Old day vs today when camera pointing at monitors ;-)

H

halong

Guest
In the old day when we point the camera at a CRT monitor we see hum
noise, something like horizontal bars rolling up/down

Today when pointing the same camera at the LCD monitor we don't see
such thing anymore

Why ?
 
halong wrote:
In the old day when we point the camera at a CRT monitor we see hum
noise, something like horizontal bars rolling up/down

Today when pointing the same camera at the LCD monitor we don't see
such thing anymore

Why ?

Because the pixels are dead slowly switching, compared to a crt.
The crt pixel fades in milli(?micro)seconds, and thats the reason
for the bad videocamera picture.
The slow pixels in lcd displays are responsible for badly visible
fast moving things on screen.
 
halong wrote:
On Feb 1, 8:57 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnll
wrote:
halong wrote:
In the old day when we point the camera at a CRT monitor we see hum
noise, something like horizontal bars rolling up/down
Today when pointing the same camera at the LCD monitor we don't see
such thing anymore
Why ?
Because the pixels are dead slowly switching, compared to a crt.
The crt pixel fades in milli(?micro)seconds, and thats the reason
for the bad videocamera picture.
The slow pixels in lcd displays are responsible for badly visible
fast moving things on screen.

we don't talk about the motion video. I recall in the old RCT monitor,
even with still images there's also rolling hum-noise.

In other words, if a fly watches the LCD monitor what would the fly
seeing ?

Ps. the fly'eyes can see much faster than human eyes

The fly would only have a problem with the crt.
 
On Feb 1, 8:57 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnll>
wrote:
halong wrote:
In the old day when we point the camera at a CRT monitor we see hum
noise, something like horizontal bars rolling up/down

Today when pointing the same camera at the LCD monitor we don't see
such thing anymore

Why ?

Because the pixels are dead slowly switching, compared to a crt.
The crt pixel fades in milli(?micro)seconds, and thats the reason
for the bad videocamera picture.
The slow pixels in lcd displays are responsible for badly visible
fast moving things on screen.
we don't talk about the motion video. I recall in the old RCT monitor,
even with still images there's also rolling hum-noise.

In other words, if a fly watches the LCD monitor what would the fly
seeing ?

Ps. the fly'eyes can see much faster than human eyes
 
halong wrote:
On Feb 1, 8:57 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnll
wrote:
halong wrote:
In the old day when we point the camera at a CRT monitor we see hum
noise, something like horizontal bars rolling up/down
Today when pointing the same camera at the LCD monitor we don't see
such thing anymore
Why ?
Because the pixels are dead slowly switching, compared to a crt.
The crt pixel fades in milli(?micro)seconds, and thats the reason
for the bad videocamera picture.
The slow pixels in lcd displays are responsible for badly visible
fast moving things on screen.

we don't talk about the motion video. I recall in the old RCT monitor,
even with still images there's also rolling hum-noise.
LCD monitors don't refresh the screen like CRTs do, they don't need to.

I used the highest refresh rate available with my CRT monitor, 85 Hz.
That made the flicker imperceptible (except to a camera that
periodically blinks at the same time that a horizontal line on the
screen does).

With my LCD, I use the lowest, 60 Hz.

In other words, if a fly watches the LCD monitor what would the fly
seeing ?
A steady image.

Ps. the fly'eyes can see much faster than human eyes
Then the fly sees the CRT like rows of strobe lights.
 
On Feb 2, 2:07 am, Beryl <fo...@road.net> wrote:
halong wrote:
On Feb 1, 8:57 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnll
wrote:
halong wrote:
In the old day when we point the camera at a CRT monitor we see hum
noise, something like horizontal bars rolling up/down
Today when pointing the same camera at the LCD monitor we don't see
such thing anymore
Why ?
Because the pixels are dead slowly switching, compared to a crt.
The crt pixel fades in milli(?micro)seconds, and thats the reason
for the bad videocamera picture.
The slow pixels in lcd displays are responsible for badly visible
fast moving things on screen.

we don't talk about the motion video. I recall in the old RCT monitor,
even with still images there's also rolling hum-noise.

LCD monitors don't refresh the screen like CRTs do, they don't need to.

I used the highest refresh rate available with my CRT monitor, 85 Hz.
That made the flicker imperceptible (except to a camera that
periodically blinks at the same time that a horizontal line on the
screen does).

With my LCD, I use the lowest, 60 Hz.

In other words, if a fly watches the LCD monitor what would the fly
seeing ?

A steady image.

Ps. the fly'eyes can see much faster than human eyes

Then the fly sees the CRT like rows of strobe lights.
Thanks you guys, that make sense now, ...about our little fly
friend ;-)

But I still wonder why it happens way? It's because, I know the video
sent to the LCD is the same as it has been sent to the CRT monitor.
That means, the video is scanned line by line, pixel by pixel, left to
right top to bottom. So, how can the image appears as a still image
at once ?

Hmmm why ?
 
On 2010-02-03, halong <ccon67@netscape.net> wrote:
On Feb 2, 2:07 am, Beryl <fo...@road.net> wrote:
halong wrote:
On Feb 1, 8:57 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnll
wrote:
halong wrote:
In the old day when we point the camera at a CRT monitor we see hum
noise, something like horizontal bars rolling up/down
Today when pointing the same camera at the LCD monitor we don't see
such thing anymore
Why ?
Because the pixels are dead slowly switching, compared to a crt.
The crt pixel fades in milli(?micro)seconds, and thats the reason
for the bad videocamera picture.
The slow pixels in lcd displays are responsible for badly visible
fast moving things on screen.

we don't talk about the motion video. I recall in the old RCT monitor,
even with still images there's also rolling hum-noise.

LCD monitors don't refresh the screen like CRTs do, they don't need to.

I used the highest refresh rate available with my CRT monitor, 85 Hz.
That made the flicker imperceptible (except to a camera that
periodically blinks at the same time that a horizontal line on the
screen does).

With my LCD, I use the lowest, 60 Hz.

In other words, if a fly watches the LCD monitor what would the fly
seeing ?

A steady image.

Ps. the fly'eyes can see much faster than human eyes

Then the fly sees the CRT like rows of strobe lights.

Thanks you guys, that make sense now, ...about our little fly
friend ;-)

But I still wonder why it happens way? It's because, I know the video
sent to the LCD is the same as it has been sent to the CRT monitor.
That means, the video is scanned line by line, pixel by pixel, left to
right top to bottom. So, how can the image appears as a still image
at once ?

Hmmm why ?
Remeber the RADAR screens in movies made in the 70s and 80s where the
bright stripe moves around the display leaving behind an image that
gradually fades?

With a TV screen the bright line is horizontal and moves vertically
at a much higer rate and the fading is also much quicker.

the bright line itself consists of a dot produced by the scanning beam,
but as each pass across the screen takes less than 0.1ms I don't think
even the fly can resolve that motion.


with an LCD there's no fading between scans the pixels just update in
order and stay the same until the next update

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
 
On Feb 3, 6:07 am, Jasen Betts <ja...@xnet.co.nz> wrote:
On 2010-02-03, halong <cco...@netscape.net> wrote:



On Feb 2, 2:07 am, Beryl <fo...@road.net> wrote:
halong wrote:
On Feb 1, 8:57 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnll
wrote:
halong wrote:
In the old day when we point the camera at a CRT monitor we see hum
noise, something like horizontal bars rolling up/down
Today when pointing the same camera at the LCD monitor we don't see
such thing anymore
Why ?
Because the pixels are dead slowly switching, compared to a crt.
The crt pixel fades in milli(?micro)seconds, and thats the reason
for the bad videocamera picture.
The slow pixels in lcd displays are responsible for badly visible
fast moving things on screen.

we don't talk about the motion video. I recall in the old RCT monitor,
even with still images there's also rolling hum-noise.

LCD monitors don't refresh the screen like CRTs do, they don't need to..

I used the highest refresh rate available with my CRT monitor, 85 Hz.
That made the flicker imperceptible (except to a camera that
periodically blinks at the same time that a horizontal line on the
screen does).

With my LCD, I use the lowest, 60 Hz.

In other words, if a fly watches the LCD monitor what would the fly
seeing ?

A steady image.

Ps. the fly'eyes can see much faster than human eyes

Then the fly sees the CRT like rows of strobe lights.

Thanks you guys, that make sense now, ...about our little fly
friend ;-)

But I still wonder why it happens way? It's because, I know the video
sent to the LCD is the same as it has been sent to the CRT monitor.
That means, the video is scanned line by line, pixel by pixel, left to
right top to bottom.  So, how can the image appears as a still image
at once ?

Hmmm why ?

Remeber the RADAR screens in movies made in the 70s and 80s where the
bright stripe moves around the display leaving behind an image that
gradually fades?

With a TV screen the bright line is horizontal and moves vertically
at a much higer rate and the fading is also much quicker.

the bright line itself consists of a dot produced by the scanning beam,
but as each pass across the screen takes less than 0.1ms I don't think
even the fly can resolve that motion.

with an LCD there's no fading between scans the pixels just update in
order and stay the same until the next update

--- news://freenews.netfront.net/ - complaints: n...@netfront.net ---

Oh, I see.

So, if I heard you right, each pixel on the LCD screen somehow has its
own memory, or a capacitor to hold up the charge, even the scanning
time or "charging time" for each pixel is just a few nano second
according to the video signal

Hmmm, that's sound possible but I don't know they people make it, or
there's a real memory like DRAM or SDRAM???

Wonder whatever it is...

Thanks,
 
On Feb 3, 10:15 pm, halong <cco...@netscape.net> wrote:
On Feb 3, 6:07 am, Jasen Betts <ja...@xnet.co.nz> wrote:



On 2010-02-03, halong <cco...@netscape.net> wrote:

On Feb 2, 2:07 am, Beryl <fo...@road.net> wrote:
halong wrote:
On Feb 1, 8:57 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnll
wrote:
halong wrote:
In the old day when we point the camera at a CRT monitor we see hum
noise, something like horizontal bars rolling up/down
Today when pointing the same camera at the LCD monitor we don't see
such thing anymore
Why ?
Because the pixels are dead slowly switching, compared to a crt.
The crt pixel fades in milli(?micro)seconds, and thats the reason
for the bad videocamera picture.
The slow pixels in lcd displays are responsible for badly visible
fast moving things on screen.

we don't talk about the motion video. I recall in the old RCT monitor,
even with still images there's also rolling hum-noise.

LCD monitors don't refresh the screen like CRTs do, they don't need to.

I used the highest refresh rate available with my CRT monitor, 85 Hz..
That made the flicker imperceptible (except to a camera that
periodically blinks at the same time that a horizontal line on the
screen does).

With my LCD, I use the lowest, 60 Hz.

In other words, if a fly watches the LCD monitor what would the fly
seeing ?

A steady image.

Ps. the fly'eyes can see much faster than human eyes

Then the fly sees the CRT like rows of strobe lights.

Thanks you guys, that make sense now, ...about our little fly
friend ;-)

But I still wonder why it happens way? It's because, I know the video
sent to the LCD is the same as it has been sent to the CRT monitor.
That means, the video is scanned line by line, pixel by pixel, left to
right top to bottom.  So, how can the image appears as a still image
at once ?

Hmmm why ?

Remeber the RADAR screens in movies made in the 70s and 80s where the
bright stripe moves around the display leaving behind an image that
gradually fades?

With a TV screen the bright line is horizontal and moves vertically
at a much higer rate and the fading is also much quicker.

the bright line itself consists of a dot produced by the scanning beam,
but as each pass across the screen takes less than 0.1ms I don't think
even the fly can resolve that motion.

with an LCD there's no fading between scans the pixels just update in
order and stay the same until the next update

--- news://freenews.netfront.net/ - complaints: n...@netfront.net ---

Oh, I see.

So, if I heard you right, each pixel on the LCD screen somehow has its
own memory, or a capacitor to hold up the charge, even the scanning
time or "charging time" for each pixel is just a few nano second
according to the video signal

Hmmm, that's sound possible but I don't know they people make it, or
there's a real memory like DRAM or SDRAM???

Wonder whatever it is...

Thanks,
I think it all makes clear now,

http://www.ercservice.com/learning/tft-device-design.html

Thanks guys for sharing your knowledge
 

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