[FFmpeg-user] Glossary: Nyquist

[Mark Filipak (ffmpeg)]

On 10/01/2020 01:20 AM, Eduardo Alarcón wrote:
> Nyquist is a noun, not an adjective, for Harry Nyquist. ...

Hi Eduardo, Thanks.

Well, technically, a noun used as an adjective: "Nyquist sampling", makes it an adjective, but no 
matter.

What if I narrow the scope to solely the sampling theory? thusly:

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 [2].
   [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 appearance of SD media made from 2K
       samples, SD mastering prior to the advent of 2K sampling (e.g.
       DVDs mastered before the advent of HD) generally ignored the
       Nyquist principle and were undersampled. HDs sampled at 2K and
       UHDs sampled at 4K are likewise undersampled.
   [2] As a convenience, the Nyquist threshold is currently (in 2020)
       specified solely by horizontal sample count rounded up to whole
       kilo-samples (2K, 4K, 8K).
                         display    Nyquist threshold
       UHD 16:9-2160:  3840 x 2160         8K
            4:3-2160:  2880 x 2160         8K
        HD 16:9-1080:  1920 x 1080         4K
            4:3-1080:  1440 x 1080         4K
        SD  16:9-576:  1024 x 576          4K
             4:3-576:   768 x 576          2K
            16:9-480:   853 x 480          2K
             4:3-480:   640 x 480          2K

>... The Nyquist–Shannon
> sampling theorem is applicable to analog to digital conversion of signals
> (continuous to discrete), images are a type of signal.

Well, I thought that was what I wrote. What doesn't work for you?

The reason I wrote "both horizontally & vertically" was to resolve that, unlike sampling a 
1-dimensional (serial) signal, 2-dimensional sampling (e.g. from film) or within a camera, requires 
the Nyquist principle be applied in both dimensions. But perhaps that's not what you find lacking. 
Could you suggest different wording maybe?

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