Yep, the settings @Syh linked to are the ones I’m reffering to.
You might have a little bit of room to play with scanline dark and scanline bright to expand the dynamic range futher (lowering scanline bright and raising scanline dark), but you’ll get soft clipping with anything more than a couple notches. Honestly, I would just leave these as-is (1.00 for both). Regarding bright boost, I wouldn’t go any lower than 0.50 with dark pixel bright boost and you may want to raise this a notch or two depending on how your display is configured. Bright pixel bright boost is a bit tricky. You can raise this all the way to 3.00 but this results in soft clipping and will most likely result in eye strain, and the high contrast together with the scanlines can play tricks on the eyes resulting in pseudo-aliasing, making the scanlines look like they lack a consistent width and/or spacing. Even 2.00 is probably too much, but again this will depend on how your display is configured and how bright it is to start with. You can also mitigate this somewhat by adding glow (glow strength 0.01 or 0.02, I wouldn’t go higher than this as it can start to look quite harsh). I need to play around with glow and bright pixel bright boost some more because I think the dynamic range can be expanded a bit more with these parameters.
Ideally, all color bars except 0 should be visible without eye strain and clearly distinguishable from each other. Intensity should rise in a linear fashion with roughly equal steps between shades.
On viewing distance:
“As a rule of thumb, the viewing distance should be roughly two to three times the screen size for standard definition (SD) displays.”
We’re emulating an SD display, so you should take the width of the viewable 4:3 area on your display and multiply that by 2-3 to get the correct viewing distance.
Of course, one might counter that arcade monitors were ~27 inches and you were typically 2-3 feet from those when playing, taking the angle of the screen into consideration. One could counter this by saying that arcade games weren’t set up for the proper viewing distance for the content they were displaying and that you’re still better off sitting a bit further back so that the cognitive low-pass filter can do its job.
Personally, I find 240p content to be too harsh at such close distances, and I think this explains why people frequently add such excessive blur with shaders. If you scroll up to the comparisons made with the close up of Link that I posted, you’ll see that the combo of 3.00 for horizontal sharpness and 1.00 for subtractive sharpness is still not quite as sharp as the consumer-grade CRT, demonstrating that they were actually capable of being quite sharp, contrary to popular opinion. The 3.00/1.00 combo comes closer than anything else I’ve seen to a CRT’s sharpness/blur. I’m not saying it’s perfect, but it’s the standard to beat IMO.