Why YV12 will cause color banding?

[pig_10]

In my knowledge, reduction of amplitude resolution, which is reduce the color sampling bit depth in video, will cause color banding. But reduction of frequency resolution, which is reduce the pixel dimension will not.
I remember YV12 is just reduced the chroma sampling resolution, and every sample should still contains full of 24bit bit depth. So why color banding in YV12 still happens? I think reduce chroma resolution will just cause some blur, am I wrong?

[Wilbert]

The reduction in lumarange [0,255] to [16,235] could cause banding.

[Warperus]

YV12 can contain both full range color space(s) (0-255) and TV range color space(s) (16-235).
Correct transformation of color space will not cause color banding.
There is yet one simple, robust and commonly used transformation mechanism though... as you can expect, the wrong one. It is ignoring color space issue completely. Simply put everything above 235 is considered 235 and everything below 16 is considered 16. For the most part it is what software and hardware players (or decoders) do with unrecognised (properly) source files.
If you take color space issue into account in video processing and transform colorspace as neccessary you won't get color banding.