had that as their horizontal resolution (720 pixels).
This story changes a bit though with color CRTs, where you did have discrete sets of patches of different phosphor chemistries called triads. There was absolutely a fixed number of them on a glass, so you could conceivably consider that as the native resolution for that given display, with each triad being a pixel, and each patch being a subpixel. The distance between these was the aperture pitch, much like how you have a pixel pitch on a typical flatpanel display.
The kicker then is that as you say, there's no strict addressing. From what I understand there were multiple electron guns scanning across the screen simultaneously, only being able to hit the specific color they were assigned, but the patch they were hitting wasn't addressed, they just scanned across the screen like the single electron gun did in monochromatic CRTs. You'd then get resolution invariance by just the natural emission spread providing you with oversampling / undersampling without any kind of digital computational effort. It's not really true resolution independence like with the monochrome ones, I'd say. I even recall articles where they were testing freshly released CRT monitors, and discussing how sharp the beam was, resulting in what kind of resolution adherence.
[0] an earlier version of this comment said "extract from" here; for various reasons you might already know, that's a different thing, and would not actually be true.
It still basically should be, so long as well-designed sites give you the "small screen"/mobile layout.
Even apart from that, a lot of laptops still have 1280x800 as the default resolution, and that's only double the width of 640x480. Honestly, I'd actually be more worried about OS and browser chrome eating up the space than websites themselves being unusable.
> "It still basically should be, so long as well-designed sites..."
I believe that their point wasn't that "the web" has intrinsically changed, it was that too many sites are not well designed in this respect.
edit: they actually replied just before me and it seems that wasn't their point, but it would be my point (though I personally don't care about being able to use such a low resolution).
It was 50/50 for me as well but the screen source code is fairly readable and if I remember right eerily over-commented for Unix code! The function names actually make sense.
I can appreciate these articles as they are but I personally don’t like them. They are junk food level of infotainment to me. Something I’d find on a Wikipedia summary section that covers general points.
A CRT - to name one - is a device whose actual understanding will challenge people in profound ways. To ask “how does a screen even work?” and to begin to answer this question will require a bit more than a summary form of “thing goes from point A to point B”. The history of this discovery is a stack of books and in and of itself is fascinating - the experiments and expectations and failures and theories as to why and how. I suppose I just expect more of the site. The illustrations are nice. Oh and my moniker is just a coincidence.
Would be nice if you could give a hint on all the disabled chapters. Either a tooltip or even just a title attribute. Are they paid? Do I have to login? Not ready yet?
LCD on paper you see lots of drawbacks, in practice modern state of the art LCD for TV is pretty damn good. We will soon have RGB LED Backlight LCD with WHVA+ Panel that is about as wide angle as IPS, 95%+ REC 2020 colour, and 1-2ms response time.
Phosphorescent blue OLEDs should reduce current OLED display energy usage by 20-30%. But it still seems to be way off for phones and mass usage.
I think it's fairly common for technologies to get really good just as they're becoming obsolete. Vacuum tubes, CRTs, optical disks, photographic film... in fact, they're often in some respects better than the early generations of the technology that replaces them.
But OLEDs just have too many advantages where it actually matters. Much lower power consumption, physically more compact (no need for backlight layers), etc.
You might add ICE cars to that list. All kinds of cool stuff being developed around small turbocharged engines and other efficiency gains, excellent transmissions, etc.
None of that really helps LCDs primary downsides of poor contrast ratio and relatively high energy consumption. Backlit displays will always inherently score worse on these metrics vs self emissive displays.
peak brightness is not contrast. If anything higher peaks mean worse contrast, even for systems with local dimming zones due to bleed between zones / gradients in display content which do not align with backlight zones.
LCDs as a transmissive display technology work by emitting a bunch of photons and then selectively filtering some out to achieve the desired color / pixel brightness. Any filtered photon is wasted energy, this is inherent to the display technology and is not limited to dark content, just exacerbated by it.
Given that, all things equal there is no way for LCD to equal the efficiency of a self emissive display, at best it's a question of when will the luminous efficiency of OLED exceed that of white/blue backlight LEDs... and honestly we're likely already at or past that point.
I happen to have a stereo microscope at my desk, so I put my Pixel 9 under there. At 100x mag (10x ocular x 10x objective) it looks like there are 3 layers: as I move my head around slightly (so the image is moving over my retinas), the blue moves faster and the red almost stays still, with green somewhere in the middle.
I know this is HN, but I honestly clicked this link initially thinking it was going to be a detailed analysis of how screen plays are constructed and executed in football.
The ticker on the right is quite nice, but I perceive the sound as coming from within my nose (if that makes any sense) to the point that I thought something was going on with my sinuses for a full 3 seconds, and got panicked.
>The fact that they ever made it out of the research lab and into our homes is astonishing to me.
What is astonishing about LCDs? I don't mean to diminish the difficulty of scaling up the process, but if you think of early LCD displays they don't seem farfetched to be shipped to consumers.
One random example is that your eyes are extremely sensitive to the tiniest defect or variation. So making a large display that looks good and is uniform is very challenging. Not to mention scaling up all the various processes like the photolithography and working with very large and thin glass panels.
It's all engineering but it's surprisingly hard to move things from the lab to manufacturing at scale. Years and years and lots of problem solving. Some efforts/approaches fail and you never hear of them.
You are moving the goal posts from it being a consumer product to requiring it to be large, good, and uniform. Yes, there was engineering work to make such a consumer product, but it is something I would expect there to have been line of sight for.
The first LCD products I remember were things like 7 segment digital watches and calculators where the LCD was passive and the "pixels" were large. I am not super familiar with how that went from lab to consumer product but I imagine even there it was non-trivial.
It took a long time to progress to modern LCD displays. It took years to get from small black and white displays, to small color, to larger and larger displays. Productizing this stuff includes building machines, factories, ASICs, and figuring out a lot of technology as you go along.
There are some sentences in this that are technically vague enough to pass, but I don't think are strictly speaking correct, and I believe will likely lead to a mistaken understanding:
> modern displays don't paint the image line-by-line (...) They light up each pixel simultaneously, refreshing the entire display at once.
The entire screen area is lit all the time now, yes, but refresh still typically happens line by line, top to bottom [0], left to right [0], for both LCDs and OLEDs. It's a scanning refresh, not a global refresh (sadly).
You can experimentally confirm this using a typical smartphone. Assuming a 60 Hz screen refresh, recording in slow motion will give you enough extra frames that the smartphone camera also likely operating in a scanning fashion (rolling shutter) won't impact the experiment. On the recording, you should see your screen refreshing in the aforementioned fashion.
[0] actual refresh direction depends on the display, this is for a typical desktop monitor
I was glad they at least mentioned how IPS (PLS) and VA differ from older TN.
But you're right both LCD and OLED refresh a stored voltage on the cell (or caps) on a roughly line by line (OLED can easily be 5 clocks on the GIP to cancel internal transistor offset voltages).
I was mostly annoyed that they didn't mention the circular polarizer on OLEDs. Although there is discussion of going to color filters with Quantum Dot OLED, the circular polarizer is what makes the blacks so black on mobile OLED devices.
Also, didn't really mention pentile RGGB sub-pixel pattern which is dominant in mobile OLED (which is more than 50% of devices). Now they're moving to "tandem" stacked OLED for higher brightness and lower current density, but no latteral sub-pixel pattern.
Maybe slightly off topic but I was surprised to discover that my glasses with photoreactive lenses (SpecSavers ‘Reactions’) are actually circularly polarised but only when they go dark. I originally thought they didn’t work because they didn’t interact with another pair of polarised sunglasses (no changing brightness as I rotated one lens in front of the other) but later noticed that my phone screen with its circularly polarised IPS screen was almost black in bright sunlight… until I took my glasses off.
There were a few things I personally found lacking as well, albeit they're fairly minor.
Regarding CRTs, at the vector CRTs section, they mention "they were mostly monochrome and so the phosphor dots could be tightly packed" - this is not true either I believe, monochrome CRTs had a uniform phosphor coat on the inside, no subpixel patches. I'd have also liked if they delved a bit into the decay times of the various phosphor chemistries used for color CRTs, and how they compare to LCDs and OLEDs. It's an entertaining comparison, grounds motion performance related discussions really well.
Regarding LCDs, I missed the mention of multi-layer LCDs, especially since they bring up tandem OLEDs.
Regarding OLEDs, now that you mention, the subpixel layouts were left unaddressed.
Regarding quantum dots, I missed both the mention of QDEL as a somewhat promising future contender, and the mentioning of the drawback of their typical implementation. External light also provides them with energy to activate, which I believe is at least partially the cause behind the relatively poor black levels of QD-OLEDs in environments with significant ambient light (+ something about it not being possible to put a polarizer in front of them?)
I was also generally expecting a more in-depth look by the title, would have loved to learn about the driving electronics, maybe learn about why OLEDs aren't ran anywhere near as fast as their full potential (I'd assume throughput limitations), etc. Overall, it basically only covers as much as my own enthusiast but not in-the-area self gathered over the years too.
> Regarding CRTs, at the vector CRTs section, they mention "they were mostly monochrome and so the phosphor dots could be tightly packed" - this is not true either I believe, monochrome CRTs had a uniform phosphor coat on the inside, no pixel patches.
This is one of the reasons why emulated versions of Asteroids (arcade game) can never match the real thing: the razor-sharp, perfectly straight lines with zero aliasing used to paint the display. The computer also has fine-grained control of how bright to make the electron beam that raster displays typically don't allow (this is perhaps as simple as holding the beam in place, or drawing back and forth over the same line segment), meaning that your ship's projectiles and enemy shots appear as super-bright points with a phosphor bloom around them, glittering in the dark. Most emulators simply draw them as nondescript pixels. I suppose with some effort a CRT simulator can be hooked up to the emulator... but it still wouldn't be the same.
I'm glad I got to play an authentic Asteroids before I died. Working machines are getting rarer. Some of those who come after me may not get that chance.
My first and only time playing Asteroids in its original vector CRT glory was a bit shocking to me. I remember the evolution of CRTs in the 80s and 90s. My family had a small B&W CRT that fascinated me with its image quality, in that it always reminded me more of a b&w photo than color CRTs reminded me of color photos.
Still, that vector CRT that I saw perhaps a dozen years ago was quite a surprise. Lack of rastering and the utterly insane brightness sent me down a rabbit hole. I ultimately concluded I'm not ever likely to own a basement Asteroids cabinet.
I had similar reactions, only it all happened while I was in grade school!
Oh yes! The bright projectiles really add to the game impact. And on some cabinets, the lines were not perfectly straight. It looked for all the world like the phosphor coating had a bit of texture to it. Now being older, I realize an effect like that could just be a marginal DAC too.
IMHO the best vector experiences, in order are:
STAR WARS
This is a color vector display cranked up to the nines! The processor handling the vector drawing is fast! Tons of vectors are possible with only subtle impact on display refresh speed and overall quality. There is some global image size artifacts that happen when some of the brightest objects occupy a significant percentage of the display.
And that is a feature! Love it. Get into a sit down cabinet if you ever get the chance.
TEMPEST
This game is not for everyone. Most of these drive people to their limits, but TEMPEST ramps up and beyond normal human limits! Not everyone can play this game at its peak. Same can be said of nearly everything on this list, but without that aggressive ramp up.
ASTEROIDS
I prefer the original cabinet with the somewhat slower object motion. That one is a bit easier to play. Depending on the operator and how hard they drive the CRT, image brightness ranges from a bit old, washed out and tired looking to WOW! How do those tiny projectiles not just carve a line right into the phosphors.
Cinematronics games: TAIL GUNNER, STAR CASTLE, RIP OFF.
These use overlays for a bit of color. Oh, I forgot ARMOR ATTACK, which uses large ones like STAR CASTLE.
The quality of the vectors is not quite as good as the ATARI displays and this too is a feature. That gives Cinematronics a bit of charm I find quite enjoyable
And sound! Hoo boy! STAR CASTLE has great, loud --> I mean loud sounds with full bass notes able to rumble you and the cabinet!
OTHER COLOR VECTOR GAMES
I like playing all of these, but they simply were not peak experiences. Still damn good, if you ask me:
MAJOR HAVOC, GRAVITAR, A Two Player tandem Asteroids game I cannot recall. Fun though!
And last place: QUANTUM played with the Trackball. You circle atoms over and over. This game looks cool and is hard.
GRAVITAR uses the Asteroids movement dynamics to great effect! A fun thing in this game is massive changes in scale happen often. Rare to see.
Vector gaming delivered many of my very highly cherished arcade gaming experiences for sure.
ATARI and Tektronix deserve special mention in this context:
Atari made color vector games work! Did anyone else? Those look amazing! And hold up today in my view.
Tektronix invented both a pure storage tube CRT. Their graphics terminals often doubled as Minicomputers programmable in Tek Basic. The large ones offered a 4K vector space! Crazy good detail for the 70's. And one in good condition, operating in a reduced light room is beautiful to use.
My first manufacturing CAM software experience was on one of these. Used a fixed record length cassette so that many "files" could be accessed almost like a floppy disk drive. User data went right to the paper tape puncher / reader. 1200 baud punch, reads could be faster, up to 9600, if one had a good reader unit.
One ran applications from that cassette and stored and used user data from the paper tape.
But I digress!
Right near the end, Tek managed to get both storage graphics and dynamic refresh capable graphics, both in a different color. I only got to use one of those one time. I loved it because many different work flows were possible.
Man, for the chance to code a UI on one today!
One last thought: in my view vector displays are best on a CRT, mostly because of the image contrast and speed possible, but great vector experiences can also be had on a wall, or perhaps a screen with some coating to bring out the best possible.
We may yet see vectors appear from time to time in these and other ways simply because of how great they are. Hope so, and building a small, color capable one using a low power laser and screen with coatings sure to deliver motion trails is on ky bucket list.
The article also assumes all LCDs are transmissive, and the bulk are, but reflective (and transflective) LCDs are a thing.
Assuming a 60Hz refresh rate, does it take ~16ms (± the vblank inteval) for a complete cycle from top-left to bottom-right? Or does the scan happen faster than that (with something else being the limiting factor on overall refresh rate)?
Yes, the refresh cycle takes ~16.6 ms. There's another "point" chasing behind the refresh "point", that will be where the panel's response time has finished catching up with the refresh. In between these points, the pixels are slowly morphing from one color to the next. On LCDs, the area between these two points is quite sizeable, definitely more than a few lines, sometimes even hundreds of lines. On a 1080p 60 Hz display, just 1 ms of response time corresponds to 64.8 lines (6% of the screen) being constantly in flux, for example.
The difference between LCDs and CRTs in this regard then, is that on a CRT you only ever got light during that chase section. The initial state is full darkness, and the final state is full darkness too. It's a pulse.
I don't know how common it is now, but a lot of high-resolution LCDs with dual LVDS interfaces were essentially two separate panels, with one lane feeding the top half and the other the bottom half.
Indeed, one feature of active-matrix (and even passive-matrix) displays is that it needs only m + n signal lines to address a pixel in an m + n display. To change the color of a pixel, a signal goes out over the lines corresponding to the row and column of the addressed pixel, selecting it; and then another signal is transmitted over another line to actually change the value of that pixel. In this scheme, it would be impossible to address all pixels simultaneously. Nor would you actually want to, as this would require millions of control lines to drive the display!
Not only was the initial diagram all/explaining, but the "pop"-"pip" on zoom-unzoom of the image was just as nice as playing with a sheet of bubble wrap.
Wow, and that ruler on the right side, even with the sound.
One of the nicest pages I have been on.
And the landing page... https://www.makingsoftware.com/
It just keeps on giving.
Agreed, very talented communicator. Reminds me of the wonderful work of Bartosz Ciechanowski
https://ciechanow.ski/archives/
So crisply done. I wish if Dan writes textbooks for all science & math books for High School students. World would be a better place for those who struggle to understand academics.
Adding my congrats as well. The combination of well-written explanations for the semi-technical layperson combined with clear, intuitive graphics is a powerful instruction platform.
Agreed, absolutely stunning diagrams and visual design.
This appears to be a lovely project. I wish the author all possible luck and success. I haven't joined a mailing list in a very long time, but I sure did in this case.
CRT displays are one of those analog technologies that are arguably much cooler than their digital successors. Think – a literan raygun, a particle accelerator, inside your monitor, creating the image you're looking at.
Active matrix flat panels felt like incredibly cool technology when they became available in the 1990s.
Each individual pixel is driven by a transistor and capacitor that actively maintain the pixel state? Insane manufacturing magic.
Dead pixels used to be a big problem with LCD displays. Haven’t thought about that in at least twenty years.
True – but on the other hand, it was "only" a few million elements, and very large ones, compared to, say, the DRAM chips of the time. Monitors certainly make the engineering feat more tangible, though!
It’s certainly one the bits of tech that would be an insane pitch if invented today: “Yes, please stick your face in front of this particle accelerator. I assure you, it’s completely safe. You may experience some visual side effects but that’s completely intended.”
It's much cooler if you haven't used it. That mass of a 19in was crazy. Then you had all of those that had the high pitched noise. And if you were unlucky you had to degauss them. Cool concept, but in practice the digital successors are better.
"I was there" too and somehow this is not my reaction at all.
Everyone knows the obvious reasons we don't use crts any more.
It's true but it's a most uninteresting observation that only cares about practical aspects. Practical aspects matter, none of my own desks has a crt, but they do not define life itself.
Those facts do not at all invalidate the point about the desirable aspects which have been lost, or the fact that the merely interesting and remarkable aspects are interesting and remarkable.
The desirable and/or interesting and remarkable features of a crt are still cool, impressive, fun, desirable, even though we all voluntarily choose to use something else basically everywhere we want a screen because of the practical reasons that just happen to overwhelm.
Trust me, I remember. Cool does not equal convenient. Once a friend and I dragged three extra CRTs to a demo party just so we could put them side by side and write a program that displayed random scrolling messages. Controllable via an IRC bot, even! Today you could do that with a single ultrawide…
Mostly. But multi-scanning to different resolutions is something I'll miss.
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
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.
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-phosp...
[1] https://www.researchgate.net/figure/Phosphor-persistence-of-...
[2] https://www.researchgate.net/figure/Stimulus-succession-on-C...
> The phosphor still drops off very quickly [0][1][2], roughly within a millisecond.
It's phosphor chemistry dependent. Different color patches on the same glass would decay at different rates even. But yeah, 1 ms is a good lower bound, although when I last researched this, it was definitely the best case scenario for CRTs. I'm fairly sure the ~500 Hz OLEDs that are already floating around are beating the more typical CRTs of old already.
> That’s why you would need a 1000 Hz LCD/OLED screen with really high brightness (and strobing logic) to approximate CRT motion clarity.
At 1000 Hz you wouldn't need the strobing anymore (I believe?), that's the whole point of going that fast. We're kinda getting there btw! Hopefully with HDMI 2.2 out, we'll see something cool.
> On a traditional NTSC/PAL CRT, 1 ms is just under 16 lines, but the latest line is already much brighter than the rest.
That doesn't really math for me. NTSC would be 480 visible lines at 60 Hz, and so 480 lines / ~16.6 ms = 28.8 lines/ms (6% of the screen). Note that of course PAL works out to the same number: 576 lines / 20 ms = 28.8 lines/ms (just 5% of the screen here though!).
I'm not quite sure what you're saying here. My assertion is that a visible image persists on the screen longer than it appears in the slo-mo clip. You can just point a camera with an adjustable shutter speed at a CRT and see it for yourself. Here's an example (might need to copy the URL and open in a new tab, they don't like hotlinking):
https://i.sstatic.net/5K61i.png
The brightly-lit band is the part of the frame scanned by the beam while the shutter was open. The part above is the afterimage, which, while not as bright, is definitely there.
That link shows an error with Access Denied to me. I didn’t deny that an afterimage is there. I meant to point out that the brightest part by far, which what is most prominently perceived by the eye, isn’t much more than one scanline, in SD.
> The part above is the afterimage, which, while not as bright, is definitely there.
Yes it's there, but it's much less bright than the the scanned area, so it will be hardly perceptible relative to the bright part. The receptors in the eye will hardly respond to it after being excited so strongly by the bright part.
I'm not sure about this calculation though. Phosphor decays exponentially with a time constant of roughly 5ms (according to HP [1]). This means when a new frame comes at 60Hz refresh rate there is still 10-15% of the previous frame related excitation is present. This means there is considerable amount of nonlinearity, hence the performance is even worse than 10ms LCD/OLED displays.
Genuine question: why do you think CRTs are better?
[1] https://hpmemoryproject.org/an/pdf/an_115.pdf
That HP reference is from 1970; CRTs did improve over time. The references I gave show that the intensity drops to below 10-15% within about a millisecond. The difference with LCD/OLED displays is that the latter are sample-and-hold, meaning that they show the image at full brightness for the duration of the whole frame. Their pixel response time may be faster than CRT phosphor persistence, but that is less relevant. The problem with LCD/OLED is that they hold the picture for the duration of the frame, which means that a depicted moving object that is supposed to move smoothly during the duration of a frame, is shown as not moving for that duration, which the eye perceives as motion blur. That motion blur is significantly reduced on CRTs, because they show the object only for a fraction of the frame duration at high brightness, as if under a stroboscope, which makes it easier for the eye (or brain) to interpolate the intervening positions of the object.
> Genuine question: why do you think CRTs are better?
CRTs are worse in most aspects than modern displays, but they are better in motion clarity. As to why I think that: I used both in parallel for many years. The experience for moving objects is very different. It is a well-known drawback of sample-and-hold display technologies. And it is supported by the more systematic analyses done by the likes of Blur Busters.
>The problem with LCD/OLED is that they hold the picture for the duration of the frame
Not necessarily. For example on VR headsets the LCD/OLED will only hold the picture for 10% of the frame.
Yeah, they do backlight strobing (LCD) or black frame insertion (OLED), to reduce blurring during smooth eye movements, at the cost of overall screen brightness. I actually think small CRTs would be perfect for VR headsets in this regard, as they are naturally have very short frame persistence.
One likely problem for battery powered headsets is the (I believe) relatively high CRT power draw. Another is probably the fact that they aren't used for anything else anymore, meaning CRT development has stopped a long time ago. There were quite small CRTs in the past for special applications, but probably not as small as is optimal for modern VR headsets. Both for optics and weight and space reasons.
> Genuine question: why do you think CRTs are better?
They have many disadvantages, but an advantage is that CRTs mostly remove the "persistence blur" induced by smooth pursuit eye movements on sample-and-hold displays like LCD and OLED. Here is an explanation:
https://news.ycombinator.com/item?id=42604613
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.
What model is your new monitor?
The ASUS PG27UCDM 26.5" 4K UHD (3840 x 2160) 240Hz Gaming Monitor [0] paired with an RTX 5090 for my home desktop, but I got a USB switcher (for peripherals), and keep it on my standing desk that I plug in my work laptop too with a USB-C to DisplayPort cable. Only 60hz on the work laptop but I really like having a quad monitor setup in a T shape (3 27” monitors and the laptop plugged in with screen open below the central monitor, which is the OLED). It’s great for both productivity and for gaming. I turned off HDR for work, though.
The only annoying thing is every couple hours it asks me to run a 7 minute pixel refresh cycle to avoid burn in, but according to the dashboard I run it every 2.5 hours or so when I go on breaks, so I think I’m good.
Overall the monitor is just fantastic, my LAN party buddies and I dreamed about OLEDs like this back in 2003 and kept saying it was “just around the corner”. The biggest thing is in dark scenes in games there’s absolutely zero noticeable smearing.
[0] https://www.microcenter.com/product/689939/asus-pg27ucdm-265...
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.
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.
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)
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.
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.
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.
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?
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.
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
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.
That's the cool thing about analog video, it doesn't really have the concept of horizontal resolution. Especially when it's monochrome. It's made up of lines that continuously change brightness as they're drawn.
Color composite video, as far as I understand, does have a limit to the horizontal resolution because in all three standards the color information is encoded as a high-frequency signal added to the main (luminance) one, so that frequency is your upper limit on how quickly the luminance can change.
S-video, VGA, and component should, in theory, allow infinite horizontal resolution and color.
> It's an illusion.
In a sense, all vision is.
All our senses are.
Except the pain of hitting your pinky on a corner. That one's very real
I'm much more interested in the hardware driver. This thing gets digital encoded input, has to decode it, and then multiplex it to 8 million pixels. 60 times a second. Being able to hit at least 4 million different levels (talking about 4K 60fps 12 bit color).
The input is roughly serial, so it takes a massive serial to parallel conversion.
But the output of the scaler chip is still serial, just now it's guaranteed to have the same dimensions as the panel itself, and includes whatever OSD overlay might be active, and any gamma/contrast/whatever adjustments. I believe in some cases, this is also where dithering takes place, to take a 6-bit panel and try to give it 7-bit (or, yikes, 8-bit) color depth by PWMing pixels that have intermediate values.
Look at the connector pinout of the panel itself. There's only 50 pins or so, and a lot of them are grounds. Whether the scaler-to-panel format is eDP, or LVDS (FPD-Link), or V-by-One, it's all still differential serial lanes at that point.
Around the perimeter of the panel, then, are the actual TCON and row/column driver chips, bonded right to the ITO traces on the glass, flip-chip-on-glass style. These have an outrageous number of pins, and directly connect to the gate (row) and source (column) traces. It's here that the serial becomes parallel, and the next stop is the transistors themselves (hence the MOSFET signal terminology of gate and source) in the individual pixels.
Older displays would have basically a bunch of serial-to-parallel register chips with each one's SO connected to the next one's SI. I ran across a fasincating video of replacing a bad chip in such a display, which happens to be gas plasma so the voltages involved are also pretty high too:
https://www.youtube.com/watch?v=6W3H5wOy5sY
Yeah, with an electron beam it's clear that it's a continuous signal and a single beam is being controlled, but how do you drive millions of individual digital pixels all at once, how does the signal get routed correctly to each one if them?
with older HDMI/DVI displays, AFAIK you sync pixel clock to "address generator" for the matrix, with major issue becoming scaler AFAIK.
DVI (and thus older HDMI) being essentially "VGA that skipped Digital to Analog conversion" you're riding the beam, including porches.
Teletypes were long gone by the time I started playing with computers, but computing definitely existed before CRTs were the dominant output format.
I have to take issue with the usage of the terms "pixel" and "subpixel" with regards to CRT. CRTs do not display discrete pixels. They display discrete scanlines, each one made up of a smoothly varying voltage across the line (and thus resolution is a function of both the DAC in the display device in the case of systems that generate a digital signal and then convert it to analog for display, and the hardware inside the CRT monitor). Also, there is no mapping between any "pixels" represented within that varying voltage and the separate color phosphor dots.
Even "digital RGB" isn't digital in terms of the CRT. It's only "digital" because each color channel has a nominal on and off voltage, with no in-between (outside of the separate intensity pin). However, the electron gun still has a rise and fall time that is not instant.
Displays didn't truly become digital for the masses until the LCD era, with DVI and HDMI signals. Even analog HD CRTs could accept these digital signals and display them.
I don't think this is an entirely fair characterization either. Note that everything I lay out here is just based on accumulated information gathered over the years due to vague interest, I haven't worked on or with CRTs (did use them though).
Monochromatic CRTs were well and truly resolution agnostic, there were legitimately no pixels or subpixels or anything similar to speak of. That said, the driving signal still had to be modulated to produce an image, and so it's not magic either. You can conceivably represent [0] all the available information in them using just 720 samples per line, which is exactly why DVDs had that as their horizontal resolution (720 pixels).
This story changes a bit though with color CRTs, where you did have discrete sets of patches of different phosphor chemistries called triads. There was absolutely a fixed number of them on a glass, so you could conceivably consider that as the native resolution for that given display, with each triad being a pixel, and each patch being a subpixel. The distance between these was the aperture pitch, much like how you have a pixel pitch on a typical flatpanel display.
The kicker then is that as you say, there's no strict addressing. From what I understand there were multiple electron guns scanning across the screen simultaneously, only being able to hit the specific color they were assigned, but the patch they were hitting wasn't addressed, they just scanned across the screen like the single electron gun did in monochromatic CRTs. You'd then get resolution invariance by just the natural emission spread providing you with oversampling / undersampling without any kind of digital computational effort. It's not really true resolution independence like with the monochrome ones, I'd say. I even recall articles where they were testing freshly released CRT monitors, and discussing how sharp the beam was, resulting in what kind of resolution adherence.
[0] an earlier version of this comment said "extract from" here; for various reasons you might already know, that's a different thing, and would not actually be true.
Years ago I had an LG 32" wide-screen CRT TV. I chose that model because it had a VGA port. It advertised a resolution of 640x480.
I was thrilled when my computer let me choose a resolution of 848x480, and it worked perfectly.
Back in those days, the web was usable at that resolution.
It still basically should be, so long as well-designed sites give you the "small screen"/mobile layout.
Even apart from that, a lot of laptops still have 1280x800 as the default resolution, and that's only double the width of 640x480. Honestly, I'd actually be more worried about OS and browser chrome eating up the space than websites themselves being unusable.
> "It still basically should be, so long as well-designed sites..."
I believe that their point wasn't that "the web" has intrinsically changed, it was that too many sites are not well designed in this respect.
edit: they actually replied just before me and it seems that wasn't their point, but it would be my point (though I personally don't care about being able to use such a low resolution).
The 480 height is the bigger issue.
Try browsing on your phone in landscape mode.
Yes, fair, and that's also when OS/browser chrome takes an even bigger bite out of the viewport.
Am I the only one who read this as the terminal program "screen" (the terminal multiplexer)?
It was 50/50 for me as well but the screen source code is fairly readable and if I remember right eerily over-commented for Unix code! The function names actually make sense.
Ha, I did that too.
I can appreciate these articles as they are but I personally don’t like them. They are junk food level of infotainment to me. Something I’d find on a Wikipedia summary section that covers general points.
A CRT - to name one - is a device whose actual understanding will challenge people in profound ways. To ask “how does a screen even work?” and to begin to answer this question will require a bit more than a summary form of “thing goes from point A to point B”. The history of this discovery is a stack of books and in and of itself is fascinating - the experiments and expectations and failures and theories as to why and how. I suppose I just expect more of the site. The illustrations are nice. Oh and my moniker is just a coincidence.
Sure, but I sent this to my nerdy early teen nephews and they actually liked it! This is no small feat.
Agree. It is the equivalent of a coffee table book.
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If the author is here.
Would be nice if you could give a hint on all the disabled chapters. Either a tooltip or even just a title attribute. Are they paid? Do I have to login? Not ready yet?
LCD on paper you see lots of drawbacks, in practice modern state of the art LCD for TV is pretty damn good. We will soon have RGB LED Backlight LCD with WHVA+ Panel that is about as wide angle as IPS, 95%+ REC 2020 colour, and 1-2ms response time.
Phosphorescent blue OLEDs should reduce current OLED display energy usage by 20-30%. But it still seems to be way off for phones and mass usage.
I think it's fairly common for technologies to get really good just as they're becoming obsolete. Vacuum tubes, CRTs, optical disks, photographic film... in fact, they're often in some respects better than the early generations of the technology that replaces them.
But OLEDs just have too many advantages where it actually matters. Much lower power consumption, physically more compact (no need for backlight layers), etc.
You might add ICE cars to that list. All kinds of cool stuff being developed around small turbocharged engines and other efficiency gains, excellent transmissions, etc.
For me, OLEDs fall into a category exemplified by Anton Gudim's "YES, BUT" comic series.
YES, OLEDs consume less power, offer truer color reproduction, and are physically more compact.
BUT, they are prone to CRT-like burn-in.
SSDs, the same thing.
YES, SSDs are much faster and immune to mechanical failure.
BUT, they tend not to last as long as HDDs due to limited write cycles, and their price per GiB is still much higher.
None of that really helps LCDs primary downsides of poor contrast ratio and relatively high energy consumption. Backlit displays will always inherently score worse on these metrics vs self emissive displays.
>downsides of poor contrast ratio
In terms of TV. LCD have higher peak brightness. The Sony Bravia 10 will be out soon, hopefully it will showcase the world what LCD could be.
Not to mention cheaper at larger size panel.
peak brightness is not contrast. If anything higher peaks mean worse contrast, even for systems with local dimming zones due to bleed between zones / gradients in display content which do not align with backlight zones.
The energy efficiency of LCDs is very good, typically better than OLED screens, except on very dark content.
LCDs as a transmissive display technology work by emitting a bunch of photons and then selectively filtering some out to achieve the desired color / pixel brightness. Any filtered photon is wasted energy, this is inherent to the display technology and is not limited to dark content, just exacerbated by it.
Given that, all things equal there is no way for LCD to equal the efficiency of a self emissive display, at best it's a question of when will the luminous efficiency of OLED exceed that of white/blue backlight LEDs... and honestly we're likely already at or past that point.
I happen to have a stereo microscope at my desk, so I put my Pixel 9 under there. At 100x mag (10x ocular x 10x objective) it looks like there are 3 layers: as I move my head around slightly (so the image is moving over my retinas), the blue moves faster and the red almost stays still, with green somewhere in the middle.
Put a magnifying glass on your LCD display and you can see the sub pixel pattern...
A few decades ago I worked on a huge machine that made LCD color filters.
Or just a drop of water…
Or sneeze on them.
I know this is HN, but I honestly clicked this link initially thinking it was going to be a detailed analysis of how screen plays are constructed and executed in football.
It’s late and time for bed! LoL.
I was expecting a Ciechanowski link lol.
The drawings are really good. Any idea what tool is used to make them? I emailed the author but have not heard back.
From the FAQ on the main page:
> How do you make the illustrations?
> By hand, in Figma. There's no secret - it's as complicated as it look
Everything on the site seems high quality, very much looking forward to the upcoming articles
This is a great project. I want to show it to as many teenagers as I can.
The ticker on the right is quite nice, but I perceive the sound as coming from within my nose (if that makes any sense) to the point that I thought something was going on with my sinuses for a full 3 seconds, and got panicked.
Wonderful content and website otherwise!
Very cool looking website. Looking forward to the quality content
what a beautiful project. cant wait for this to be completed
So fascinating!
See also the author's page linked from the post. More very well-done content https://typefully.com/DanHollick
>The fact that they ever made it out of the research lab and into our homes is astonishing to me.
What is astonishing about LCDs? I don't mean to diminish the difficulty of scaling up the process, but if you think of early LCD displays they don't seem farfetched to be shipped to consumers.
One random example is that your eyes are extremely sensitive to the tiniest defect or variation. So making a large display that looks good and is uniform is very challenging. Not to mention scaling up all the various processes like the photolithography and working with very large and thin glass panels.
It's all engineering but it's surprisingly hard to move things from the lab to manufacturing at scale. Years and years and lots of problem solving. Some efforts/approaches fail and you never hear of them.
You are moving the goal posts from it being a consumer product to requiring it to be large, good, and uniform. Yes, there was engineering work to make such a consumer product, but it is something I would expect there to have been line of sight for.
I was just giving one example.
The first LCD products I remember were things like 7 segment digital watches and calculators where the LCD was passive and the "pixels" were large. I am not super familiar with how that went from lab to consumer product but I imagine even there it was non-trivial.
It took a long time to progress to modern LCD displays. It took years to get from small black and white displays, to small color, to larger and larger displays. Productizing this stuff includes building machines, factories, ASICs, and figuring out a lot of technology as you go along.
Some interesting history here: https://www.varjukass.ee/Kooli_asjad/Ylikool/telekom/displei...
I'm not saying that it wasn't nontrivial, but that it wasn't surprising that it was able to happen.
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