Understanding NTSC
You don't actually need to understand how any of this NTSC stuff works to use Cathode Retro, but if you're curious about it, this is the section for you!
Cathode Retro includes, as part of its effect, an emulation of NTSC signals. NTSC is a TV standard that was developed in the United States but has been used in many countries for over-the-air TV broadcast. Due to the way that picture information was encoded in an NTSC broadcast (and over Composite and S-Video connections), there are certain characteristic artifacts that were present on output devices at the time (early composite PC monitors, video game consoles, etc), and it is sometimes desired to emulate these artifacts, either for properly emulating composite artifact colors or just for nostalgia's sake.
A note: This is going to be predominantely about broadcast and color TV in the United States (and anywhere else that NTSC was used). While many of the principles were the same in all locations, the specifics were different. If you're looking for in-depth details of SECAM or PAL, sorry.
The next few sections are going to walk through how NTSC works, starting with how the original NTSC standard defined its scanline format and synchronization from black & white TV up through the addition of color, with some notes on the differences between composite video and S-Video and a note on the way many old consoles performed a trick to get progressive rather than interlaced frames.
Another note: Sources are inconsistent as to whether, when referring to interlaced fields (a field being half of a full 30hz frame), "even" or "odd" is first. Cathode Retro and these docs have settled on a 1-based count starting from the first full scanline, so "odd" fields are the first field in an interlaced frame, and "even" fields are the second.