Does a pixel change luminance by simply increasing and decreasing value, or does it have to flush before changing?

[xMax]

its a very simple question. assuming all conventional LCDs recieving digital signals from a DVI graphics card function in the same manner.

so if i picked a green subpixel anywhere in the frame, and this pixel had a luminance value of 64, and if it had to change to a value of 192 in the proceeding frame, then does it simply increase to 192 or does it have to flush to an off state before increasing?

and what about infinite sustained persistence: if i had the entire display set to a background color whose value was Red=127 Green=127 Blue=127, and the image was to remain unchanged for a whole year, then would the screen have to be refreshed at some point in time, or can it remain completely idle, as if to say the graphics card wouldn't even need to send signals to the display. and if it had to be refreshed, then how would that work.

:sun:

 

[cirthix]

1: it changes directly and does not go to an off state before increasing
2: thats a controller question and not an lcd issue. lcds are like ram in the sense that they constantly are draining, by removing signal from the controller, you will lose the image. it wouldnt be too hard for a controller to have some ram on it that retains an image, but that depends on teh controller. i know of no controllers that currently offer image retention.

 

[xMax]

i dont get it. all i know is that the liquid crystals end up twisting at varying amounts to allow more or less light to pass through the vertical or horizontal shutters, which in turn in determines the luminance. now this twisting part, does it have to keep getting refreshed ? because i dont see why. it should remain if the image on the screen doesnt change.

basically, ill make it simple since im not exactly very familiar with this kind of knowledge. does the light passing through the color filter end up being drained or not, assuming the simplest scenario where the image remains static.

 

[f95toli]

I am not sure how it is implemented in displays; but the state of a liquid crystal only depends on the strenght of the elecric field . As long as the field is stable nothing will change.

 

[cirthix]

nope, you've got to keep that electric charge steady to keep it at a certain amount of opacity. if you turn off the controller, there's no electric charge, so it will quickly turn clear. if you want to change the state of a pixel, change the state of the electric field accordingly. if you want the screen to retain its image, you'll need a controller that keeps a frame and constantly displays it.

 

[f95toli]

No, it is not the charge, it is the field (E, not Q).
Liquid crystals are basically long molecules that change their orientation according to the strenght of the local E-field.
(but of course you need to apply a voltage difference between the electrodes to align the molecules)

Btw, what kind of crystals are used in the most recent screens? Smectic C*?

 

[V00D00]

some newer technologies will retain whatever image you put on them. I'm not talking LCD, it might be OLED, but I'm not sure. I read about it somewhere that paper-thin flexible screens have been developed that retain the image after the charge is gone. You only need electricity to change the image. It sounds kind of like OLED, but I want to say that it's something else...

 

[cirthix]

its not oled, but yeah, i remember that screen. i forget what its called too 🙁

 

[icarus4586]

i dont get it. all i know is that the liquid crystals end up twisting at varying amounts to allow more or less light to pass through the vertical or horizontal shutters, which in turn in determines the luminance. now this twisting part, does it have to keep getting refreshed ? because i dont see why. it should remain if the image on the screen doesnt change.

basically, ill make it simple since im not exactly very familiar with this kind of knowledge. does the light passing through the color filter end up being drained or not, assuming the simplest scenario where the image remains static.

An electric field is required to keep the molecules in each pixel aligned correctly. This field will dissipate naturally. If the controller is able to sustain the field without input over DVI, then the image could remain unchanged indefinitely. (read: as long as power is being supplied) However, the pixels will naturally lose this orientation if there is no electric field.
I have no idea what you mean by "does the light passing through the color filter end up being drained..."

 

[xMax]

i think i didnt phrase the question properly. lets forget about this whole idea of wether the pixel changes without even using a graphics controller.

lets just assume the typical setup where there is a graphics card hooked up to a display and constantly transmitting digital signals. if i kept the same image on the screen, like a picture screensaver, for about a whole day, then will the luminance value (0-255) of any sub pixel change. that is does the electric field or electric charge, which ever one it is, actually end up changing if the sub pixels dont need to change luminance value, or does it remain the same.

and if it remains, then for how long does it remain. assuming a typical LCD.

thats it. thats my question?

 

[Loki726]

Think of it like this. You have a compass that is pointing north (call this the lcd crystal) and think of north to represent the color 0. Now, you can apply a magnetic field across the compass, and depending on how strong it is, the compass will point to some direction between north and south (between 0 and 255).

The compass will only point to that new direction as long as the magnetic field is applied. As soon as you remove the field, the compass will return to point north. The time it takes for the compass to return to north will bet determined by the strength of he earth's magnetic field, the strength of the compass's magnetic field, the mass of the needle, the friction between the needle and the pivot point, etc... but it will be relatively fast