3 ms·

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 t

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

f1shy 1y ago
And still it was possible as a side attack, with just looking at the reflected brightness of a screen, to get a perfect image back.
layer8 1y ago
The phosphor still drops off very quickly [0][1][2], roughly within a millisecond. That’s why you would need a 1000 Hz LCD/OLED screen with really high brightness (and strobing logic) to approximate CRT motion clarity. On a traditional NTSC/PAL CRT, 1 ms is just under 16 lines, but the latest line is already much brighter than the rest. The slow-motion recording showing roughly one line at a time therefore seems accurate. [0] https://blurbusters.com/wp-content/uploads/2018/01/crt-phosphor-versus-strobe-backlights.png https://blurbusters.com/wp-content/uploads/2018/01/crt-phosp... [1] https://www.researchgate.net/figure/Phosphor-persistence-of-CRT-monitor-Phosphor-persistence-lasts-approximately-64-ms_fig16_5550239 https://www.researchgate.net/figure/Phosphor-persistence-of-... [2] https://www.researchgate.net/figure/Stimulus-succession-on-CRT-vs-LCD-monitors-Schematic-of-the-luminance-course-of-a-disk_fig4_47358140 https://www.researchgate.net/figure/Stimulus-succession-on-C...
- wincy 1y ago
  I definitely like my new 240hz 4k oled HDR monitor, though. They're getting there! The data rate it's pushing through the displayport cable for uncompressed 4k HDR is something 80gb/s though. Absolutely mind boggling. Huge upgrade from my 1440p 165hz IPS monitor that had huge amounts of smearing when playing games.
  - BenjiWiebe 1y ago
    What model is your new monitor?
    - wincy 1y ago
      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-265-4k-uhd-(3840-x-2160)-240hz-gaming-monitor https://www.microcenter.com/product/689939/asus-pg27ucdm-265...
      - archagon 1y ago
        I hear OLEDs aren’t ideal for text display (and, ergo, productivity uses). Does this not match your experience with this monitor?
- hinterlands 1y ago
  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 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 1y ago
    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.
  - cubefox 1y ago
    > 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.
- bgnn 1y ago
  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 https://hpmemoryproject.org/an/pdf/an_115.pdf
  - layer8 1y ago
    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.
    - charcircuit 1y ago
      >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.
      - 1y ago
- perching_aix 1y ago
  > 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!).

f1shy 1y ago

And still it was possible as a side attack, with just looking at the reflected brightness of a screen, to get a perfect image back.

layer8 1y ago

The phosphor still drops off very quickly [0][1][2], roughly within a millisecond. That’s why you would need a 1000 Hz LCD/OLED screen with really high brightness (and strobing logic) to approximate CRT motion clarity. On a traditional NTSC/PAL CRT, 1 ms is just under 16 lines, but the latest line is already much brighter than the rest. The slow-motion recording showing roughly one line at a time therefore seems accurate. [0] https://blurbusters.com/wp-content/uploads/2018/01/crt-phosphor-versus-strobe-backlights.png https://blurbusters.com/wp-content/uploads/2018/01/crt-phosp... [1] https://www.researchgate.net/figure/Phosphor-persistence-of-CRT-monitor-Phosphor-persistence-lasts-approximately-64-ms_fig16_5550239 https://www.researchgate.net/figure/Phosphor-persistence-of-... [2] https://www.researchgate.net/figure/Stimulus-succession-on-CRT-vs-LCD-monitors-Schematic-of-the-luminance-course-of-a-disk_fig4_47358140 https://www.researchgate.net/figure/Stimulus-succession-on-C...

wincy 1y ago
I definitely like my new 240hz 4k oled HDR monitor, though. They're getting there! The data rate it's pushing through the displayport cable for uncompressed 4k HDR is something 80gb/s though. Absolutely mind boggling. Huge upgrade from my 1440p 165hz IPS monitor that had huge amounts of smearing when playing games.
- BenjiWiebe 1y ago
  What model is your new monitor?
  - wincy 1y ago
    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-265-4k-uhd-(3840-x-2160)-240hz-gaming-monitor https://www.microcenter.com/product/689939/asus-pg27ucdm-265...
    - archagon 1y ago
      I hear OLEDs aren’t ideal for text display (and, ergo, productivity uses). Does this not match your experience with this monitor?
hinterlands 1y ago
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 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 1y ago
  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.
- cubefox 1y ago
  > 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.
bgnn 1y ago
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 https://hpmemoryproject.org/an/pdf/an_115.pdf
- layer8 1y ago
  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.
  - charcircuit 1y ago
    >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.
    - 1y ago
perching_aix 1y ago
> 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!).