Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

How does a screen work?

makingsoftware.com

Post reply on HN
Print view View original

51–60 of 111 posts

Re: How does a screen work?

#51

Post by grishka »

somat wrote: post #43
grishka wrote: post #14

Earlier quoted context omitted.

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 di…

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 rad…

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.

Re: How does a screen work?

#52

Post by bgnn »

layer8 wrote: post #38
hinterlands wrote: post #12

Earlier quoted context omitted.

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 accu…

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

Re: How does a screen work?

#54

Post by layer8 »

hinterlands wrote: post #45
layer8 wrote: post #38

Earlier quoted context omitted.

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 accu…

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 s…

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.

Re: How does a screen work?

#55

Post by mikepurvis »

rahimnathwani wrote: post #47
mikepurvis wrote: post #46

Earlier quoted context omitted.

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.

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.

Re: How does a screen work?

#56

Post by layer8 »

bgnn wrote: post #52
layer8 wrote: post #38

Earlier quoted context omitted.

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 accu…

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…

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.

Re: How does a screen work?

#58

Post by BenjiWiebe »

wincy wrote: post #42
layer8 wrote: post #38

Earlier quoted context omitted.

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 accu…

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?

Re: How does a screen work?

#59

Post by stalco »

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!

Re: How does a screen work?

#60

Post by tempestn »

hinterlands wrote: post #24
ksec wrote: post #17

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), e…

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.
Post reply on HN