Digital video chroma sub-sampling literally has quarter chroma resolution in 4:2:0 video which is or at least was fairly common for live action stuff. It's obviously not going to be great for recording output from a computer, with sharp coloured edges, but live action scenes look fine.
I don't think anybody would claim that their 4:2:0 Blu ray has "low resolution" because it used chroma sub-sampling.
> None of this supports the parent's claim that TV went "from black&white 625x625 to color 300x300", which is just wrong on several levels.
Obviously no one here has experienced pure crystal-clear BW-tv and what happened when they turned the color-carrier on. You had to adjust the focus so that horizontal resolution was below 320. And of course the vertical focus was similarly affected, as there was no separate screws for that.
The "Luma" resolution is, in theory 625x625, but the "chroma" resolution is approximately 1/4 of that. That's OK, because the way our eyes work.
So "detail" remains at the 625x625 resolution, but the color information isn't that high. And our brains fill in the rest.