[FFmpeg-user] Glossary: Nyquist

Anatoly anatoly at kazanfieldhockey.ru
Mon Oct 5 04:44:04 EEST 2020

On Sun, 4 Oct 2020 10:37:41 -0400
"Mark Filipak (ffmpeg)" <markfilipak at bog.us> wrote:

> On 10/04/2020 03:52 AM, Rodney Baker wrote:
> > On Sunday, 4 October 2020 7:13:20 ACDT Mark Filipak (ffmpeg)
> > wrote:  
> >> On 10/03/2020 02:05 PM, Anatoly wrote:  
> >>> On Sat, 3 Oct 2020 11:05:03 -0400  
> >>
> >> -snip-
> >>  
> >>> You should learn than what spectrum is.  
> >>
> >> Oh, please. Be easy with me. I'm just a simple electrical engineer.
Btw, here where I'm, to be qualified as electrical engineer, I need to
pass exams that include topics about spectrum and Fourier transform.
How else would you deal with THD(Total Harmonic Distortion) parameter
for example? By country standard THD at my wall socket must not
exeed 12% or I may claim to electric company, refuse to pay for
electricity or so on.
> >>  
> > [...]
> > 
> > Fourier, not Taylor. All images are made up of sine waves.  
> You're kidding, eh?
No, Rodney Baker telling absolute truth. All JPEG,MGEG and many other
things works that way. I've read in historical books that at beginning
of 20th century many people not beleaving that Fourier really
applicable to AM radio that according to Fourier analysis
produces carrier and two sidebands in spectrum, until it became
possible to observe using very first spectrum analysers.

> I just posted this: Demystifying Digital Camera Specifications (was
> Glossary: Nyquist)
Are you watched "Part 2" ?

>I don't think spacial image resolution is 
>related to frequency at all.
Then watch mentioned above video at 8:07
He didnt explain this, but those plots actually is so called frequency
responces (attenuation vs frequency). 
What do you see on upper plot there?
X axis is "spatial frequency / line pairs" as distance between two pairs
of lines of picture of alternating black and white lines.
"Nyquist sampling carrier"=Fo is distance between neightbor CCD pixels.
"Optical Nyquist"=Fo/2 is distance between pairs of black and white
lines that still can be reprodused according to Nyquist.
Lower grap is the same, but for electrical part.
So consecuence should be: to shot 320 pairs of black-white lines (640
lines total) we need at least 640 pixels on CCD.
There's no complex quantum mechanics to deal with, just somple X-Y plot
and simple logic indeed.
Btw: for real waves frequency may be expressed trough real wavelenght.
Also: Just occasionaly found this:  "Face perception: An integrative
review of the role of spatial frequencies"

>Not github. I'm a human being. Github is for Martians.
May say this approach is not good. It's like saying "System photo
cameras is for Martians" and continue to use cheap Point-and-shot camera
that is designed for kids, while pretending to be a kind of
advanced photographer. I think if you want to achieve results that is
close to best experts, you should learn powerful tools that best
experts use, although they may be not simple.

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