Image resolution: Spatial resolution versus actual resolution

[nji9]

It's about the resolution of an image.

Say you have an image of 2000 pixel x 3000 pixel.

Then 2000 pixel x 3000 pixel is it's ACTUAL resolution.
That seems to be an important measure.
Really?

What if the image has been resized from a say 20 pixel x 30 pixel source?
Or if its right from a photo gadget with poor optics/ sensor etc., so it's
blurred, noised etc.?

Instead of the actual "pixel number" wouldn't it be much more important
to know its REAL resolution (in prof terms: the SPATIAL resolution)?

By that you get to know that something with your photo taking isn't
as it should be/ as expected...
Or you know that the image could be (HQ) shrinked without loosing information?
Etc.

There are many approaches to calculate the spatial resolution.
From "poor man" to academic.
I tested, coded some of them.
And there is one I think is reliable and quite easy to implement.

If interested I will provide more information...

[cday]

You are asking for an option to display an image's "EFFECTIVE resolution", a parameter that possibly is not well known, could you prodvide some links to resources that give some background on that parameter?

And sure, if it can be easily implemented, there would probably be interest in adding support...

[nji9]

Illustration of the alg's results on some of my images:

1982:
higher-quality fixed focus lens @ analog 35mm slide film (100 ISO),
13 MP med-price digitally scanned.

1982.png

The "outliers" (> 70% res.) are very dark images... i.e. noise = artificial res.
==>
Effective/ actual/ spatial resolution of the source is only 1/3 (per dimension) = 13MP/9 = 1.4MP !

2007++
Med-price compact camera (Canon A530, auto ISO), 5MP.

2007.png

==>
Max. effective resolution: 70-80% (due to bayer sensor): 2.8 MP.

2011++
Higher-Price compact camera (Canon S95, , auto ISO), 10MP.

2011.png

The "outliers" (>80%) are manual processed images.
==>
Max. effective resolution: abt. 75% (due to bayer sensor), i.e. 6MP!.
However the majority the images is far below (mean: abt. 45%, i.e. 2MP!)