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That's one thing I never understood. With CRT's, you still had discrete pixels (either clusters of 3 RGB dots, or 3 RGB bars). But no matter the resolution (w

by derekp7 13y ago

That's one thing I never understood. With CRT's, you still had discrete pixels (either clusters of 3 RGB dots, or 3 RGB bars). But no matter the resolution (within the CRT's limits), nothing looked blotchy. Whereas on an LCD, you can always tell when it isn't running in a native resolution (or even divisor). So what is the difference? Other than a CRT would naturally do analog interpolation, couldn't an LCD or graphics adapter be programmed to simulate the same effect?

majormajor 13y ago
The hardware side is where things start getting out of my area of knowledge, but my understanding is that yes, CRTs had a native upper bound on their resolution which had to do with the dot pitch of the display. I would guess that the way this worked in practice is that for lower resolutions they were effectively partially lighting up multiple phosphors per pixel on each pass? I imagine the difference between this an an LCD is that the amount of time a single pixel was lit by the beam on a CRT is far, far lower than the refresh rate of an LCD. I believe there were monitors that went both ways with this, not just letting you run lower than native but also higher than native (I had a 17" CRT that claimed to support 1600x1200, but not without a lot of blurriness, for instance). edit: man, it's really hard to find specific info about how exactly that worked online these days
bhauer 13y ago
I am not a hardware guy, but from my understanding a CRT uses an electron gun a distance from the screen to cause a matrix of phosphors to emit light. Hence the depth of CRTs. The electron gun can repeatedly scans from top to bottom, left to right (or whatever direction). It can be adjusted to make any number of vertical "lines" as it sweeps over the phosphor matrix, but the matrix has a fixed dot-pitch. Because an electron beam is being shot at the matrix from a distance, there's a certain degree of bleed-over to neighboring phosphors. Firing electrons at the phosphors at coordinate 100,200 means a little bit of energy is also received by 99,199 and other neighboring "virtual pixels." In other words, while the phosphor matrix was just as rigid as the pixel matrix of an LCD, the power source that caused light to be emitted was not perfectly matched 1:1 with the matrix. There isn't an electron gun for each pixel, there is a single electron gun for the whole display. By comparison, each pixel in an LCD monitor (putting aside the three internal pixels for colors) is an individual mask over a uniformly white back-light. The panel adjusts the opacity of the mask to allow more or less of the white backlight through. The mask over a backlight is what gives LCDs a challenge with viewing angle (because there's a non-zero gap between the light source and the mask and the mask itself has a non-zero depth). Finally, as I understand it, a plasma television is a bit like both. It's a matrix of phosphors like a CRT, but with individual power sources for each pixel like an LCD. Because light is emitted at the surface, plasmas tend to have very good viewing angles. OLED then is, in my opinion at least, a spiritual successor to plasma. OLED emits light at its surface like an LCD or plasma, but uses no mask layer over a backlight, like a CRT or plasma. (Take all of the above with a grain of salt because I'm just a layperson when it comes to hardware.)

by derekp7 13y ago

majormajor 13y ago

The hardware side is where things start getting out of my area of knowledge, but my understanding is that yes, CRTs had a native upper bound on their resolution which had to do with the dot pitch of the display. I would guess that the way this worked in practice is that for lower resolutions they were effectively partially lighting up multiple phosphors per pixel on each pass? I imagine the difference between this an an LCD is that the amount of time a single pixel was lit by the beam on a CRT is far, far lower than the refresh rate of an LCD. I believe there were monitors that went both ways with this, not just letting you run lower than native but also higher than native (I had a 17" CRT that claimed to support 1600x1200, but not without a lot of blurriness, for instance). edit: man, it's really hard to find specific info about how exactly that worked online these days

bhauer 13y ago

I am not a hardware guy, but from my understanding a CRT uses an electron gun a distance from the screen to cause a matrix of phosphors to emit light. Hence the depth of CRTs. The electron gun can repeatedly scans from top to bottom, left to right (or whatever direction). It can be adjusted to make any number of vertical "lines" as it sweeps over the phosphor matrix, but the matrix has a fixed dot-pitch. Because an electron beam is being shot at the matrix from a distance, there's a certain degree of bleed-over to neighboring phosphors. Firing electrons at the phosphors at coordinate 100,200 means a little bit of energy is also received by 99,199 and other neighboring "virtual pixels." In other words, while the phosphor matrix was just as rigid as the pixel matrix of an LCD, the power source that caused light to be emitted was not perfectly matched 1:1 with the matrix. There isn't an electron gun for each pixel, there is a single electron gun for the whole display. By comparison, each pixel in an LCD monitor (putting aside the three internal pixels for colors) is an individual mask over a uniformly white back-light. The panel adjusts the opacity of the mask to allow more or less of the white backlight through. The mask over a backlight is what gives LCDs a challenge with viewing angle (because there's a non-zero gap between the light source and the mask and the mask itself has a non-zero depth). Finally, as I understand it, a plasma television is a bit like both. It's a matrix of phosphors like a CRT, but with individual power sources for each pixel like an LCD. Because light is emitted at the surface, plasmas tend to have very good viewing angles. OLED then is, in my opinion at least, a spiritual successor to plasma. OLED emits light at its surface like an LCD or plasma, but uses no mask layer over a backlight, like a CRT or plasma. (Take all of the above with a grain of salt because I'm just a layperson when it comes to hardware.)