dot pitch

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Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

I need to write a program, which would be counting the time of exposure dot
pitch and energy, which has to be delivered to dot pitch to make the
picture clear and visible.
has it any connection to the signal generated by RAMDAC?

 

[Guest]

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

> I need to write a program, which would be counting the time of exposure
dot
> pitch and energy, which has to be delivered to dot pitch to make the
> picture clear and visible.
> has it any connection to the signal generated by RAMDAC?

Time of exposure? Depends on the phosphor but ideally is 1/frequency with
square waveform (impossible in practise). Dot pitch and energy are display
device specific.. you don't count them, you measure them.. the question is
how you propose to do that?

 

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Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"joe smith" <rapu@ra73727uashduashfh.org> wrote in message news:<c7e030$7p7$1@phys-news1.kolumbus.fi>...
> > I need to write a program, which would be counting the time of exposure
> dot
> > pitch and energy, which has to be delivered to dot pitch to make the
> > picture clear and visible.
> > has it any connection to the signal generated by RAMDAC?
>
> Time of exposure? Depends on the phosphor but ideally is 1/frequency with
> square waveform (impossible in practise). Dot pitch and energy are display
> device specific.. you don't count them, you measure them.. the question is
> how you propose to do that?

the answer is: I have no idea but I have another question. is there
any connection between the size of the dot pitch and the time of its
exposure as
I was told that it's needed.
example: RAMDAC 135 MHz; 1/135 MHz = 7.4 ns
according to the example I think there's no need but now I'm not sure.

 

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Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

sonkar@wp.pl (sonia) wrote:

>I need to write a program, which would be counting the time of exposure dot
>pitch and energy, which has to be delivered to dot pitch to make the
>picture clear and visible.
>has it any connection to the signal generated by RAMDAC?

Sounds like you don't have enough knowledge to be writing such a
program. Assuming you have a clue about how CRT's work, it really
isn't very hard to calculate the exposure time. More difficult will
be finding information on the amount of energy required to cause the
phosphors to glow.

 

[Guest]

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"sonia" <sonkar@wp.pl> wrote in message
news:52eee87b.0405060857.6e6173e5@posting.google.com...
> I need to write a program, which would be counting the time of exposure
dot
> pitch and energy, which has to be delivered to dot pitch to make the
> picture clear and visible.
> has it any connection to the signal generated by RAMDAC?

I'm not at all clear on what it is you're asking here, but taking
the last question first:

There is a connection between the amount of energy delivered to
a given phosphor dot in a color CRT and the signal produced
by the RAMDAC, obviously, or else the RAMDAC's output
(the video signal) could not be used to control the overall
intensity or "gray scale" of the image. However, you cannot
directly calculate the energy delivered from anything about the
RAMDAC, as the video amplifier and CRT biasing actually
determine this.

The "time of exposure" for a given dot is very brief - it is on
the order of the pixel period (not exactly the same, since the
CRT really doesn't see discrete "pixels" within the video
signal, and non-linearities in the beam sweep complicate matters),
and so for most timings commonly in use will be somewhere in
the 5-10 nanosecond range, or slightly longer. This exposure
(assuming a static image) is of course then repeated at the
refresh rate, typically 60-85 Hz or so. So a good approximation
is that each phosphor dot sees a 10 ns burst of energy every
15 milliseconds.

The final question would be how much energy is actually received
by the phosphor during that burst. This is also a bit more
complicated to figure out than it might first appear. Each
beam of a color CRT, when "full on," supplies a beam current
of somewhere in roughly the 100 microamp to 1 mA range
(generally more toward the low end of this range), which is
driven by a potential difference (from the screen, or "2nd anode"
of the tube to the cathode) of something like 25-35 kV. This
means that each beam represents at most somewhere around
10W of power. Most of this does not make it to the phosphors,
though - it's intercepted by the shadow mask, to the tune of
something like 75-80% of the energy going there. Then, the
beam is generally a good deal larger than any individual phosphor
dot, so only a fraction of what makes it through the mask strikes
any given dot. Exactly how much does make it is complicated
by the dot shape, beam size, the mask, and the angle of the
beam - but clearly it's going to be somewhere around a few
percent of the total original beam energy at best.

Hope this helps.

Bob M.

 

[Guest]

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"Bob Myers" <nospamplease@address.invalid> wrote in message news:<1wPmc.1077$vB4.626@news.cpqcorp.net>...
> "sonia" <sonkar@wp.pl> wrote in message
> news:52eee87b.0405060857.6e6173e5@posting.google.com...
> > I need to write a program, which would be counting the time of exposure
> dot
> > pitch and energy, which has to be delivered to dot pitch to make the
> > picture clear and visible.
> > has it any connection to the signal generated by RAMDAC?
>
> I'm not at all clear on what it is you're asking here, but taking
> the last question first:
>
> There is a connection between the amount of energy delivered to
> a given phosphor dot in a color CRT and the signal produced
> by the RAMDAC, obviously, or else the RAMDAC's output
> (the video signal) could not be used to control the overall
> intensity or "gray scale" of the image. However, you cannot
> directly calculate the energy delivered from anything about the
> RAMDAC, as the video amplifier and CRT biasing actually
> determine this.
>
> The "time of exposure" for a given dot is very brief - it is on
> the order of the pixel period (not exactly the same, since the
> CRT really doesn't see discrete "pixels" within the video
> signal, and non-linearities in the beam sweep complicate matters),
> and so for most timings commonly in use will be somewhere in
> the 5-10 nanosecond range, or slightly longer. This exposure
> (assuming a static image) is of course then repeated at the
> refresh rate, typically 60-85 Hz or so. So a good approximation
> is that each phosphor dot sees a 10 ns burst of energy every
> 15 milliseconds.
>
> The final question would be how much energy is actually received
> by the phosphor during that burst. This is also a bit more
> complicated to figure out than it might first appear. Each
> beam of a color CRT, when "full on," supplies a beam current
> of somewhere in roughly the 100 microamp to 1 mA range
> (generally more toward the low end of this range), which is
> driven by a potential difference (from the screen, or "2nd anode"
> of the tube to the cathode) of something like 25-35 kV. This
> means that each beam represents at most somewhere around
> 10W of power. Most of this does not make it to the phosphors,
> though - it's intercepted by the shadow mask, to the tune of
> something like 75-80% of the energy going there. Then, the
> beam is generally a good deal larger than any individual phosphor
> dot, so only a fraction of what makes it through the mask strikes
> any given dot. Exactly how much does make it is complicated
> by the dot shape, beam size, the mask, and the angle of the
> beam - but clearly it's going to be somewhere around a few
> percent of the total original beam energy at best.
>
> Hope this helps.
>
> Bob M.



thanks for help

 

[Guest]

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"Bob Myers" <nospamplease@address.invalid> wrote:

>The final question would be how much energy is actually received
>by the phosphor during that burst. This is also a bit more
>complicated to figure out than it might first appear. Each
>beam of a color CRT, when "full on," supplies a beam current
>of somewhere in roughly the 100 microamp to 1 mA range
>(generally more toward the low end of this range), which is
>driven by a potential difference (from the screen, or "2nd anode"
>of the tube to the cathode) of something like 25-35 kV. This
>means that each beam represents at most somewhere around
>10W of power. Most of this does not make it to the phosphors,
>though - it's intercepted by the shadow mask, to the tune of
>something like 75-80% of the energy going there. Then, the
>beam is generally a good deal larger than any individual phosphor
>dot, so only a fraction of what makes it through the mask strikes
>any given dot. Exactly how much does make it is complicated
>by the dot shape, beam size, the mask, and the angle of the
>beam - but clearly it's going to be somewhere around a few
>percent of the total original beam energy at best.

Can this be approached from the other side? i.e. do the phosphur
makers state how much energy it takes to light-up X amount of the
stuff?

 

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Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"chrisv" <chrisv@nospam.invalid> wrote in message
news:kv12a0dd30l84oaqmi4fd9ho6for6nksdc@4ax.com...
> Can this be approached from the other side? i.e. do the phosphur
> makers state how much energy it takes to light-up X amount of the
> stuff?

Yes, but not in a way that lends itself to this level of
discussion - or at least as I am assuming from the
original inquiry.

Bob M.

 

[Guest]

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"Bob Myers" <nospamplease@address.invalid> wrote in message news:<I5doc.1277$AG1.45@news.cpqcorp.net>...
> "chrisv" <chrisv@nospam.invalid> wrote in message
> news:kv12a0dd30l84oaqmi4fd9ho6for6nksdc@4ax.com...
> > Can this be approached from the other side? i.e. do the phosphur
> > makers state how much energy it takes to light-up X amount of the
> > stuff?
>
> Yes, but not in a way that lends itself to this level of
> discussion - or at least as I am assuming from the
> original inquiry.
>
> Bob M.




one more question. is there any connection between pixel size and its
time of exposure? I mean the substantial values. is it possible to
caunt it?

 

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Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

"sonia" <sonkar@wp.pl> wrote in message
news:52eee87b.0405120732.f9b6577@posting.google.com...

> one more question. is there any connection between pixel size and its
> time of exposure? I mean the substantial values. is it possible to
> caunt it?

CRTs don't really HAVE pixels per se - they do have individual
phosphor dots, but these really don't correspond in any way to
the "pixels" of the image (unlike the LCD and other fixed-format
technologies). The size of the individual phosphor dot does, of
course, have some slight impact on how long any part of it is
struck by the electron beam, but this really doesn't affect the
issue at hand here - which is how long the beam illuminates a
given unit area of phosphor, and how much energy is thus
received by that phosphor.

Bob M.