# [FFmpeg-user] Glossary: Nyquist

Mark Filipak (ffmpeg) markfilipak at bog.us
Sat Oct 3 23:43:20 EEST 2020

```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.

> And how any complex waveform
> (with it's "information density") may be represented as a sum of many
> simple sinewaves.

Ah, now that would be a Taylor series, no? It's been about 4-1/2 decades but I think it's a Taylor
series.

> Then you'll understand that all that may be simplified to the
> picture I draw, and to that the definition of Nyquist-Shannon theorem
> literally states (again):
> "If a function x(t) contains no frequencies higher than B hertz, it is
> completely determined by giving its ordinates at a series of points
> spaced 1/(2B) seconds apart.
> A sufficient sample-rate is therefore anything larger 2B samples per
> second."

Again, you bring up signals and sample rate. A video frame is not a signal. A camera or a film
scanner has a sample rate, but that sample rate is not bandwidth limited -- i.e. there is no
(realistic) limit to the analog image frequency, so 2B samples is meaningless. Even for a single,
static picture, Nyquist still applies.

Sorry, but I don't see that you disagree with my glossary entry:

Nyquist sampling: The principle [1] that, to most faithfully reproduce an image at a given digital
display's resolution, samples must be made at or above twice the display's resolution, both
horizontally & vertically.
[1] The Nyquist principle applies to film sampling and to digital cameras, but, provided that
resolution is unchanged, not to transcoding (because the transcoder inputs are already digital). As
proved by the improved sharpness of SD media made from 2K flim samples, SD mastering prior to the
advent of 2K sampling (e.g. DVDs mastered from film before the advent of HD) generally ignored the
Nyquist principle and were undersampled. HDs sampled at 2K and 4K UHDs are likewise undersampled.

>>> Maybe it's a fun to discuss such a things, but I think here is not
>>> right place to do it, beacuse it has no straight relation to ffmpeg
>>> usage.
>>
>> If not ffmpeg.org, then where? doom9.org? -- no organization there, a
>> glossary would get lost. Or Wikipedia? Ha!
> I really don't know. Maybe because of my prsonal approach that is to
> create my own resources for my own projects, then just link to it.
>> The audience is here. ...Perhaps Wikipedia some day.
>>
> Then I may wish you to show worthy draft of your project to audience
> before the audience gets completely bored. Good luck!

Thank you. Do you think I should just post the whole thing? I can't.

--
What if you woke up and found yourself in a police state?
African-Americans wake up in a police state every day.
```