Hi:

What is the difference between "frame rate" and "refresh rate"?

Is it best for the frame rate to have a frequency the same as the
power supply [60 Hz in USA/Canada, 50 Hz in Europe/Asia]? Is this true
even if the video is digital and played through a digital plasma
screen?

In digital video, how is the sample rate mathematically related to the
frame rate?

In digital video, how is the sample rate mathematically related to the
refresh rate?


Thanks,

Radium

Radium wrote:
I am not aware that they are related in any way.

The highest frame rate of any DSLRs that I am aware of is 10 frames per
second on high-end Canon SRLs. According to Ct (which in turn cited sources
in Canon corporation) this frame rate is artificially lowered because at
many venues a higher fps rate is considered filming and the fees are
significantly higher than for photography.

On the other hand the only refresh rate that comes to my mind would be the
time until a flash can fire again.

Huuu? Where do you find a DSLR with a frame rate of 60 fps? That's nuts.

Huuuu? What does digital video have to do with SLR cameras?

jue

That's really interesting... because I have a Canon Powershot A530,
and the manual (which is for both the A530 and A540) mentions that the
A540 can shoot 640x480, 30fps, and 320x240, 30fps.

My A530 can only shoot at 20 fps at 320x240 (or 10 fps at 640x480).
Using Nero's VCD Burning Tools, I was able to create a Video CD that
would play on my DVD player... video was a bit jerky, though.

Makes me wonder whether I should just get an A540 (smaller), or
actually buy a digital camcorder next time...

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mrdarr***@gmail.com wrote:

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Well, but how many professional photographers are out there using a
Powershot for their work?

jue

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That confused me too but look at where the question has been
crossposted and its obvious the OP is erm... clutching at straws for
an answer.

Doc

On 6 Jul, 08:30, Dr Hfuhruhurr <doc.hfuhruh***@gmail.com> wrote:

What baffles me is how does he type wearing a straitjacket?

On 6 Jul, 12:53, contrex <mike.j.har***@gmail.com> wrote:
Crayon in mouth. It's common practice. Apparently.

Doc

On 7/06/2007, Tarquin Fin-tim-lin-bin-whin-bim-lim bus stop F'tang
F'tang Olé Biscuitbarrel posted this:
I see that you guys already know Radium :-)

In article <1183699771.323363.75***@g37g2000prf.googlegroups.com> Radium <gluceg***@gmail.com> writes:
  One is how fast information frames come, one is how fast the screen is
refreshed.


  Not really.  It helps in reducing the visibility of hum bars if all three
are the same, but power supplies are way better now, so that is of little
import.

  Yes, it is unimportant even if the video is digital and shown on plasma.


  By an integer multiple.

  What makes you think it is?

    Alan

On Jul 6, 1:29 am, Radium <gluceg***@gmail.com> wrote:

Twice. 24 to 48 for high motion film or field rates using two stops at
each frame. As applied interlacing, and apart from detail,
deinterlaced line rates are accountable for a multiple again twice
over to equal perceived smoothness.

Depends on the digital video card capabilities and whether or not it's
limited to the vertical sync of the monitor.  A monitor maximum sync
at 60Hz isn't going to help a card capable of rendering 100 frames a
second, so it's a parity function while within specification limits of
the hardware.

Radium wrote:

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Whatever the answer I wish you had not x-posted this to a photogrpahy group.

For PAL television the field rate is 50 Hz and the frame rate is 25 Hz. For
NTSC television the field rate is 59.94 Hz and the frame rate is 29.97 Hz
(or more accurately 60 times 1000/1001 and 30 times 1000/1001 respectively).

Both PAL and NTSC use 2 to 1 interlace which means that each field contains
only alternate horizontal scan lines. So in "625 line" PAL with 576
horizontal active lines per frame, each field refresh contains only 288
lines. In "525 line" NTSC with 480 horizontal active lines per frame, each
field refresh contains only 240 lines.

When viewed on a large scale the sample rate for the picture as a whole is
the same as the field rate which is the same as the refresh rate, i.e. 50 Hz
(PAL) or just under 60 Hz (NTSC). Movement is generally perceived on a large
scale so it is seen as though it were sampled at 50 or 60 Hz.

Fine vertical detail (i.e. detail which goes vertically across the
horizontal scan lines) is only sampled once per frame, on alternate field
refreshes, so this has a sample rate of only 25 or 30 Hz, and can flicker
violently if there is too much difference in intensity between adjacent
horizontal lines.

Large LCD and Plasma screens use "de-interlacing" to avoid this, but this
has drawbacks because it has to either display one field for twice it's
original sample period (i.e. display a 1/50th second exposure for 1/25th
second) or start doing clever things like only doing this for fine details,
or guessing where the patterns of the image should be in the missing lines
of each field by examining the picture details from adjacent fields and
lines. Most large screens use the "clever" approach, but none of this
processing can be done perfectly and it tends to introduce lag, smearing or
exaggerate mpeg artefacts by freezing them on the screen for twice the
length of time they would be displayed by a CRT display which is not
de-interlaced.

Modern large screens also have to resample the whole picture from 576 lines
to the 768 lines of the display which inevitably reduces the resolution to
about half of 768. This is why standard definition looks poor on an "HD
ready" screen but looks virtually the same as 768 line HD when displayed on
a CRT at 576 lines from an RGB Scart.

Modern HD ready screens also use heavy edge sharpening to try and offset
their lower-than-SD resolution when displaying standard definition, but this
also exaggerates mpeg artefacts (erroneous detail information), which is
another reason why these artefacts are objectionable and intrusive on HD
ready screens, when they are barely noticeable on a CRT.

It is an unfortunate fact that, since most TV we actually watch is still SD
but most TV's on sale now are "HD ready" with poor SD performance, it is no
longer possible to buy a new TV which is capable of displaying the majority
of TV broadcasts properly. For most broadcasts we can only get proper
pictures on "legacy" CRT TV's which have a limited lifespan and cannot be
replaced.

In article <f6rd2n$7ml$1$8302b***@news.demon.co.uk>, Stephen wrote:
Nice to see such a clear explanation. If only the programme makers understood
it so well.

It's unfortunate that nobody is ever likely to see such clear HD pictures with
such a smooth rendition of movement as the ones that were being shown at trade
shows like IBC more than twenty years ago. The interlaced signals were derived
from Plumbicon tube cameras, subject to control by vision engineers, and
displayed on cathode ray tubes with no digital processing in between. For a
while I thought it a normal symptom of the approach of old age that caused me
to be cynical about the notion that "progress" always represents an
improvement, but since then its even closer approach has disabused me of this.
It seems a waste of money to keep buying ever newer, ever more elaborate and
allegedly innovative domestic television equipment while the quality of the
material available to show on it proceeds on its present downward spiral.

Rod.

Stephen <step***@junkmail.sptv.demon.co.uk> wrote:
In a year and a half it will be moot as there will be no more of the
same old TV broadcasts.  They will all be replaced with digital
signals, and probably of better quality.

Ray Fischer wrote:
Here's an interim solution if you have one of them new fangled HD TVs-
may not be possible on all, but on my 4 year old Sony 60" what I do for
NTSC broadcasts is to split screen, and size the lo rez broadcast down
to where it's sharpest. It's about equal to the rez. I'd get on a non HD
tv. The other screen can be tuned into something slow, such as baseball
or golf, or Planet Earth.

So what do you think old CRT's did?  Nothing of course, but they had
phosphors with a persistence of 40mS or more, so the lines drawn last time
had not faded when the alternate ones were drawn - which amount to the same
thing.

Many modern CRT sets draw the whole screen 100 times a second.

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I think it is more to do with jpeg images, and sitting too close to the set,
so you can resolve (see individual) the pixels.

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Very few CRTs ever had persistence that long.  Typical persistance
figures for TV/monitor tubes (and especially color CRTs) are on the
order of a few milliseconds (to 10% of initial brightness), tops.
Longer persistence tubes were available, of course (up to several
seconds), but were generally restricted to very specialized uses
(such as radar displays).

Bob M.

Bob Myers wrote:

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All those old IBM green phosphor monitors
were very SLOOOOW....
That was in the early XT pc era.

Sjouke Burry wrote:

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So was the first TV I ever saw. It was in the early 50s and my father
used a radar crt (green phosphor) and a few other radar bits to make it.

In article <TtKdnVpMF9rRFQ7bnZ2dnUVZ8tijn***@bt.com>, Ashley Booth wrote:
Same here. One of our neighbours had built a huge box to receive this newfangled
kind of wireless programme with pictures. I remember the picture was very small,
and round, and green. With hindsight it was probably a VCR97 or something of
that ilk, which would have made it 6" diameter. It seemed to require a lot of
fiddling about with some brass stair-rods which had been woven into a lot of
wire netting in the attic, which meant nothing to me at the time of course, but
I think would probably have been a slot aerial, for either Sandale or Kirk
o'Shotts on Band 1, so quite big.

Rod.

Right - that was one of the exceptions.  The original IBM 8514
monitor (which is the one I believe you're thinking of) was a
fixed-frequency 1024 x 768 monitor - one of the earliest to
provide that format - but at the atrociously slow rate of
43.5 Hz, interlaced.  Had it not used a long-persistence
phosphor, the slow refresh would have driven all its users
crazy in short order.  Unfortunately, long-persistence phosphors
also tend to produce fairly large spot sizes, so this was a tradeoff
between trying to avoid flicker and still produce an acceptable
image at this "high resolution."

Bob M.

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