Difference Between Scandoubler Fx and Scale Filters

[ArthorFonzarelli]

I'm a few weeks in to owning a MiSTer, and have just now gotten around to playing with some of the display settings.

After researching and testing, I've found that the HQ2x option for the Scandoubler Fx setting looks the best through HDMI on my HD monitor than the various scale filter configurations found on the github. It seems to produce a clear image while smoothing the pixel edges, where as the "HiRes" filters produced a similar smoothing result, but made the entire image look blurry in the process.

I'm curious as to what the difference is between what Scandoubler Fx does and what the scale filters do. I'm assuming that there is some difference because they are two different settings, and not simply different options in the same setting.

Feel free to get as technical as you want, I'm looking to understand as much as I can.

also, forgive me if this has been discussed elsewhere, if it has just point me in the right direction. I've searched, but perhaps I wasn't thorough enough.

[FoxbatStargazer]

I think the hi-res filters are supposed to be *for* cores that are already high resolution, not to make things appear more high-res. 400p+ stuff like ao486 and monochrome Atari ST or Amiga RTG, perhaps to add an appropriately subtle scanline effect, along with some blur that reminds you of those older 31khz+ CRTs.

Hq2x is a simple upscaling algorithm that turns every one pixel into four. It modifies the original analog signal, so your 320x240 console turns to a 640x480 output, which you could see directly on for example a VGA CRT monitor. If you use HDMI/scaler out then it is further upscaled again to whatever video mode you are using, and will apply any filters if you select them too.

[ArthorFonzarelli]

That makes sense, thanks for clearing that up!

I noticed that there are also Hq3x and Hq4x in that same algorithm family. Are those not included as a result of the available hardware on the MiSTer, or is there simply not the interest? It seems that there are many who believe that Hq2x has no place on the MiSTer to begin with (which confuses me), so the latter explanation wouldn't surprise me.

[FoxbatStargazer]

Hq2x is part of the "scandoubler" line. It's some quick and dirty effects that have to apply on the analog side, so I imagine there isn't much time/resources to do too fancy of effects here on most cores. Its primarily designed to provide 31khz output on 15 khz cores, so you can use them on a VGA CRT, multisync PVM and the like, and fake some scanlines so it looks more like a 15khz TV. So there's room to take 240p at 15khz to HQ2X at 31khz and not much more.

The scaler side is pretty limited compared to something like Retroarch but maybe Hq3x or 4x is possible there, I wouldn't know myself.