I read in this paper by Toshiba, which is in regards to optics in machine vision, that
In machine vision, which processes each pixel of an image sensor at high brightness levels, the permissible circle of confusion (δ) is calculated based on the pixel pitch (Ppix) or the diameter of the Airy disk (DAiry) that represents a limit to the optical resolution of an image created by a lens. In the case of monochrome cameras, the larger of these values is used as δ.
Nevertheless, I've also read many answers in regards to other questions on pixel size and Coc that pixel size tends to not be the limiting factor but rather other factors. Per the accepted answer to the question, Clarification for Effect of Pixel Size on Depth of Field:
Actually, this isn't right. The CoC criterion is the largest blur that will be perceived by the viewer as a point. At low resolutions, this may be limited by pixel size, but generally in real world use other factors are dominant — display size, distance of viewer, etc.
As well as the fact that circle of confusions tend to be much larger than even a grid of 2x2 cells on a sensor. (C.f.: the accepted answer to How do depth of field and the circle of confusion relate to pixel size on the sensor?)
I'm sure this might also relates to a demo I saw on Steve Yedlin's site, where he displayed that the difference between a 2k and 4k output is perceptually nothing, as the average viewer in average viewing conditions was not able to resolve the extra pixels.
To me it seems like that the first statement of circle of confusion criterion being equal to the size of either the airy disk /pixel pitch contradicts the other statement, where it pixel size doesn't determine the coc criterion.
What am I not seeing?
Side Note: I've already written quite a few questions and have gotten even more incredible answers, although I tend to take some time to truly grasp them. Nevertheless, if anyone knows any great reliable resources to learn a lot of these things, it would be much appreicated. I understand that searching on the internet may be the best tool, but obviously there is the dilemma of if the particular source is reliable resources.