What is the definition of "resolution"?

Thanks, Arvo. I sometimes compare "texture" by looking at the FFT magnitude plots of images but I have never tried anything else such as complex arithmetic on DFT plots - I have neither the tools** nor the knowledge to do that.

** at my age, I find that Python, Matlab, Octave, etc have too steep a learning curve.

Interlacing...

I had the word acuity in my mind then forgot it.

I was referring to pixels / inch or line pairs / mm or whatever is used to define what is necessary to achieve the appearance that someone wants.

I keep saying to myself there is no point getting involved with these word / interpretation games.

You don't control the resolution in modern cameras, it is set by the system, and as resolution is set in the output media the "appearance" is limited to zoom, especially with modern printers who's algorithms do a far better job of interpolation than anything a user can achieve.

Ahh, I really shouldn't get involved in these in depth discussions as often ideas are summarily dismissed...

Thanks to Arvo for providing the answer already :-)
While such transformations into the frequency domain are mathematical, an appreciation of how they look in the frequency domain, and how different response functions and signals combine, can help one understand the total system response and the final result.
There are also many practical uses of using FFT, DFT,...

Yes, for looking at texture, I use the GIMP Threshold function set to 0.5 on the magnitude plot out of G'MIC's FFT.

I use the Threshold function so that all frequencies over 50% "power" come out pure white as can be seen above, especially useful to me for comparisons. This plot tell me that "MTF50" is sort of occurring around 0.2cy/px because the edges of the plot represent Nyquist, and the original image was taken in 2x2 binned mode on-sensor, i.e. 10 um pixels.

I wondered if a computer monitor screen might have an MTF similarly to Norman Koren's work on scanners:

It seems like it might, if one accounts for the magnification factor and views at 100% zoom:

Human Visual Acuity excluded from the above Open Office spreadsheet.

Typo in I11 should say H6/30, not H7.

<snip>

P.P.P.S. found definitions of printer and monitor MTF - see Section 3.3 - they include human visual acuity!

corp.dxomark.com/wp-content/uploads/2017/11/2012-CPIQ_Spacial_Metrics_Copyright.pdf

AI just gave me this:

So if I have a camera with a sensor pixel pitch of 5 um then that is a spatial frequency of 100 lp/mm. A 100 ppi monitor has a spatial frequency of about 100/25/2 = 2 lp/mm per the above chart, in other words a magnification factor of about 50.

Of all the measurements of "resolution" I prefer Acutance as implied by the Edge Spread Function (ESF) at right:

DPR test image, Sigma sd Quattro H, QuickMTF slant-edge.

According to Falk Lumo, a 10 to 90% rise of 1.26 px is optimal - any more tends toward soft and any less implies over-sharpening.

www.falklumo.com/lumolabs/articles/sharpness/index.html Section 1.2.2

all i know is shooting extreme macro at 10x pixel size needs to be between 5um and 10um for max resolving power. how does that relate to your charts.

Yes, we all know that you shoot extreme macro, Donald. I have no idea how that relates to the conventional resolution charts posted in this thread.

Anybody?

I have a vague memory from prior work as an Electrical Engineer. Convert the polar values to Cartesian co-ordinates. Multiply the rectangular values. Convert the result back to polar ...

Never mind ...

Pardon the late reply:

So we would say px per square mm after converting film "grains" to the equivalent digital pixels - the so-called 'pixel density'.

So an 'APS-C' sensor with 5 um pixel pitch would have the same pixel density as a 'full frame' with 5 um pitch - but a different MP.