Here is how it looks (Photoshop as the analysis tool, magic wand, tolerance set to zero, anti-aliasing off, contiguous on, 44,600 pixels of the same value):
Just an example of a poor edit to get "vivid red", maybe due to clipping in a raw converter too. I was trying to show a trivial check for posterization.
Banding is considered to be a form of posterization; I know of a very few corner cases where posterization with 8 bits is unavoidable on a photo. Pushing too far may result in posterization for whatever the image bit depth is, and usually what results in posterization on a display or in print is about the same for any editing space bit depth.
it was that long a go i will see if i can find the raw if there was even one.
i cant even remember how i lit the shinny little seed. i have one in the studio atm and finding it quite hard to replicate the lighting.
In my experience it is usually only with gradients like a cloudless sky or in smaller scene elrments where posterization can become visually unacceptable if edits are pushed too far.
If I pixel peep I would expect that maybe most images will have some posterization but the question then becomes is it noticeable and unacceptable under normal viewing conditions for the particular image.
I doubt that to be found on the main subject of a high-quality image, and posterization isn't about pixels, it's about significant clusters of pixels having no colour variations and thus lacking details.
Posterization, to me, is just quantization that manifests visibly. Contour banding is one of the most common and obvious forms that people see, common when they or their software use too much NR for 8-bit displays. If you want to polish a noisy image, you should always add a tad of equally-distributed noise (not Gaussian; it has unnecessary outliers) at a higher precision before converting to 8 bits.