# What is "pixel rate"?

Discussion in 'Professional Video Production' started by GreenXenon, May 6, 2009.

1. ### GreenXenonGuest

Hi:

What does the term "pixel rate" refer to?

Thanks

GreenXenon, May 6, 2009

2. ### SmartyGuest

Here is a technical explanation / definition of pixel rate:

http://www.planetanalog.com/features/multimedia/showArticle.jhtml?articleID=194300407

Richard Crowley, if you should happen to be reading this............ I seem
to recall a somewhat famous troll who lurks around here at least once before
asking these types of technical questions and then endlessly revising and
reposting variations on the same topic. The last appearance a year ago maybe
dealt with some RF issue. Is this "GreenXenon" or am I confusing this
current legitimate query / poster with another person?

Thanks,

Smarty

Smarty, May 6, 2009

3. ### SmartyGuest

Sorta' looks like the same guy, formerly known as GreenXenon Radium. The
last trolling issue was antialiasing and jaggies, with other time wasters
also such as "What video specifications are measured in Hz?"

Where do these creeps and douche bags come from?

Smarty, May 6, 2009
4. ### GreenXenonGuest

That website states "The pixel rate is a function of the horizontal
and vertical resolution multiplied by the screen refresh rate [60 Hz
in USA and Canada]. The table shows typical pixel rates for various
standards. "

However, something is wrong with that 'table'. Notice on the VGA, the
resolution is 640 X 480 but the pixel rate is 25 MHz. That is wrong.
The table even admit that the pixel rate requires that H and V
resolutions be multiplied by 60 to get the pixel rate.

By their own words they are wrong, because 640 X 480 X 60 = 18,432,000
Hz or 18.432 MHz.

So the pixel rate for VGA should be 18.432 MHz, not 25 MHz!

This is so immeasureably frustrating and confusing. If, for VGA, the H-
res is 640, the V-res is 480, the refresh rate is 60 Hz, and the pixel
rate = H-res X V-res X refresh, then just how can the pixel rate be 25
MHz????????!!!!!!!?!?!?!?!?!?!?!

WTF is going on
here??????????????????!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!?!?!?!?!?!?!?!?!?!

Whoever made the table deserves to have a 12 lb steel book slammed on
their heads for getting it wrong!

I'm so upset!

GreenXenon, May 6, 2009
5. ### SmartyGuest

Did you read the link I sent you? Did you specifically see the very explicit
and very obvious caution:

"A simple multiplication of the horizontal resolution by the vertical
resolution by the screen refresh rate results in a pixel rate significantly
lower than the actual pixel rate. This is because approximately 30 percent
of the video signal is taken up by vertical and horizontal blanking
intervals that are not part of the active displayed image."

This accounts for the "immeasurably frustrating and confusing" mistake /

Pixels are being transmitted __ONLY____ during a fraction of the time when
blanking and retrace are not occurring. The pixels are thus sent at a higher
transmission rate determined by the number of actual pixels transmitted in
the shorter remaining period, roughly 70% of the total period for the
example cited. If only pixels were being sent and there were no need to send
blanking and retrace information, then the rate for sending pixels would
indeed be slower, in your example 18.43 versus 25 MHz.

Do you mind me asking you......... WTF is a 12 lb. steel book?

Smarty

Smarty, May 6, 2009
6. ### Richard CrowleyGuest

Yes indeed. This infamous troll uses several aliases repeatedly
including "Green Xenon" and "Radium" and likely several others.
We can take some small comfort knowing that he/she/it pulls the
same kind of trolling stunts on several other newsgroups.

Richard Crowley, May 6, 2009
7. ### GreenXenonGuest

Something with which you smack jerks who purposely mislead you.

GreenXenon, May 7, 2009
8. ### GreenXenonGuest

That is another question I have.

In the old days of B&W films, what components of a video signal [in
the film itself] would be considered "frequency"?

I can think of two - temporal frequency [usually measured in Hz or
cycles per second] and spatial frequency [usually measured in cycles
per meter]. What else?

Also if an image is high-pass filtered, it looks sharper, if low-pass
filtered it looks dull. The type of frequency being altered here is
called the "spatial frequency". Or so I guess.

Stationary pictures do not have a temporal frequency component. Movies
do.

GreenXenon, May 7, 2009
9. ### SmartyGuest

A potentially useful item, no doubt. Please identify a URL with a source for

Smarty, May 7, 2009
10. ### SmartyGuest

We are making huge progress. You have both posed and then correctly answered

Smarty, May 7, 2009
11. ### SmartyGuest

Thanks Richard. There was a familiar tone to Radium's original message which
has a weird juxtaposition of ignorance and knowledge. My take is that the
questions are being posed by someone who is reasonably astute yet prefers to
play mind games.

Perhaps an escapee from "Second Life" who has run out of Linden
Dollars.......??????

Smarty, May 7, 2009
12. ### GreenXenonGuest

What entities in a single stationary negative image of a B&W film are
measured in Hz?

What will the image look like if I change the frequencies of those
entities to 0.1 Hz?

GreenXenon, May 7, 2009