[briantw]

You're confusing the analogue horizontal resolution, with the high bandwidth of up to 5 MHz, with the digital number of vertical lines, which is fixed at 625 per frame, or the low bandwidth of 15 625 lines per second. No amount of chroma noise will change the latter. And as for the former, the analogue horizontal resolution, the higest horizontal resolution you could get, even at 6 MHz bandwidth, would have been 380 analogue lines - nowhere near 625. So, that's 625 lines down, and that's fixed - you couldn't change it. And only about 380 across, and yes, that could be affected by noise, chroma subcarrier, etc.

And speaking of chroma subcarrier, yes, you will often see crappy chroma fuzz on a black-and-white image, but the reason for that is that the TV set did not have a chroma filter (exactly what they are talking about in this thread). In fact, as I'm answering that, I'm realising that THAT was probably the reason they had to filter out the colour - because it would look crappy on older black-and-white sets that did not have a chroma filter installed. Bingo!

But I have a couple of circuits from like 30 years ago that converted NTSC or PAL to RGB, and yes, they have the required filter, or you did indeed see the little blockies from NTSC or diagonal fringing on PAL colour transients.

Interesting discussion!