No, discarding fields is not what I meant. Let me try to explain.
My capture card, a Dazzle DVC 100, only captures 480i. From what I've read, when it is fed 240p 60 fps video, it places each frame of the 240p video on a different field. So what I'd like to be able to do in OBS is to display each field on it's own to get the 240p 60fps video back. (Field 1 -> Frame 1, Field 2 -> Frame 2, etc.)
Does this make it more clear?
that's exactly what that does. if I had JUST set it to discard, then it would have thrown out every other field, resulting in 240p30, but since I also set it to "double" then it does that twice, first isolating one field, then the other, so you get back the original 240p60 video
also the main branch of OBS has a setting which does exactly the same thing, marked as "retro/scandoubling" which reconstructs the original "double scan" or "double strike" of 240p video, just make sure that you set the field order to match your capture device (NTSC supposedly standardizes bottom field first, but the dazzle always uses top field first for some reason)
also if games look washed out when captured this way, it's probably because most of those old games were originally intended to be viewed on CRTs, which had a gamma of about 2.5, as opposed to today's 2.2. I found that changing the gamma setting to 0.7 compensates nicely for this
also some old games appear to suffer from black crush when captured from the dazzle (check by plugging the game console into an old CRT television, then comparing with the capture to see if there's details in the blacks that you can see on the TV but not on the capture), if so, you may find that setting the dazzle to NTSC-J as opposed to NTSC-M helps (no idea why, I guess either the N64 or the dazzle has something wrong with its black levels)