>>3562823Harder to do a sample that I thought it would be. Original is very clean, and on all auto conversions that I tried, I got no artefacts.
Anyway. Usually black and white image gets converted from coloured one, so colours stand out from each other. For example, red of same brightness will look the same as blue of same brightness in black and white. In film photography only way to augment those differences would be by using coloured filters. In digital photography same can be achieved when you convert coloured photograph into bw.
The conversion that you used was a very aggressive with large difference between reds and yellows. And you ended with these glitches where transitions between these two colours are the harshest. Slightly less aggressive conversion, and you'd be without anything.
Colours in this case matter little. The scene is extremely monocromatic as is, you just make sure you're without artefacts, then if you wish for the same look that you have here, you put a very aggressive clipping curve on top of it.
