[HN Gopher] How does a screen work?
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How does a screen work?
Author : chkhd
Score : 287 points
Date : 2025-07-13 14:09 UTC (8 hours ago)
(HTM) web link (www.makingsoftware.com)
(TXT) w3m dump (www.makingsoftware.com)
| p44v9n wrote:
| So fascinating!
| qwertox wrote:
| 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.
| consumer451 wrote:
| 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.
| mrbluecoat wrote:
| 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.
| seemaze wrote:
| Agreed, very talented communicator. Reminds me of the wonderful
| work of Bartosz Ciechanowski
|
| https://ciechanow.ski/archives/
| retrac wrote:
| 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
| YZF wrote:
| 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 wrote:
| 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 wrote:
| 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)
| hinterlands wrote:
| 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 wrote:
| 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 wrote:
| 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...
| wincy wrote:
| 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 wrote:
| What model is your new monitor?
| hinterlands wrote:
| 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.
| layer8 wrote:
| 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.
| bgnn wrote:
| 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
| layer8 wrote:
| 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.
| snovymgodym wrote:
| > It's an illusion.
|
| In a sense, all vision is.
| grishka wrote:
| All our senses are.
| flysand7 wrote:
| Except the pain of hitting your pinky on a corner. That
| one's very real
| grishka wrote:
| 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 wrote:
| 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
| Sharlin wrote:
| 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 wrote:
| 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.
| grishka wrote:
| 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.
| charcircuit wrote:
| >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.
| YZF wrote:
| 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.
| charcircuit wrote:
| 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.
| YZF wrote:
| 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/Koo
| li_asjad/Ylikool/telekom/displei...
| charcircuit wrote:
| I'm not saying that it wasn't nontrivial, but that it
| wasn't surprising that it was able to happen.
| YZF wrote:
| 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.
| ryandamm wrote:
| Or just a drop of water...
| nu11ptr wrote:
| Am I the only one who read this as the terminal program "screen"
| (the terminal multiplexer)?
| nyarlathotep_ wrote:
| Ha, I did that too.
| vicurve wrote:
| 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.
| ksec wrote:
| 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.
| hinterlands wrote:
| 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.
| tempestn wrote:
| 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.
| kec wrote:
| 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.
| vicurve wrote:
| 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.
| meindnoch wrote:
| Agree. It is the equivalent of a coffee table book.
| jorkingit wrote:
| 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 stack of books of "the experiments
| and expectations and failures and theories as to why and how".
| The history of this discovery is all of history leading up
| until that point and in and of itself is fascinating - the
| sociopolitical conditions and details of every single person's
| life and their astrological charts as to why and now. I suppose
| I just expect more of the site. Oh and my moniker is not a
| coincidence.
| fabiensanglard wrote:
| The drawings are really good. Any idea what tool is used to make
| them? I emailed the author but have not heard back.
| cyberlimerence wrote:
| 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
| benetttttt wrote:
| what a beautiful project. cant wait for this to be completed
| Sharlin wrote:
| 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.
| pavlov wrote:
| 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.
| Sharlin wrote:
| 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!
| LocalH wrote:
| 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.
| rahimnathwani wrote:
| 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.
| mikepurvis wrote:
| 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.
| rahimnathwani wrote:
| The 480 height is the bigger issue.
|
| Try browsing on your phone in landscape mode.
| mikepurvis wrote:
| Yes, fair, and that's also when OS/browser chrome takes
| an even bigger bite out of the viewport.
| swores wrote:
| > " _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).
| killjoywashere wrote:
| 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.
| mikecarlton wrote:
| See also the author's page linked from the post. More very well-
| done content https://typefully.com/DanHollick
| vojtechrichter wrote:
| Very cool looking website. Looking forward to the quality content
| apricot wrote:
| This is a great project. I want to show it to as many teenagers
| as I can.
| stalco wrote:
| 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!
| ekunazanu wrote:
| Everything on the site seems high quality, very much looking
| forward to the upcoming articles
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(page generated 2025-07-13 23:00 UTC)