optical illusion - strobe effect in LCDs?

[dopple]

when you have a grid of pixels this is what can happen http://eyetricks.com/0101.htm

anyone notice this on white backgrounds especially a strobe effect akin to the sparkle of the AG coating, pretty microscopic and moves as you move your eyes like in that optical illusion above.

i saw this on a Apple thunderbolt display which is AG coating free and PWM free so no sparkles or other sources of flicker.

 

[dopple]

or maybe this is because of the LED array behind the display. a combo of pixel array and LED array creating a moving picture as you move your eyes, or eve when you hold your gaze at a spot but the picture around the spot where you gaze moves even when the picture is static and flicker free just like in the optical illusion linked above.

 

[dopple]

i just experimented with this effect a little more as if it were a pixel grid..

here is the image if the brightness is low http://imageshack.us/photo/my-images/32/34800299.jpg/
and here where the brightness of pixels is increased http://imageshack.us/photo/my-images/692/47677829z.jpg/

seems like this optical illusion effect is more prominent when the brightness is lowered. comments welcome.

 

[dopple]

ah-hoy shout out for the intelligentsia in here to make head or tail of this.

 

[dopple]

i did some more research on this
here is a video showing fast moving waves on the LCD screen between 10-30 seconds
http://www.youtube.com/watch?feature=player_embedded&v=kIviL42c28c#!

i think the underlying principle behind these waves is the pixel arrangement which causes the optical illusion which is visible in this video.

i guess only some people have the eyes to catch this or be irritated by it.

this effect is probably being confused with the PWM flicker or AG coating. but that S series model in this youtube video has neither a matte coating nor PWM flicker. It still has the fast moving waves so this is due to the pixel structure.

 

[Mr.Pixel]

when you have a grid of pixels this is what can happen http://eyetricks.com/0101.htm

anyone notice this on white backgrounds especially a strobe effect akin to the sparkle of the AG coating, pretty microscopic and moves as you move your eyes like in that optical illusion above.

The illusion you linked to is dependent on the angular size of features in your field of view. As you increase the size of the image, or move closer to it, you should find that the "black" dots become increasingly lighter until they match the original white color. The same is true if you decrease the size of the image, or move further away. When the illusion grid appears the same size as the pixel grid does from a normal viewing distance, you should find the effect is no longer visible.

Pixel structures also contain the RGB subpixels, typically with larger gaps between the pixels than between the subpixels. The varying sizes helps to lessen some optical effects, though that is very likely not their intended purpose.

or maybe this is because of the LED array behind the display. a combo of pixel array and LED array creating a moving picture as you move your eyes, or eve when you hold your gaze at a spot but the picture around the spot where you gaze moves even when the picture is static and flicker free just like in the optical illusion linked above.

Very few displays have a grid of LEDs directly behind the LCD. LED displays tend to have a strip of LEDs along 1-2 edges, and the light from this is spread over the entire display by a diffuser.

i did some more research on this
here is a video showing fast moving waves on the LCD screen between 10-30 seconds
http://www.youtube.com/watch?feature=player_embedded&v=kIviL42c28c#!

i think the underlying principle behind these waves is the pixel arrangement which causes the optical illusion which is visible in this video.

i guess only some people have the eyes to catch this or be irritated by it.

this effect is probably being confused with the PWM flicker or AG coating. but that S series model in this youtube video has neither a matte coating nor PWM flicker. It still has the fast moving waves so this is due to the pixel structure.

The "waves" are a moire pattern, caused by the interfering patterns of the LCD pixels and the camera sensor pixels. The effect is not visible, or at least greatly reduced, when seen in person because human vision does not use a regular grid of photoreceptors.

When it is visible to humans, this is known as the "screen-door effect". It's visibility depends on the individual person, pixel size, pixel gap size, and viewing distance.

PWM tends to show up as straight lines scrolling across a screen, but the severity is highly dependent on properties of the light and the camera recording it.

 

[dopple]

i thought the screen door effect was separate from the moire pattern. while the former would be static the moire pattern runs along quickly.

i guess the screen door effect would lead to the moire pattern though.

 

[Mr.Pixel]

I guess I should clarify more about the screen-door effect. When I say "screen-door effect" I'm including any effects that may be visible to humans because of the pixel gaps, not just the fact that the gaps are visible. When I look at a display, moving my head slightly nearer and farther from a close distance results in what looks like moire patterns (with color effects too), but this is not easily visible when I am static.

If you look at the contrast sensitivity function (CSF) of humans, you'll note there is a sharp falloff in sensitivity for high-frequency details regardless of their contrast. The dark pixel gaps against white pixels gives very high contrast, but until you move close enough the detail is lost in the optical blur. Moving slightly closer can move details the size of the pixel gaps up the sensitivity scale quickly, making them become suddenly much more visible.

I guess I wouldn't call the screen door effect a moire pattern, but it can lead to several effects that I do not yet have a clear explanation for.

 

[dopple]

I guess I should clarify more about the screen-door effect. When I say "screen-door effect" I'm including any effects that may be visible to humans because of the pixel gaps, not just the fact that the gaps are visible. When I look at a display, moving my head slightly nearer and farther from a close distance results in what looks like moire patterns (with color effects too), but this is not easily visible when I am static.

If you look at the contrast sensitivity function (CSF) of humans, you'll note there is a sharp falloff in sensitivity for high-frequency details regardless of their contrast. The dark pixel gaps against white pixels gives very high contrast, but until you move close enough the detail is lost in the optical blur. Moving slightly closer can move details the size of the pixel gaps up the sensitivity scale quickly, making them become suddenly much more visible.

I guess I wouldn't call the screen door effect a moire pattern, but it can lead to several effects that I do not yet have a clear explanation for.

being the non technical guy that i am, its satsfying to have separated and named the effects which were an issue in lcds.. dot pitch/ppi/coating/sparkle/pwm flicker/screen door effect/moire pattern/low brightness high contrast... quite a lot of learning in a short space of time.

and several effects yet to discover.. but thats enough to identify a decent monitor now.